Last week, we were talking parthenogenesis or the lack of a male component within a species.
I could easily make the argument that cloning or budding is by far the most dominant form of reproduction on the planet. After all, single celled organisms out-number and out-mass multicellular creatures by a significant margin and they invariably reproduce by asexual means.
Which raises the interesting question of why do we have sex in the first place?
If it is possible for a complex organism to reproduce by cloning, why bother with sex? What is its evolutionary advantage?
The answer lies in genetic variation.
Life on Earth began about three billion years ago and involved single celled organisms for about the first 2.5 billion years. Each daughter cell was an exact copy of the mother cell or, more accurately, a single mother cell split into two daughters.
Variation in genetic material did happen, but only slowly and through random mutations.
These included accidents in copying genetic material such as a guanine and adenosine switching places. They also involve external factors such as environmental chemicals or solar radiation changing the structure of a DNA molecule or a nucleotide. But these mutations were purely chance.
Still, many multitudes of species evolved over this incredibly long time.
The process was just exceedingly slow due to the rate at which genes mutated.
Somewhere in those initial 2.5 billion years bacteria learned an interesting new trick. Two bacteria from separate species would meet and instead of one devouring the other, they would occasionally exchange genetic material.
In effect, they would make love and not war.
The result was a different route to genetic diversity. By exchanging DNA or genes, direct modification allowed the expression of new genes and could result in a whole new species. It all depended on the success of the resulting cellular machinery.
The species would only flourish if the new genes resulted in an organism more fit for survival. In a competitive soup of single-celled creatures, some were better than others at utilizing resources.
These are the species which came to dominate ancient life. Survival of the fittest is all about being able to use your resources to ensure procreation of the next generation.
Around 600 million years ago, bacteria developed another new trick. Multicellular colonies developed with cells joining into a single organism instead of remaining detached. Colonies of organisms have existed on our planet for a very long time but in multicellular creatures, cells began to specialize.
Instead of every cell reproducing at will, the formation of a multicellular structure required a concerted form of reproduction.
There are a number of different hypotheses proposed in the scientific literature for how sexual reproduction first evolved and certainly a number of different reasons for why it became a significant pathway for evolution. But simply put, sexual reproduction in the form of exchangeable genetic material is the best or "most fit" method of ensuring multicellular creatures could procreate.
More importantly, perhaps, for life on this planet is that it allowed for a more rapid successful mutation rate.
If you trace the genetic tree far enough into our past, it is easy to recognize that life on Earth arose from a common ancestor - a single-celled organism with all of the requisite genetic machinery.
It is also likely that the trick of forming multi-cellular reproducing organism was another bottleneck in the development of life.
Still, it has given us the diversity of living creatures on this planet with a multitude of ways in which sexual reproduction can or does occur. From the vantage point of human existence, we tend to think that we represent some sort of normal or typical animal species.
We tend to think monogamous male/female is the way reproduction occurs throughout the whole animal kingdom.
Nothing could be further from the truth. Indeed, humans are not monogamous, but that is for a different column.
In the animal kingdom, though, just about every form of reproduction can and does occur. Homosexuality is prevalent as are polygamous relationships.
And some species even change sex, depending upon the environmental need.
Consider the cute orange and white clownfish from Finding Nemo.
They exist as a large dominant female, a breeding male and several non-breeding females associated in a group.
If the dominant female dies for some reason or is even just removed from the equation, the breeding male changes sex to become the dominant female.
One of the non-breeding females then steps up to become the breeding male.
In the movie, Nemo's father Marlin would have changed sex to become a dominant female after Nemo's mother was eaten. In any case, there is much more to sexual reproduction than the birds and the bees. Indeed, how birds and bees reproduce is fascinating.
Life is about creating life in all its glorious ways.
