Female chimps with powerful mums may remain in the family group for longer, according to new research by Duke University and North Carolina State University.
Chimps are unusual among mammals because it’s the daughters, rather than the sons, that tend to leave the family unit at puberty. The sons will remain to help defend territory, while the daughters will head off when they are between 11 and 13 years old.
It’s a risky business – they can be attacked by other females when they join a new group, often end up at the bottom of the pecking order, and tend to get pregnant later.
The new research, which took place at Gombe National Park in Tanzania, analysed 45 years’ worth of data from 31 female chimps and revealed that when daughters had a high-ranking mother, they would tend to stay close rather than leave. This is despite the risk that they could mate with their own male relatives.
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While chimp siblings usually show little interest in each other, it is not unknown for high-ranking males to force their sisters into breeding with them. In Gombe, four offspring were born from such matings, but only one survived into adulthood. “Breeding with a brother is a pretty costly mistake,” said Kara Walker, a primatologist from North Carolina State University.
But for the females, the benefits of inheriting your mum’s social clout and having someone who can offer support and share the best feeding spots, could offset the risks of potentially mating with a close male relative.
According to Anne Pusey, a professor of evolutionary anthropology at Duke University, we could learn a lot about human migratory patterns by studying chimpanzees, as young men are also more likely to stay in the family unit than women.
Reader Q&A: Is it possible for humans and chimpanzees to interbreed?
Asked by: Pauline Hetherington, Surrey
Genetic analysis suggests there may have been a long period of cross-breeding between early ancestors of the humans and chimpanzees, before they finally split into the Homo and Pan (chimp) genera around six million years ago.
But today, although humans and chimpanzees share 99 per cent of the DNA sequences that code for proteins, that DNA is packaged differently into the chromosomes.
The human chromosome number two is actually two ape chromosomes joined end-to-end, and nine other chromosomes have inverted sequences of genes compared with their equivalents in chimps.
Humans and chimps also have differences in their individual genes that are far bigger than the differences between any two unrelated humans.
These are big obstacles, but not necessarily insurmountable. Other animals with comparable genetic differences, such as zebras and horses, have bred successfully in the past, although the offspring are almost always sterile.
There are documented cases of Soviet experiments in the 1920s where artificial insemination was attempted using female chimps and human sperm. However, none of these experiments resulted in a pregnancy, much less the birth of a ‘humanzee’. There are various urban legends of other later experiments in different labs worldwide, but there’s no evidence that the result was ever any different.