DURHAM, N.C. -- In a discovery that suggests the fathering instinct might be more fundamental to primate evolution than previously believed, researchers have shown that male baboons give preferential protection to their own genetic offspring.
The finding that male baboons somehow recognize their own genetic offspring -- despite the fact that multiple males may mate with each female in a troop -- also raises important scientific questions about how such recognition occurs, said the researchers who made the discovery.
The research was published in the Sept. 11, 2003, issue of the journal Nature by researchers from Duke University, the National Museum of Kenya, Princeton University, UCLA and the Brookfield Zoo in Illinois. Lead author on the paper is Duke postdoctoral fellow Jason Buchan, and the other co-authors are Duke Assistant Professor of Zoology Susan Alberts, UCLA Professor of Anthropology Joan Silk and Princeton Professor of Ecology and Evolutionary Biology Jeanne Altmann. The research was sponsored by the National Science Foundation, the Chicago Zoological Society, the L. S. B. Leakey Foundation and the National Geographic Society.
Said Alberts of the findings, "If male baboons care for their kids -- and baboons are almost among the least likely societies where you would expect to see this -- then it suggests that paternal care has really deep evolutionary roots in primates."
In their research, the scientists studied members of five wild savannah baboon groups in Amboseli, Kenya and adjacent areas near the foot of Mount Kilimanjaro. These groups have been study subjects by scientists for some three decades and have become so habituated to human observers that they basically ignore them.
To determine the genetic heritage of adult males and juveniles, the researchers laboriously collected and analyzed the DNA of fecal samples from the animals. The researchers also observed the males and juveniles over a period of three years between July 1999 and July 2002. Those observations concentrated on the instances in which adult males protected offspring from aggression by other animals.
Although paternal care certainly encompasses a broader range of behaviors, said Alberts, such protection against aggression is the easiest to observe and quantify. Also, such male protection offers obvious survival advantages for the juveniles, she said.
The sample collections and observations were carried out by Kenyan field assistants Raphael Mututua, Serah Sayialel and Kinyua Warutere.
The scientists analyzed the resulting genetic and behavioral data to determine the interactions between adult males and three different types of juveniles:
- -- genetically related juveniles that are their offspring
- -- those juveniles that were the "behavioral offspring" of the males; that is, they were the offspring of females with whom the males had mated, and
- -- unrelated juveniles.
"We found that males unequivocally gave more protection to those juveniles they had fathered than to those they hadn't," said Alberts. "So that led us to the next question of how can the males tell? It may be that at least one source of information is behavioral. The male might prefer offspring of females that the male had mated with. And if that's the case, then the male might show at least some preference to behavioral offspring -- the kids from females the male had mated with.
"And if there's a behavioral explanation, the males shouldn't differentiate between their genetic and behavioral offspring. However, they did differentiate between these two types of kids very strongly. So the only explanation we're left with is that the males recognize and prefer their genetic offspring."
According to Alberts, previous studies of baboons had not been able to show such paternal care of genetic offspring. For one thing, she said, before DNA analysis, it had been all but impossible to identify unambiguously the genetic offspring of a given male in such troops. Also, she said, laboratory studies attempting to show such paternal care in captive animals had not yielded such evidence.
"So, until now many researchers had been skeptical that males showed paternal behavior toward their own offspring," said Alberts. "They had increasingly concluded that these apparent paternal caring behaviors are really a mating effort; that males care for the kids as an incentive for the mother to mate with them.
"The reason that laboratory studies were not successful, we believe, is that they attempted to isolate one cue that the male used," said Alberts. "But we are led to conclude from our studies that males use multiple cues to identify their offspring -- including perhaps pheromones, physical and behavioral resemblance, or the amount of mating time with the female.
"Even humans don't just use one cue to identify their offspring," said Alberts. "We use all the information we have available to us."
According to Alberts, she and her colleagues have already launched studies to explore what pheromones or odor molecules might provide males clues to the genetic identity of offspring. They are also studying how the father-infant relationships develop -- whether they are initiated by the father or by the mother.
More broadly, she said, the researchers are exploring the "balance of costs and opportunities" that males must strike in deciding whether to remain with a troop that includes their offspring, or to strike out and join another troop. The former decision, she said, confers the advantage of protecting one's own offspring. And the latter decision creates greater risk of death during a troop transfer or battles for new mates, but potentially greater mating opportunities in a greater number of groups.
"However, a central question we want to ask next is, if males care for their offspring does it affect the offspring's survival chance?" asked Alberts. "And if it does, then that would be a really exciting finding, because it constitutes a real pressure on males in terms of this balance of costs and opportunities."