14 DAY TRIAL // A new astonishing finding explains us the origin of the behavior of our ancestors of employing caves as shelter.
Recently, a team from Iowa State University led by anthropologist Jill Pruetz had signaled in savanna chimpanzees from Senegal the habit of employing sharpened sticks to hunt small animals (particularly bush-babies).
Now the same team discovered on the same chimp population at Fongoli the ape's behavior of sheltering in caves to protect themselves from the scorching heat, the first known case on apes.
Local people (Malinke) had signaled to the researchers in 2001, at a site known as Fongoli, that chimpanzees occupied caves during the hottest period of the year, but approaching the chimps was very difficult. "It took years and years for the chimpanzees to get habituated [to the researchers' presence]. As soon as we would walk anywhere close, it would scare them out of the caves", explained Pruetz.
Even so, the research could measure how much the chimps used the caves by the clues left behind on sandy cave floors: tracks, feces, and food remains. The cave was mostly used at the end of the dry season in May and June.
In April and May the top temperatures in the Senegalese savanna near the caves can rise to 107.6 degrees Fahrenheit (42 degrees Celsius) while in the largest of the three small caves employed by the chimpanzees never went over 84.2 degrees Fahrenheit (29 degrees Celsius). "The behavior appears to be an adjustment to heat stress," Pruetz said. "This is one of those cases in which the apes genuinely surprise us, exceeding our expectations and imaginations", noted William McGrew of Cambridge University in England.
Most wild chimpanzee behavior researches are made on forest populations, but the Senegalese chimpanzees, inhabiting arid savanna dominated by open grassland and sparse woodland, are more useful for us in explaining the roots of the human behavior and evolution, as 4 million years ago our ancestors were basically just a type of savanna chimps. "Cave use is just one of several strategies the chimpanzees use to cope with their difficult environment, where both shade and water are critical resources", noted Pruetz.
Lack of a nearby water source earlier in the dry season could be the factor that impedes more extensive cave inhabiting throughout the year. The team also signaled cave use in other close chimpanzee populations, like Baniomba, where "[chimpanzees] seem to use caves even more than at Fongoli. But we don't yet have any systematic data", said Pruetz.
The deeper Baniomba caves could be occupied on a daily basis during two weeks in the summer. "The finding would be notable in itself, but the implications for reconstructing the evolutionary origins of shelter in our ancestors make it even more so. Some monkeys use caves to stay warm at night", observed McGrew.
The new study shows "not the nocturnal use of caves for overnight sleeping but rather [daytime use] for siestas, socializing, and picnicking. No one expected this."
Early humans seemed to have extensively employed caves rather to avoid the cold, especially during the night. "Primates very often don't use available shelter, even to get out of the rain. The finding opens up a whole set of questions, given that this behavior isn't seen in other regions of Africa. Are they right at the edge of what chimpanzees can handle in terms of temperature ? or is it a cultural thing?" asked anthropologist Jim Moore of University of California San Diego. "By building up our understanding of how such environments shape [modern human relatives], we can better model our early ancestors," he added.