Natural Selection

Before we proceed to the issue of whether speciation occurs more rapidly during some periods than during others, we should consider the basic mechanism whereby natural selection works, which in turn requires us to understand something about the nature of asexual and sexual reproduction. Unicellular organisms that reproduce asexually - by dividing their one cell into two identical daughter cells that then increase in size until they are large enough to divide once more. Each cell - each organism is exactly like all of its "family" members in terms of its genetic content.

There are certainly advantages to this form of reproduction, including the fact that such organisms do not need a partner but can reproduce whenever environmental conditions are optimal for it to do so. It is often difficult for organisms that reproduce sexually to find a sexual partner at exactly the right moment in terms of environmental conditions (Burkhardt 40).

However, there are significant evolutionary costs to asexual reproduction as well, the primary one being that if all organi

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