Humans may not be alone in finding bulging biceps attractive. A new study, published in the Biological Journal of the Linnean Society, suggests that in the kangaroo community too, an impressive set of guns may woo the ladies—even if those ladies are eight-foot marsupials.
The study, conducted by Australian researchers from Murdoch and Curtin Universities, was performed post-mortem, which is to say the kangaroos had died and were being dissected. The initial purpose of the work was to determine the difference in muscle mass between male and female kangaroos. No surprise, the male, as in many species, was bigger, but there may have been more than just sexual dimorphism at work.
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During mating rituals, male kangaroos will fight rivals to impress potential partners. A lot of that fighting involves grabbing and shoving, and after a lifetime of brawling, the males’ already prodigious arms might become more bulked-up still. A less savory side of the musclebound males is that they might also use their considerable strength to press their advantage with females they fancy but that don’t fancy them in return—simply overpowering a prospective mate, according to Rod Wells, an Australian marsupial expert from Flinders University. Any male that was larger than average to begin with, would then pass that trait onto its offspring, reinforcing the bigness advantage in the next generation.
If there was any doubt that the males know what they’re doing with all this muscle-flexing, there’s this: reclining males of breeding age strike signature poses that show off their arms—the better to advertise their overall goods. So far, no signs of waxing or tattoos.