�y��vlog

For humans, even the thought of polyandry can jack up a man's sperm quality.

Adult relationships vary in form across societies and include not only the type most common around the world today — heterosexual monogamy — but also same-sex marriage, nonmarital unions, polyamory, polygyny and polyandry.

While the tomb reveals evidence of polygyny - men having children with multiple women - it also shows that polyandry was also widespread: women having children with multiple men.

But Prof Machoko said polyandry was once practised in Kenya, the Democratic Republic of Congo and Nigeria, and it is still practised in Gabon, where the law allows it.

“I wouldn’t suggest polyandry if the gender ratio was not so severely imbalanced,” Yew-Kwang Ng, who is Malaysian, wrote in his regular column on a Chinese business website this month.