A recent study led by the University of Bath, published in Nature Communications, reveals that mammals with more complex brains tend to have smaller size differences between males and females.
This phenomenon, known as sexual size dimorphism (SSD), varies significantly across mammal species.
Sexual size dimorphism refers to the difference in size between males and females of a species. In some species, like elephant seals, males are much larger than females.
In others, like dolphins, males and females are about the same size.
Humans fall somewhere in the middle, with males generally being larger than females, but with considerable overlap in size across the population.
Scientists from the Milner Center for Evolution at the University of Bath examined the genomes of 124 mammal species.
They grouped the genes into families with similar functions and measured the size of these gene families. Their findings were intriguing:
- Species with significant size differences between males and females had larger gene families related to olfactory functions (sense of smell) and smaller gene families associated with brain development.
- Conversely, species with minimal size differences between sexes, known as monomorphic species, had larger gene families linked to brain development.
The researchers suggest that in species with large SSD, traits like a strong sense of smell are crucial for identifying mates and territories.
On the other hand, mammals with smaller SSDs may invest more in brain development, leading to more complex social structures and behaviors. These species may compete for mates through means other than size, such as intelligence or social skills.
Dr. Benjamin Padilla-Morales, who led the research, explained, “We were surprised to see such a strong link between large SSD and expanded gene families for olfactory function. Even more interestingly, the gene families under contraction were linked with brain development.
This suggests that species with small SSD have larger gene families associated with brain function and tend to show more complex behaviors, like biparental care and monogamous breeding systems.”
The study raises fascinating questions about how traits like SSD shape the evolution of brains and genomes in mammals. The researchers are now interested in exploring how other factors, such as testes size, influence the evolution of mammalian genomes.
This study highlights the intricate relationship between physical traits and genetic evolution in mammals.
It shows that while size can be a crucial factor in sexual selection for some species, brain complexity and associated behaviors play a significant role for others.
This research opens new avenues for understanding the diverse evolutionary strategies across the animal kingdom.
