In a paradigm-shifting discovery, a fresh analysis of mammalian size across hundreds of species reveals that males are not, in fact, larger than females in most cases, challenging a scientific doctrine established by none other than Charles Darwin. This comprehensive study, published in Nature Communications, scrutinizes 429 mammalian species and arrives at a startling conclusion: males are larger than females in only 45 percent of the cases. The study’s lead author, Kaia Tombak, an evolutionary biologist, describes the findings as a rebuttal to the “really strong inertia toward the larger male narrative,” which she attributes to “Western societal biases.”
Contrary to the commonly held view that males usually outsize females in mammalian species—a view that Darwin himself took for granted—the study suggests that sexual size dimorphism (SSD) is not as straightforward as once thought. The research, which looked at wild, non-provisioned populations, found that an almost equal proportion of species exhibit no size difference between the sexes, and a significant number,16 percent, even feature larger females.
The team’s meticulous approach to gathering and analyzing data appears to have been key in overturning long-standing assumptions. They evaluated sexual size dimorphism through a statistical lens, ensuring that the species were not just categorized based on arbitrary body mass cut-offs, but by also considering variance around the mean. This rigorous methodology sheds new light on a topic that has been surprisingly constrained by biases and inadequate data.
Evolutionary biologist Malin Ah-King from Stockholm University, who was not involved in the research, comments on the broader implications of this study:”The questioning and reevaluation of prevailing assumptions about sex differences is part of an ongoing process that I call the female turn.” This perspective underlines a paradigm shift in the understanding of sexual selection and mammalian biology.
The study also reports a striking variance in SSD among mammalian orders. For instance, half of rodent species were sexually monomorphic, and nearly half of bat species showcased larger females. This challenges the focus of past SSD research on a few select taxa and highlights the diversity of mammalian reproductive strategies beyond physical size and dominance.
Crucially, the researchers underline that the “larger males” narrative has persisted due to a historically male-centric view of sexual selection. This bias has overshadowed the complex and varied nature of mating systems and competition among both sexes. By moving away from presumptions of size-related sexual selection in males, the study paves the way for new lines of inquiry. It invites scientists to contemplate why many mammals are monomorphic in body size and to investigate alternative mechanisms of sexual selection, such as agility, olfactory signaling, and strategies not solely linked to size.
Relevant articles:
– Males aren’t actually larger than females in most mammal species
– New estimates indicate that males are not larger than females in most mammal species, Nature.com
– Male mammals aren’t always bigger than females, Science News Magazine
– Sorry, Darwin: Most male mammals aren’t bigger than females, Popular Science