Why sex?
Where we learn between sexual and asexual reproduction, and why there could be such as things as sex at all
I don’t remember exactly when we did it for the first time, but it was probably over one billion years ago and we were still very small organisms made out of single cells, a bit like bacteria still are. We felt that asexual reproduction was coming to its limits, and that sexual reproduction would be the right way to go. But why? What urged us to do it over and over again for the million years to come?
To get a glimpse of why sex arose one has to imagine how the world was before sex started. It was a world mainly populated by small organisms, such as bacteria and single-celled precursors of plants, and they all multiplied simply by cloning each other. They thus created more or less identical scores of twins from generation to generation. In fact, today these small organisms still do it the same way, while most modern animals do it sexually (with very few exceptions in the realms of insects, fish, reptiles or birds).
Then, nearly one thousand million years ago, it suddenly all changed. We decided to reproduce sexually from then on, meaning that we made a big difference between male and female, that we decided to mix up our genes each time we made new babies and that we wanted each offspring to have different traits. In short, it was the beginning of individualism.
But why did that happen? Well, the reason was most probably that the mixing of genes between each new generation allowed us to compose new traits quicker, traits that would fit better those highly changing environments in which we were living. Evolution could thus act quicker and more easily on each of us individual offspring. Now, you need to know here that animals don’t reproduce so often as bacteria do (humans for example have a generation time of approximately 25 years, while bacteria reproduce every half of an hour!). So one of the main advantages for sexual reproduction might have been that it allowed slowly reproducing organisms to give rise to many different individuals each time they reproduced, by mixing their gene pools.
However, this reason for the existence of modern sex is just a hypothesis and the definitive argument for why we do it is still a major scientific mystery. But science is made out of good hypotheses. This one would imply that sex evolved as an alternative to a short life. So, even if we don’t really know why we’re doing it, it is quite sure that when it comes to evolution, sexual reproduction has given us some very practical results, “even if that is not why we do it”, to paraphrase the Nobel Laureate Richard Feynman.
By the way, it is interesting to note that today, after having been sexual human for hundreds of thousands of years, we seem to slowly be rediscovering our asexual origins in the last decades. In fact, genetic technologies and the discovery of stem cells are making cloning just a bit more practical than ever. So we might soon go back to asexual reproduction.
