If you believe some reports, the future of humanity is a super race of genetically-engineered women who can reproduce without men.

“Take men’s genetic contribution to humanity out of the equation and – in theory – women could live a third longer,” said the UK’s Daily Mail.

The Mail – and a host of other outlets – was covering new research that created mice with two mothers, which lived much longer than those conceived normally.

But experts in the mechanisms of ageing say specific aspects of the way the research was conducted mean it’s way too soon to declare men a genetic burden who are imposing limits on human lifespan. So before you ditch your boyfriend or husband, New Scientist answers a few questions about what this intriguing experiment really tells us.


What’s all the fuss about?

The excitement surrounds an experiment by Tomohiro Kono of the Tokyo University of Agriculture and Manabu Kawahara of Saga University, who were intrigued by why male mammals usually die younger than females. They suspected that the explanation may lie partly in a phenomenon called “imprinting” – differing activity of genes due to chemical modifications depending on whether they are inherited from the mother or the father. Paternally imprinted genes may have particularly free rein in males, Kono’s team reasoned, and may govern traits such as living fast and dying young.

However, paternally imprinted genes will also have effects in females. So the researchers used methods similar to those used for cloning to create a group of “bi-maternal” female mice from two eggs – eliminating the need for sperm and its cargo of paternally imprinted genes.

So what did the researchers find?

The resulting mice lived for an average of around 840 days – more than 180 days longer than normally-conceived females from the same strain. They were also smaller. Kono says the most likely interpretation is that it is due to imprinted genes and suggests that one culprit could be a paternally imprinted gene called Rasgrf1, which has previously been shown to affect growth.

Specialists in the mechanisms of ageing agree that this is a fascinating possibility, but remain to be to be convinced that Kono’s results are conclusive.

“The most likely interpretation”. I take it there are disagreements?

Yes. There were only 13 mice in each group, which were all relatively short-lived. In other experiments, females from the same strain have lived for an average of around 860 days – longer than both groups in the experiment. “This makes it trickier to interpret the claim that the bi-maternal mice are unusually long-lived,” says Richard Miller, who studies the genetics of ageing at the University of Michigan in Ann Arbor.

What’s more, the strain used in the experiment is unusual in that its males typically live longer than females. That makes it particularly hard to tell how the results relate to normal sex differences in lifespan.

I’m beginning to think we need men after all.

There is also the fact that Kono and Kawahara had to manipulate two genes to create their bi-maternal mice – so the differences in lifespan might be due to this genetic manipulation, rather than the absence of paternally imprinted genes.

Journal reference: Human Reproduction, DOI: 10.1093/humrep/dep400