I have published this essay in other formats: format (10.7 megabytes) and format without visible links (the closest experience to reading a book), to honor different methods of digesting this essay, but this html version comprises the online textbook that I intended this essay to be. NASA recruited my father to work in Mission Control during the Space Race, and I was trained from childhood to be a scientist.
The skull was unlike anything seen before, having a flattened cranium with a heavy brow ridge above large eye sockets.
Nearby, workers also uncovered an assortment of thick and heavily fossilized bones.
It is the variation in the alleles of a genome as they are expressed in sexual reproduction and the mixing of alleles that occurs.
These alleles are mostly not the product of mutations, but rather reside in the total genome of a population.
See the genetics section for a further treatment of alleles in a genome.