Male kangaroos with big arm and shoulder muscles not only fare well in wrestling their opponents to establish mob hierarchy - they also attract females.
A new study by researchers at Murdoch University's School of Veterinary and Life Sciences in Perth shows forelimb musculature in male kangaroos plays a big role in attracting females.
And they know it, showing off their biceps and pectorals to potential sexual partners.
"Dominant males frequently adopt poses which best display their muscularity and size," Murdoch's Natalie Warburton said.
But there were no survival advantages to having larger forelimb muscles.
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In fact, the extra bulk could be a disadvantage.
"Under conditions of extreme environmental stress, there is evidence that male mortality is greater, suggesting that maintaining this additional musculature incurs a significant cost," Dr Warburton said.
"This is consistent with sexually-selected traits in other species."
