The variety would be less, this is because if carbon had seven electrons then it wouldn't be able to bond with as many different atoms at the same time.
Vestigial structures are inherited from ancestors, but have lost much or all of their original function due to different selection pressures acting on the descendant. The hipbones of bottlenose dolphins are vestigial structures. However, as the dolphin lineage adapted to life at sea, this function was lost.
Humans' genomes are about 99.9% the same.
