Human

=== Life cycle ===

{{See also|Childbirth|Life expectancy|}}
[[File:Tubal Pregnancy with embryo.jpg|thumb|A 10&nbsp;mm [[human embryo]] at 5 weeks]]
Most [[human reproduction]] takes place by [[internal fertilization]] via [[human sexual intercourse|sexual intercourse]], but can also occur through [[assisted reproductive technology]] procedures.<ref name="She2016">{{cite book| vauthors = Shehan CL |url={{GBurl|id=-gSeCAAAQBAJ|p=406}}|title=The Wiley Blackwell Encyclopedia of Family Studies, 4 Volume Set|date=2016|publisher=John Wiley & Sons|isbn=978-0-470-65845-1|page=406|name-list-style=vanc}}</ref> The average [[gestation]] period is 38 weeks, but a normal pregnancy can vary by up to 37 days.<ref>{{cite journal | vauthors = Jukic AM, Baird DD, [[Clarice Weinberg|Weinberg CR]], McConnaughey DR, Wilcox AJ | title = Length of human pregnancy and contributors to its natural variation | journal = Human Reproduction | volume = 28 | issue = 10 | pages = 2848–2855 | date = October 2013 | pmid = 23922246 | pmc = 3777570 | doi = 10.1093/humrep/det297 }}</ref> Embryonic development in the human covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a [[fetus]].<ref name="nursing">{{cite book | vauthors = Klossner NJ | url = {{GBurl|id=B47OVg25g-QC|q=fetal stage begins|p=103}} | title = Introductory Maternity Nursing | date = 2005 | page = 103 | publisher=Lippincott Williams & Wilkins | quote = The fetal stage is from the beginning of the 9th week after fertilization and continues until birth | isbn = 978-0-7817-6237-3 | access-date = 30 July 2022 }}</ref> Humans are able to [[Labor induction|induce early labor]] or perform a [[caesarean section]] if the child needs to be born earlier for medical reasons.<ref name="WHO2014">{{cite web|author=World Health Organization|date=November 2014|title=Preterm birth Fact sheet N°363|url=https://www.who.int/mediacentre/factsheets/fs363/en/|url-status=live|archive-url=https://web.archive.org/web/20150307050438/https://www.who.int/mediacentre/factsheets/fs363/en/|archive-date=7 March 2015|access-date=6 March 2015|work=who.int}}</ref> In developed countries, [[infant]]s are typically {{Convert|3|-|4|kg|lb|abbr=on|lk=off|0}} in weight and {{Convert|47|-|53|cm|in|abbr=on|lk=off|0}} in height at birth.<ref>{{cite journal | vauthors = Kiserud T, Benachi A, Hecher K, Perez RG, Carvalho J, Piaggio G, Platt LD | title = The World Health Organization fetal growth charts: concept, findings, interpretation, and application | journal = American Journal of Obstetrics and Gynecology | volume = 218 | issue = 2S | pages = S619–S629 | date = February 2018 | pmid = 29422204 | doi = 10.1016/j.ajog.2017.12.010 | s2cid = 46810955 | doi-access = free }}</ref><ref>{{cite web|date=18 March 2019|title=What is the average baby length? Growth chart by month|url=https://www.medicalnewstoday.com/articles/324728|access-date=18 April 2021|website=www.medicalnewstoday.com|language=en|archive-date=27 January 2021|archive-url=https://web.archive.org/web/20210127193402/https://www.medicalnewstoday.com/articles/324728|url-status=live}}</ref> However, [[low birth weight]] is common in developing countries, and contributes to the high levels of [[infant mortality]] in these regions.<ref name="Khor2003">{{cite journal | vauthors = Khor GL | title = Update on the prevalence of malnutrition among children in Asia | journal = Nepal Medical College Journal | volume = 5 | issue = 2 | pages = 113–122 | date = December 2003 | pmid = 15024783 }}</ref>

Compared with other species, human childbirth is dangerous, with a much higher risk of complications and death.<ref>{{cite journal| vauthors = Rosenberg KR |date=1992|title=The evolution of modern human childbirth |journal=American Journal of Physical Anthropology|language=en|volume=35|issue=S15|pages=89–124|doi=10.1002/ajpa.1330350605|issn=1096-8644}}</ref> The size of the fetus's head is more closely matched to the [[pelvis]] than in other primates.<ref name="Pavlicev">{{cite journal | vauthors = Pavličev M, Romero R, Mitteroecker P | title = Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma | journal = American Journal of Obstetrics and Gynecology | volume = 222 | issue = 1 | pages = 3–16 | date = January 2020 | pmid = 31251927 | doi = 10.1016/j.ajog.2019.06.043 | pmc = 9069416 | s2cid = 195761874 }}</ref> The reason for this is not completely understood,{{#tag:ref|Traditionally this has been explained by conflicting [[evolutionary pressure]]s involved in bipedalism and encephalization (called the [[obstetrical dilemma]]), but recent research suggest it might be more complicated than that.<ref name="Pavlicev" /><ref>{{cite news|title=The real reasons why childbirth is so painful and dangerous| vauthors = Barras C |date=22 December 2016|publisher=BBC}}</ref>|group=n}} but it contributes to a painful labor that can last 24 hours or more.<ref>{{cite web | vauthors = Kantrowitz B | date = 2 July 2007 | title = What Kills One Woman Every Minute of Every Day? | work = [[Newsweek]] | url = https://www.msnbc.msn.com/id/19389326/site/newsweek/ | archive-url = https://web.archive.org/web/20070628160443/https://www.msnbc.msn.com/id/19389326/site/newsweek/ | archive-date = 28 June 2007 | quote = A woman dies in childbirth every minute, most often due to uncontrolled bleeding and infection, with the world's poorest women most vulnerable. The lifetime risk is 1 in 16 in [[sub-Saharan Africa]], compared to 1 in 2,800 in [[developed countries]]. }}</ref> The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and [[natural childbirth]] remain hazardous ordeals in developing regions of the world, with [[maternal death rates]] approximately 100 times greater than in developed countries.<ref name="Rush2000">{{cite journal | vauthors = Rush D | title = Nutrition and maternal mortality in the developing world | journal = The American Journal of Clinical Nutrition | volume = 72 | issue = 1 Suppl | pages = 212S–240S | date = July 2000 | pmid = 10871588 | doi = 10.1093/ajcn/72.1.212S | doi-access = free }}</ref>

Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care is mostly done by the mother.<ref>{{cite book|vauthors=Laland KN, Brown G|url={{GBurl|id=2KcbFVBSxWYC}}|title=Sense and Nonsense: Evolutionary Perspectives on Human Behaviour|date=2011|publisher=Oxford University Press|isbn=978-0-19-958696-7|page=7|language=en|access-date=30 July 2022}}</ref> [[Altricial|Helpless at birth]], humans continue to grow for some years, typically reaching [[sexual maturity]] at 15 to 17 years of age.<ref name="Kail">{{cite book|vauthors=Kail RV, Cavanaugh JC|url={{GBurl|id=E-n5E7oyCgoC|p=296}}|title=Human Development: A Lifespan View|publisher=[[Cengage Learning]]|year=2010|isbn=978-0-495-60037-4|edition=5th|page=296|access-date=30 July 2022}}</ref><ref name="Schuiling">{{cite book|vauthors=Schuiling KD, Likis FE|url={{GBurl|id=QTDFDAAAQBAJ|p=22}}|title=Women's Gynecologic Health|publisher=[[Jones & Bartlett Learning]]|year=2016|isbn=978-1-284-12501-6|page=22|quote=The changes that occur during puberty usually happen in an ordered sequence, beginning with thelarche (breast development) at around age 10 or 11, followed by adrenarche (growth of pubic hair due to androgen stimulation), peak height velocity, and finally menarche (the onset of menses), which usually occurs around age 12 or 13.|access-date=30 July 2022}}</ref><ref name="Phillips">{{cite book|vauthors=Phillips DC|url={{GBurl|id=84StBAAAQBAJ|p=18}}|title=Encyclopedia of Educational Theory and Philosophy|publisher=[[SAGE Publications]]|year=2014|isbn=978-1-4833-6475-9|pages=18–19|quote=On average, the onset of puberty is about 18 months earlier for girls (usually starting around the age of 10 or 11 and lasting until they are 15 to 17) than for boys (who usually begin puberty at about the age of 11 to 12 and complete it by the age of 16 to 17, on average).|access-date=30 July 2022}}</ref> The human life span has been split into various stages ranging from three to twelve. Common stages include [[Infant|infancy]], [[childhood]], [[adolescence]], [[adult]]hood and [[old age]].<ref>{{cite journal| vauthors = Mintz S |date=1993|title=Life stages|journal=Encyclopedia of American Social History|volume=3|pages=7–33}}</ref> The lengths of these stages have varied across cultures and time periods but is typified by an unusually rapid growth spurt during adolescence.<ref>{{cite journal | vauthors = Soliman A, De Sanctis V, Elalaily R, Bedair S | title = Advances in pubertal growth and factors influencing it: Can we increase pubertal growth? | journal = Indian Journal of Endocrinology and Metabolism | volume = 18 | issue = Suppl 1 | pages = S53-62 | date = November 2014 | pmid = 25538878 | pmc = 4266869 | doi = 10.4103/2230-8210.145075 | doi-access = free }}</ref> Human females undergo [[menopause]] and become [[Infertility|infertile]] at around the age of 50.<ref>{{cite journal | vauthors = Walker ML, Herndon JG | title = Menopause in nonhuman primates? | journal = Biology of Reproduction | volume = 79 | issue = 3 | pages = 398–406 | date = September 2008 | pmid = 18495681 | pmc = 2553520 | doi = 10.1095/biolreprod.108.068536 }}</ref> It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring, and in turn their children (the [[grandmother hypothesis]]), rather than by continuing to bear children into old age.<ref name="Diamond1997">{{cite book | vauthors = Diamond J |author-link=Jared Diamond |title=Why is Sex Fun? The Evolution of Human Sexuality |publisher=Basic Books |location=New York|year=1997 |pages=167–170 |isbn=978-0-465-03127-6}}</ref><ref name="Peccei2001">{{cite journal | vauthors = Peccei JS |title= Menopause: Adaptation or epiphenomenon? |journal=Evolutionary Anthropology |volume=10 |issue=2 |year=2001 |pages=43–57 |doi=10.1002/evan.1013|s2cid=1665503 }}</ref>

The life span of an individual depends on two major factors, genetics and lifestyle choices.<ref name="USC">{{cite news | vauthors = Marziali C |date=7 December 2010 |title=Reaching Toward the Fountain of Youth |url=https://uscnews.usc.edu/health/reaching_toward_the_fountain_of_youth.html|archive-url=https://web.archive.org/web/20101213203112/https://uscnews.usc.edu/health/reaching_toward_the_fountain_of_youth.html|url-status=dead|archive-date=13 December 2010 |work=USC Trojan Family Magazine |access-date=7 December 2010}}</ref> For various reasons, including biological/genetic causes, women live on average about four years longer than men.<ref>{{cite web | vauthors = Kalben BB |title=Why Men Die Younger: Causes of Mortality Differences by Sex |publisher=Society of Actuaries |year=2002 |url=https://www.soa.org/news-and-publications/publications/other-publications/monographs/m-li01-1-toc.aspx |url-status=live |archive-url=https://web.archive.org/web/20130701185241/https://www.soa.org/news-and-publications/publications/other-publications/monographs/m-li01-1-toc.aspx |archive-date=1 July 2013 }}</ref> {{as of|2018|}}, the global average [[life expectancy at birth]] of a girl is estimated to be 74.9 years compared to 70.4 for a boy.<ref>{{cite web|date=2018|title=Life expectancy at birth, female (years)|url=https://data.worldbank.org/indicator/SP.DYN.LE00.FE.IN|access-date=13 October 2020|website=World Bank|archive-date=24 January 2021|archive-url=https://web.archive.org/web/20210124203646/https://data.worldbank.org/indicator/SP.DYN.LE00.FE.IN|url-status=live}}</ref><ref>{{cite web|date=2018|title=Life expectancy at birth, male (years)|url=https://data.worldbank.org/indicator/SP.DYN.LE00.MA.IN|access-date=13 October 2020|website=World Bank|archive-date=24 February 2021|archive-url=https://web.archive.org/web/20210224133034/https://data.worldbank.org/indicator/SP.DYN.LE00.MA.IN|url-status=live}}</ref> There are significant geographical variations in human life expectancy, mostly correlated with economic development{{snd}}for example, life expectancy at birth in [[Hong Kong]] is 87.6&nbsp;years for girls and 81.8 for boys, while in the [[Central African Republic]], it is 55.0&nbsp;years for girls and 50.6 for boys.<ref>{{cite book | vauthors = Conceição P, etal | title = Human Development Report | date = 2019 | publisher = United Nations Development Programme | url = https://hdr.undp.org/sites/default/files/hdr2019.pdf | isbn = 978-92-1-126439-5 | access-date = 30 July 2022 | archive-date = 20 March 2021 | archive-url = https://web.archive.org/web/20210320094952/http://hdr.undp.org/sites/default/files/hdr2019.pdf | url-status = live }}</ref><ref name="MLT">{{cite web|url=https://hdr.undp.org/sites/all/themes/hdr_theme/country-notes/MLT.pdf|title=Human Development Report 2019|language=en|publisher=[[United Nations Development Programme]]|access-date=30 July 2022|archive-date=22 April 2022|archive-url=https://web.archive.org/web/20220422102059/https://hdr.undp.org/sites/all/themes/hdr_theme/country-notes/MLT.pdf|url-status=dead}}</ref> The developed world is generally aging, with the median age around 40 years. In the [[third world|developing world]], the median age is between 15 and 20 years. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older.<ref>{{cite web | url = https://www.cia.gov/library/publications/the-world-factbook/ | title = The World Factbook | archive-url = https://web.archive.org/web/20090912045414/https://www.cia.gov/library/publications/the-world-factbook/ | archive-date = 12 September 2009 | publisher = U.S. Central Intelligence Agency | access-date = 2 April 2005 }}</ref> In 2012, the United Nations estimated that there were 316,600 living [[centenarians]] (humans of age 100 or older) worldwide.<ref name="WORLD2012">{{cite web|url=http://www.unfpa.org/webdav/site/global/shared/documents/publications/2012/UNFPA-Report-Chapter1.pdf|title=Chapter 1: Setting the Scene|year=2012|publisher=UNFPA|access-date=11 January 2013|archive-url=https://web.archive.org/web/20130612052543/http://www.unfpa.org/webdav/site/global/shared/documents/publications/2012/UNFPA-Report-Chapter1.pdf|archive-date=12 June 2013}}</ref>
{| class="wikitable" style="width: 80%; margin-left: auto; margin-right: auto; border: none;"
|+
! colspan="5" | Human life stages
|-
|[[File:Redheaded child mesmerized 2.jpg|100px|center]]
|[[File:Ромський хлопчик (Мукачево).jpg|100px|center]]
|[[File:Boy in Dar es Salaam (14453809622).jpg|100px|center]]
|[[File:Pataxo001.jpg|100px|center]]
|[[File:An old age.JPG|100px|center]]
|-
|[[File:Baby playing with yellow paint. Work by Dutch artist Peter Klashorst entitled "Experimental".jpg|100px|center]]
|[[File:Ethnie dong 6511a.jpg|100px|center]]
|[[File:Portrait of a Persian lady in Iran, 10-08-2006 (cropped).jpg|100px|center]]
|[[File:Punjabi woman smile.jpg|100px|center]]
|[[File:HappyPensioneer.jpg|100px|center]]
|- style="text-align: center;"
|style="width: 20%"|[[Infant]] boy and girl
|style="width: 20%"|Boy and girl before [[puberty]] ([[child]]ren)
|style="width: 20%"|[[Adolescent]] male and female
|style="width: 20%"|[[Adult]] man and woman
|style="width: 20%"|[[Elderly]] man and woman
|}