Tuesday, March 02, 2010

Fingers and Toes

Thanks to Ryan Gregory for alerting me to the latest issue of Carnival of Evolution [Carnival of Evolution #21: The Superstar Edition].

One of the articles that caught my attention was on the evolution of human fingers [The toe bone’s connected… errr… related to the finger bone]. It's a report on the work of Campbell Rolian on the evolution of human fingers and hands. His result suggest that bipedalism led to selection for long big toes and short little toes because this was better for running and walking. As a consequence of this selection for toes, the digits of the hand also changed since, from a developmental perspective, fingers and toes are related. Thus, early humans developed hands with larger thumbs and shorter fingers. This byproduct of selection for toes gave rise to hands that were better for tool-making and foraging.

I don't know if this is how hands and feet actually evolved but I really like the thought process. It shows that Campbell Rolian is thinking like a pluralist by not treating everything as a direct consequence of natural selection. The blogger, Peter McDougall, interviews Campbell Rolian and this is what he says ...
There’s a tendency, especially among anthropologists, to diagnose everything as an adaptation. You come up with a ‘Just So’ story that describes why a trait exists. Problem is, there’s really no basis for the story and it risks turning the trait into something that it’s not. There have to be some aspects of our development that are merely artifacts—byproducts of the evolution of other traits, or things that just came about by chance in the process of building other parts of our body. For example, there’s nothing adaptive about having white bones. Our bones are white because the calcium phosphate compound that is the main ingredient of our bones happens to reflect all wavelengths of light not because having white bones gives us a particular advantage. So I’m excited that what we’ve found offers an example of a non-adaptive trait. The initial changes in human hands that led to our improved tool use were really just a result of changes to our feet. It was a byproduct of bipedalism. Our study provides a warning out there to human anthropologists to think of alternative hypotheses to some of the ‘Just So’ stories they come up with.
Nice to see there are some smart anthropologists who understand evolution.

Rolian, C., Lieberman, D.E., Hallgrímsson, B. (2010) THE CO-EVOLUTION OF HUMAN HANDS AND FEET. Evolution. 2009 Dec 31. [Epub ahead of print] [PubMed] [DOI: 10.1111/j.1558-5646.2009.00944.x]


  1. As a former student of human evolution, I must say that this study makes enormous sense to me! In fact, it is a real forehead-slapper ("Of COURSE!) and I don't see why it should upset other paleoanthropologists.

    But then maybe I was lucky by studying paleoanthropology at UofT. "Just-So Stories" were highly discouraged, at least at the time.



  2. As an aside, one of scientists who re-popularized the notion of morphological integration back in the late 70s/early 80s (that integrated traits can coevolve and thus selection on trait one will also change the other trait as a by-product) and demonstrated numerous examples of direct versus indirect selection acting on skeletal elements was an anthropologist: Jim Cheverud.

    So yeah, there are numerous anthropologist who avoid just-so stories.