The evolution of sex is the hardest problem in evolutionary biology

                                                                              ---John Maynard Smith

Don't feel embarrassed when you are reading this article, there is much more here than that in sex. Let us look at nature. Sex is like a battlefield. Animals would go to every violent collision to make sure that their spices survive. Because they know without sex they are just going to be history. Sex caused evolution and evolution caused sex. If we look at nature it is all about sex. I don't know any person who really doesn't like sex. But sometimes I wonder, how it all get started?

mating | source
Let look at the sea life. It is full of simple single cell creatures. They don't need to have sex for reproduction. They can reproduce by themselves. A single cell can make two cell or more. It guarantees 100 percent of pure genes of the mother. This is called asexual reproduction.

asexual and sexual reproduction | source

So, you can ask me if it guarantees 100 percent purity of gene, then what is the problem? Well, there is a problem. This problem is directly connected with evolution. If something is 100 percent pure how will it evolve? How will the variety be created?

Let us think about nine lions with same genetic code. So, if a virus attacks one of the lions, it will affect all the lions as they have the same genetic code and they will just be history like the dinosaurs. So, now we can see being 100 percent pure is the biggest flaw for their survival. But sex gives variety and variety causes evolution. Evolution is the cause for our survival.

Different types of butterflies | source

Let me give an example how variety gives us the power of survival. In Amazon where all the trees are of golden color, all the butterflies will be of golden color. It will help them to hide from birds. If there is any butterfly of black color, the guarantee of their survival is so less. But now if because of pollution the trees turn into black, none of the butterflies will survive except the darker color.

Historically, first sexual reproduction happened by a kind of coral deep in the ocean 600 million years ago. Those corals couldn't move. So, how can you do sex if you can't move? Well, they throw out their sperms and eggs to let the ocean water to carry it. But, the eggs and sperms of the same coral didn't use to reproduce. They would wait for a different kind. Why? Nobody knows.

Coral throwing sperms and eggs | source

Now the question is how can you make sure that your sperms and eggs are safe in the water? Any predator can come and eat them. The answer is, you swamp them with eggs and sperms so that they can't eat them all.

500 millions ago, a new kind of fish evolved. A new stage of reproduction system was evolved with them. They didn't put the fate of their eggs on the ocean current to carry them. The male fish could directly target their sperm with the eggs of the female fish and they could have been fertilized.

Male and female fish are guarding their eggs | source
But in this process, there is a big problem. When eggs are fertilized they are fragile as well as exposed. So some other predator can come and eat the eggs. So, the parents had to guard them all the time. In this problem, they would starve and that would cause their death.

When we think about the shark, we think that they are killing machine. They have very sharp teeth. But did you know that they were the one who really started the modern pattern of sex? Instead of guard the eggs they were the one who used to put their sperms directly in female sharks body. So, the baby shark was protected inside the mother's worm until then became a killing machine.

Sharks mating | source

So, the question is how do they do it? The first thing what shark developed with evolution was the penis. They are the one, who are physically connected during sex. During the mating, the male shark bites the female shark's neck. This may seem violent but the skin of the female shark's neck is two times thicker than the males. The male shark put the teeth under the skin of the female shark to make the fertilization process faster.

Until now i talked about the mating of different kinds of fish in the sea. How the creature first came in the lands. With time one kind of fish developed legs out of their fins. This fish started moving toward the lands. When their feet became steady enough, they find their new home. These fish are named tetrapods. They are the ancestors of the reptiles. They conquered the lands. But they faced one problem. Before the used to throw their sperm in the sea water but now, they won't survive in the land.

Tetrapod | source

The solution was internal fertilization like sharks but then went even farther. They developed a process called amniotic eggs. This amniotic egg not only takes care of the young tetrapod but also the hard shell of the egg kept it from drying out. This is how life evolved through sex from ocean to land and how the reptile conquered the land.

References

1. https://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction
2. https://www.allaboutscience.org/evolution-of-sex.htm
3. https://evolutionnews.org/2011/07/spinning_fanciful_tales_about_/
4. http://www.pbs.org/wgbh/evolution/sex/advantage/index.html
5. https://www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of-sex-824

Please let me know through your comments and upvote, how did you like it or any suggestion. Until my next post --

Steem on people !