O que significa Moreover, genes would undoubtedly have changed during the human revolution after 200,000 years ago, but more in response to new habits than as causes of them. ?

See a translation

There is not a full clause after but. The whole thing after but is just acting as an adverb.

Simple sentence:

Genes changed.

More complex:

Genes changed in response to new habits.

Genes changed more in response to new habits than as causes of them.

Adding a 'but' here just adds contrast between the initial statement and the information following but.

Genes changed, but more in response to new habits than as causes of them.

A simple example:

I like sandwiches.

I like sandwiches, but moreso with turkey than ham. (You see there is no full clause after but here...there are more uses for 'but' than just to separate clauses.)

Sorry...it's kind of complex, so hard to explain simply.