Expert: John Shea - 3/27/2009

Question
I am a believer in the aquatic hominid theory for the emergence of H. h Sapiens.  My question regards our species relative stability in the evolutionary process.  As evidenced by other species, a large population minimizes the effect of random mutations.  Is it necessary for speciation to involve a small, isolated population; or is it possible for major evolutionary changes with such a large population the is H. h Sapiens today?  for example if ethnic or racial similarities maintain an unbroken lineage over melinea can this lead to speciation?

Answer
Hi Chris
Isolation and genetic drift/divergence is thought to be the most common source of speciation among large mammals.  You are right that large breeding populations evolve slowly, even a favorable mutation faces significant odds against becoming common.  So, rapid and reproductively-significant evolutionary change in a large human population is unlikely, barring (1) some kind of catastrophic reduction in population and fragementation of the species into isolated breeding populatons, or (2) some other process that isolates groups of humans from one another (i.e., interstellar space travel is a common scenarios, but any civilization smart enought to figure out the technology to do this would probably also figure out a way to maintain sufficient genetic diversity to retain links to the parent populations).
Most of the "racial" characteristics among living humans are so variably expressed and the underlying genetics so trivial that I'd be skeptical they would persist over a period long enough for speciation to occur (probably on the order of 0.5-1.0 Million years, at minimum, if species-level differences among living mammals are any guide.
Cheers,
John Shea