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'{{Short description|Procreative biological processes of humanity}} {{Sex (biology) sidebar}} '''Human reproduction''' is [[sexual reproduction]] that results in [[human fertilization]] to produce a human offspring. It typically<!-- NOTE: "Typically" is here because, as is clear from the rest of the lead and lower in the article, human reproduction can also be achieved via artificial insemination and assisted reproductive technology. Also, human cloning can theoretically be done, see [[animal cloning]].--> involves [[sexual intercourse]] between a [[sexual maturity|sexually mature]] human [[male]] and [[female]].<ref name=":1">{{Citation |last=Jones |first=Richard E. |title=The Male Reproductive System |date=1991 |work=Human Reproductive Biology |pages=72–93 |publisher=Elsevier |doi=10.1016/b978-0-12-389770-1.50008-1 |isbn=9780123897701 }}</ref> During sexual intercourse, the interaction between the [[male reproductive system|male]] and [[female reproductive system]]s results in fertilization of the [[ovum]] by the [[sperm]] to form a zygote.<ref name=":1" /> While normal cells contain 46 [[chromosome]]s (23 pairs), gamete cells only contain 23 single chromosomes, and it is when these two cells merge into one [[zygote]] cell that [[genetic recombination]] occurs and the new zygote contains 23 chromosomes from each parent, giving it 46 chromosomes (23 pairs).<ref name=":2">{{Cite web |title=Gametogenesis – an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/medicine-and-dentistry/gametogenesis |access-date=2022-09-12 |website=sciencedirect.com}}</ref> The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 9-month [[gestation period]] that is followed by [[childbirth]]. The fertilization of the ovum may be achieved by [[artificial insemination]] methods, which do not involve sexual intercourse.<ref name=":3">{{Cite journal |last1=Ombelet |first1=W. |last2=Van Robays |first2=J. |date=2015 |title=Artificial insemination history: hurdles and milestones |journal=Facts, Views & Vision in ObGyn |volume=7 |issue=2 |pages=137–143 |issn=2032-0418 |pmc=4498171 |pmid=26175891 }}</ref> [[Assisted reproductive technology]] also exists. == Biological and legal requirements == In order for human reproduction to be achieved, an individual must have undergone [[puberty]] first, requiring [[ovulation]] in females and the [[spermarche]] in males to have occurred prior to engaging in [[sexual intercourse]] or achieving [[pregnancy]] through non-penetrative means. Before puberty, humans are [[infertile]], as their genitals lack reproductive function (only being able to discharge [[urine]]). Legal factors also play a vital role in the achievement of human reproduction: a [[Minor (law)|minor]] under the [[age of consent]] cannot give legal consent to sexual intercourse or artificial alternatives to reproduction, the former case of which is liable to have the older party charged with [[statutory rape]], depending on jurisdictions.<ref name="Cusack">{{cite book|author=Carmen M. Cusack|title=Laws Relating to Sex, Pregnancy, and Infancy: Issues in Criminal Justice|publisher=[[Springer Publishing|Springer]]|isbn=978-1137505194|year=2015|page=10|access-date=August 31, 2021|url=https://books.google.com/books?id=ZArACQAAQBAJ&pg=PT10|quote=Voluntary sexual intercourse with a post-pubescent minor who is younger than the legal age of consent is described as statutory rape. [...] In most states, age of consent is delimited between 16 years old and 18 years old. [...] In almost every jurisdiction, prepubescent children may not engage in any sexual contact. [...] Engaging in sexual contact with a prepubescent child is a serious criminal offense and a felony.|archive-date=May 9, 2021|archive-url=https://web.archive.org/web/20210509005922/https://books.google.com/books?id=ZArACQAAQBAJ&pg=PT10|url-status=live}}</ref><ref name=ojjdp>{{cite web |url=http://www.ncjrs.gov/pdffiles1/ojjdp/208803.pdf |title=Statutory Rape Known to Law Enforcement |access-date=2021-08-31 |publisher=U.S. Department of Justice - Office of Juvenile Justice and Delinquency Prevention |archive-date=2007-10-21 |archive-url=https://web.archive.org/web/20071021131957/http://www.ncjrs.gov/pdffiles1/ojjdp/208803.pdf |url-status=live }}</ref> Even for minors above the age of consent, [[comprehensive sex education]] advises both consenting parties to use [[contraception]] to avoid both [[sexually transmitted infection]]s and [[Teenage pregnancy|early, unplanned/unwanted pregnancies]]. Pregnancy in girls under the age of 15 is especially discouraged due to their reproductive systems having yet to reach full maturity.<ref name=savethechildren>{{cite journal | author = Mayor S |title = Pregnancy and childbirth are leading causes of death in teenage girls in developing countries | journal = BMJ | volume = 328 | issue = 7449 | pages = 1152 | year = 2004 | pmid = 15142897 | pmc = 411126 | doi = 10.1136/bmj.328.7449.1152-a }}</ref> == Anatomy == {{Further|Human reproductive system}} ===Male reproductive system === {{Further|Male reproductive system}} The male reproductive system contains two main divisions: the [[testicle]]s where [[sperm]] are produced, and the [[human penis|penis]] which discharges the sperm as [[semen]] (this is known as an [[ejaculation]]). In humans, both of these organs are outside the [[abdominal cavity]]. Having the testicles outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3&nbsp;°C less than the normal body temperature i.e. 37&nbsp;°C. In particular, the extraperitoneal location of the testicles may result in a 2-fold reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissues compared to tissues at 37&nbsp;°C.<ref>{{cite journal | author = Baltz RH, Bingham PM, Drake JW | year = 1976 | title = Heat mutagenesis in bacteriophage T4: The transition pathway | journal = Proc. Natl. Acad. Sci. USA | volume = 73 | issue = 4| pages = 1269–1273 | pmid = 4797 | pmc = 430244 | doi = 10.1073/pnas.73.4.1269 | bibcode = 1976PNAS...73.1269B | doi-access = free }}</ref> If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external [[scrotum]] rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production. === Female reproductive system === {{Further|Female reproductive system}} The female reproductive system likewise contains two main divisions: the external genitalia (the [[vulva]]) and the internal genitalia. The [[Egg cell|ovum]] meets with the [[sperm cell]]: a sperm may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome. The fertilization usually occurs in the [[fallopian tube]]s, but can happen in the uterus itself. The [[zygote]] then becomes [[Implantation (human embryo)|implanted]] in the lining of the uterus, where it begins the processes of [[embryogenesis]] and [[morphogenesis]]. When the [[fetus]] is developed enough to survive outside of the [[uterus]], the cervix dilates and contractions of the uterus propel it through the birth canal, which is the [[vagina]], and thereby gives external life to the newborn [[infant]]. This process is called [[childbirth]]. The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the [[Ovary|ovaries]] of the female fetus before birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later [[zygote]] and [[embryo]]. Over a regular interval known as the [[menstrual cycle]], in response to hormonal signals, a process of [[oogenesis]] matures one ovum which is released and sent down the fallopian tube. If not fertilized, this egg is flushed out of the system through [[menstruation]]. == Process of fertilization == [[File:Biological life cycle of humans 2.png|thumb|Basic processes involved: <br>1. [[sexual maturity|maturity]]; 2. [[spermatogenesis]] and [[oogenesis]]; 3. [[vaginal intercourse]] with [[internal fertilization]]; <br>4. [[zygote]]; 5. [[Human embryonic development|embryonic development]]; <br>6. [[childbirth]]; 7. [[adolescence]].]] [[Image:Da Vinci Coition of a Hemisected Man and Woman Luc Viatour.jpg|thumb|200px|right|"Coition of a Hemisected Man and Woman" ({{Circa|1492}}) by [[Leonardo da Vinci]]]] Human reproduction normally begins with copulation, though it may be achieved through [[artificial insemination]], and is followed by nine months of pregnancy before childbirth. Pregnancy can be avoided with the use of contraceptives such as [[condom]]s and [[intrauterine device]]s.<ref>{{Cite journal |last1=Teal |first1=Stephanie |last2=Edelman |first2=Alison |date=2021-12-28 |title=Contraception Selection, Effectiveness, and Adverse Effects: A Review |url=https://jamanetwork.com/journals/jama/fullarticle/2787541 |journal=JAMA |language=en |volume=326 |issue=24 |pages=2507–2518 |doi=10.1001/jama.2021.21392 |pmid=34962522 |s2cid=245557522 |issn=0098-7484 |access-date=2022-09-12 |archive-date=2022-08-26 |archive-url=https://web.archive.org/web/20220826082329/https://jamanetwork.com/journals/jama/fullarticle/2787541 |url-status=live |doi-access=free }}</ref> === Copulation === {{Main|Sexual intercourse}} Human reproduction naturally takes place as [[internal fertilization]] by sexual intercourse. During this process, the man inserts his erect [[Human penis|penis]] into the woman's [[vagina]] and then either partner initiates rhythmic [[pelvic thrust]]s until the man achieves [[orgasm]], which leads to [[ejaculation]] of [[semen]] containing sperm into the vaginal canal. The sperm and the ovum are known as the [[gametes]] (each containing half the genetic information of the parent, created through [[meiosis]]).<ref name=":2" /> The sperm (being one of approximately 250 million sperm in a typical ejaculation) travels through the vagina and cervix into the uterus or fallopian tubes. Only 1 in 14 million of the ejaculated sperm will reach the fallopian tube. The egg simultaneously moves through the fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a [[zygote]]. Upon [[Human fertilization|fertilization]] and [[Implantation (human embryo)|implantation]], gestation of the fetus then occurs within the uterus.<ref>{{cite journal |author=Ghazal, S, Kulp Makarov, J |url=http://www.glowm.com/section_view/heading/Egg%20Transport%20and%20Fertilization/item/316 |title=Egg Transport and Fertilization |journal=The Global Library of Women's Medicine |year=2014 |issn=1756-2228 |doi=10.3843/GLOWM.10317 |access-date=May 8, 2016 |display-authors=etal |archive-date=May 13, 2016 |archive-url=https://web.archive.org/web/20160513065553/http://www.glowm.com/section_view/heading/Egg%20Transport%20and%20Fertilization/item/316 |url-status=live }}</ref><ref>{{cite web |url=https://www.ucsfhealth.org/education/conception_how_it_works/ |title=Conception: How It Works |publisher=The Regents of The University of California |year=2002 |access-date=May 8, 2016 |archive-date=March 15, 2016 |archive-url=https://web.archive.org/web/20160315083424/https://www.ucsfhealth.org/education/conception_how_it_works/ |url-status=live }}</ref><ref>{{cite web |url=http://www.completefertility.co.uk/fertility_basics.php |title=Fertility Basics |work=Complete Fertility Centre Southampton |publisher=Complete Fertility Ltd |year=2015 |access-date=May 8, 2016 |archive-date=May 8, 2016 |archive-url=https://web.archive.org/web/20160508060750/http://www.completefertility.co.uk/fertility_basics.php |url-status=live }}</ref><ref>{{cite web |url=http://www.webmd.com/baby/guide/understanding-conception |title=Conception & Pregnancy: Ovulation, Fertilization, and More |publisher=WebMD, LLC |year=2016 |access-date=May 8, 2016 |archive-date=May 8, 2016 |archive-url=https://web.archive.org/web/20160508202313/http://www.webmd.com/baby/guide/understanding-conception |url-status=live }}</ref> [[File:Pregnancy chance by day near ovulation.jpg|thumb|Chance of [[human fertilization|fertilization]] by [[menstrual cycle]] day relative to ovulation<ref name="DunsonBaird1999">{{cite journal|last1=Dunson|first1=D.B.|last2=Baird|first2=D.D.|last3=Wilcox|first3=A.J.|last4=Weinberg|first4=C.R.|author4-link=Clarice Weinberg|title=Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation|journal=Human Reproduction|volume=14|issue=7|year=1999|pages=1835–1839|issn=1460-2350|doi=10.1093/humrep/14.7.1835|doi-access=free|pmid=10402400}}</ref>]] [[Pregnancy rate#Pregnancy rate for sexual intercourse|Pregnancy rates for sexual intercourse]] are highest during the [[menstrual cycle]] time from some 5 days before until 1 to 2 days after ovulation.<ref>Pages.242,374 in: {{cite book|title=Taking Charge of Your Fertility|url=https://archive.org/details/takingchargeofyo00toni|url-access=registration|last=Weschler|first=Toni|publisher=HarperCollins|year=2002|isbn=0-06-093764-5|edition=Revised|location=New York|pages=[https://archive.org/details/takingchargeofyo00toni/page/359 359–361]}}</ref> For optimal pregnancy chance, there are recommendations of sexual intercourse every 1 or 2 days,<ref>{{cite web|url=https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/how-to-get-pregnant/art-20047611|title=How to get pregnant|website=[[Mayo Clinic]]|date=2016-11-02|access-date=2018-02-16|archive-date=2020-05-18|archive-url=https://web.archive.org/web/20200518223708/https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/how-to-get-pregnant/art-20047611|url-status=live}}</ref> or every 2 or 3 days.<ref>{{cite web|url=https://www.nice.org.uk/guidance/cg156/ifp/chapter/trying-for-a-baby|title=Fertility problems: assessment and treatment, Clinical guideline [CG156]|website=[[National Institute for Health and Care Excellence]]|access-date=2018-02-16|archive-date=2018-02-17|archive-url=https://web.archive.org/web/20180217082533/https://www.nice.org.uk/guidance/cg156/ifp/chapter/trying-for-a-baby|url-status=live}} Published date: February 2013. Last updated: September 2017</ref> Studies have shown no significant difference between different [[sex positions]] and pregnancy rate, as long as it results in [[ejaculation]] into the [[vagina]].<ref name=americanpregnancy>{{cite web|url=http://americanpregnancy.org/getting-pregnant-ebook/p7M7O0q1c71703C/gettingpregnant.pdf|title=The Essential Guide to Getting Pregnant|website=American Pregnancy Association|author=Dr. Philip B. Imler & David Wilbanks|access-date=2018-02-16|archive-url=https://web.archive.org/web/20180601033115/http://americanpregnancy.org/getting-pregnant-ebook/p7M7O0q1c71703C/gettingpregnant.pdf|archive-date=2018-06-01|url-status=dead}}</ref> ===Alternative methods=== As an alternative to natural sexual intercourse, there exists [[artificial insemination]], where sperm is introduced into the female reproductive system without the insertion of the penis.<ref name=":3" /> There are also many methods of [[assisted reproductive technology]], such as [[in vitro fertilization]], where one or more [[Oocyte|egg cells]] are retrieved from a woman's ovaries and co-incubated with sperm outside the body. The resulting embryo can then be reinserted into the womb of the woman.{{citation needed|date=October 2022}} ===Pregnancy=== {{Main|Pregnancy}} Pregnancy is the period of time during which the fetus develops, dividing via [[mitosis]] inside the uterus. During this time, the fetus receives all of its [[nutrition]] and oxygenated blood from the mother, filtered through the [[placenta]], which is attached to the fetus' [[abdomen]] via an [[umbilical cord]]. This drain of [[nutrient]]s can be quite taxing on the mother, who is required to ingest slightly higher levels of [[calorie]]s. In addition, certain [[vitamin]]s and other nutrients are required in greater quantities than normal, often creating abnormal eating habits. Gestation period is about 266 days in humans. While in the uterus, the baby first endures a very brief zygote stage, then the embryonic stage, which is marked by the development of major organs and lasts for approximately eight weeks, then the fetal stage, which revolves around the development of bone cells while the fetus continues to grow in size.<ref>{{cite book|author1-link=Gregory J. Feist|last1=Feist|first1=Gregory J.|last2=Rosenberg|first2=Erika L.|title=Psychology: Perspectives and Connections|date=11 October 2011|publisher=McGraw Hill|isbn=978-0-07-803520-3|pages=(171–172)|edition=Second|url-access=registration|url=https://archive.org/details/isbn_9780078035203}}</ref> It is estimated that about 3-5% of couples are infertile and the fecunditity of couples is around 30% for each menstrual cycle.<ref>{{Cite journal |last=Spira |first=A. |date=February 1986 |title=Epidemiology of human reproduction |url=https://pubmed.ncbi.nlm.nih.gov/3549765 |journal=Human Reproduction (Oxford, England) |volume=1 |issue=2 |pages=111–115 |doi=10.1093/oxfordjournals.humrep.a136353 |issn=0268-1161 |pmid=3549765 |access-date=2022-09-12 |archive-date=2022-06-15 |archive-url=https://web.archive.org/web/20220615224544/https://pubmed.ncbi.nlm.nih.gov/3549765/ |url-status=live }}</ref> ===Labor and birth=== [[Image:Postpartum baby2.jpg|250px|thumb|Newborn infant and mother]] {{Main|Childbirth}} Labor is separated into 4 stages. The first stage involves latent phase and active phase separated by the dilation of the cervix for 6 to 10&nbsp;cm. The second stage is the pushing stage. The third stage involves the delivery of the placenta. And the last stage is the contraction of the uterus.<ref>{{Cite journal |last1=Liao |first1=John B. |last2=Buhimschi |first2=Catalin S. |last3=Norwitz |first3=Errol R. |date=June 2005 |title=Normal labor: mechanism and duration |url=https://pubmed.ncbi.nlm.nih.gov/15899352 |journal=Obstetrics and Gynecology Clinics of North America |volume=32 |issue=2 |pages=145–164, vii |doi=10.1016/j.ogc.2005.01.001 |issn=0889-8545 |pmid=15899352 |access-date=2022-09-12 |archive-date=2022-06-15 |archive-url=https://web.archive.org/web/20220615124921/https://pubmed.ncbi.nlm.nih.gov/15899352/ |url-status=live }}</ref> Once the fetus is sufficiently developed, chemical signals begin the process of birth, which begins with the fetus being pushed out of the birthing canal. The newborn, which is called an [[infant]] in humans, should typically begin [[Respiration (physiology)|respiration]] on its own shortly after birth. Not long after, the placenta eventually falls off on its own. The person assisting the birth may also sever the umbilical cord. ==Discovery of mechanism== While most ancient human societies believed that [[sexual intercourse]] was necessary for reproduction, the reasons some sex did not result in children, and the mechanism by which mating produced children were not understood. The theory of [[preformationism]] was popular in [[Ancient Greece]] and [[Christendom]] for centuries. Because they are too small to see with the naked eye, it was only after his invention of the microscope that [[Antonie van Leeuwenhoek]] discovered [[spermatozoa]] in 1677. [[Mitosis]] and [[meiosis]] were not discovered until the late 1800s. ==See also== *[[Heterosexuality]] *[[Antinatalism]] *[[Evolution of sexual reproduction]] *[[Female infertility]] *''[[Human Reproduction (journal)]]'' *''[[Journal of Human Reproductive Sciences]]'' *[[Male infertility]] *[[Natalism]] *[[Paternal age effect]] *[[Reproduction]] *[[Reproductive system]] *[[Reproductive rights|Legislation on human reproduction]] *[[Reproductive health#Reproductive health|Reproductive health]] ==References== {{Reflist}} [https://www.altrui.co.uk/resources/the-human-egg-cell-explained/ Altrui - The Human Egg Cell Explained] ==Further reading== * Hopwood, Nick, Rebecca Flemming, Lauren Kassell, eds. ''Reproduction: Antiquity to the Present Day'' (Cambridge UP, 2018). Illustrations. xxxv + 730 pp. {{ISBN|978-1-107-06802-5}} [https://www.amazon.com/Reproduction-Antiquity-Present-Nick-Hopwood/dp/1107068029/ excerpt] also [http://www.h-net.org/reviews/showpdf.php?id=53889 online review] 44 scholarly essays by historians. * {{cite book |title=The Seeds of Life: From Aristotle to da Vinci, from Sharks' Teeth to Frogs' Pants, the Long and Strange Quest to Discover Where Babies Come |year=2017 |first=Edward |last=Dolnick |publisher=Basic Books |isbn=978-0465082957}} {{Pregnancy}} {{Reproductive physiology}} {{Authority control}} [[Category:Human reproduction| ]]'