Growth {development} begins at fertilization, continues through embryo and fetus, and includes birth, infant, toddler, child, adolescent, and adult stages.
All body parts can be for, and form by, one organism, and one organism can be for, and form by, all parts {autopoiesis}. Organisms can generate themselves.
Genes can have different effects if they are from mothers or fathers {imprinting, development}|. Imprinting affects at least 75 human genes with imprinting centers, such as genes that make placenta and head. Mouse Nest gene is on X chromosome and causes maternal behavior: nest-building, retrieving babies, and cleaning babies. Imprinting silences mother's Nest gene. Father's Nest gene expresses.
cause
Fertilized egg cells need one male and one female pro-nucleus. Eggs with two male, or two female, pro-nuclei cannot live. CG-site methylation inactivates mother or father genes at imprinting centers. Imprinting ceases several days after conception, then sometimes recurs, and then finishes halfway through gestation.
gene types
Perhaps, father-imprinted genes make muscles, hypothalamus, amygdala, and preoptic region, and mother-imprinted genes make forebrain, cortex, striatum, and hippocampus.
In development, environmental aspects {nurture, development} have equal importance with genes {nature, development} [Carey, 1987] [Winick, 1978].
Animals have two or three embryonic-cell types {germ layer}|: endoderm, mesoderm, and ectoderm. Germ layers develop from coelom tubes.
Outer tube {ectoderm}| becomes senses, nerves, and outer skin.
Cells between ectoderm and endoderm {mesoderm}| become muscles and glands in three-germ-layer animals. Two-germ-layer animals have no mesoderm.
Inner tube {endoderm}| becomes digestive tract.
Brain and nerves develop structures and functions {brain, development} {nervous system, development}. Neurons move by amoeboid motion to final locations, guided by glia. At final locations, special molecules bind neurons together in layers or masses. Neurons send out dendrites and axons, which grow toward targets marked by chemicals, mostly to same-type neurons. Brain makes more dendrites and axons than it can use, so it eliminates many after growth finishes.
multisensory to unimodal development
During maturation, brain transforms multisensory regions to unimodal regions.
topological maps
During development, brain coordinates sense-organ movements and perceptions using attention mechanisms, to align sensory maps in superior colliculus and to maximize sensitivity.
consciousness
During human development, consciousness increases gradually as brain develops structures and functions [Aoki and Siekevitz, 1988] [Borrell and Callaway, 2002] [Carey, 1987] [Schaeffer-Simmern, 1948]. Embryos before three weeks old are unlikely to have sensations, because neurons are just forming. Children older than three can remember sensations.
Head evolved {cephalization} to hold sensors and integrate sense and muscle ganglia.
During development, invertebrates can change actions to opposite actions {reactive inhibition}.
Children develop ideas about their and other minds {theory of mind, development}. Knowing what relation moving or stationary objects have to oneself {intentionality, mind} begins at nine months old. Following another's eye direction toward distant objects begins at nine months old. At age 12 to 24 months, infants realize that people are pointing at or looking at something. Knowing that another person is looking at same object {attention sharing}, so two people attend to same thing, begins at 18 months old.
At age 24 to 36 months, toddlers start talking about goals, feelings, and thoughts. Later, they learn that perceptions from their viewpoint differ from perceptions from other viewpoints. Later, they learn that beliefs can be false and that people can deceive.
By four years old, children know that they and other people have beliefs and goals and that these guide behavior {belief-desire reasoning}.
autism
Autistic children appear to have no theory of mind.
animals
Animals seem to have no theory of mind.
test
False-belief tests can check if people have theories of mind. People can see someone place something at a location and see someone else move it while the first one is not looking. Tests ask people to name place where the first one will look for something.
People with theories of mind realize that the first one does not know that something moved, so the first one will look at the original place. People with no theory of mind will think only that something is now in new position and that everyone knows where it is, so the first one will look in the new place. If people do not know where the first one will look, they are still developing theories of mind.
From neural tube, glial processes extend into outlying regions {glial trail}. Developing neurons move along glial trails to final locations. Neurons that develop near each other in neural tube are near each other in outlying regions.
Axon tips {growth cone} have filopodia that guide axons to correct regions and synapses. Proteoglycans cover dendrites and cell bodies afterward. chABC enzyme cuts proteoglycans and allows more axon connections.
Axon-tip growth cones have cilia-like projections {filopodia} that guide axons to correct regions and synapses.
Development involves cell specialization {differentiation, cell}.
Maturational processes {induction, cell} make cells differentiate and control cell specialization.
During development, structural, functional, and behavioral changes {maturation}| can be due only to physiological growth. Maturational processes include cell induction.
directions
Muscle maturation and control start close to trunk and progress toward limbs. Maturation goes from head to tail {cephalocaudal sequence, maturation}.
enrichment
Enriched environments featuring interactions, not just passive stimulation, can transiently raise brain protein, RNA, and hexokinase levels but not gene-expression amounts. Enriched environments can increase dendritic branching and synapse number but not cell volume [Carey, 1987] [Shatz, 1992].
Cell division and specialization determine later cells and tissues {fate mapping}.
Nucleoproteins {organizer} can determine embryonic regions.
Maturation and muscle control begin at head and progress toward tail {cephalocaudal sequence, development}.
Maturation increases movement precision {mass action to differentiation sequence}.
Proteins {morphogen, protein} can set up concentration gradients across embryos.
Embryos have development stages that correspond to phylogenetic-evolution stages {recapitulation, development} {ontogeny recapitulates phylogeny}. First embryo stage corresponds to simple and ancient ancestor. Following embryo stages are later and more-complex ancestors. Last stage is current species.
Individual development {ontogeny}| continues from conception to death and includes structure, function, and behavior changes. Genes and development processes determine growth, form, and behavior.
Species begin with simple and ancient ancestor species and evolve to become more-complex species {phylogeny}|.
Embryonic development follows taxonomy and reflects organism evolution recorded in fossils {threefold parallelism}>: development, taxonomy, and fossil record.
Development makes body structures by cell division {morphogenesis}|. Cell differentiation decreases cell adhesion, increases cell deformability, and increases cell motility. Morphogenesis increases serine proteinase, cysteine proteinase, aspartic proteinase, and metalloproteinase. Cell receptors for regulated trophoblast implantation, mammary gland involution, embryonic morphogenesis, and tissue remodeling alter.
Development makes body structures by cell specialization {epigenesis}|.
Development stages {development stages} are gestation of embryo and fetus, birth, infant, toddler, child, adolescent, and adult.
Pregnancy {gestation}| has embryonic and fetal stages. Human embryonic and fetal development takes 280 days or 40 weeks [Winick, 1978].
cells
Approximately 50 cell divisions happen from zygote to newborn, making 256 or so cell types and 10^15 cells.
DNA
DNA one-dimensional molecules can encode embryo development in three spatial dimensions and one time dimension, because embryonic development uses relative times and positions.
development genes
Development genes have many and long introns and many regulatory regions. Development genes express in same order as order on chromosome, which is also spatial order of organism tissues and organs. Development genes turn on and off in cascades. Successive stages depend on previous stages. Transcription factors and receptors cause different gene-regulation and gene-expression patterns and so different cell types.
fertilization
At fertilization, maternal-effect genes code transcription factors that establish top-to-bottom embryo polarity. Bicoid morphogen, at one pole, sets up top-to-bottom gradient. Follicle-cell maternal-effect genes code transcription factors that establish front-to-back embryo polarity. Nanos morphogen, at other pole, sets up gradient across embryo.
Dorsal protein transcription factor, similar to rel protein and NF-kappaB, concentrates in cell nucleus ventrally, and cytoplasm dorsally, in all embryo cells. Cactus and Toll genes can partition dorsal protein to cell locations. Perhaps, Toll proteins are receptors.
gap genes
After first cell divisions, gap genes code transcription factors, with zinc fingers, that make bands along embryo by working with maternal-effect genes and by repressing each other. Gap genes are hunchback, Kruppel, knirps, and hunchback-maternal. Gap genes also regulate genes expressed later. Transcription-factor binding sites are high-affinity or low-affinity, so transcription-factor concentration affects which genes transcribe and how much, leading to gradients and bands.
segmentation genes
After gap-gene expression, segmentation genes code transcription factors that make number of segments, pair segments, and give polarity to segments. Segmentation genes work with gap-gene products and interact with each other, using autofeedback, to sharpen segment boundaries. Segmentation genes include pair-rule genes, such as fushi tarazu gene, even-skipped gene, hairy gene, runt gene, and eve gene.
homeotic genes
After segmentation-gene expression, homeotic genes, such as vertebrate HOX genes, code transcription factors that determine body-part type, such as antenna or thorax. Homeotic genes work with pair-rule pairs to make segments differentiate. All homeotic genes evolved from one gene by gene duplication. Homeotic genes have homeoboxes, which make homeodomains, which bind to DNA promoter sequences to control transcription. All animals have homeotic genes.
torso and polehole genes
After segmentation-gene expression, head and tail develop. For transcription factors only in head and tail, torso gene makes protein-tyrosine-kinase membrane receptors. Polehole gene, similar to raf proto-oncogene, makes protein-serine, threonine kinase that acts on head and tail growth-factor receptors.
proneural genes
After head and tail develop, proneural genes, such as daughterless and achaete-scute, code for transcription factors, with helix-loop-helix, that make neural precursor cells to start brain development. da enhances achaete-scute. enc inhibits achaete-scute.
neurogenic genes
Then neurogenic genes, such as notch, split enhancer, big brain, mastermind, and neuralized, make cell-to-cell signal proteins for cell adhesion, signal transduction, membrane channels, and transcription factors. Neurogenic genes develop cells and inhibit nearby cells.
selector genes
Then selector genes, such as cut gene, code for homeobox transcription factors that make neuron types.
neurotrophic genes
After neurons creation, neurotrophic genes code for secreted neurotrophic factors that keep neurons alive, differentiate neurons, and make neurotransmitters, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), CNTF, and NT-3. Other genes code neurotrophic-factor receptor proteins.
information from mother
Fetus can use information about mother and environment, such as orientation information. Fetus needs to know relation to mother to aid survival.
1 day: Cell division makes egg cell into a many-celled ball {blastomere}, with same volume and mass as egg cell.
1 day: Cell division {cell cleavage} makes egg cell into blastomere.
4 days: Human embryos {morula} have 10 to 30 cells.
5 days: Human embryos have several hundred cells in one layer in a hollow sphere {blastocoel} {blastocyst}, with inside cavity filled with fluid. Human blastocyst has extra cells at one spot.
5 days: Lower-animal embryos have cell spheres {blastula}.
1 week: Embryos several days old have stem cells {embryonic stem cell, gestation}| (ES cell). Embryonic stem cells can uptake and insert genes by homologous recombination. Adding altered stem cells can change mice embryos. Mouse blastocysts have inner cell layer, which can culture with fibroblasts or with leukemia inhibiting factor to prevent further differentiation.
1 week: Cells that will make brain and spinal cord first roll into a hollow cylinder {periventricular germ layer}, then multiply around that cavity, and then migrate outwards to form neuroblasts.
1 week: Cells that will make brain and spinal cord first roll into periventricular germ layer, then multiply around that cavity, and then migrate outwards to form brain nuclei {neuroblast}. Later cells pass through earlier cells, so younger cells are on outside.
1 to 3 weeks: Neuroblasts make cell slab {cortical plate} in embryo upper layer. Two hemispheres form around ventricles.
10 days: Two fluid cavities, yolk sac and amnion sac, develop inside cell sphere {chorion} {gastrula}.
10 days: Two fluid cavities develop inside gastrula. Fluid cavities {amnion sac}| can have ectoderm inside.
10 days: Two fluid cavities develop inside gastrula. Fluid cavities {yolk sac}| can have endoderm inside, to later make primitive gut.
10 days: Yolk sac has endoderm {primitive gut} inside.
10 days: In hard-shell eggs, one cavity {subgerminal space} is away from yolk, under dividing cells.
14 days: Embryo has 800 cells. Ectoderm disk lies under endoderm. Mesoderm grows between endoderm and ectoderm and splits into two sheets, one on ectoderm and one on endoderm, with a fluid cavity {coelom, development}| between sheets.
14 days: Endoderm disk has line {primitive streak}| of cells along longitudinal body-axis top. At anterior end, primitive streak becomes more specialized and has no segments, like notochord.
2 to 3 weeks: Ectoderm above notochord makes first neural plate, then neural groove, then neural folds, and then neural tube {neural tube}|.
2 to 3 weeks: Neural tube has inner ventricular zone {ependyma} around central ventricle, intermediate-zone or mantle-layer gray matter, and marginal-zone or pia white matter. Ependyma becomes CNS neurons and glia.
2 to 3 weeks: Neural-tube mantle layer becomes dorsal sense neurons {alar plate} and ventral-motor-neuron basal plate.
2 to 3 weeks: Neural-tube mantle layer becomes dorsal-sense-neuron alar plate and ventral motor neurons {basal plate}.
2 to 3 weeks: Mesoderm {neural crest}| lies next to neural tube and makes adrenal medulla, sympathetic ganglia, and dorsal-root ganglia.
2 to 9 weeks: Embryo {embryo, animal}| grows first at head and then down sides. First, disk sides curve up and around notochord at head. Then disk sides curve down to tail. Body folding makes digestive-system foregut and hindgut.
2 to 9 weeks: In vertebrates, embryos are cylindrical bodies {neurula}, with ectoderm layer on outside reaching over notochord, mesoderm layer, and inner endoderm tube.
2 to 9 weeks: Ventral-body-wall constriction makes a tube {umbilical cord}| {umbilicus} come out from belly. Tube has outer ectoderm, middle mesoderm, and inner endoderm.
15 days: Egg yolk {yolk, egg}| can be throughout cell {isolecithal}, at one end {telolecithal} or in center {centrolecithal}. Mammalian eggs have little yolk.
3 weeks: Brain interneurons send axons down brainstem to spinal cord and up to forebrain {interneuron development}. Axons transmit messenger chemicals to other neurons to integrate central nervous system. Medulla oblongata appears at neural-tube first flexure. Soon after, diencephalon appears at second flexure. Last neuroblast cells, having left-right asymmetry, migrate.
4 weeks: Forebrain telencephalon and diencephalon, midbrain, and hindbrain pons and medulla differentiate {brain divisions}.
4 weeks: Embryo floats in amniotic sac, connected to uterus wall only by umbilical cord. Embryo has large head, gills, tail, somites on notochord sides, and beating heart {head and heart development}.
4 weeks: Guided by chemical or electrical signals with no learning, brainstem and spinal-cord ventral motor cells grow axons to trunk, limb, and viscera muscles {motor cell and movement}. Fetal birds and mammals have varied movements, even before sense nerves appear.
4 weeks: Embryo has mesoderm muscle precursors {somite}| on notochord sides.
4.5 weeks: Spinal ganglia begin forming {spinal ganglia development}. Pons and cerebellum appear at neural-tube third flexure.
5 weeks: Sensory nerve tracts begin {sense-nerve development}. Epithelial sensory cells project to brainstem and spinal-cord dorsal half, which also receive from head sensory receptors. Old cortex, cerebral medulla, and basal ganglia appear at neural-tube fourth flexure.
6 weeks: Arms and legs appear, reflex-arc elements appear, sympathetic ganglia form segmental masses, hypothalamus and epithalamus begin, and cerebral hemispheres start {hypothalamus development}. Embryo is 12 millimeters long.
7 weeks: Thalamus, corpus striatum, and hippocampus begin {thalamus development}. Y-chromosome stimulates cell division and causes embryonic gonad medulla to differentiate into testis.
7.5 weeks: Spinal reflexes work, and limbic lobe begins {limbic lobe development}.
8 weeks: Embryo is 25 millimeters {cerebral cortex development}. Face has eyes, ears, and nose. Arms and legs have fingers and toes. Embryo has small tail and all internal organs. Brainstem has many projections into cerebral cortex to guide cortical-neuron migration and differentiation. Eight weeks ends embryonic period and begins fetal period.
9 weeks: Anterior commissure appears {anterior commissure development}. Testis secretes androgenic hormones to organize genitalia and brain. Fetus has red, wrinkled skin.
9.5 weeks: Hippocampal commissure appears {hippocampal commissure development}.
10 to 23 weeks: Corpus callosum appears {corpus callosum development}, but, in the next three months, it trims most callosal axons.
10.5 weeks: Spinal cord has internal structure {spinal cord development}. Fetus has localized movements. Neocortex parietal lobe starts.
10.5 weeks: Baby teeth {deciduous teeth}| appear.
12 weeks: Sex differences are present {brain layer development}. Fetus is 75 millimeters. Deepest cortical layers five and six appear.
12.5 weeks: Spinal cord has reached next organization stage {brain connection development}. Connections from neocortex to hippocampus start.
14 weeks: Long sensory tracts appear in spinal cord, and flocculonodular lobe appears {sensory tract development}.
15 to 25 weeks: First neocortical cells are around cerebral-hemisphere cavities and move into cortex {neocortex development}.
16 weeks: Spinal-cord ventral-root myelination begins {myelination development}, old cerebellar vermis is in position, corpora quadrigemina appear, neocortex has first layering stage, and parietal and frontal lobes separate.
18 weeks: Occipital lobe and temporal lobe separate {brain lobe development}.
19.5 weeks: Tract myelination from spinal cord to cerebellum and pons begins, and dorsal-root myelination begins {tract myelination development}.
20 weeks: Pyramidal tracts from cortex begin {pyramidal tract development}. Fetuses have REM sleep, indicating dreaming. Inner neocortex layers mature. Fetuses can have voluntary movements. Fetuses can move eyes, which aids eye development. Hair appears. Fetus is 250 millimeters. Malnutrition, narcotics, and emotional stress raise blood epinephrine level and cause hyperactivity.
22 weeks: Outer neocortical layers mature {outer neocortex development}. Bone ossification and teeth calcification begin.
24 weeks: Some left-temporal-lobe and parietal-lobe regions become asymmetric {brain asymmetry development}. Ventral commissure myelinates. Cranial nerves myelinate through midbrain. All cerebral-hemisphere commissures are complete. Brain has all cortical layers.
26 weeks: Brain areas that will attain mature tissue structure only at adolescence are the last to receive neurons {brain final development}.
28 weeks: Tract from spinal cord to thalamus myelinates through midbrain {brain convolution development}. Tract from spinal cord to cerebellar vermis myelinates. Cerebellum configuration is in place. Cerebral convolutions and fissures start.
32 weeks: Secondary and tertiary sulci start {brain sulci development}.
32 to 40 weeks: Brain weight increases four times during last two gestation months {brain weight development}. It continues to increase during first infancy months, while making more axons, dendrites, and synapses. After that, neuron number is constant. In fetus, sorting, editing, and removing sense and motor connections depends on maternal-environment external-stimuli timing and spatial arrangement.
40 to 41 weeks: Size at birth relates to maternal size, so large women have large babies {birth, development}.
newborn {neonate}| {newborn} {neonatal}.
Newborns can follow slowly moving lights, react to brightness changes, turn in touched-cheek direction, cry, thrash, yell, cough, vomit, turn away from stimuli, lift chin while lying on stomach, smack lips, chew on fingers, flex limbs, extend limbs, react to loud sounds, creep, shiver, jerk, arch back, draw in stomach, and twist {behavior, newborn}. If spoken to, newborns can smile, coo, and make hand gestures. Newborns can find breast in few feedings. At feeding, mothers speak to and smile at newborn girls more than boys.
Almost all central-nervous-system neurons are present at birth {brain development, newborn}. Most brain connections are present at birth in humans. Brainstem, thalamus, amygdala, and deep cerebellum are active. Dendrites are growing, and synapse number is increasing.
cells
After birth, only some neurons can divide and reproduce. During maturation, 80% of neurons die.
learning
Brain growth before birth and during infancy aids learning, and learning aids growth, because both use self-organizing processes.
hormone
In fetus and infancy, sex hormones influence visual cortical areas.
All senses are present {cognition development, newborn}.
sound
If newborns are alert, high sound frequencies cause freezing, but low ones soothe crying and increase motor activity. Rhythmic sounds quiet newborns. Newborns can make vowel sounds and several consonants. In first few days, newborns can discriminate among different speech syllables and emotional tones. Newborns prefer to hear mother's voice.
smell
In first few days, newborns can distinguish people by odor.
vision
Newborns learn mother's face in two or three days. Newborns can detect patterns in recurring events and objects and make rules about perceptual distinctions. Gaze focuses only at 20 centimeters away. Newborns have wide-open eyes that can move stepwise to fixate on bright places or to track stimuli in motion. Newborns turn toward faces that approach closely and speak gently.
cognition
Newborns can record recent-event times and locations. Neonates are conscious and have emotions. Newborns can learn but need longer times for memory consolidation. Newborns express puzzlement, surprise, pleasure, and displeasure. Newborns can try to avoid experiences.
Newborns have random bowel movements {defecation development}. Urination is often but tiny.
Newborns can eat seven to eight times a day {eating development}.
00 to 01 week: Newborn males are 50 centimeters and 3.5 kilograms {first stage of development}. Fat is under skin. Girls have less muscle mass, greater fat proportion, smaller water proportion, faster development rate, and smaller variation. At birth, males are heavier and longer than females. Males are more susceptible to postnatal and perinatal complications. By bone age, newborn girls are like five-week-old boys.
00 to 01 week: Skull has six soft spots {fontanelle}|, which harden to bone by two years old.
Reflexes include ankle clonus, arm reflex, Babiniski reflex, eye reflex, eyelid closing reflex, inner thigh reflex, jaw-jerk, Moro reflex, necking reflex, pupillary reflex, reach-and-grasp reflex, rooting response, newborn traction, voice reflex, and withdrawal reflex {reflex, newborn}.
Newborns sleep 80% of time, with seven to eight short naps per day {sleep, development}.
0 to 1 month: Inadequate eye accommodation and convergence cause infants not to attend to objects within arm reach {cognition development, 0 to 1 month}. During first month, infants can pursue objects with eyes and head. Babies less than a month old can imitate facial expressions. Over first weeks, infants learn to recognize individuals by voice. According to Piaget, infants have reflex schemas, such as sucking and grasping.
0 to 4 months: Infants less than 16 weeks old look at positions, not at objects {vision development, 0 to 4 months}. They do not know size, shape, or color. They can follow movements. They believe that moving objects differ from stationary objects. They believe that objects are solid and permanent.
Breastfeeding {breastfeeding}| {nursing, development} provides nutrients and antibodies but often stops at five months in USA.
In first months, parents tend to handle boys more than girls {handling, development}.
Mutual trust develops between baby and mother {bonding, development}|. Conflicts also happen as baby explores forbidden objects in wrong places or ways, or wants to do one thing while mother wants to do another. Such conflicts start when infants can reach and grasp objects. Such conflicts lead to playfulness, teasing, testing, sharing, games, and understanding. Baby knows mother's attention and emotions through interactions. Infant games have easy patterns in time and space and contribute to curiosity and companionship.
Infants and children are always testing to improve perceptions and reactions {cognition development, 0 to 12 month}. Infants never confuse themselves with objects outside themselves. Infants recognize that other people have motivations and emotions. Traditional nursery songs, chants, and rhymes are in all cultures, so babies know musical communications before they can speak. Baby soon knows mother and father as particular individuals. Infants are most interested in events caused by human movements.
Babies stimulate gentle and questioning talk, which has regular beats and gentle moods. Baby talk has changing intonation and rhythm and has head, eyebrow, and eye movements. Infants watch intently, reply {pre-speech} on beat, smile, and move head and body. Baby pre-speech is developmentally necessary to actual speech.
Infant boys have spontaneous penile erections {sex development, infant}. Infant girls can have spontaneous vaginal lubrication.
0 to 4 years: Children grow rapidly, but growth rate slows from 20 centimeters per year to 6 centimeters per year {physical development, 0 to 4 years}. From age 2, child height relates to average parent height, with equal influence from both. Nutrition is greatest environmental influence on growth. Severe psychological stress can affect growth. Fastest growth is in spring.
0.5 to 2 months: Infants stick up chins, take two to four naps a day, empty bowels three to four times a day usually when awake, eat one liter a day, and coo using tongue {second stage of development}.
1 month: Infants eat five to six times per day, 600 milliliters total {physical development, 1 month}.
1 month: Infants can establish eye contact {vision development, 1 month}. Infants can have gaze aversion.
1 to 4 months: According to Piaget, infants adjust schemas after encountering new stimuli {accommodation, schema}. Infants do not think about their effect on environment yet.
1 to 4 months: According to Piaget, infants join hearing, looking, and smiling to previous schemas {assimilation to schema}.
1 to 4 months: According to Piaget, infants have repeated hearing, looking, and smiling {primary circular reaction}.
1 to 6 months: Infants have two emotions: undifferentiated excitement associated with tension or need and undifferentiated relaxed quiescence {emotion development, 1 to 6 months}. Fear is undifferentiated reaction to strange, unexpected, or dangerous stimuli.
From one to six months after birth, idealized human faces and/or voices cause smiles {smiling response development}.
From 1 to 12 months, babies fear noises, falling, fast movements, light flashes, strange objects, and people and animals associated with pain {emotion development, 1 to 12 months}.
1.5 months: Babies notice objects {cognition development, 1.5 months}.
1.5 months: Reflexes open and close eyes, change pupil size, cry, suck, yawn, frown, sneeze, swallow, vomit, close hand, turn head, arch back, and vocalize {reflex development, 1.5 months}.
1.7 months: Babies can smile {cognition development, 1.7 months}.
2 months: Pyramidal tracts myelinate through medulla oblongata, fibers from spinal cord to cerebellum myelinate, and optic tracts myelinate {brain development, 2 months}.
2 months: Babies can imitate vocalizations, hand opening, and soft clapping {cognition development, 2 months}. Probably perception and motor behavior are together. Imitation behavior involves both imitator and imitated equally. Babies babble when talked to. Legs start growing fast. Visual attention is greatly increased.
2 months: Boy calorie intake is greater {physical development, 2 months}.
2 months: Eye and head movements can predict moving-object future positions, but arm movements do not relate to vision {vision development, 2 months}.
2 to 3 months: Eye accommodation begins. Infants can put chest up. Bowels empty twice a day, usually when waking or eating. Infants can eat solid foods {third stage of development}. Environments affect babbling.
2 to 3 months: Infants visually attend to nearby objects and take visual interest in their arms {vision development, 2 to 3 months}. First visually directed arm-swiping movements develop, but infants grasp objects only if hand touches them.
2 to 6 months: Axon-collateral dendrites branch greatly {brain development, 2 to 6 months}. Most synapses develop several months after birth.
2.5 months: Baby eats three to four times a day, one liter a day {physical development, 2.5 months}.
3 months: Babies have directed arm movements and look back and forth between objects and hands {behavior, infant}. Babies can reach to touch but miss. Babies put objects or hands in mouth. Babies can laugh. Same-stimulus repetition is boring. Babies can sit with support.
3 months: Cortex begins to function, convolutions begin, conscious motor acts begin, and brain controls primitive reflexes {brain development, 3 months}. Cells in cortical layers five and six are functioning but not other cortical cells. Intraorganismic short circuit is present and stable. Parietal lobes are active.
3 to 4 months: Babies can know depth, orientation, size constancy, shape constancy, completion, motion parallax, and binocular parallax {cognition development, 3 to 4 months}. Using three dimensions and depth uses convergence and eye coordination. Babies recognize people as strangers. Infants watch their two hands as they contact and manipulate each other. Infants can distinguish human faces. Infants make sounds in response to internal states.
4 months: Redundant axons are gone, and synaptic fields are complete {brain development, 4 months}. Interhemispheric fibers receive myelin sheaths.
4 months: Laughter first appears {cognition development, 4 months}. It requires safe or playful moods and unexpected situations.
4 months: Grasp reflex ends {reflex development, 4 months}. Infants can have bowel movements at eating time.
4 to 7 months: Eye accommodation is same as for adults, meaning plays role in perception, and babies can eat cereals and vegetables {fourth stage of development}.
4 to 8 months: According to Piaget, infants react to stimuli {secondary circular reaction}, so action repeats. Infants treat objects out of sight as if they are not there.
Five-month-olds seemed surprised that drawbridges can go through boxes {drawbridge study}.
5 months: Babies can use both arms together under visual control and can reach rapidly to grasp objects {physical development, 5 months}. Babies play with toes.
5 months: Reach and touch reflex ends {reflex development, 5 months}.
6 months: Neocortex layers one, two, and three myelinate {brain development, 6 months}. Babies can make all language sounds. Eye acuity is the same as for adults. Frontal lobes become active. Theta waves appear.
6 to 12 months: Babies have strong affection for mother and are afraid of, or distressed by, strangers {cognition development, 6 to 12 months}.
7 months: Delta and alpha waves appear {brain development, 7 months}.
7 months: Babies can sit up without help {physical development, 7 months}. Babies can roll.
7 to 12 months: First tooth appears. Babies express anxiety at surprise, can sit with no support, and can sleep through night with two or three day naps {fifth stage of development}. Babies probably do not dream. Urination can cease for one to two hours.
07 to 24 months: Infants can have acquired fear of separation from mother {emotion development, 7 to 24 months}.
7.5 months: Brain-wave pattern is continuously present {brain development, 7.5 months}.
8 months: Babies can crawl {physical development, 8 months}.
8 to 12 months: According to Piaget, infants coordinate secondary schemas by goal-directed activities, problem solving, and associating actions to future actions {cognition development, 8 to 12 months}. Infants treat hidden objects as if they are still there.
9 months: Layer 3c and layer 4 cortical neurons are functional {brain development, 9 months}. Sensory tracts between thalamus and primary sensorimotor cortex are ready. Motor tracts between motor cortex and cerebellum are ready. Thalamus and lower gyrus-cinguli layers are in intraorganismic short circuit. Brain-wave waking and sleeping patterns are like adult.
9 months: Infants know other's wishes or intentions in shared things, and mother's purposes and experiences become primary {cognition development, 9 months}.
9 months: Forefinger grasping ends {reflex development, 9 months}.
9 to 12 months: Reaching-behavior control allows infants to reach anywhere, not just along sightlines {physical development, 9 to 12 months}.
10 months: Babies can creep {physical development, 10 months}. Babies can walk with help.
Babies produce all speech sounds {babbling}|. Babies can make 90 different language sounds.
12 months: Pyramidal tract has myelin {brain development, 12 months}.
12 months: Attachment to people develops attention and representation {cognition development, 12 months}. One-year-old infants play reciprocal or cooperative games, typically with parents, involving companionship, shared experiences, and symbol use. Babies like familiar playmates. One-year-old infants have short-term memory. Infants are aware that objects are there, though they do not see them.
12 months: Infants want to please parents {emotion development, 12 months}. Infants want to satisfy their wills right away. Conditioned fear reactions correlate with pain.
12 months: Infants can communicate needs, feelings, and motives to other people {language development, 1 year}. Infants make sounds about their experiences, addressed as comments or queries to others for affirmation or complements. Infants create baby words to specify objects to others. Infants understand household-object names. First-year infants imitate sounds, discriminate phonological distinctive features, and develop phoneme boundaries.
12 months: Babies can reach accurately for objects using hands and fingers {physical development, 12 months}. Babies have six teeth. Males are 70 centimeters long and 9.5 kilograms.
12 to 18 months: Toddlers can creep using feet, pull themselves up, and grasp like adults. Toddlers sleep 50% of time, urinate every four hours, eat three times a day, like some foods, and do not like wet diapers {sixth stage of development}.
12 to 18 months: According to Piaget, children actively experiment with environments, using curiosity, trial, error, and close observation {tertiary circular reaction}. Children know object spatial positions.
12 to 24 months: Infants use nouns as substitutes {overextension} for categories, features, or functions {chain complex nucleus} {prototype, noun}. Children do not overextend nouns that they hear.
12 to 24 months: Infants can direct angry expressions, such as having tantrums, kicking, thrashing, screaming, and holding breath, at things or people {emotion development, 12 to 24 months}. Children learn to use aggression. Children fear noises, strange events, falling, dark, being alone, and people and animals associated with pain.
12 to 24 months: Children associate words with sounds, based on context {language development, 12 to 24 months}. Familiar-object or people names are earliest words, but children also learn words expressing feelings and needs, so all word classes are present. For young children, words share features and functions. Word classes used by children do not correspond to classes used by adults.
12.5 months: Children can imitate words {language development, 12.5 months}.
13 months: Children can throw balls {physical development, 13 months}.
14 months: Children can walk sideways and put one cube on another {physical development, 14 months}. Children can stand without help and climb stairs. Attention level increases. First meaningful speech begins.
14.5 months: Children can walk backwards {physical development, 14.5 months}.
15 months: Neocortical layer five and six axons extend tangentially into layer one {brain development, 15 months}.
15 months: Children make two-word phrases {language development, 15 months}.
15 months: Children can walk without help {physical development, 15 months}.
17 months: Children can use stick to get toys {cognition development, 17 months}.
Language areas activate {brain development, 18 months}. Pre-frontal lobes activate, along with self-consciousness.
First life stage {infancy} ends at 18 months.
18 months: Children can say 4 to 50 words, with average of 22 words {language development, 18 months}. Children make two-word phrases. Children have no frustration if not understood.
18 months: First, words stand for whole sentences {syncretic meaning}.
At age 18 months, pre-frontal lobes and language areas become active, and self-consciousness begins {self-consciousness, development}.
18 to 24 months: According to Piaget, children use conceptual and symbolic thought for planning and foresight, imitate after delay, play, use combinations, and have imaginary objects {cognition development, 18 to 24 months}.
19 months: Children can put shapes into boards {cognition development, 19 months}.
19 months: Speech using words that refer to oneself, like "I", "my", "mine", "me", and "myself", or names with verbs, begins at 19 months and is common by 27 months {language development, 19 months}.
19.5 months: Children can follow directions for pointing {cognition development, 19.5 months}.
23.5 months: Children can mend simple breaks in dolls {cognition development, 23.5 months}.
2 years: Fissures between brain lobes are present {brain development, 2 years}. Children have 75% of adult brain. Cerebellum is 80% of adult weight. Vertical exogenous fibers connect cortex with subcortex. Subcortical association fibers, layer-one tangential fibers, and horizontal exogenous fibers develop. Cortex layer 3b is functional and has thalamus and association-area tracts. Association-area outer sections are functional. Cortex motor tracts modify sense pathways.
2 years: Children do not know that minds have beliefs, hopes, and desires {cognition development, 2 years}. Children like to imitate, like to identify, can build towers of 6 to 7 blocks, can repeat two digits, can name doll body parts, and can tell objects by use. Young children first draw heads and then draw legs and arms. Two-year-old children attach arms to largest previous shape. When drawing, young children try to organize all lines into patterns, rather than copying real world.
24 months: Children like to have mother present {emotion development, 24 months}. Personality begins.
24 months: Children acquire grammar {language development, 24 months}. First, children combine verb and noun or adjective. Two-year-olds do not realize that they have thoughts or that speech has words. Vocabulary is 6 to 126 words.
24 months: Children average 0.8 meters and 12.5 kilograms {physical development, 24 months}. Handedness begins.
2 to 3 years: Children identify with parents, usually same-sex parents, and usually have several more role models {emotion development, 2 to 3 years}.
identification
Identification depends on perceived similarities between child and adult. Identification is unconscious and does not involve imitation. Identification is stable. Identification has motives, traits, and behaviors. Identification results in sex typing, conscience, and guilt.
dependence
Children are highly dependent on adults. Children cling, touch, cry, and seek affection {separation anxiety}. Children use aggression, including whining, sulking, and peevishness. Children begin to use defense mechanisms, such as withdrawal, regression, denial, repression, and projection.
2 to 3 years: Children learn tense, number, and other word-association rules and build simple sentences from words {language development, 2 to 3 years}. Two-word sentences, like action-object and actor-action, use main word in one position and another general word to add meaning. Children express locations or desires, not what they think. Children can comment on topics if they can use predicates. Children cannot understand or use metaphors.
2 to 4 years: Abdomen is large, protruding, and round {physical development, 2 to 4 years}.
2 to 4 years: According to Piaget, children can use language and symbolism, play make-believe, distinguish between objects and thoughts, treat feelings and desires as more important than reality, use main object stimuli, manipulate symbols, and imitate in thought {pre-conceptual thought} {pre-operational stage}. They cannot make classes or sets and cannot use other viewpoints.
2 to 5 years: Child independence correlates with achievement {cognition development, 2 to 5 years}. Boys and girls are equally independent. Achievement motive remains at same level until adulthood.
2 to 5 years: Fears of stimuli or actual danger decrease, while fears of accidents, darkness, ghosts, and dreams increase {emotion development, 2 to 5 years}. Fear reactions, such as crying, panic, withdrawal, trembling, and clinging, decrease. Fear correlates with intelligence.
2 to 5 years: Children first play alone, then alongside peers, then cooperate with peers, and then organize play with peers {group play, toddler}. Friendships are first with children of same sex, age, and traits, followed by fewer and stronger friendships.
2 to 5 years: Heart rate slows, blood pressure increases, and respiration is deeper and slower {physical development, 2 to 5 years}.
2 to 8 years: Left-hemisphere damage before age 8 or 9 allows language acquisition, but with several months to three years delay {brain development, 2 to 8 years}.
25 months: Children that receive little affection stay frustrated, have tantrums, and are aggressive {emotion development, 25 months}. If mother goes away for day, children protest loudly but then accept others. If mother goes away longer, children become indifferent to mother.
25 months: Children can walk up and down stairs with no help {physical development, 25 months}.
29 to 30 months: Toddlers can use two nouns together {language development, 29 to 30 months}.
3 years: Children begin to know about minds and mental states {cognition development, 3 years}. Competitiveness starts. Children do not notice stimulus changes or single out stimulus parts.
36 months: Children can repeat words that they hear {echolalia}.
3 years: Children no longer need mother present {emotion development, 3 years}.
36 months: Children can use four-word sentences {language development, 36 months}. Sound articulation improves greatly. Verbal mediation begins. Children have 900-word vocabularies, can use 100 words, have frustration if not understood, use five-word phrases, have good understanding, and have adult grammar.
3 years: Boys and girls are same size, 0.95 meters and 15 kilograms {physical development, 3 years}. All baby teeth are present. Children can run and turn smoothly, jump up 30-centimeter stairs with both feet, stand on one foot for one second, build towers of 9 to 10 cubes, fold paper in half but not diagonally, and draw less repetitively. Children sleep 20% in REM sleep.
3 to 10 years: Average height does not differ between boys and girls {physical development, 3 to 10 years}. However, height variation for 10-year-old boys is 26 centimeters.
3 to 4 years: Children can understand described situations but cannot apply learning to actual situations {cognition development, 3 to 4 years}. They can perform Piaget's class inclusion task if it slightly changes. They can match objects explored by touch or vision. They construct coherent value systems, using model codes or people.
reasoning
They do not necessarily reason as expected, because context is more important to them, and premises can lack enough context. They can reason deductively about spontaneous activities. They can make comparisons that depend on transitive reasoning: if a = b, and if b = c, then a = c.
reality
Children cannot separate appearance, what something looks like, from reality, what it actually is. They know only real world and do not fantasize or pretend.
3 to 5 years: According to Piaget, young children cannot think that objects exist independently of sensory experience {cognition development, 3 to 5 years}. Young children cannot think about several objects simultaneously. Young children have no mental structures representing class hierarchies. Young-children thoughts are successive separate moments, with current one dominant. Children first learn possible viewpoints, then reasoning about relationships, then combining and ordering in physical world, and then combining and ordering mentally.
3 to 5 years: Children learn about narrative and fantasy and build sentence chains and trees {language development, 3 to 5 years}.
3 to 6 years: Hippocampus becomes mature, so memory can be long term {brain development, 3 to 6 years}. Brain growth is earlier than general body growth, so brain is 95% of adult size by age 6 years.
3 to 8 years: Familiar stimulus parts have labels {cognition development, 3 to 8 years}.
Only children older than 3.5 years can pass theory-of-mind tests {false-belief test}.
4 years: Brain is 80% of adult weight {brain development, 4 years}. Vertical exogenous fibers extend to cortex layer 3b. Layer 3a becomes functional. Limbic system begins.
4 years: Children know if other people can and cannot see and hear them {cognition development, 4 years}. Children can pretend. Children can report facts that they see or know. Children know that others have thoughts just as they do. Girls and boys perform the same on verbal, quantitative, and spatial tests. To identify objects requires many details.
4 years: Dependency is high but on peers, not parents {emotion development, 4 years}. Competitiveness is strong, especially among boys and in lower classes. Aggression does not correlate with competitiveness. Jealousy, fear, sensitiveness, and aggressiveness start to decline.
48 months: Children have 1500-word vocabularies {language development, 48 months}. Children can use 5.3 words in sentences and use compound sentences. Word inflection begins. Toddlers know most regular grammar rules but leave auxiliary words out. Children can name several objects from memory, name pictures containing several items, repeat 10-word sentences, count to four, and tell differences between geometric figures. Relative verbal ability stays the same until adulthood.
4 years: Children can run at different speeds with smooth changes, jump forward, skip but not hop, throw with just arm, draw circles and crosses but not diamonds, trace short straight lines, and fold paper diagonally {physical development, 4 years}. Children can detect differences in spatial orientation, such as reverse, tilt, and rotate, but not react to them. Boys and girls are same size, 1.02 meters and 17 kilograms. From four years on, muscles grow faster than other body parts.
4 to 5 years: Half of children stimulate their genitals {sex development, 4 to 5 years}. Children can show sexual play, voyeurism, and exhibitionism.
4 to 6 years: Nightmares peak, because anxiety is high and children cannot handle stress {emotion development, 4 to 6 years}.
4 to 7 years: According to Piaget, children can use intuitive thought, make classes, realize that objects belong in classes, use quantifiers, use no logic, and be still centering {cognition development, 4 to 7 years}. Measurement ability begins at four, and children can make same lengths as objects. At four and a half years old, children can use body to measure. At seven years old, children can use inanimate objects to measure.
4 to 7 years: Children cannot use interaction or no interaction between two variables to determine object properties, such as number, quantity, time, or space {conservation concept}.
4 to 10 years: Before age 10, children form informal groups {group play, 4 to 10 years}.
4 to 10 years: Growth rate slows slowly {physical development, 4 to 10 years}. Average growth is 5 centimeters per year.
5 years: Temporal-pole fissure is complete {brain development, 5 years}.
5 years: Children can organize memories, so they can recover from speaking interruptions {cognition development, 5 years}. Children can draw squares and triangles but not diamonds, trace long straight lines, draw people, recall 4 to 5 numbers immediately, and pick up tiny pellets and place them. Children have good balance, show handedness, act independently, dress themselves, use toilet alone, play alone unsupervised, solve small problems, imitate activities, and talk and think to themselves.
5 years: Children have well-defined personalities {emotion development, 5 years}. Approach-avoidance conflict is common, leading to gratification delay or inhibition. Quarrels are verbal and longer. Seeking attention and approval shows dependency, as do touching and clinging. Dependency in girls stays the same until age 14. Children like nurturance from opposite-sex parent more.
5 years: Children have 2000-word vocabularies {language development, 5 years}.
5 years: Boys and girls are same size, averaging 1.08 meters and 19 kilograms {physical development, 5 years}. Relative height at age five highly correlates with adult relative height. Reaction to infection is at lower temperature but lasts longer.
5 to 10 years: Immediate-memory capacity increases, impulsitivity decreases, and reflectivity increases, because children become more aware and fear making mistakes {cognition development, 5 to 10 years}. Other fears are darkness, aloneness, imaginary creatures, and dangerous animals. Perhaps, these fears relate to parental punishments. Morals and conscience develop.
6 years: Frontal-lobe, parietal-lobe, and occipital-lobe fissurations are mostly complete {brain development, 6 years}. Brain is 90% of adult weight. Parietal-lobe and occipital-lobe surface areas are complete. Layer 2 is functional. Neural connections maximize at age 6, and pruning is later.
6 years: Children learn genital shapes. Children learn ethnic-group identifications {cognition development, 6 years}. Children learn prejudice, mostly from parents. Grade-school children know that minds have beliefs, hopes, and desires. Boys can do mazes better. Girls use verbal strategies for solving such problems more than boys. Young children do not understand false beliefs and unreal photographs, because they cannot represent fantasies yet. More boys than girls have reading difficulties. Boys have more restlessness at school and are more difficult to teach.
6 years: Boys can match colored blocks {Koh's blocks} {Koh blocks} to patterns, and do spatial ability tests, better than girls.
6 years: Children have 2500-word vocabularies and can read {language development, 6 years}.
6 years: Children average 1.15 meters and 21 kilograms {physical development, 6 years}. Abdomen is flat. Brain is 90% of adult brain. First tooth is lost. Children can throw balls well, count up to 9, go through mazes, and react to orientation changes, because they have learned up-down and right-left.
6 to 7 years: Ability to sustain attention increases greatly, in all cultures {cognition development, 6 to 7 years}. Children learn sex as people category.
Children explore and stimulate their bodies and genitals {sex development, 6 years}. Such exploration and stimulation is necessary for normal psychological sexual development. Before puberty, both boys and girls typically masturbate and achieve orgasm.
Some children have fear of school {school phobia}. Children can have little inhibition, behave well, come from intact families, have not experienced long or frequent separations from home, and have parents that express great concern for them. Refusal to go to school is anxiety about leaving home, not fear of school. Children like elementary school up to fourth grade.
6 to 12 years: Attention shifts more often and faster {cognition development, 6 to 12 years}. Expectancies depend on situations. Children have more worries about mistakes. 25% of children have regular nightmares, and some have night terrors.
6 to 12 years: Boys initiate more aggression than girls, and their aggressions are longer {emotion development, 6 to 12 years}. Girls are more nurturing and protective than boys. School-age boys like nurturance from men better than from women. Other children do not like highly dependent children.
6 to 12 years: Limbs lengthen relative to trunk, blood pressure increases, and pulse decreases {physical development, 6 to 12 years}. Before 9 years old, boys are taller than girls, but, after 9, girls are taller. Boys' growth is two years behind girls' growth. Girls are taller than boys until age 15.
Lymphatic organs, such as tonsils and lymph nodes, grow greatly in early childhood. Boys have higher basal metabolism than girls and have greater vital capacity than girls, because androgens cause greater physical activity.
Adults tolerate wider boy behavior range {expectations based on sex, 12 years} {sex development, 12 years}. Parents allow boys to roam neighborhood and encourage girls to stay home. Boys play more outside, are more physically active, and play less with dolls. Boys' rooms contain more educational material and sports equipment than girls' rooms. Most children's books are about boys, men, and male animals. They show that boys are aggressive, constructive, helpful, active, and adventuresome. They show that girls are passive, immobile, and deferential.
7 to 8 years: At age seven, children can recreate mental states and reverse logical processes or transformations {reversibility concept}.
7 to 8 years: Children can notice stimulus parts {cognition development, 7 to 8 years}. Children can separate personal experiences from problem contexts.
7 to 8 years: Children can understand metaphors {language development, 7 to 8 years}. Speech articulation becomes as good as adults. Verbal mediation is well developed. Deaf children use imagery instead of sounds and have same ability to solve problems.
7 to 8 years: Children's morals depend on obedience to orders from adults {values development, 7 to 8 years}.
7 to 11 years: According to Piaget, children can perform concrete operations {serialization, Piaget}, relate objects by scale or quantity, include objects in classes, relate parts to wholes, play using logical rules, use flexible thinking, consider other views, communicate extensively, make mental representations, know relations, and understand relations among relatives {cognition development, 7 to 11 years}.
7 to 11 years: According to Piaget, children at this stage can perform concrete operations {serialization, development}.
8 years: Fear of death or parent death {death phobia}| peaks after children learn that death is irreversible.
8 to 11 years: Morals depend more on right and wrong, justice, equality, groups, and situations {values development, 8 to 11 years}. Conscience develops through identification with others and from fear of love or approval loss. Punishment can reduce moral-standard internalization.
9 to 11 years: Boys do not express interest in girls {sex development, 9 to 11 years}.
9 to 14 years: Adolescence begins earlier for boys than girls {physical development, 9 to 14 years}.
9 to 14 years: In early adolescence {pubescence}|, heart grows more rapidly. Boys lose fat, but girls keep same ratio. Ossification speeds up at puberty. Skin problems begin at pubescence.
9 to 17 years: Girls prefer to have attractive faces, no body hair, small frames, and moderate breasts {sex preference}. Boys prefer tallness, large muscles, and face and body hair.
9 to 17 years: Expectations for boys are strength, courage, activity, sports, ambition, and persistence {expectations based on sex, 9 to 17 years} {sex development, 9 to 17 years}. Parents allow boys more aggression. Expectations for girls are friendliness, good manners, neatness, emotion expression, and demureness. Parents allow girls more dependency and nurturing behavior. Girls use verbal aggression.
10 years: Frontal-lobe surface area is complete, and all fissuration is complete {brain development, 10 years}.
10 years: Vague outlines can suggest objects, and children can recall 6 to 7 numbers immediately {cognition development, 10 years}.
10 to 12 years: Growth rate increases rapidly, before slowing at 15 or 16 and then stopping at 17 or 19 years {physical development, 10 to 12 years}.
10 to 14 years: Same-sex gang behavior predominates {group play, 10 to 14 years}.
10 to 18 years: Groups are more structured but still short-lived {group play, adolescent}. Girls conform more. Low-status people conform more. Younger children conform more than older children. Adolescents like strong relationships. Adolescents have clique talking groups and activity groups. Adolescents have friends of same age, track, class, and interests. Adolescents tend to set up seemingly separate cultures, designed to exclude adults.
11 years: According to Piaget, children at this stage can perform formal operations, think abstractly, analyze, judge, reason, deduce, consider problems not related to reality, apply rules to things, and combine rules and generalize {combinative structure}. They can think about thinking, possibilities, self, future, and things not in experience.
11 years: Boys start to show interest in girls {sex development, 11 years}.
11 to 14 years: Brain-wave pattern is like adult {brain development, 11 to 14 years}.
11 to 15 years: Boys can experience ejaculation {nocturnal emission}| during sleep.
11 to 15 years: At 11, boys are slightly heavier, but, at 15, girls are heavier {physical development, 11 to 15 years}. Bone and muscle growth rate increases.
11 to 15 years: Sex organs mature {sex development, 11 to 15 years}. Puberty averages two and a half years later in males than in females.
boys
Boys typically start at age 13, peak at age 14, and decline at age 15.5. Boys can start as early as 9.5 years or as late as 13.5 years.
girls
Girls typically start at age 11, peak at age 12, and decline at age 13. Girls can start as early as 7.5 or as late as 11.5 years. Breast buds appear at age 11, as areola diameter increases and small mound appears. One or two years before menarche, breast enlarges, nipples project, uterus grows, and pubic hair appears. At age 13, with range from 11 to 15, menarche starts and pigmented pubic hair grows. Climate does not affect menarche time. Menarche time has not decreased much over history. Malnutrition can delay menarche. Fertility is one to three years after puberty.
attitudes
Adolescent sexual attitudes are aggressive, exciting, shameful, dangerous, pleasant, and sharing.
cause
Gonadotropin-releasing-hormone (GnRH) release from hypothalamus triggers puberty, causing pituitary to secrete hormones that affect testes or ovaries. Kiss-1-gene enzyme {kisspeptin} activates GPR54, which also affects puberty.
12 years: Except for prefrontal lobe, layer two functions {brain development, 12 years}. Alpha waves dominate EEG. Central association areas and frontal lobes can function. Reticular formation completes myelination at puberty.
12 years: TV viewing peaks {cognition development, 12 years}.
12 years: Children average 1.50 meters and 38.5 kilograms {physical development, 12 years}. Most permanent teeth are in. Lymphoid tissue grows steadily until 11 or 12, and then growth rate declines.
adolescence
Average boy starts adolescence. Just before puberty, forehead becomes higher and wider, mouth widens, lips become fuller, and chin juts out more.
During adolescence, average male loses subcutaneous fat and increases muscle bulk. Subcutaneous-fat growth rate slows only in girls.
Growth in shoulder width is greater in males. Growth in pelvic breadth is similar between sexes.
rate
Children with fast early growth usually finish growing earlier, while late developers finish growing later. Growth is regular.
12 to 14 years: Adolescents understand metaphors {language development, adolescent}.
Sexual organs and characteristics can mature {puberty}|.
Teenagers {adolescence}| can demand to be independent, adjust to peers, adjust to sex changes, prepare for jobs, and develop philosophies. Adolescents are ready to change themselves and try hard. Adolescent values are honesty, naturalness, tolerance, low activity, materialism, morals, consistency, and heroes. At 18, people choose vocations. Adolescence varies among cultures. Heredity, diet, climate, culture, and emotional influences start adolescence.
12 to 18 years: Girls perform better on verbal tests {cognition development, 12 to 18 years}. Boys perform better on quantitative and spatial tests. Girls do better in school until late adolescence. Adolescents become more curious about world and are eager for knowledge. Adolescents want knowledge based on their experiences.
12 to 18 years: Adolescents have many moods and instabilities, associated with rapid sexual development {emotion development, adolescent}.
13 years: Cerebellum is at adult weight {brain development, 13 years}. Substantia-nigra dark pigmentation is complete.
13 to 16 years: First menstrual period was at 16.5 years in 1840 and is at 13 now {sex development, 13 to 16 years}.
14 years: Prefrontal-lobe lower layers function {brain development, 14 years}. Cortex layers one and two function, except in prefrontal lobe. These layers affect association areas and short-and-long circuit reorganizations. Waking and sleeping EEGs show sudden transitions.
14 to 16 years: Boys experience first seminal-fluid discharge, either through masturbation or through spontaneous nocturnal emission {sex development, 14 to 16 years}. Adolescent girls rarely experience spontaneous orgasm during sleep. Many adolescent girls do not masturbate or feel need.
culture
Reading, adults, and peer groups typically provide information about orgasm and sexual arousal. Dating begins. Sexual consciousness and interest in opposite sex rise.
Boys' sexual interest focuses on overt sexual activity earlier than, and more than, girls' interest. Western society encourages adolescent males to be overtly sexual. It encourages adolescent females to be socially attractive but not overtly sexual.
homosexuality
Homosexual fantasies and/or physical contact can happen, in boys and girls. Boys are more likely to be sexually attracted to younger boys. Girls are more likely to be sexually attracted to older girls. Having juvenile overt physical or sexual homosexual contact does not affect adult homosexual or bisexual behavior.
15 to 18 years: Boys are heavier {physical development, 15 to 18 years}.
15 years: Boys' first orgasm typically happens {sex development, 15 years}. Boys average three orgasms per week from age 16 to 30. 50% of girls have orgasm before age 20, and 90% have orgasm by age 35. Girls average two orgasms per week from age 26 to 30.
17 years: Girls have mature bones {physical development, 17 years}.
17 to 20 years: Prefrontal-lobe layers three, four, five, and six function {brain development, 17 to 20 years}. Association areas are still developing.
18 years: Myelin is still forming in reticular formation and association areas {brain development, 18 years}.
Mature people {adult} are objective about selves, have history sense, know their roles, know others, accept others, have others accept them, have purposes, are self-actualizing, have self-control, and have self-knowledge.
Illiterate or inexperienced adults rely on context, rather than words, to understand communications {language development, adult}.
Speed and ability peak between late teens and late thirties and then gradually decline. Adult appearance depends on appearance at age 5 {physical development, adult}. Adult males average 12 centimeters taller than adult females. In last 150 years, children around world have grown to greater adult heights and have matured earlier. Adult height has increased by approximately 1 centimeter per decade.
At age 35, all brain parts are complete {brain development, adult}. Frontal lobes have myelin.
Growing old {aging, development} changes DNA, protein, hormones, cells, tissues, and organs.
causes
Autoimmunity or immune-system breakdown can cause aging. Pituitary hormone and/or thymosin decrease can cause aging. Thymus thymosin keeps immune system active. Structural-molecule changes, as collagen has more cross-links and stiffens, can cause aging.
effects
Aging impairments typically result from disease, trauma, or disuse, not age itself.
effects: biology
Brain deterioration causes most aging effects. Random brain activity increases. Serum globulin becomes higher. Fracture-healing rate decreases.
effects: behavior
Performance ability peaks at 26 and then slowly declines. Slower decision making, especially for tasks in which responses cause signals for next response, slows activities slightly. Older people pay attention to responses more, rather than to next task.
Older people learn facts and skills more slowly but do not forget more rapidly. Verbal ability peaks at 50 and sharply declines after 70.
effects: senses
Signals from sense organs to brain and among brain parts become weaker. Ability to understand speech does not decrease with age, unless people cannot hear frequencies below 1800 Hz, three octaves above middle C. Trauma causes most hearing loss. Aging causes reduced sensitivity to vibration and pain. Smell loses sensitivity.
Aging causes reduced fine-joint-movement sensitivity, reduced clear-focus distance, reduced resting pupil size, increased yellow eye pigment, reduced overall acuity, slight visual-field narrowing, color-discrimination loss, and increased glare susceptibility.
effects: personality
Personality has few trends with age. Adjusting to aging does not relate to health or wealth.
individual differences
Aging rate and effects differ among individuals, and differences become greater with age.
defenses
Aging defenses are apoptosis, suppressor genes, gene redundancy, DNA editing, RNA editing, DNA repair, anti-oxidant free-radical scavenging, defective-protein removal, and damaged-cell removal by immune system.
long life
Physical fitness, genetic factors, low mental pressure, low-fat diet, low-calorie diet, psychological well-being, and living in highlands can contribute to long life. Lowering body temperature and food-intake rate slows aging in animals.
theories
Mammals, even wild animals in zoos, age after adulthood. Perhaps, genetics determines aging, and childhood, sexual maturity, adulthood, and senescence involve separate genetic programs. Perhaps, aging results from diminished energy, slower repair, and increased damage. Perhaps, aging results from free-radical oxidation.
Species have age limits {age limit}. Age limits and population structure can maximize reproductive fitness. People can live to 130 years.
Oxygen-containing molecules can gain electrons, make free radicals, and react with cell molecules {anti-oxidant theory of aging}. Superoxide dismutase (SOD) returns oxygen-containing molecules to normal. Antioxidant vitamins can scavenge free radicals.
Lifetimes {lifespan} can increase by delaying reproduction.
Human cells can divide up to 50 times {aging, cell} {cell, aging}. All cells, except cancer cells, have programmed lifespans. Gene redundancies can affect cell lifespans.
diseases
Genes or accumulated defects can cause old-age diseases. Defects include frame-shift mutations and nucleic-acid-coding, transcription, translation, microsatellite, gene-expression, and post-translational-modification errors.
cell changes
In aging, neurons have more Nissl bodies, are larger, have more axons, have more synaptic bulbs, have more dendrites, and have more myelination. Nerve-fiber length, size, and compactness increase.
cell death
Cells first deteriorate, then become senescent, then stop dividing, and then die.
telomeres
Telomeres decrease in length with each replication. After telomeres reach threshold length, cells can have senescence.
chemicals
In aging, nucleic-acid-to-protein ratio changes. Somatic-cell DNA mutates. DNA-repair-mechanism efficiency decreases. Oxygen uptake decreases. Anti-oxidants have less effect. Lysosomes increase. Intestine calcium-ion transport decreases. Cholesterol excretion decreases.
chemicals: free radicals
DNA damage affects biological aging and Alzheimer's disease. Free radicals from mitochondria and other chemical reactions can damage DNA, but vitamin E binds free radicals.
chemicals: protein
In aging, enzymes can change. Cell amyloid deposits can increase. In amyloidosis, frame-shift mutations cause protein-folding errors.
chemicals: proteins and slower aging
Sirtuins can slow aging.
Mouse, worm, and fruitfly Daf protein is similar to human insulin. Mouse, worm, and fruitfly TOR gene repression slows aging by decreasing cell growth and regulating glucose metabolism.
Mouse, worm, and fruitfly Fox0 is similar to human IGF-1. Yeast, worm, and fruitfly TOR gene repression slows aging by decreasing cell growth and regulating glucose metabolism.
Fruitfly Methuselah protein is similar to human CD97 protein. Decreased fruitfly Methuselah protein slows aging by resisting stress and increasing neuron signaling.
Worm Clock (clk-1) protein is similar to human CoQ protein. Worm Clock gene repression slows aging by regulating CoenzymeQ synthesis.
Worm Amp-1 protein is similar to human AMPK protein. Increased Amp-1 protein slows aging by regulating stress responses and metabolism.
Decreased mouse and rat growth hormone slows aging by decreasing body size.
Decreased mouse P66Shc protein slows aging by decreasing free-radical creation.
Mouse catalase is similar to human CAT protein. Increased mouse catalase slows aging by changing hydrogen peroxide.
Mouse Prop1 or pit1 protein is similar to human Pou1F1 protein. Decreased mouse Prop1 or pit1 protein slows aging by regulating pituitary gland.
Increased mouse Klotho protein slows aging by regulating insulin, IGF-1, and vitamin D.
Yeast, worm, and fruitfly SIR2 gene makes sir2 protein. Humans SIRT1 gene makes sirt1 protein. Sirtuins {silent information regulators} {sirtuin} slow aging, by mediating stress responses and deacetylating histones to make DNA coil tighter and prevent extra DNA production. Low calorie intake, high salt, high heat, and low nitrogen intake can increase PNC1-gene production, remove nicotinamide, and increase sirtuins. Low calorie intake causes mitochondria to respire instead of ferment, making low NADH and high NAD and increasing sirtuins. Red-wine and knotweed have resveratrol, which increases sirtuins.
Glycosylation make products {advanced glycosylation endproducts} (AGE) that damage DNA, lipids, and proteins.
Small deposits {drusen} can be outside cells.
Species-specific germline genes {gerontogene} can affect aging rates or maximum lifespans.
Fatty proteins {lipofuscin} can be in cells.
Human fibroblasts in culture can only divide 50 times {replicative senescence} {replication limit}. For species, allowed-doubling number is proportional to lifespan.
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Date Modified: 2022.0225