1. Study suggests bonobos help strangers without being asked

    November 14, 2017 by Ashley

    From the Duke University press release:

    A passer-by drops something and you spring to pick it up. Or maybe you hold the door for someone behind you. Such acts of kindness to strangers were long thought to be unique to humans, but recent research on bonobos suggests our species is not as exceptional in this regard as we like to think.

    Famously friendly apes from Africa’s Congo Basin, bonobos will go out of their way to help strangers too, said Jingzhi Tan, a postdoctoral associate in evolutionary anthropology at Duke University.

    A previous study by Tan and associate professor of evolutionary anthropology Brian Hare found that bonobos share food with strangers. Now, in a new series of experiments, the team is trying to find out just how far this kindness goes.

    The researchers studied wild-born bonobos at the Lola ya Bonobo sanctuary in the Democratic Republic of Congo.

    In one experiment, they found that bonobos will help a stranger get food even when there is no immediate payback.

    Sixteen bonobos were led one at a time into one of two adjacent rooms separated by a fence. The researchers hung a piece of apple from a rope just above the empty room, visible but out of reach.

    The apes couldn’t access the fruit or the rope. But if they climbed the fence they could reach a wooden pin holding the rope to the ceiling and release the dangling fruit, causing it to drop within reach of any bonobo that entered the next room.

    The bonobos released the fruit roughly four times more often when an unfamiliar bonobo was in the adjacent room than when the room was empty.

    What’s more, the bonobos didn’t wait to be asked for help, they just offered it. The researchers changed the size of the mesh surrounding the stranger’s room so that in some trials they were able to stick their arms through the openings in the screen to beg for the treat, and in other trials they were not. The bonobos helped just as often whether the stranger gestured for help or not.

    Bonobos’ impulse to feel for strangers isn’t entirely under conscious control, the researchers also found. In another experiment, they had 21 bonobos watch a series of short videos. In some videos, the apes saw a familiar group member either yawning or making a neutral expression. In other videos they watched complete strangers from the Columbus Zoo in the U.S. behaving the same way.

    Just as watching another person yawn can make you yawn, yawning is contagious in bonobos too. Previous studies suggest the phenomenon is linked to a basic form of empathy called “emotional contagion,” when one person’s mood triggers similar emotions in others around them.

    The researchers found that stranger yawns were just as contagious as those of groupmates.

    The impulse to be nice to strangers is likely to evolve in species where the benefits of bonding with outsiders outweigh the costs, said Tan, now a postdoctoral scholar at the University California, San Diego.

    Female bonobos leave the group where they were born to join a new group when they reach adulthood, where they form bonds with other unrelated adults they’ve never met. Bonobos, like humans, may simply be eager to make a good first impression.

    “All relationships start between two strangers,” Tan said. “You meet a stranger, but you may meet them again, and this individual could become your future friend or ally. You want to be nice to someone who’s going to be important for you.”


  2. Bigger brains led to bigger bodies in our ancestors

    April 19, 2016 by Ashley

    From the American Museum of Natural History media release:

    mind mazeNew research suggests that humans became the large-brained, large-bodied animals we are today because of natural selection to increase brain size.

    The work, published in the journal Current Anthropology, contradicts previous models that treat brain size and body size as independent traits responding to separate evolutionary pressures. Instead, the study shows that brain size and body size are genetically linked and that selection to increase brain size will “pull along” body size. This phenomenon played a large role in both brain- and body-size increases throughout human evolution and may have been solely responsible for the large increase in both traits that occurred near the origins of our genus, Homo.

    “Over the last four million years, brain size and body size increased substantially in our human ancestors,” said paper author Mark Grabowski, a James Arthur postdoctoral fellow in the Division of Anthropology at the American Museum of Natural History. “This observation has led to numerous hypotheses attempting to explain why observed changes occurred, but these typically make the assumption that brain- and body-size evolution are the products of separate natural selection forces.”

    That assumption is now being questioned, based on a large body of work that has shown that genetic variation–the fuel of evolution–in some traits is due to genes that also cause variation in other traits, with the result that selection on either trait leads to a correlated response in the unselected trait. Consider the leg bone, or femur, of an elephant. As the bone gets longer, it also gets wider. If artificial selection is used to produce a tall elephant, its legs likely won’t just become long, they’ll also get wider. Part of this effect is due to shared genetic variation, or covariation, among traits in the femur. Grabowski set out to explore this kind of genetic relationship between human brain size and body size, and its impact on our evolution.

    With brain- and body-size covariation patterns from a range of primates and modern humans, Grabowski created a number of models to examine how underlying genetic relationships and selection pressures likely interacted across the evolution of our lineage. His findings demonstrate, for the first time, that strong selection to increase brain size alone played a large role in both brain- and body-size increases throughout human evolution. This phenomenon also may have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors likeAustralopithecus (the most famous of which is the Lucy fossil) to Homo erectus.

    In other words, while there are many scientific ideas explaining why it would be beneficial for humans to evolve bigger bodies over time, the new work suggests that those hypotheses may be unnecessary; instead, body size just gets pulled along as the brain expands.

    While selection no doubt played a role in refining the physical changes that came with larger body sizes, my findings suggest it was not the driving force behind body-size evolution in our lineage,” Grabowski said. “Therefore, evolutionary models for the origins of Homo based on an adaptive increase in body size need to be reconsidered.”