The Advantages of Sexual Reproduction:
Asexual reproduction, of course, generally results in offspring that are genetically identical to their parent. Sexual reproduction, on the other hand, since it occurs through the mixing of genes from two different parents, results in offspring that are genetically distinct from
either of their parents. This, it is thought, is the key to why most animal species reproduce sexually.
Back in 1930, the geneticist and evolutionary theorist R. A. Fisher noted that in sexually-reproducing populations, the continual production of and recombination of sex cells means that every individual is genetically unique, and that there will be a tremendous amount of genetic variability within a sexually-reproducing population. Since genetic variability provides the “raw material” with which natural selection works, the more genetic variability there is within a population, the greater is its capacity to change in response to a changing environment. Furthermore, the more genetic variability there is in the population, the
faster it can evolve in response to a changing environment. These observations have led to two major hypotheses regarding the advantages of sexual reproduction over asexual reproduction.
The first hypothesis regards the advantages of sexual reproduction in fluctuating physical environments. The evolutionary theorist George Williams likened reproduction to a raffle. You can either have many tickets with different numbers (sexual reproduction) or many copies of the same ticket, bearing the same number (asexual reproduction). If you know what number will be drawn in the raffle, it’s in your best interest to have many copies of the winning ticket; that way, you’ll win big. But if you
don’t know what number will be drawn in the raffle, it’s obviously in your best interest to have as many
different tickets as possible. That way, you maximize your chances of having at least one of them come up a winner.
This is known as the “bet-hedging hypothesis” or the “tangled-bank hypothesis.” The idea is that, in an environment which fluctuates unpredictably, it’s best to produce offspring with as much genetic diversity as possible. In that way, parents maximize the likelihood that at least some of their offspring will happen to inherit gene combinations that allow them to survive.
According to this hypothesis, sexual reproduction should be favored in unstable, unpredictable environments, while asexual reproduction should be favored in stable, predictable environments. Experiments tend to support this conclusion. For example, when species alternate between sexual and asexual reproduction, they tend to reproduce asexually in the Spring and Summer, when conditions are relatively stable, and then switch to sexual reproduction in the Fall and Winter, when conditions are much less stable and predictable.
The rotifer species Polyarthra remata
(Phylum Rotifera). Many rotifers
switch between sexual and asexual reproduction in response to
changing environmental conditions.
The Advantages of Sexual Reproduction
Linear Mode
