Research indicates that mammal species with more advanced brains often show less size variation between males and females.
In several mammalian species, there is a noticeable size difference between males and females, referred to as sexual size dimorphism (SSD). For instance, male elephant seals can be up to three times larger than their female counterparts. Conversely, dolphins exhibit no size difference between genders. Humans fall somewhere in the middle, as the average male is larger than the average female, although there is significant overlap in size within the population.
To explore the connection between this phenomenon and genetic evolution, scientists from the Milner Centre for Evolution at the University of Bath in the UK investigated the genomes of 124 mammal species.
The researchers categorized genes into families based on similar functions and assessed the size of these gene families. Their analysis revealed that species with a significant size disparity between the sexes had larger gene families related to the sense of smell and smaller ones linked to brain development.
This suggests that species with minimal size differences between males and females (termed monomorphic) tend to possess larger gene families that are associated with brain development.
In their publication in Nature Communications, the authors propose that in species exhibiting a pronounced SSD, reliance on olfactory capabilities may be essential for mate selection and territory identification.
On the other hand, mammals with limited SSD likely focus on enhancing their brain function while developing intricate social structures, implying that they select mates using strategies beyond just physical size.
Dr. Benjamin Padilla-Morales, who led the study at the Milner Centre for Evolution at the University of Bath, expressed his astonishment at the significant statistical correlation identified between a large SSD and expanded gene families related to olfactory capabilities. He also highlighted the intriguing finding that gene families associated with brain development were diminished.
“This could suggest that species with a minor SSD possess larger gene families tied to brain function, which may lead to more complex behaviors, such as shared parenting and monogamous mating systems.”
“It demonstrates that while size is a critical factor for sexual selection in certain species, it may not be as significant in others.”
“This raises questions about how traits like SSD influence the evolution of mammalian brains and genomes.”
Looking ahead, the researchers aim to examine the relationship between testis size and the genetic evolution of mammals.
The study included contributions from researchers at the Universities of Bath and Sheffield, Cardiff University, and UNAM (Mexico).
