Research suggests why homosexual behaviour may help our evolution as a species.

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Survival of genetic homosexual traits explained

But some of the points made are:

• Women tend to have more children when they inherit the same - as yet unidentified - genetic factors linked to homosexuality in men.
  

• Female relatives of gay men had more children on average than the female relatives of straight men. But the effect was only seen on their mother's side of the family.

• Their findings also support earlier findings that when mothers have several sons, the younger ones are progressively more likely to be gay.

• The "maternal" and "immune" effects only account for 21% of male homosexuality, leaving 79% of the causation still a mystery. This leaves a major role for environmental factors, or perhaps more genetic factors. "Genes must develop in an environment, so if the environment changes, genes go in a new direction,"