Gorillas are solid fathers, dogs are terrible dads, and humans run the gamut. This long confounded scientists, who had plenty of reason to believe that paternal behavior had a genetic basis, but struggled to prove that hypothesis in the context of behavioral variables. Now, a team of Harvard researchers has located specific DNA segments that influence paternal behaviors, the closest scientist have come to finding the “dad genes” — or at least proving they exist.
In so doing, they’ve also stumbled onto a bunch of new questions.
For the study, published today in the journal Nature, researchers looked at two sisters species of common house mice — Peromyscus maniculatus, also known as the Deer Mouse, and Peromyscus polionotus, or the Oldfield Mouse. The species made an ideal experimental model because they have very different approaches to parenting. Deer mice mate with many partners, and consequently can have litters with pups from multiple fathers, whereas Oldfield mice are monogamous. While data shows that females in both species were attentive mothers, there were significant between fathers. Oldfield mice were involved in raising their offspring, but deer mice dads were relatively absent.
Researchers tested the impact of different parenting styles by cross-fostering mice, having oldfield mice raise deer mices and vice versa. When they later observed how those pups parented themselves, the found, “no measurable effect based on who raises them,” Hopi Hoekstra, evolutionary biologist and co-author of the study explained in a news release. “It’s all about who they are genetically.”
Researchers then cross-bred the deer and oldfield mice, then cross bred the offspring from that to create a second generation of hybrid mice with parts of the genome of each species. When they mapped the genome differences across both species, they saw that mutations that increased maternal care did not affect paternal care. This told them that parenting behavior in males and females may have evolved independently.
Scientists then zeroed in on the hypothalamus, a part of the brain responsible for social behavior, they observed differences in gene expression between both species. That’s when the gene responsible for the production vasopressin, a hormone is thought to be responsible for nest building, jumped out. They tested if this gene impacted parenting by administering vasopressin to oldfield mice, the better fathers. When they did this, their nest-building dropped precipitously. In human terms, they left and went to the bar.
“Before our study we had no idea how these parental behaviors evolved, whether there was one gene that mediates all of the differences in behavior, or if it was 10 or 20,” said Andres Bendesky, a postdoctoral researcher who helped lead the study. With this new data, experts now have “molecular handles” they need to start understanding the genetics and complex circuitry of the dad brain, which is composed of a lot more than NBA stats.