Why should mitochondria define species?
HUMAN EVOLUTION Vol. 33 - n. 1-2 (1-30) - 2018
Stoeckle M.Y.
Program for the Human Environment
The Rockefeller University
1230 York AVE
New York, NY 10065
USA
Email: mark.stoeckle@rockefeller.edu
Thaler D.S.
Biozentrum, University of Basel
Klingelbergstrasse 50/70
CH - 4056 Basel
Switzerland
Email: david.thaler@unibas.ch davidsthaler@gmail.com
The amount of color variation within each red box of the Klee diagram illustrates the far greater mitochondrial diversity among chimpanzees and bonobos than among living humans. (From the journal Ecology and Evolution, online at https://onlinelibrary.wiley.com/doi/epdf/10.1002/ece3.2394).
Abstract
More than a decade of DNA barcoding encompassing about five million specimens covering 100,000 animal species supports the generalization that mitochondrial DNA clusters largely overlap with species as defined by domain experts. Most barcode clustering reflects synonymous substitutions. What evolutionary mechanisms account for synonymous clusters being largely coincident with species? The answer depends on whether variants are phenotypically neutral. To the degree that variants are selectable, purifying selection limits variation within species and neighboring species may have distinct adaptive peaks. Phenotypically neutral variants are only subject to demographic processes—drift, lineage sorting, genetic hitchhiking, and bottlenecks. The evolution of modern humans has been studied from several disciplines with detail unique among animal species. Mitochondrial barcodes provide a commensurable way to compare modern humans to other animal species. Barcode variation in the modern human population is quantitatively similar to that within other animal species. Several convergent lines of evidence show that mitochondrial diversity in modern humans follows from sequence uniformity followed by the accumulation of largely neutral diversity during a population expansion that began approximately 100,000 years ago. A straightforward hypothesis is that the extant populations of almost all animal species have arrived at a similar result consequent to a similar process of expansion from mitochondrial uniformity within the last one to several hundred thousand years.
Key words: Species evolution, mitocondrial evolution, speciation, human evolution.
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