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During a time when great sheets of ice was known to have covered large parts of the supercontinent in the south known as Gondwana land, the first mammal-like reptiles appeared on Earth.
According to the latest genome research, the mammal-like creatures were a little different from other animals in that a rogue and seemingly insignificant "Y-chromosome" suddenly appeared in the male species. Prior to this time, animals had enjoyed a pair of identical "X-chromosomes" with gender determined by simple environmental factors such as temperature (for example, a low enough temperature in the environment would usually result in the birth of more males, and a warmer temperature would normally create more females). Now, the mammals with this new chromosome made the gender determination independent of environmental factors.
As David Page of the Whitehead Institute in Cambridge, Massachusetts, described the Y-chromosome's function:
'It [the Y-chromosome] said, I will no longer respond to these environmental cues; if I am present, the male pathway will be followed.' (1)
So important is this discovery in the genes of mammals that it holds the key to the evolution of the human race.
## SPECIAL UPDATE ##
26 March 2005
A detailed analysis of the X-chromosomes in women compared to the X- and Y-chromosomes of men conducted by Huntington Willard of Duke University in Durham, North Carolina, USA, says women are genetically more complicated than men.
This may seem like stating the obvious since the Y-chromosome is indeed smaller in size than the X-chromosome. Therefore men would have less genetic information than women.
Does this mean that women, being more genetically complicated, are better than men? No. It just means men don't need the extra genetic information to achieve their goal(s).
However, to compensate for this apparent "genetic efficiency" in achieving things, men are also more genetically susceptible to mutations such as radiation penetrating and damaging or changing the genes (could this be how the Y-chromosome was originally created?) as there is no additional X-chromosome to wrap around and protect the X- and Y-chromosomes. This makes men more easily able to evolve over time if the changes are favourable to the opposite sex.
Women, on the other hand, are better in looking after the core genetic code needed by humans to look human and survive by having two X-chromosomes. So should one X-chromosome get damaged, there is a better chance for the other chromosome to carry undamaged information, which can aid later in sex through the production of a quality human egg.
What the study has actually shown is that women do indeed use both X-chromosomes. Before the study, scientists thought only one of the X-chromosomes is made inactive and the other X-chromosome provides all the information needed for women (and men) to build the body and perform the tasks needed to survive and hence achieve certain goal(s) during their lifespan. Now scientists realise active genes are found in both chromosomes.
In the case of men, this gender has to rely on the only X-chromosome for making men look human and able to survive in the same way as women can. But it is the Y-chromosome that help to make men for who they are — men.
This rogue little chromosome helps with building extra muscles, make general changes in appearance to help women become more sexually attracted to men, and increases male sexual drive and sperm production as needed for the human species to survive better and ensure there is sex between the opposite genders (rather than among the same sex).
For women, the extra X-chromosome provides the human species with the necessary in-built checks to ensure the essential genes for defining our species as human remain intact.
Another discovery made in the study is that not all active gene sequences in just one or the other X-chromosome of women are used in men. While men may use some of the same gene sequences as women do in order to be human and perform tasks common to both sexes, women have some 200 to 300 genes in the X-chromosomes used only by women. In other words, there are genes in the X-chromosome uniquely expressed for women relative to men.
In essence, women should be considered as having a different human genone than men. (2)
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