Claim:
Male kangaroos intentionally display their muscles to attract female mates. For this purpose they flex their biceps. Without fail they do this when meeting females for mating purposes and this action often ends in success for these male kangaroos. 8.5/10 Rating
Though male kangaroos appear to flex their muscles for show, researchers in a 2013 study claimed it is currently impossible to discern whether such behavior is conscious, intended to attract female kangaroos or otherwise. One author stated this wasn’t possible as humans have yet to gain full insight into animal consciousness and it wouldn’t be possible to establish one way or the other whether this claim was accurate or false.
Men kangaroos often display their muscles to impress potential partners when mating has long been an urban legend on social media platforms, like TikTok (archive). A version of this myth first surfaced there on April 5, 2024 (archive).
“Kangaroos don’t just flex their biceps to impress women; male kangaroos do too!” read the caption accompanying this post. Studies indicate that male kangaroos often adopt poses to show off their muscular arms in order to attract females.”
As per one research study, male kangaroos with prominent forelimb muscles do draw female attention due to strong genetic markers; however, researchers were unable to ascertain if or whether male kangaroos actively “flexed” their muscles for effect while mating with females.
Therefore, until science enables humans to study consciousness in animals, the notion that male kangaroos intentionally brandish guns at female partners to show off will remain unverifiable.
How Did This Claim Originate? The assertion that male kangaroos flex their muscles to attract females appears to have its basis in a 2013 paper from the Biological Journal of the Linnean Society titled: “Sexual Selection on Forelimb Muscles of Western Grey Kangaroos (Skippy was clearly Female).”
After this study was released, numerous media outlets published articles with headlines like, “Kangaroo males try wooing potential mates with bulging biceps,” and: “How kangaroos attract partners: Male kangaroos use bulging biceps to seduce potential partners.”
Smithsonian Magazine — published by U.S. research institute Smithsonian Institution — ran an article that featured images showing male kangaroos striking poses that flaunted off their arms, with its subhead reading:
An exercise-going female human knows just how much men love showing off their muscles at gym classes, but flexing biceps in front of ladies may not only be used by humans as an effective strategy; even male kangaroos do it! According to recent research published in Biological Journal of Linnean Society, male kangaroos strike poses which showcase their arms when trying to win over potential mates.
Such reporting likely led social media users to believe that male kangaroos consciously flex their biceps in an effort to impress female kangaroos; however, that wasn’t really what happened… What Did the 2013 Study Find?
Murdoch University and Curtin University teams from Perth, Australia conducted this joint research initiative.
Abstract of its findings published July 12, 2013 was as follows. A significant positive allometry among male forelimb musculature, particularly muscles involved in male-male combat (a group of muscles associated with grasping (shoulder adduction, elbow flexion; and pulling: arm retraction and elbow flexion; and pulling (arm retraction and elbow flexion), strongly supports sexual selection of this musculature. In addition to contributing locomotion for these animals, their forelimbs also serve as signals, weapons and clasping aids; further contributing their significance when competing for mates during battle for mating contests – all traits which would help enhance male chances.
Short version: males who develop larger biceps are more likely to thrive under sexual selection – an evolutionary mechanism by which certain members of a species gain an advantage in mating over others, according to Cambridge. Sexual selection involves choosing traits which increase mating success for an individual and not vice versa.
Female kangaroos may perceive males with larger biceps as stronger and thus better partners; however, no statement in the abstract makes clear whether or not these muscles were deliberately displayed to impress women.
As with the other aspects of this study, nothing suggested any such conclusion was reached by it either. Instead, the research revealed that muscles found on kangaroo forelimbs (including their biceps) are sexually selected traits; females could select males based on whether or not they possess larger biceps; however, no evidence was present suggesting males deliberately contracted those muscles when mating with females.
What Did the Study’s Authors State? Natalie Warburton of Murdoch University and co-author of 2013 Study confirmed in an email response from her research team that their study “didn’t test male behavior or female preference”.
She indicated that authors did not indicate in their study that males “flex their biceps to impress females”, rather, larger forelimb muscles may indicate competitiveness among men in order to gain access to females more readily. She further elaborated that larger biceps gave males an added physical edge should combat with another male take place.
Warburton continued, “we don’t yet understand to what degree females rely on visual cues to select male partners for mating purposes,” adding, “[N]evertheless, we don’t yet understand whether or not these visual signals help females make informed choices when selecting potential mates”.
Warburton quoted two separate studies conducted by Peter Jarman – an established scholar on mammalian herbivore behavior and ecology and macropodidae marsupials including kangaroos. Jarman discovered that dominant males tend to adopt poses that best show off their muscularity and size, according to Warburton. According to Warburton’s interpretation of these results: – Jarman observed “dominant males will frequently adopt poses which best display their muscularity and size”.
“Advances in the Study of Behavior,” Volume 20.”
Unfortunately, Peter J. Jarman did not specify on page 11 his 1991 journal article entitled “Social Behavior and Organization in the Macropodoidea” of Advances in the Study of Behavior Vol 20 that this flexing behavior was intended to impress females.
Bill Bateman, an associate professor from Curtin University’s school of molecular and life sciences, confirmed Warburton’s statement by emailing that males tend to reach up to their tallest height and flex their muscles when confronting rivals or predators to prepare themselves for battle and “prep for show downs.”
“If the rival or predator backs off without fighting back, that signal has worked without having to risk fighting – an honest indicator of just how buff and capable this male is for combat. Evolutionarily speaking, muscle flexing as an indicator signal becomes easier since more animals will use muscle tension as a signal when getting ready for fight rather than simply getting prepared.”
He noted it is impossible to know whether male kangaroos use muscle-flexing techniques on purpose to impress females (in bold italics):
If your questions revolve around animal consciousness and whether their muscles are subconscious or conscious flexed then we simply don’t have answers; what consciousness means in humans alone remains one of humanity’s enduring unanswered questions; however flexing muscles by roos is definitely adaptive in the evolutionary sense: showing their muscles to attract females while discouraging other males may help that individual pass its genes to future generations. Muscles serve as an honest signal that high quality males exist among them and showing them off can both attract females while discouraging other males from competing with them for resources from males of similar quality or quality males among roos displaying muscles is beneficial in helping ensure gene propagation into future generations – show off those muscles to increase female attraction while discouraging other males from competition for resources between generations!
Bateman explained how male kangaroos’ display of muscle strength through flexing is similar to human behaviors such as showing health and attractiveness through muscles; yet how the other males and females respond is unknown, though in terms of evolutionary fitness it appears effective by giving big males access to more females for breeding and mating purposes.
Bateman responded that there have not been any studies showing male kangaroos intentionally flex their biceps to impress females, while Warburton explained how Jarman’s work “makes statements about likely visual cues of increased overall forelimb muscle mass.
Diana Fisher, an associate professor and marsupial expert from Australia’s University of Queensland, stated that while male kangaroos flexing their muscles may seem unlikely, such action have never been demonstrated as being important factors in female mating choice and male paternity success.
“Numerous studies of sexual selection among kangaroos have illustrated their reproductive success; such research reveals how body size and hierarchy status influence female choice as well as having genetic health (and being accessible- having large spatial overlap with them),” according to Fisher’s observation.
“Long arms and large arm muscles play an essential part of male fighting ability and hierarchy. All studies that have looked into paternity have discovered that large males with strong arms tend to find mating successes less frequently with female partners who prefer smaller men.”
Simply stated, forelimb development could just be part of everyday kangaroo life.
