Nathan M. Young a,1, Günter P. Wagner b, and Benedikt Hallgrímsson c
-Author Affiliations
aDepartment of Orthopaedic Surgery, University of California, San Francisco, CA 94110;
bDepartment of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06405; and
cDepartment of Cell Biology and Anatomy, University of Calgary, Calgary, AB, Canada T2N4N1
Edited* by David Pilbeam, Harvard University, Cambridge, MA, and approved December 29, 2009 (received for review October 14, 2009)
Abstract
The long legs and short arms of humans are distinctive for a primate, the result of selection acting in opposite directions on each limb at different points in our evolutionary history. This mosaic pattern challenges our understanding of the relationship of development and evolvability because limbs are serially homologous and genetic correlations should act as a significant constraint on their independent evolution. Here we test a developmental model of limb covariation in anthropoid primates and demonstrate that both humans and apes exhibit significantly reduced integration between limbs when compared to quadrupedal monkeys. This result indicates that fossil hominins likely escaped constraints on independent limb variation via reductions to genetic pleiotropy in an ape-like last common ancestor (LCA). This critical change in integration among hominoids, which is reflected in macroevolutionary differences in the disparity between limb lengths, facilitated selection for modern human limb proportions and demonstrates how development helps shape evolutionary change.
Abstract
The long legs and short arms of humans are distinctive for a primate, the result of selection acting in opposite directions on each limb at different points in our evolutionary history. This mosaic pattern challenges our understanding of the relationship of development and evolvability because limbs are serially homologous and genetic correlations should act as a significant constraint on their independent evolution. Here we test a developmental model of limb covariation in anthropoid primates and demonstrate that both humans and apes exhibit significantly reduced integration between limbs when compared to quadrupedal monkeys. This result indicates that fossil hominins likely escaped constraints on independent limb variation via reductions to genetic pleiotropy in an ape-like last common ancestor (LCA). This critical change in integration among hominoids, which is reflected in macroevolutionary differences in the disparity between limb lengths, facilitated selection for modern human limb proportions and demonstrates how development helps shape evolutionary change.
bipedalism hominin integration macroevolution serial homology
Footnotes
1To whom correspondence should be addressed. E-mail:nathan.m.young@gmail.com.
Author contributions: N.M.Y. designed research; N.M.Y. performed research; N.M.Y. and B.H. contributed new reagents/analytic tools; N.M.Y., G.W., and B.H. analyzed data; and N.M.Y., G.W., and B.H. wrote the paper.
↵*This Direct Submission article had a prearranged editor.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0911856107/DCSupplemental.
This article contains supporting information online at www.pnas.org/cgi/content/full/0911856107/DCSupplemental.
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