Original sex

Two recent discoveries have just given us a better picture of the story of original sex. 

Once upon biological time, about 180 million years ago, nature came up with “sex.” We can only surmise what it must have been like – sexually “quiet” – as there was only the X chromosome in the mammalian scene.

There was none of that genetic ingredient yet that would spin off what we now know as the “Y” chromosome that gives rise to the male species in mammals which includes humans.   

Human females generally have XX as their 23^rd pair of chromosomes while males have XY. (There are cases where there are more than 2 Xs or there are females who have XY chromosomes, but I will reserve that story for another column.) 

If it were not for the Y, “sex” as we know it between male and female and the web of industries that rely on it, from media to paraphernalia, would have been the stuff of fiction.  

Because of the Y coming into the scene 180 million years ago, things got quite interesting and then we had another “sex” coming into the stage of life. Without this “Y,” we would not have men even if there are, I am sure, many times in a woman’s life when we seem justified in asking what men are really for.  

A team from the Swiss Institute of Bioinformatics and their colleagues in Australia had recently come up with the timeline as to when the Y made its chromosomal debut. 

They reportedly spent 29,500 computing hours to figure out when the Y chromosome evolved  into the scene. How did they do it? 

They compared the Y chromosomes of 15 different mammals from 3 major mammalian groups, namely, placentals like apes, rodents, elephants and humans,  marsupials such as kangaroos, and strange egg-laying mammals called “monotremes” like the echidnas.

They studied the genes present in the Y chromosome of these mammals and found two kinds of genes that seem to be responsible for the emergence of the Y.

The first is the SRY gene, which is a very small portion of the Y chromosome. This is also the gene found in the human male chromosome. 

Worth the wait?

The scientists found this SRY gene in placentals and marsupials which appeared around 180 million years ago. The other Y-enabling gene is AMHY, which is found in monotremes which appeared in the scene of life 175 million years ago.

These two genes did not seem to have emerged from the same process but they seem to have produced the same result – a Y chromosome – that put an end to the longtime blanket monopoly of the X.  

But that is not all we know now about original sex. British scientists from the Wellcome Trust Sanger Institute have also identified the protein in the egg cell that seems to act as a glue for a sperm to bind with it.

In 2005, Japanese researchers discovered the counterpart sperm “glue.” Without these binding proteins, sperm and egg would not really unite and no fertilization could therefore happen and no embryo would come about.

Discoveries like the two I mentioned help us piece together the story of original sex. We now know that it has been around for only 180 million years. 

Homo sapiens have only been around for around 200,000 years. Much of the recorded intrigue and scandals surrounding sex only appeared in the last 550 years or so with the advent of the printing press.

It took 180 million years for it to get to print but I leave it up to you to judge if it was worth the wait. – Rappler.com

Maria Isabel Garcia is a science writer. She has written two books, Science Solitaire and Twenty One Grams of Spirit and Seven Ounces of Desire. Her column appears every Friday and you can reach her at sciencesolitaire@gmail.com.