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The evidence that the number two chromosome of humans was the result of two ape chromosomal fusions is fairly clear just by looking at the karyotypes of the two primates. This is why humans have 46 chromosomes instead of 48, like apes. In order for this event to lead to an entirely new species, the sexual reproduction of at least two members of the same species that inherited this chromosomal fusion would have to take place. Once this occurred, a brand new species with only 46 chromosomes would be instantly created that could no longer sexually reproduce with the original ancestor.
How could two near simultaneous events such as this occur? There are a variety of possibilities, but nature generally takes the path of least resistance with the minimal amount of time required to get the job done. That is what this blog is all about, life finding ways to get things changed in a big geologic hurry. Mutations take a long time to occur, and “good” mutations take even longer. However, if these mutations result from huge masses of DNA shifting about within and between chromosomes, then, changes can add up in a hurry.
How do we speed up this natural mutation rate? Well, we either use chemicals or we use radiation. Millions of years ago, apes probably were not exposed to large doses of ionizing radiation as found in nuclear power plants, so the odds are that any mutagenic accelerations were the results of exposure to chemicals. The most likely candidates (in the case of apes) would be through the eating of “moldy” or dirty fruits. Soil bacteria like Streptomyces produce a wide variety of mutagenic agents called radiomimetic drugs. These are drugs that mimic the effects of ionizing radiation on DNA, the core of chromosomes. It is well known that such mutagens can lead to dramatic chromosomal damage in sex cells, leading to genetic defects in offspring.
It is not hard to imagine that two genetically “defective” but viable individuals with similar traits might be physically attracted to one another and subsequently reproduce, generating an entirely new primate genera (Hominids). Once a species is formed and segregates itself from the original ancestral line, it goes its own way with regard to genetic diversity and drift. This is probably how many species have formed and evolved over short geologic time spans (adaptive radiation).