An Introduction to Zoology
Chapter Five: Animal Reproduction:
Why Reproduce?:
It might seem like a strange question to ask, but why do organisms reproduce? Well, it might make more sense to ask, “Why do organisms die?” Those two questions are much more closely-linked than you might suspect at first.
Suppose that organisms were born “immortal” – that is, suppose living things didn’t grow old and eventually die. In such a world, would reproduction be necessary? Yes it would. The fact of the matter is that true immortality simply isn’t possible. Even if organisms didn’t age and die, they’d still be susceptible to disease, predators, and accidents. So, for that reason alone, reproduction is necessary. The genes of any organism that
doesn’t reproduce will soon be eliminated from the gene pool by virtue of the fact that true immortality simply isn’t possible.
Genes that promote reproduction can persist indefinitely, since they’ll be passed down from one generation to the next. On the other hand, any genes that have the effect of preventing their possessors from reproducing will soon be eliminated from the gene pool, no matter
how beneficial they might be in other ways.
Another reason why reproduction is necessary is that it’s necessary in order for evolution to occur. The genetic makeup of an individual does not change during its lifetime. This severely limits its ability to change in response to changing environmental conditions. But because of reproduction – especially sexual reproduction –
populations of organisms can and do experience genetic change over time, and so they change in response to their environments. That is, populations
evolve in response to their environments.
Odd as it might seem at first, it appears that organisms are, in effect, genetically “programmed” to grow old and eventually die. Why is this advantageous? Well, the brute fact of it is that once you’ve successfully reproduced and raised your offspring to independence, from an evolutionary perspective you have no further “purpose.” What’s more, by surviving past the point where your children need your support, you’re consuming resources that
they could be using. You’re thus competing with your own offspring for limited resources and thus reducing the probability of their survival and reproduction. In other words, weird as it might seem, there comes a time when it’s in your best genetic interest to die and thus improve your offspring’s chances of survival.
Introduction
Linear Mode
