Tweak in gene expression may have helped humans walk upright
Now, researchers at the Stanford University School of Medicine and the HudsonAlpha Institute for Biotechnology in Huntsville, Alabama, have identified a change in gene expression between humans and primates that may have helped give us this edge when it comes to walking upright. And they did it by studying a tiny fish called the threespine stickleback that has evolved radically different skeletal structures to match environments around the world.
The threespine stickleback is remarkable in that it has evolved to have many different body structures to equip it for life in different parts of the world. … ue to changes in the regulatory DNA sequence near this gene, freshwater sticklebacks express higher levels of GDF6, while their saltwater cousins express less. … Kingsley and his colleagues wondered whether changes in GDF6 expression levels might also have contributed to critical skeletal modifications during human evolution. … In previous surveys, they found over 500 places in which humans have lost regulatory regions that are conserved from chimps and many other mammals. Two of these occur near the GDF6 gene. They homed in on one in particular. … “This regulatory information was shared through about 100 million years of evolution,” said Kingsley. “And yet, surprisingly, this region is missing in humans.”
The fact that humans are missing the hind-limb-regulatory region probably means that we express less of the gene in our legs and feet during development, but comparable amounts in our nascent arms, hands and skulls. Loss of this particular regulatory sequence would also shorten lateral toes but not the first toe of feet. This may help explain why the big toe is aligned with other short, lateral toes in humans. Such a modification would create a more sturdy foot with which to walk upright. More.
A number of other explanations of varying types are on offer, as noted elsewhere,
Ah yes, walking. There is a “uniquely human” way of walking upright and there’s no shortage of theses as to why: carrying infants or scarce resources, and saving energy strut the stage. Or it is due to climate change or rough terrain? Don’t assume a “chimpanzee starting point,” counsels one expert.
See also: Human origins: The war of trivial explanations
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Here’s the summary:
Changes in bone size and shape are defining features of many vertebrates. Here we use genetic crosses and comparative genomics to identify specific regulatory DNA alterations controlling skeletal evolution. Armor bone-size differences in sticklebacks map to a major effect locus overlapping BMP family member GDF6. Freshwater fish express more GDF6 due in part to a transposon insertion, and transgenic overexpression of GDF6 phenocopies evolutionary changes in armor-plate size. The human GDF6 locus also has undergone distinctive regulatory evolution, including complete loss of an enhancer that is otherwise highly conserved between chimps and other mammals. Functional tests show that the ancestral enhancer drives expression in hindlimbs but not forelimbs, in locations that have been specifically modified during the human transition to bipedalism. Both gain and loss of regulatory elements can localize BMP changes to specific anatomical locations, providing a flexible regulatory basis for evolving species-specific changes in skeletal form. (paywall) – Vahan B. Indjeian, Garrett A. Kingman, Felicity C. Jones, Catherine A. Guenther, Jane Grimwood, Jeremy Schmutz, Richard M. Myers, David M. Kingsley. Evolving New Skeletal Traits by cis-Regulatory Changes in Bone Morphogenetic Proteins. Cell, 2016; DOI: 10.1016/j.cell.2015.12.007