A big difference, with the sound reaching the left ear first, indicates the sound came from the left. A big difference, with the sound reaching the right ear first, indicates the sound came from the left.

I think it should be "came from the right" in the second sentence.

However, it does not follow that if the genome is not very complex, the brain must not be very complex, because the brain may be built not just based on the genome, but also based on information from the outside environment.

This is a good point, and can be taken even further. From the start, the brain is not just determined by the genome. In addition to the direct effects of outside stimuli on the development of the brain's wiring, there are also significant epigenetic effects, and such effects can be transgenerational.