Monday, 19 January 2009

Has evolution stopped for humans?


It is an amazingly widespread misconception that evolution has somehow stopped for us humans, and it betrays a misunderstanding of what evolution is.

Populations evolve whenever the genes in the pool last year aren't the same as the genes in the pool this year. Sometimes this change is due to random, undirected events (e.g. a random member of the population getting bitten by a snake, taking their alleles with them to the grave), and sometimes it is due to 'directed choosing' (i.e. natural selection, which can eventually craft exquisite designs for an organism).

For evolution to stop, therefore, everyone must be genetically identical. That way, no matter whether lightning struck someone, or whether one person happened to have more kids than another competitor, the proportion of frequencies of the various genes in the population wouldn't budge.

This clearly isn't the case in humans. For one, we know that mutations are always popping up, whether as a consequence of cosmic rays, carcinogens or copying errors. For another, meiosis ensures that the alleles in two individuals (and thus the population) are so thoroughly shuffled that the same two parents can safely go on producing a new child every minute without every producing two children with identical genotypes. (Identical twins aside, of course!)

And because these two principal causes of genetic variation aren't the slightest bit defunct, we can be sure that people are, and will be, enormously varied, genetically speaking. That's really all evolution requires; since humans don't all reproduce in equal proportion (some have terminal cancers at age 6, some are better looking or more powerful than others, some voluntarily forgo sex, etc.), some genes will be passed on more than others. In other words, evolution is still occurring.

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