View source for Human development (biology)

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{{Otheruses4|biological human development|psychological human development|Human development (psychology)}}

'''Human development''' is the process of [[growing]] to maturity. In biological terms, this entails growth from a one-celled [[zygote]] to an adult [[human being]].

== Biological development==
[[Image:Sperm-egg.jpg|thumb|right|A spermatozoon fertilizing an ovum]]

Development begins with [[fertilization]], the process by which the male [[gamete]], the [[spermatozoon|sperm cell]], and the female gamete, the [[oocyte]], fuse to give rise to a [[diploid]] [[cell (biology)|cell]], the zygote. In pregnancy the 3 stages are commonly referred to as ZEF - meaning Zygote, Embryo, Fetus.

In medicine, pregnancy is defined as beginning when a fertilized [[zygote]] becomes [[implantation|implanted]] in a woman's [[uterus]]. This occurs when the zygote then becomes embedded into the [[endometrium]] (lining of the uterus) where it forms a [[placenta]], for the purpose of receiving essential [[nutrients]] through the [[uterus]] wall. The [[umbilical cord]] in a newborn child signifies the remnants of implantation.

The zygote undergoes rapid [[mitosis|mitotic]] [[cell division|division]]s with no significant growth (a process known as [[cleavage (embryo)|cleavage]]) and [[cellular differentiation]], leading to development of an [[embryo]].


[[Childbirth]] is the process in which the baby is born. It is considered by many to be the beginning of a person's life, where age is defined relative to this event in most cultures.

=== Physical stages ===

Terms for stages of age-related physical development include, with their approximate age ranges:

* [[Life]]
** [[Prenatal development|Prenatal]] (fertilisation - birth)
***[[Human embryogenesis|Embryo]] - (fertilisation - 8 weeks of gestational phase)
****[[Zygote]], the point of [[conception]], fertilization
****[[blastocyst]] the period between conception and embryonic stages
****[[Embryo]]; the embryonic period starts at three weeks and continues until the end of the 8th week of pregnancy 
***[[Fetus|Foetus]] (8 weeks of gestational phase - birth)
**[[Child]] ([[Childbirth|birth]] - age of majority)
***Neonate (newborn) (0-30 days)
***[[Infant]] (baby) (1 month-1 year)
***[[Toddler]] (1-4)
***[[Play age]] (3 - 6 years)
***[[Primary school]] age (also called '''prepubescence''') (4-12)
****[[Elementary school]] age (also called '''middle childhood''') (4-8)
****[[Preadolescence]] (preteen, or '''late childhood'''. The child in this and the previous phase are called ''schoolchild'' (''schoolboy'' or ''schoolgirl''), when still of primary school age.) (9-12)
**[[Adolescence|Adolescence and puberty]] (teenage) (13-19)
**[[Adult]] (20-death)
***[[Young adult]] (20-25)
***[[Early adulthood]] (20-39)
***[[Middle age]] (40-59)
***[[Advanced adult]]/[[Senior citizen]] (60+)
*[[Death]] (occurs at various ages, depending on person)
** [[Decomposition]] (breakdown of the body after death)

Also sometimes used are terms that specify one's age in numbers, such as:
* Child (0-12)
* Teenager (13-19)
* [[Twentysomething (term)|Twentysomething]] (20-29)
* [[Thirtysomething (term)|Thirtysomething]] (30-39)
* [[Fortysomething (term)|Fortysomething]] (40-49) (formerly also Quadragenarian, rarely used since 1980)
* [[Fiftysomething (term)|Quinquagenarian]] (50-59)
* [[Sixtysomething (term)|Sexagenarian]] (60-69)
* Septuagenarian (70-79)
* Octogenarian (80-89)
* Nonagenarian (90-99)
* [[Centenarian]] (100-109)
* [[Supercentenarian]] (110+)

===Comparison table===
{{See|Table of development periods}}
{|class="wikitable"
|-
|
|
| years<ref>Approximately</ref>
|-
| rowspan="6" | [[Child]]
| [[prenatal]]
| &gt;0
|-
| [[infancy]]
| 0 - walking
|-
| [[toddlerhood]]
| walking - 3
|-
| [[play age]]
| 3-6
|-
| [[preadolescence]]
| 10 - [[puberty]]
|-
| [[adolescence]]
| puberty - 19
|-
| rowspan="2" | [[Young adult]]
| [[twentysomething]]
| 20-29
|-
| [[thirtysomething]]
| 30-39
|-
| rowspan="2" | [[Middle age]]
| [[Fortysomething (term)|fortysomething]]
| 40-49
|-
| [[quinquagenarian]]
| 50-59
|-
| rowspan="6" | [[Advanced adult]]
| [[sexagenarian]]
| 60-69
|-
| septuagenarian
| 70-79
|-
| octogenarian
| 80-89
|-
| nonagenarian
| 90-99
|-
| centenarian
| 100-109
|-
| supercentenarian
| 110
|- style="display: none"
|
|
|
|}

=== Physical development milestones ===

* Ability to lift and control the orientation of the head
* [[crawling (locomotion)|Crawling]] begins
* [[Walking]] begins
* [[Speech communication|Speech]] begins
* [[human voice|Voice]] lowers in pitch (especially noticeable in boys)
* [[Pubic hair]] appears
* [[Genitals]] and reproductive organs mature
* [[Menses]] begin (females)
* [[Body hair]] and [[facial hair]] appears

Note: the [[Tanner stages]] can be used to approximately judge a child's age based on physical development.

== See also ==
* [[Child development]]
* [[Developmental biology]]
* [[Auxology]]
* [[Embryogenesis]]
* [[Mammalian embryogenesis]]
* [[Life-history theory]]

==Footnotes==
{{reflist|2}}

{{Human}}

{{Humandevelopment}}

{{Embryology}}
[[Category:Human development| ]]
[[Category:Humans|Development]]
[[Category:Developmental psychology]]

[[es:Crecimiento humano]]
[[fr:Développement humain (biologie)]]
[[id:Tahap perkembangan manusia]]
[[it:Sviluppo umano (biologia)]]
[[nl:Levensfase]]
[[pl:Okresy rozwojowe człowieka]]

{{WH}}
{{WS}}
{{jb1}