We know from part 1 that reproduction can happen randomly and that males and females aren’t necessary to produce offspring. So why does sex really exist? To understand this, you have to go back to our genetic beginnings. Single-celled organisms started life on earth, (and are still the most numerous and successful), from there they mutated and multiplied. As these new organisms became more elaborate they faced new dangers. One major issue is attacking parasites. Disease ridden bacteria and viruses become a paramount threat. By mutating and replicating, the healthy cells lived long enough to reproduce. However, as life forms became more elaborate, mutations became slower. That put the process in peril. A species’ success depends on mutating faster than the bad bugs. So nature decided to try something new and VIOLA, sex was born! Nature’s experiment so begins – combine genetic material in faster ways to keep up with the replicating villains. This makes us better, healthier carriers for good cells. Sexual unions formed powerful combinations of strong cells and it worked so it stayed.
It takes complex organisms, like animals, relatively long to reproduce, so mutation through sex kept the healthy alive to stay ahead of the bugs. The healthy disease resistance genes were passed on to the next generation. In his 1993 book, The Red Queen, Matt Ridley argues this disease – resistance theory. He explains that the virus that causes AIDS has mutated and changed its genitic makeup more times in a decade than humans have changed in millions of years. So through the millennia, to fight the onslaught of bacteria and viruses trying to kill us we had to find a way to beat them at their game. Sex kept many species, (including ours) alive. As evolution plundered on, males and females became the preferred delivery systems of chromosomes; 23 from dad and 23 from mom. Oh and don’t forget the two sex cells. A XY chromosome = your buying blue, and XX=your buying pink.
I know what your’re thinking, could there be anything more un- romantic? Are we simply vessels driven by cells to combine chromosomes in order to keep the species alive? Is that why we are attracted to each other? Science says yes, religion says no. Romantics and realists can argue it ad infinitum, but there is one thing that we can all agree on. Humans (or my fav abbreviation -H. Saps), do it best. We think about it more, have it more, enjoy it more and bond stronger from it than almost all other animals- Stay tuned to find out why and how it has become the cornerstone of our success.