> Mutation happens randomly, then natural selection will sometimes prune out bad mutations. That's all. That is not all. Beneficial mutations sometimes occur;

> Mutation happens randomly, then natural selection will sometimes prune out bad mutations. That's all. That is not all. Beneficial mutations sometimes occur; and because they provide a benefit they spread through the population [caveat below]. Bostrom's question is valid: if some change to the brain's chemistry could provide a boost to intelligence, why hasn't a mutation providing that change already swept through the population? There's nothing wrong with the question, and it does have answers, e.g. constraints (no simple set of mutations can provide the specified change) or tradeoffs (the change would result in a net fitness loss; intelligence isn't everything) or just insufficiently large benefits (any rare gene, e.g. a new mutation, is likely to die out by chance simply because it's rare; providing a larger benefit helps its chances of survival. [1]) [1] http://rstb.royalsocietypublishing.org/content/365/1544/1195.full http://rstb.royalsocietypublishing.org/content/365/1544/1195...