Editing Evolution (section)

=== Pangenesis and heredity ===

The mechanisms of reproductive heritability and the origin of new traits remained a mystery. Towards this end, Darwin developed his provisional theory of [[pangenesis]].<ref name="Liu-2009">{{cite journal |author1=Y.-S. Liu |author2=X. M. Zhou |author3=M. X. Zhi |author4=X. J. Li |author5=Q. L. Wang |s2cid=19919317 |date=September 2009 |title=Darwin's contributions to genetics |journal=Journal of Applied Genetics |volume=50 |issue=3 |pages=177–184 |doi=10.1007/BF03195671 |issn=1234-1983 |pmid=19638672}}</ref> In 1865, [[Gregor Mendel]] reported that traits were inherited in a predictable manner through the [[independent assortment]] and segregation of elements (later known as genes). Mendel's laws of inheritance eventually supplanted most of Darwin's pangenesis theory.<ref name="Weiling-1991">{{cite journal |last=Weiling |first=Franz |date=July 1991 |title=Historical study: Johann Gregor Mendel 1822–1884 |journal=[[American Journal of Medical Genetics]] |volume=40 |issue=1 |pages=1–25; discussion 26 |doi=10.1002/ajmg.1320400103 |pmid=1887835}}</ref> [[August Weismann]] made the important distinction between [[germ cell]]s that give rise to [[gamete]]s (such as [[sperm]] and [[egg cell]]s) and the [[somatic cell]]s of the body, demonstrating that heredity passes through the germ line only. [[Hugo de Vries]] connected Darwin's pangenesis theory to Weismann's germ/soma cell distinction and proposed that Darwin's pangenes were concentrated in the [[cell nucleus]] and when expressed they could move into the [[cytoplasm]] to change the [[Cell (biology)|cell]]'s structure. De Vries was also one of the researchers who made Mendel's work well known, believing that Mendelian traits corresponded to the transfer of heritable variations along the germline.<ref name="Wright84">{{harvnb|Wright|1984|p=480}}</ref> To explain how new variants originate, de Vries developed [[Mutationism|a mutation theory]] that led to a temporary rift between those who accepted Darwinian evolution and biometricians who allied with de Vries.<ref>{{harvnb|Provine|1971}}</ref><ref>{{cite journal |last1=Stamhuis |first1=Ida H. |last2=Meijer |first2=Onno G. |last3=Zevenhuizen |first3=Erik J. A. |date=June 1999 |title=Hugo de Vries on Heredity, 1889–1903: Statistics, Mendelian Laws, Pangenes, Mutations |url=https://archive.org/details/sim_isis_1999-06_90_2/page/238 |volume=90 |issue=2 |pages=238–267 |journal=[[Isis (journal)|Isis]] |doi=10.1086/384323 |jstor=237050 |pmid=10439561 |s2cid=20200394}}</ref> In the 1930s, pioneers in the field of [[population genetics]], such as [[Ronald Fisher]], [[Sewall Wright]] and [[J. B. S. Haldane]] set the foundations of evolution onto a robust statistical philosophy. The false contradiction between Darwin's theory, genetic mutations, and [[Mendelian inheritance]] was thus reconciled.{{sfn|Bowler|1989|pp=307–318}}