Another piece of the puzzle explaining the "evolutionary arms race" between primates and the deadly snakes they live with has been revealed by Australian researchers.
As well as traits that help detect and defend against the reptiles such as excellent eyesight, primates that live alongside large lethal snakes appear to have developed increased venom resistance.
And for the last common ancestor between chimps, gorillas and humans, the resistance was even stronger, a University of Queensland-led study suggests.
"Madagascan Lemurs and Central and South American monkeys, which live in regions that haven't been colonised by or come in close contact with neurotoxic venomous snakes, did not evolve this kind of resistance to snake venoms," says UQ PhD candidate Richard Harris.
"It's been long-theorised that snakes have strongly influenced primate evolution, with many examples just like this, but we now have additional biological evidence to support this theory."
The study looked at toxin interactions with synthetic nerve receptors, comparing primates from Africa and Asia with those from Madagascar, which does not have venomous snakes, and those from the Americas, where cobra-related coral snakes are small, nocturnal and burrowing.
The use of artificial nerves allowed the team to study primates in ways that would "have otherwise been legally or ethically impossible," team leader Associate Professor Bryan Fry said.
The data "clearly demonstrated" that African and Asian primates evolved to resist cobra venoms.
This resistance sharply increased in the last common ancestor of chimpanzees, gorillas and humans, Dr Fry says.
"Our movement down from the trees and more commonly on land meant more interactions with venomous snakes, thus driving the evolutionary selection of this increased resistance.
"It is important to note that this resistance is not absolute - we are not immune to cobra venom, just much less likely to die than other primates."
Modern medical interventions, such as supportive care and antivenom, would largely decouple modern day humans from any such evolutionary pressures.
The work reveals "yet another piece in the puzzle" in the arms race between snakes and primates, Dr Fry says.
The research used animal-free testing techniques and was a collaboration between the University of Queensland and Oxford-Brookes University's Dr Anna Nekaris.
Australian Associated Press