The War Between the Sexes

What are little boys made of?
"Snips and snails, and puppy dogs tails
That's what little boys are made of !"
What are little girls made of?
"Sugar and spice and all things nice
That's what little girls are made of!"

In reality, the only thing separating boys from girls is their one little Y chromosome paired with a single X chromosome, as opposed to the two X chromosomes girls have.

But even in our genes, it seems boys and girls are at odds with each other. The Y-chromosome is a tiny little chromosome compared to its overbearing X partner. And oddly enough, most of it is junk DNA. Why? Well, apparently the two different sex chromosomes like taking 'pot-shots' at each other, one trying to effectively destroy the other. And, in response, the Y-chromosome has effectively run and hid itself:

"The human Y chromosome shut down most of its genes [so] that the great bulk of its length consists of non-coding DNA, serving no purpose at all - but giving few targets for the X-chromosome genes to aim at." [111]

Sexual reproduction has evolved to continually add diversity to our species, and many others, for natural selection to act upon. This is how good genes can continually be selected for. No diversity, no new genetic material to select upon. So what benefit would there be for the X-Chromosome to continue its attacks upon the poor little Y? Ridley, author of Genome, gives this scenario:

"Suppose for instance that a gene appeared on the X chromosome that specified a recipe for a lethal poison that killed only sperm carrying Y chromosomes. A man with such a gene would have no fewer children than another man. But he would have all daughters and no sons. All of those daughters would carry the new gene, whereas if he had had sons as well, none of them would have carried it. Therefore, the gene is twice as common in the next generation as it would otherwise be. It would spread very rapidly. Such a gene would only cease to spread when it had exterminated so many males that the very survival of the species was in jeopardy and males were at a high premium.

"Far-fetched? Not at all. In the butterfly Acrea encedon, that is exactly what has happened. The sex ratio is 97% female as a result." [110]

It's a frightening thought that even chromosomes could be in war with each other, especially chromosomes that are required for sexual reproduction. But what would happen if a species such as Acrea encedon actually succeeded at wiping out the males? It seems like it's a chromosome fight-to-the-death that could wipe out the entire species.

Source: Ridley, Matt. Genome. New York: Harper Perennial, 2000.

Size

The Birthday Problem

Within a group of 22 people, you have a 50% chance of finding two people with the same birthday.

This doesn’t make sense normally because there are 365 days in the year, therefore it should be a 22/365 chance of finding someone with the same birthday as you within a group of 22. But my Genetics professor proved it in class. Twice he asked a group of 30-40 students (different group each time) to start stating their birthdays. Both times he found found two students with the same birthday before he even got past the six month.

I guess babies like being born on certain birthdates?
…Or parents like babymaking on certain days.