Fat Monkeys and Chubby babies: Part 1
I love fat! I eat a ton of it and I feel amazing for it. Almost all the vitamins the human body needs are fat-soluble in their most accessible form. Not to mention how good it makes everything taste. Food is just the start though, need a natural firelighter? Try fat. Need a candle? Try fat. Need to waterproof your shoes? Try fat. You can even use fat to tan skins to make clothing like our ancestors did. No wonder animal fat was so sacred to indigenous cultures the world over.
In the last century, things have changed, however. The animal fat we’ve been eating for millions of years has suddenly and mysteriously become really bad for us, causing heart disease and all sorts of other problems. Unlike our ancestors, we are now designed to thrive on bran flakes and hydrogenated soy…
Jokes aside, the recent history of fat is muddled but let’s not go down that rabbit hole for the moment. Instead, let’s take it way back and talk about how animal fat made us human.
6 million years ago the world was changing. The North and South Pole were once again covered in Ice and the rainforests of Africa were retreating. They were giving way to more arid savannahs and grasslands. This is when our ancestors split from our common ancestor with the Chimpanzee and Bonobo. They ventured out of the forest and were forced to adapt to a new world full of grass, the massive animals that ate it, and the predators that ate them.
How did those monkeys adapt to this landscape? There is a lot we could talk about here, starting to walk more on two legs and probably becoming more dependent on each other for safety but in terms of food the most important development was that we became scavengers. Where there are lots of large herbivores there are lots of dead ones. Our ancestors couldn’t have hunted these animals and they didn’t stand much of a chance against the predators who could. This meant they would only have arrived at a carcass long after most of the meat had been stripped away. But often the bones and skulls would have been left, given other animals were unable to open them up to get at the marrow and brains inside. Chimpanzees are known to use rocks to open nuts and I think it plausible that at some point one of these monkeys had a go at smashing open these bones. When they did they would have suddenly had access to large quantities of perhaps the most nutritious and energy-dense resource around. Bone marrow and brain are almost entirely made of fat including large amounts of brain-boosting omega-3 and omega-6 fatty acids. Funnily enough, there is no better food to nourish our brain, than brain itself.
So now our ancestors had access to a huge reserve of fat at a time when they were under a lot of pressure to adapt to new environments and means of survival. This was a recipe for brain growth. However, nothing is free in evolution and our growing brain meant something else had to give. As our brains got bigger our gut shrunk. The more access we had to animal foods the less requirement we had for the large fermentative vats that herbivores carry around to turn vegetable matter into protein and fat. Just look at the size of a chimp or a gorilla’s stomach compared with a human. Eventually, animal foods became an obligatory part of our diet because we no longer had a gut that could turn plant fibre into enough of what we needed to survive.
We put these growing brains to use scavenging and eventually learning to hunt ourselves. By the time Homo Erectus was on the scene, hominids were hunting some of the biggest animals on the planet like elephants and hippos. They would have had privileged access now to those carcasses which would have contained enormous amounts of fat as generally the proportion of fat to lean muscle increases the bigger an animal gets. Smaller animals are much leaner by comparison.
This sort of hunting would have further propelled brain growth as it required new technologies like spears and handaxes for butchery. Communication and cooperation would also have been selected for requiring new neural circuitry. These were the stimuli and fat was the fuel that set us on the path to modern humans. Notice how our story differs from other predators who get the majority of their calories from protein. Cats can digest up to 70% of their calories from protein meaning they can live off much leaner meat. Humans on the other hand can only get around 40% of our energy from protein. Having given up most of our capacity to digest fibre, and living in a world scarce in carbohydrates, we became dependent on fat for our fuel.
This dependency is what Israeli paleoanthropologist Miki Ben-Dor draws on to provide an explanation for human evolution which I’d like to elaborate on here. It’s easy to think that ever since our chimp-like ancestor cracked open their first can of bone marrow, we’ve been on an inexorable path to modern humans. But our brain is an extremely expensive organ that could easily not have evolved in the way it did. Why didn’t our brain size max out at the size of Homo Erectus for example? This is a question I find fascinating because I feel it really gets to the core of what a human is and why we’re here. Ben-Dor’s theory is the first explanation I’ve come across that seems to make sense of a lot of what we know about the human story.
His answer is that once humans had learned to hunt the largest animals this would have become gradually harder through time. The number of elephants and hippos may well have declined given their slow gestation period and they may also have become much more wary of humans. Whatever the reason, Ben-Dor’s research shows that during the Pleistocene, humans were gradually hunting smaller and smaller animals. Where elephants, rhinos, and hippos had dominated the bone remains, horses and wild cattle became more prominent followed eventually by antelope and deer.
At first glance, you might think it was easier to hunt a deer than an elephant. It’s certainly less dangerous, but the technology and cognitive capacities required are actually much less. The Mbuti pygmies still hunted elephants until relatively recently by sneaking underneath them and stabbing them with a spear. Who knows how our ancestors did it but the point is that all they needed technologically was very sharp sticks and probably to be able to communicate well with each other. Not to mention a whole lot of courage.
Alternatively, think about the cognitive requirements involved in tracking a deer or antelope. It requires an astonishing level of deductive reasoning and then you’ll need an atlatl (spear thrower) or a bow and arrow to bring the animal down. Many cultures practiced Persistence hunting where they would run the animal down in the heat of the sun over many hours. Whether this was common practice during the Pleistocene is up for debate although it may have been a reason for human’s impressive long-distance running capabilities and it still requires incredible tracking abilities, if not any advanced tech.
According to this theory, the development of those cognitive faculties and new technologies were the result of humans’ appetite for fat combined with the need to hunt smaller and smaller animals.
Intriguingly, this could also explain why we teamed up with wolves when we did. Humans that were heavily dependent on hunting animals like reindeer or antelope rather than larger and fatter animals would likely have had a surplus of lean meat available that they simply couldn’t consume due to the protein ceiling talked about earlier. That is to say, if the animals were relatively lean, and there wasn’t much carbohydrate around which is reasonable to assume during an ice age, people would have had to hunt more animals than they could eat to meet their energy requirements. It would have made a lot of sense to team up with wolves which could help hunt the larger number of animals needed and could enjoy the surplus of lean meat that the humans couldn’t consume. For the first time, working together benefitted both species a lot more than competing.
Many fishing technologies, bows and arrows, and the domestication of dogs are all unique to Homo Sapiens and I believe that our insatiable love of fat was probably a big driver for these advances. The changing environment forced us to hunt smaller and smaller animals as well as learn to fish and tend wild plants while the fat itself provided the fuel our brains needed to cope with that adaptation.
With agriculture, we suddenly had a reliable source of carbohydrates year-round and fat became a lesser component of our diet. Many people’s health deteriorated as a result, although, people never stopped valuing animal fat. Look at how much fatter domestic animals are than their wild counterparts or notice how many references there are in the bible to fat animals!
Humans love fat and fat loves us.
References:
Ben-Dor M, Gopher A, Hershkovitz I, Barkai R (2011) Man the Fat Hunter: The Demise of Homo erectus and the Emergence of a New Hominin Lineage in the Middle Pleistocene (ca. 400 kyr) Levant. PLoS ONE 6(12): e28689. https://doi.org/10.1371/journal.pone.0028689
Ben-Dor M, Barkai R. Prey Size Decline as a Unifying Ecological Selecting Agent in Pleistocene Human Evolution. Quaternary. 2021; 4(1):7. https://doi.org/10.3390/quat4010007
L. Amber O'Hearn - 'The Lipivore: What is Fat for? https://www.youtube.com/watch?v=xAWReEm4l0w
Turnbull, C.M. (2015). The forest people. London: The Bodley Head.
Title Image: Ben Sutherland (Flickr) https://www.flickr.com/photos/bensutherland/443439634