Caption: Chimpanzee lifting up rocks and searching for freshwater crabs Credit: Kyoto University/Kathelijne Koops
Just so stories have plagued the study of the evolution of modern human beings since people first started being curious where they came from as a science. Some explanation of why modern humans are significantly different from other animals has to exist, so people keep making conjectures about why that is. Unfortunately, these conjectures are supported by the flimsiest of evidence. Two of these hypotheses have taken two recent hits. Those are Man the Hunter and Humanity the Fisher.
Man the Hunter was a popular theory dating back to the 1950s and 1960s that posited Humans developed their larger brains when they started consuming meat. Working in groups to bring down prey requires cooperation and that, they thought, required bigger brains. After all, cracking and eating the marrow of a bovine - a gnu or other cattle relative - would take a lot whether of cooperation was taking down and protecting the kill or chasing off predators and scavengers from a kill made by other animals. After all, the megafauna of Africa (and the rest of the world in the Pleistocene) was big, mean and had very sharp teeth relative to today. In a way, that hypothesis seemed to make sense: working in groups to get better quality food would have driven increases in the ability to get that food and it spirals from there as those who are smarter get more food and their children survive better, etc. However, there was an inconvenient relative of ours that made it problematic.
However, in studying chimpanzees, it was found they actually will band together to go hunting. The hunts are more ad hoc than what humans do, but chimps will hunt down and kill monkeys. They tear them apart and share the meat, albeit a little less than fairly by human standards. This has been known now for decades and it was one of the reasons Man the Hunter took something of a hit. However, there seemed to be no future planning associated with the hunts and that seemed to distinguish what chimps did and what humans did. But...and there always seems to be a but! a recent study found something interesting.
At least one population of chimpanzees likes to eat tortoises. They hunt them down and then smash their shells against trees until the chimpanzee can extract the meat. This seems even simpler to do since the tortoises are easier to grab and eat than hunting down monkeys. However, the key difference is the chimps will often cache the tortoise to come back later to eat it. That requires some preplanning and conceptualizing of the future, which was one of the distinguishing traits of Man the Hunter as a hypothesis. People hunted to get food for the future. Others didn't. Well, um, about that...
Wait! you say! Squirrels save acorns and nuts for the future. Yes, but, they actually fail to recover almost 75% of them! Squirrels simply don't remember most of where they bury their nuts. Chimps and people seem to be a bit different than that. And what humans and chimps do, a bit less than each other.
A second hypothesis was the explanation for humans developing the way we did was the exploitation of marine resources. Eating fish and shellfish became a popular idea in the last twenty or so years. Chimps didn't do that! Or so it was thought. It turns out, that, too, is wrong.
At least in one population of chimpanzees, they regularly crab. That is to say, these chimps from Gabon regularly hunt and eat crabs from streams and ponds in that part of Africa. Humans, at least among the apes, are not unique for eating aquatic life and these chimpanzees do not appear to be any different than others of their species, at least physically. Crab eating is also known from a macaque from southeast asia, but they are different enough to have been excluded from causing problems for the marine resources hypothesis. However, chimpanzees are our closest relatives.
Interestingly, among the chimps that crab, they do not appear to eat termites. This is something chimpanzees are noted for. Chimps will fashion long sticks and 'fish' termites from a termite mound and eat them off the stick. However, these chimps do not do so even though there are termites present in their environment. That would imply the crabs are providing for some nutritional need normally covered by consuming insects. That's interesting.
In both cases, though, chimpanzees hunting and caching their kills and chimpanzees consuming aquatic based foods, the hypotheses as to why human brains increased in sized and set us apart from the other apes have taken a serious hit. The drives were to make humanity became so different are probably far, far more complex than simply what we ate and when. Humanity isn't simple. Neither are animals. To make simple assumptions as to what makes us different are Just So Stories.
Tortoises on the menu
https://www.eurekalert.org/pub_releases/2019-05/mpif-tot052219.php
Chimps caught crabbing
https://www.eurekalert.org/pub_releases/2019-05/ku-ccc052719.php
Chimpanzees catch and eat crabs
https://www.eurekalert.org/pub_releases/2019-05/uoz-cca052919.php
Crab-fishing by chimpanzees in the Nimba Mountains, Guinea
https://www.sciencedirect.com/science/article/pii/S0047248418302069
Why Do Squirrels Bury Nuts? (and other mysteries)
https://ssec.si.edu/stemvisions-blog/why-do-squirrels-bury-nuts-and-other-mysteries
Crab-eating Macaque
https://en.wikipedia.org/wiki/Crab-eating_macaque