I thought some of you may be interested in this. It's a story that not many people know and is one that led to the near extinction of the male gender, in every mammal. Chromosomes come in pairs, as high school science should have taught you. Now if we go back millions of years ago we still have the XY chromosomes, but our Y chromosome was VERY different than our modern one. It was practically genetically symmetrical to the X chromosome. They were so similar that the two chromosomes even "checked" each other for genetic mutations and exchanged genes in order to shift the gene pool and improve characteristics. Back then gender was more likely to be defined by the temperature the fertilized egg was kept out, like certain reptiles. However the Y chromosome underwent some what of a "super mutation". This mutation isn't your average change of a base in the DNA or a break in a bond. It was a mutation that led to a whole new body part... testes. Now, before we go any further you should understand a few basic things: 1) There are 4 bases (A,C,G and T) 2) The bases are arranged in order to form a sequence (e.g. AGTCTA) 3) These bases then can only connect with their partner base. (A connect to T, and C connects to G). This means that the sequence on the opposite strand of DNA to or previous sequence would be TCAGAT. 4) Bases often form palindromes (e.g AACGTGCAA). This then forms a palindrome on the opposite DNA sequence in this case it would be TTGCACGTT. Okay, so this is where things get brutal for males. The Y chromosome undergo's 4 more of these "super mutations" and go's from having just over 1400 genes to a mere two dozen and is virtually nothing like the X chromosome. This creates a serious problem. The Y chromosome can no longer "check" itself for genetic mutations due to it losing it's closest relative chromosome leaving males at severe risk of genetic diseases and cancers. However the females are at practically no risk in comparison, why? Because they inherit two X chromosomes. The XY males are now withering in population, it seems as if nature is all be done with this brief experiment of genders. Males are being born weak and rife with genetic abnormalities leading to sever disabilities throughout the gender. But there is still one last card to be played, the palindromes. The Y chromosome has developed an insane amount after all it's cutting and hacking at it's genetic sequences (one palindrome that ALL males have is over 3 million bases long) and so in a seemingly ingenious move the Y chromosome does something that had never been done before in the history of evolution. It folded itself in half. Pushing the opposite palindromes next to each it could now "check" it's DNA strands without having to have another chromosome, saving the whole idea of inheriting the genetics to be male and not just leaving it to outside factors. However this daring move came at a price, the Y chromosome does not know which stand of DNA is mutated and so is may fix a "good" DNA sequence to become a mutated and "bad" DNA sequence and this can lead to infertility in men. The very chromosome that developed the idea of genetic males, is also responsible for taking it away. I hope you found this little battle for the male gender interesting.