This article reviews the history of FOXP2 research and how our understanding of its impact on human evolution has changed over time, highlighting the recent study by Atkinson et al, 2018 that found no evidence of a selective sweep at FOXP2.
FOXP2 was first published on in 2001 as a gene that, when mutated, caused speech and language disorders. Due to how human speech is thought to be not only a unique modern human trait but a trait which led humans to be so successful, FOXP2 attracted many scientists to study its evolutionary history, look for mutations in and around this locus, and compare its sequence between modern humans and other organisms. In 2002, two independent studies by Enard et al and Zhang et al both came to the same conclusion that FOXP2 went through a selective sweep in modern humans around 200k years ago. This matched up with the fossil and genetic evidence for the emergence of modern humans in Africa of the time. A wrench was thrown into this idea in 2007 when Krause et al published on their evidence that Neandertals and modern humans shared the same derived form of FOXP2. The common ancestor between Neandertals and modern humans most likely possessed the two amino acid substitutions, pushing back the selective sweep to >400k and showing that these mutations are not modern human specific.
Much more recently, a slightly larger wrench was thrown into the works when Atkinson et al (2018) published a study done similarly to the ones conducted in 2001-2002 but included a larger, and more diverse sample of individuals from around the world and re-assessed the entire locus, looking for that selective sweep. When using the mixed sample from HGDP (a non-African majority) the Tajima's D was negative and showed evidence of positive selection at this locus. However, when the samples were split into Eurasian and African groups, the values for D were within their expected values under a neutral model and showed no evidence of a selective sweep.
The author states that although there is no evidence for modern humans having experienced a selective sweep at this locus, FOXP2 still remains incredibly important and interesting in neurobiology when researching speech and language dysfunctions across multiple organisms. Human biology and evolution is incredibly complex and it is not surprising that FOXP2 evolution was not as straightforward as we hoped.
-Alexis W.
https://doi.org/10.1016/j.cub.2018.11.047
Fisher SE. Human genetics: The evolving story of FOXP2. Current Biology. 2019 Jan 21;29(2):R65-7.
Atkinson, EG, Audesse, AJ, Palacios, JA, Bobo, DM, Webb, AE, Ramachandran, S., and Henn, BM. No evidence for recent selection at FOXP2 among diverse human populations. Cell. 2018 174;1424–1435.
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