Feb. 28, 2005 WASHINGTON, DC (February 20, 2005) - Parenting. Establishing life partnerships. Getting to know someone else's personality. These experiences feel profoundly human, but they have more in common with the animal world than one might think, researchers said today at the 2005 Annual Meeting of the American Association for the Advancement of Science (AAAS).
Animal lovers may not be surprised by this news.
"I get the most skepticism from scientists," said Samuel Gosling of the University of Texas, Austin. "It's really the human behavior researchers who object most."
Gosling and his colleagues have determined that dogs and hyenas have clear personality traits that can be measured like they are in humans. The researchers have studied characteristics such as fearfulness and anxiety, curiosity, and sociability.
"Personality is not just unique to humans," Gosling said.
Personality measurements have implications for animal welfare, for example when dogs are matched with owners or selected for various types of work. This information should also allow researchers to explore the various biological, genetic and environmental causes for an individual animal's temperament.
But, all traits do not appear in all species. Conscientiousness and dependability are only present in chimps and humans, according to Gosling.
Some of the parenting behaviors by monkey also resemble human parenting, Dario Maestripieri of the University of Chicago said. In his research on the development of maternal responsiveness he has found that both young girls and young female rhesus monkeys actively seek out opportunities to interact with infants, which males are much less inclined to do.
"It's a way to acquire parenting skills," Maestripieri said.
Many studies have shown that early social stress can accelerate puberty in girls, Maestripieri said. "We have now shown that early stress can also accelerate the development of maternal responsiveness in both humans and monkeys," he said. Adolescent girls who grow up without a father at home reach puberty earlier and are more attracted to pictures of infants than girls who have a father at home, Maestripieri and his colleagues recently reported in Developmental Science.
Female rhesus monkeys exposed to harsh and unpredictable maternal care in infancy also showed earlier interest in infants as well as higher levels of stress hormones during development, Maestripieri said. These findings are due to be published in Proceedings B, a journal of the Royal Society.
When it comes to the tiny tamarin and marmoset monkeys, some females behave in ways that don't translate so directly to humans.
The socially subordinate female monkeys in these groups become infertile in response to social interactions with a dominant female, according to Wendy Saltzman of the University of California, Riverside. Instead of breeding, these females help to rear the dominant females' infants. Researchers think this hormonally-mediated change benefits the subordinate females, because even though these monkeys will not be passing along their own genes, they will be helping to rear closely related infants.
When subordinate females do breed, their infants are likely to be killed by the dominant female, Saltzman and her colleagues have found more recently. So, by switching off their fertility, subordinate females may avoid investing in infants that aren't likely to survive.
These monkeys have very specialized social structures that aren't common in humans, Saltzman explained.
"But, in humans too, there can be social influences on reproductive physiology. The exact phenomenon of social suppression of fertility doesn't map onto humans but can help us understand how human fertility can be influenced by social and psychological factors," she said.
Curiously, reproductive suppression doesn't seem to involve stress or aggression between the females, according to Saltzman.
In the case of small rodents called voles, researchers have delved deeper into the biological mechanisms underlying the animals' mating behavior. Prairie voles mate for life, while a closely related species, the meadow mole, is promiscuous.
The difference seems to be that the receptors for a hormone called vasopressin are concentrated in different brain areas for each species, according to Larry Young of Emory University. Young and his colleagues have found that the receptors are located in the same areas involved in reward and addiction in the monogamous voles, but they're not present there in other vole species.
The researchers have also determined that the location of the receptors is determined by a single gene, which contains stretches of extra DNA in the monogamous voles but not in the promiscuous ones. Similar variations in this gene have also been found in humans.
"Other studies have found associations between this genetic variability and autism, which is a disease that affects social bonding and behavior. So, there's an interesting question there," Young said.
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