Our common friend

Animals, plants and fungi have a common friend. Inside our cells is the remnant of another creature. This little friend provides us with power, converts the food we eat to ATP which is a molecule the cell can use when energy is needed. This friend contains it's own DNA and has it's own protein plant.

Sometime in the distant past two different cells bonded. One cell absorbed the other by endocytosis and allowed it to live inside it. The symbiosis was very successful and gave rise to most of the advanced life forms we see today.

I'm talking about the mitochondrion. It divides by itself outside of the normal cell cycle, it basically lives it's own life inside the cell. This means that the mitochondrial DNA is not inherited in the same way as the nucleus DNA. We humans get our mitochondria from our mothers. Their genes mutate and evolve and allows us to study our maternal heritage. This shows us that all living humans descend on the female side from a woman living at about 150000 years ago, sometimes called mitochondrial Eve.

The interesting thing is that the genes of the mitochondria compete in the same way as the nucleus genes. What happens when genes compete? The genes are selfish as Richard Dawkins puts it. All genes try to be the one that gets passed on to the next generation. Some do it the honest way by being good and doing something useful and some try to fool the system. An interesting thing about the mitochondrial genes is that they do not compete on the same terms as the nucleus genes as they only gets passed on the female side. Being in a male is not useful for a mitochondrial gene, it can never be passed on from a male.

So here is a radical idea. In a very selfish sense it would make sense for such a gene to cause male homosexuality. If present in a mother the gene would be passed along to all grandchildren. As we humans inherit wealth this would increase the chances for the grandchildren as they don't have to share the wealth with offspring from the male siblings of their mothers.