Editing Heredity (section)

== History ==
[[File:Aristotle's model of Inheritance.png|thumb|left|upright=1.4|[[Aristotle's biology#Inheritance|Aristotle's model of inheritance]]. The heat/cold part is largely symmetrical, though influenced on the father's side by other factors, but the form part is not.]]
Scientists in [[Classical antiquity|Antiquity]] had a variety of ideas about heredity: [[Theophrastus]] proposed that male flowers caused female flowers to ripen;<ref>{{cite journal | title=Male and female in Theophrastus's botanical works | author=Negbi, Moshe | journal=Journal of the History of Biology | date=Summer 1995 | volume=28 | issue=2 | pages=317–332 | doi=10.1007/BF01059192| s2cid=84754865}}</ref> [[Hippocrates]] speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception;<ref>{{cite book | title=Hippocratic Treatises: On Generation – Nature of the Child – Diseases Ic | publisher=Walter de Gruyter | author=Hipócrates | date=1981 | pages=6 | isbn=978-3-11-007903-6}}</ref> and [[Aristotle]] thought that male and female fluids mixed at conception.<ref>{{cite web | url=http://plato.stanford.edu/entries/aristotle-biology/ | title=Aristotle's Biology – 5.2. From Inquiry to Understanding; from hoti to dioti. | publisher=Stanford University | date=Feb 15, 2006 | access-date=March 26, 2013 | archive-date=May 7, 2019 | archive-url=https://web.archive.org/web/20190507040441/https://plato.stanford.edu/entries/aristotle-biology/ | url-status=live}}</ref> [[Aeschylus]], in 458 BC, proposed the male as the parent, with the female as a "nurse for the young life sown within her".<ref>''Eumenides'' 658–661</ref>

Ancient understandings of heredity transitioned to two debated doctrines in the 18th century. The Doctrine of Epigenesis and the Doctrine of Preformation were two distinct views of the understanding of heredity. The Doctrine of Epigenesis, originated by [[Aristotle]], claimed that an embryo continually develops. The modifications of the parent's traits are passed off to an embryo during its lifetime. The foundation of this doctrine was based on the theory of [[inheritance of acquired traits]]. In direct opposition, the Doctrine of Preformation claimed that "like generates like" where the germ would evolve to yield offspring similar to the parents. The Preformationist view believed procreation was an act of revealing what had been created long before. However, this was disputed by the creation of the [[cell theory]] in the 19th century, where the fundamental unit of life is the cell, and not some preformed parts of an organism. Various hereditary mechanisms, including [[blending inheritance]] were also envisaged without being properly tested or quantified, and were later disputed. Nevertheless, people were able to develop domestic breeds of animals as well as crops through artificial selection. The inheritance of acquired traits also formed a part of early Lamarckian ideas on evolution.{{cn|date=March 2023}}

During the 18th century, Dutch microscopist [[Antonie van Leeuwenhoek]] (1632–1723) discovered "animalcules" in the sperm of humans and other animals.<ref>{{cite web | url=http://www.leben.us/index.php/component/content/article/59-volume-3-issue-4/236-antoni-van-leeuwenhoeks-amazing-little-animalcules | title=Antoni van Leeuwenhoek's Amazing Little "Animalcules" | publisher=Leben | access-date=March 26, 2013 | author=Snow, Kurt | url-status=dead | archive-url=https://web.archive.org/web/20130424173741/http://www.leben.us/index.php/component/content/article/59-volume-3-issue-4/236-antoni-van-leeuwenhoeks-amazing-little-animalcules | archive-date=April 24, 2013}}</ref> Some scientists speculated they saw a "little man" ([[homunculus]]) inside each [[spermatozoon|sperm]]. These scientists formed a school of thought known as the "spermists". They contended the only contributions of the female to the next generation were the womb in which the homunculus grew, and prenatal influences of the womb.<ref>{{cite encyclopedia|url=http://embryo.asu.edu/view/embryo:125308 |archive-url=https://archive.today/20130409231317/http://embryo.asu.edu/view/embryo:125308 |url-status=dead |archive-date=2013-04-09 |title=Hartsoeker's Homunculus Sketch from Essai de Dioptrique |publisher=Embryo Project Encyclopedia |date=2008 |access-date=March 26, 2013 |author=Lawrence, Cera R. |issn=1940-5030}}</ref> An opposing school of thought, the ovists, believed that the future human was in the egg, and that sperm merely stimulated the growth of the egg. Ovists thought women carried eggs containing boy and girl children, and that the gender of the offspring was determined well before conception.<ref>{{cite book | title=Individual Development and Evolution: The Genesis of Novel Behavior | publisher=Psychology Press | author=Gottlieb, Gilbert | date=2001 | pages=4 | isbn=978-1-4106-0442-2}}</ref>

An early research initiative emerged in 1878 when [[Alpheus Hyatt]] led an investigation to study the laws of heredity through compiling data on family phenotypes (nose size, ear shape, etc.) and expression of pathological conditions and abnormal characteristics, particularly with respect to the age of appearance. One of the projects aims was to tabulate data to better understand why certain traits are consistently expressed while others are highly irregular.<ref>{{Cite book|url=https://books.google.com/books?id=p4o9AQAAIAAJ&q=heredity|title=Scientific American, "Heredity"|date=1878-11-30|publisher=Munn & Company|pages=343|language=en|access-date=2021-08-06|archive-date=2022-05-18|archive-url=https://web.archive.org/web/20220518005249/https://books.google.com/books?id=p4o9AQAAIAAJ&q=heredity|url-status=live}}</ref>

===Gregor Mendel: father of genetics===
[[File:Independent assortment & segregation.svg|thumb|Table showing how the genes exchange according to segregation or independent assortment during [[meiosis]] and how this translates into Mendel's laws]]
{{Main|Gregor Mendel}}
{{See also|Modern synthesis (20th century)}}
The idea of particulate inheritance of genes can be attributed to the [[Moravia]]n<ref>{{Cite book | last = Henig | first = Robin Marantz | title = The Monk in the Garden : The Lost and Found Genius of Gregor Mendel, the Father of Genetics | publisher = Houghton Mifflin | date = 2001 | isbn = 978-0-395-97765-1 | quote = The article, written by an obscure Moravian monk named Gregor Mendel | url-access = registration | url = https://archive.org/details/monkingardenlost00heni}}</ref> monk [[Gregor Mendel]] who published his work on pea plants in 1865. However, his work was not widely known and was rediscovered in 1901. It was initially assumed that [[Mendelian inheritance]] only accounted for large (qualitative) differences, such as those seen by Mendel in his pea plants&nbsp;– and the idea of additive effect of (quantitative) genes was not realised until [[Ronald Fisher|R.A. Fisher]]'s (1918) paper, "[[The Correlation Between Relatives on the Supposition of Mendelian Inheritance]]" Mendel's overall contribution gave scientists a useful overview that traits were inheritable. His pea plant demonstration became the foundation of the study of Mendelian Traits. These traits can be traced on a single locus.<ref name="Carlson p. 206">Carlson, Neil R.<!-- , et al. other editors are listed in the 2014 edition per WorldCat--> (2010). ''Psychology: the Science of Behavior'', p. 206. Toronto: Pearson Canada. {{ISBN|978-0-205-64524-4}}. {{OCLC|1019975419}}</ref>

===Modern development of genetics and heredity===
{{Main|History of genetics|History of evolutionary thought}}
In the 1930s, work by Fisher and others resulted in a combination of Mendelian and biometric schools into the [[Modern synthesis (20th century)|modern evolutionary synthesis]]. The modern synthesis bridged the gap between experimental geneticists and naturalists; and between both and palaeontologists, stating that:<ref>Mayr & Provine 1998</ref><ref>Mayr E. 1982. ''The growth of biological thought: diversity, evolution & inheritance''. Harvard, Cambs. pp. 567 et seq.</ref>

# All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists.
# Evolution is gradual: small genetic changes, recombination ordered by [[natural selection]]. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation).
# [[Natural selection|Selection]] is overwhelmingly the main mechanism of change; even slight advantages are important when continued. The object of selection is the [[phenotype]] in its surrounding environment. The role of [[genetic drift]] is equivocal; though strongly supported initially by [[Dobzhansky]], it was downgraded later as results from ecological genetics were obtained.
# The primacy of population thinking: the genetic diversity carried in natural populations is a key factor in evolution. The strength of natural selection in the wild was greater than expected; the effect of ecological factors such as niche occupation and the significance of barriers to gene flow are all important.

The idea that [[speciation]] occurs after populations are reproductively isolated has been much debated.<ref>{{cite journal | title=Genetic Divergence, Reproductive Isolation, and Marine Speciation | author=Palumbi, Stephen R. | author-link = Stephen Palumbi | journal=Annual Review of Ecology and Systematics | date=1994 | volume=25 | pages=547–572 | doi=10.1146/annurev.es.25.110194.002555}}</ref> In plants, polyploidy must be included in any view of speciation. Formulations such as 'evolution consists primarily of changes in the [[allele frequency|frequencies of alleles]] between one generation and another' were proposed rather later. The traditional view is that developmental biology ('[[evo-devo]]') played little part in the synthesis, but an account of [[Gavin de Beer]]'s work by [[Stephen Jay Gould]] suggests he may be an exception.<ref>Gould S.J. ''Ontogeny and phylogeny''. Harvard 1977. pp. 221–222</ref>

Almost all aspects of the synthesis have been challenged at times, with varying degrees of success. There is no doubt, however, that the synthesis was a great landmark in evolutionary biology.<ref>{{cite journal | title=Evolution – The Extended Synthesis. A research proposal persuasive enough for the majority of evolutionary biologists? | author=Handschuh, Stephan | author2=Mitteroecker, Philipp | journal= Human Ethology Bulletin|date=June 2012 | volume=27 | issue=1–2 | pages=18–21 | issn=2224-4476}}</ref> It cleared up many confusions, and was directly responsible for stimulating a great deal of research in the post-[[World War II]] era.

[[Trofim Lysenko]] however caused a backlash of what is now called [[Lysenkoism]] in the [[Soviet Union]] when he emphasised [[Lamarckian]] ideas on the [[inheritance of acquired traits]]. This movement affected agricultural research and led to food shortages in the 1960s and seriously affected the USSR.<ref>{{Cite journal|last=Harper|first=Peter S.|date=2017-08-03|title=Human genetics in troubled times and places|journal=Hereditas|volume=155|pages=7|doi=10.1186/s41065-017-0042-4|issn=1601-5223|pmc=5541658|pmid=28794693 |doi-access=free }}</ref>

There is growing evidence that there is transgenerational inheritance of epigenetic changes in humans<ref>{{cite journal|last1=Szyf|first1=M|title=Nongenetic inheritance and transgenerational epigenetics|journal=Trends in Molecular Medicine|date=2015|volume=21|issue=2|pages=134–144|doi=10.1016/j.molmed.2014.12.004|pmid=25601643}}</ref> and other animals.<ref>{{cite journal|last1=Kishimoto|first1=S|display-authors= etal|title=Environmental stresses induce transgenerationally inheritable survival advantages via germline-to-soma communication in Caenorhabditis elegans|journal=Nature Communications|date=2017|volume=8|doi=10.1038/ncomms14031|pmid=28067237|page=14031|hdl=2433/217772|bibcode=2017NatCo...814031K|pmc=5227915}}</ref>

===Common genetic disorders===
:*[[Fragile X syndrome]]
:*[[Sickle cell disease]]
:*[[Phenylketonuria]] (PKU)
:*[[Haemophilia]]<ref name="Carlson p. 206"/>