Recycling Old Genes

In a remarkable display of recycling, the world's first land animals reused ancestral fish fin genes to make arms and legs, wrists and ankles, fingers and toes.

Researchers have found that when animals first came out of the water, and grew legs, that is was not a case of rapid evolution of complex structures, but rather a recycling & re-purposing of old structures that already exist in the DNA.

To me this says that any mutations that may arise in a future cataclysm are unlikely to be radically new, but rather variations on the past. So physically humans are unlikely to be structurally different. But they could change dramatically in overall size, or the size of individual components - we could end up being 4 feet tall, but with ears 3 times larger than now. Our senses could become more or less keen. Our skin could become more or less hairy, or a different color.

Fossils are unable to tell us what might happen to our brains - if previous (known or unknown) species had, say, telepathy, we might re-inherit that.