Chimpanzee mothers are cautious about introducing newborns to the community. Chimpanzees are smart and curious, and they're very interested in newborns, young chimpanzees especially. They may try to reach out and touch infants, sniff them or just groom the mom to get a closer look. Moms don't really like this attention. They usually resist it. Actually, infants don't interact very much with other chimps in the first six months at all. It's only as they grow bigger and more curious that mothers allow them to seek out playmates and interact with other group members. Until recently, we thought that males didn't know which infants were theirs because they don't show any real paternal care and parents don't live in pairs. Without genetic testing, we can't tell which male is the baby's father. But we have an exciting new results at Gombe. By looking closely at how much time male spend with infants and how much they interact with them, we can see that males do seem to know which infants are theirs. They spend more time with their own kids than with other infants. Still, sometimes males can threaten infants, even kill them. This happens in many species, and is especially well studied in lions. For years, scientists found this really puzzling. Why would this behavior evolve? How could it be beneficial to kill members of your own species? Some believed that infanticide by males must be a pathological behavior, meaning that something is wrong with the individuals who do it. Now we have evidence that infanticide can be beneficial for the males as long as they only attack infants that they have not fathered. For instance, when a male lion joins a new group, he might kill the infants that were already there. Then he can mate with their mothers who are no longer nursing. This gives him the opportunity to mate with that female and quickly father her next offspring. Male chimpanzees usually stay in one group for their entire life. Still, they may occasionally kill infants within that group, especially infants that are not their own. One infanticide in Gombe occurred in August of 2013. Researchers were watching a group of chimpanzees as they sat and groomed one another. The alpha male, Ferdinand, was grooming a mother named Tanga. Tanga's young infant, Tarime, sat between them. Suddenly, Ferdinand grabbed Tarime, bit her, and carried her away from her mother. Tanga screamed and tried to take her back, but Ferdinand quickly killed the infant. So, why did Fernando attack Tarime? Genetic paternity tests revealed that Ferdinand was not Tarime's father. In fact, Tanga had spent time away from the group around the time she conceived and hadn't mated at all with Ferdinand. We're still trying to understand how males recognize whether infants are their own or not. But this case and others like it provide more evidence that they do know which infants they fathered. Ferdinand may have killed Tarime to speed up his chances to mate with Tanga and father her next offspring more quickly. On rare occasions, females also commit infanticide. Infanticide by females is mostly limited to the first two months after birth when infants are first introduced to the group. We've been looking for patterns in the female infanticides we've observed at Gombe. They are very rare and have only been recorded a handful of times over the course of 57 years. Mother-daughter pairs are often responsible for the attacks, like these females, Fifi on the left and Fanni on the right. In 1998, Fifi and Fanni teamed up to attack Gremlin and her newborn twin daughters. Here's how the attack began. Fanni had been harassing Gremlin all morning, but Gremlin closely shadowed adult male Frodo, ensuring that he was between her and Fanni at all times. But then, Frodo and the males left and Fifi arrived. Gremlin grew increasingly anxious. Fanni approached, was soon joined by Fifi, and the attack began. In this photo taken during the attack, we see Fanni standing upright, ready to hit Gremlin, while Fifi on the right blocks her escape. Gremlin in the left corner is trying desperately to protect her infants by crouching over and clutching them against her body. Fanni hits Gremlin over and over, as you see in the second photo, while Fifi tries to grab the infants. The attack continued for several minutes until Gremlin was able to retreat to a tree. It's difficult to attack in the trees. So, Fifi and Fanni lost their advantage. They continued to harass Gremlin, but we're ultimately unsuccessful in their infanticidal attack. By combining data from this attack and others, we have concluded that females kill each other's babies to compete for resources. Gremlin is a prime example. This wasn't the first time Fifi and Fanni tried to kill one of her newborn daughters. They had tried five years earlier when Gremlin last gave birth. They were also unsuccessful in this first attempt. So, rather than being killed as newborns, each one grew up and stayed with Gremlin in her community. Here they all are as adults with their own children. This is a map showing where females range within the larger community. Fifi's range isn't green, Fanni is in red, and Gremlin and her daughters in shades of blue. In the first panel, just prior to the first attack, we see that Fifi, Fanni, and Gremlin were all ranging in the same area. This area in the center of the community is full of good fruit trees. Twenty years later, as shown in the second panel, Gremlin and her daughters in blue have taken over this prime area. Meanwhile, Fifi has died, and Fanni and her family in red have been pushed toward lower quality habitat in the south. If Fifi and Fanni had killed Gremlin's infants, Fanni might have been able to stay in that great spot up north. Interestingly, when new moms are attacked by females, they often seek help from adult males. Often, these males do protect them. So, sometimes males are the threat, and sometimes they come to the rescue. No wonder chimpanzee mothers are so nervous.
