Why Humans Evolved To Need Fat

12 min read

Back To The Palaeolithic

It might seem like an impossible fantasy now, but there was a time when life was the simple sum of eating and procreating. You wake up, shrug off the mammoth furs, slap on some icy water from a stream meandering its way down from the looming foothills, then venture out onto the vast steppe that rolls out for miles before being swallowed up by the horizon.

Ideally, you’ll eventually stumble upon some hoofprints left by one of the herds of giant elk that have been spotted lumbering through the neighbourhood.

And that would be the tale of most mornings in your little slice of the Eurasian steppe. When evening came, you’d gather around the crackling fire with the rest of your tribe, share stories, and weigh up the option of joining in the giant cave orgy to cap off the night.

We stuck to doing what we were born to do.

Back in the blissful days of the palaeolithic, before agriculture had its chance to sow seeds of chaos, our ancestors carved out lives as hunter-gatherers. Of which, they did far more hunting than gathering. Their survival depended wholly on their ability to kill and thrive off their chosen prey. 

Over the course of a few million years, the homo genus emerged as smalltown players in the backwater valleys of Africa, before fanning out to dominate the globe. They evolved from plant-based omnivores into facultative carnivores proficient enough at their job to cause mass extinctions across each continent they ventured into. A display of diabolical prowess that had the unintended effect of drying up the food supply and forcing humanity to develop a new life as farmers.

And our ancestors did all that, for the love of fat. Big chunks of delicious blubber that powered the human brain to nature-breaking heights. The fact is, it would be too simplistic to call us meat-eaters, because just any meat would not do. We liked our animals plump and fluffy. 

There’s a reason why I’m fascinated by humanity’s distant past. Evolution is the lens through which you get to understand the why.

Why we’re not great with carbs

Why we can’t rely on protein

And why we thrive on fat

Humans evolved as fat-seeking specialists, and you only need to look back to the tale of the palaeolithic to gauge that for yourself.

1. We Store Far More Fat Than Our Ape Cousins

chimpanzee bodyfat

If you for some reason won’t take my word for it, just look at a shaved chimp. If bodybuilding competitions were judged on body fat alone, the laziest and fattest of those apes would wipe the floor with the most emaciated dude we could offer. 

Male chimps walk around with a ridiculous 0.005% body fat, while a human might be able to get down to 3-4% for the briefest and most uncomfortable of windows.

The homo line added this fat-storing capability for a few reasons.

To store enough energy to survive winters in unfavourable climates – The chimps didn’t get far past the tropics, whereas humans proved durable enough to conquer the globe. 

To power a significantly larger brain – The brain grew into an energy hog that demanded 20% of energy expenditure. A steady drip that required a large, unquenchable reservoir of fuel.

Humans are fantastically adept at getting fat. That’s why we survived the harsh reaches of the ice age. That’s also why you shouldn’t make a habit of eating potato fries soaked in vegetable oil. The body’s more than willing to pile the timber on, and it can be pretty reluctant to take it off.

2. An Easy Trip Into Ketosis

humans enter ketosis easily

Here’s another thing that sets us apart in the animal kingdom. We can enter ketosis without having to go into a state of starvation. Even when food was plentiful, in the height of summer, our ancestors could still tap into this fuel state. Through the power of ketones, they could have tapped into the aforementioned vast reservoirs of body fat, using them to quell hunger and gain a second wind.

That carries a huge implication, that ketosis wasn’t just for emergencies. It was meant for thriving as well as surviving. It certainly would have played a deciding role in ensuring our survival across the palaeolithic, by allowing tribes to go days, even weeks, on an empty stomach, without losing energy for the moment that mattered. The hunt.

This ketone adaptation is backed up by the fact that the brain is primarily made of ketones, and will happily suck up ketone bodies whenever they are present in the blood supply. Babies are born in ketosis, and breastmilk has a ketogenic makeup, being low in carbs and high in fat. 

There is plenty to suggest that we are biologically attuned to make the most out of fat, especially by breaking it down further into ketones.

3. Bludgeoning For Bone Marrow 

bone marrow evolution

Our ancestors split from the ape tree some 7 million years ago, leaving the safety of the dwindling forests, and heading out into the open plains of Africa to make something of themselves. A new landscape that wasn’t so rich in the wild fibrous fruit that would have comprised the bulk of the diet of our ape progenitors.

To survive in an environment with decidedly fewer trees to pluck from, we would begun to dabble in new food sources. We might have scrabbled around in the dirt for tubers, but they would have been meager in nutrition and hard to find. We might have jumped waist-deep into rivers and swished our hands around till we snabbed a couple of crabs, but that would have leaned heavily on dumb luck, which isn’t a reliable way to survive.

That leads us nicely to terrestrial meat, which was plentiful at the time, since we hadn’t set off our genocidal adventure at that point. Except we were woefully short on the ability and experience at bringing down prey of any decent size. Smaller animals might have been on the menu, but they’d typically be relatively low in nutrition and virtually devoid of fat. 

The larger animals, the mammoths, the giant ground sloths, they had plenty of blubber to spare, we just weren’t quite up to the task of hunting them. So we discovered a different trade, scavenging.

The earliest human tools we’ve found to date have been bludgeoning tools, ball-shaped stones that lacked any ability to cut through flesh, but were more than adept at crushing through bone and getting through delicious fatty bone marrow. 

Other predators had no way of breaking past the bone, and they settled for hacking off the meat and leaving behind a shrunken carcass. Which our ancestors were more than happy to settle for.

Bone marrow, as well as brains, provided a rich source of fat that spurred the growth of the homo genus into apex predators. Our brains grew larger, and with those significant upgrades to processing power, we developed the tools and tracking techniques to take down prey that dwarfed us in size and strength.

4. The Suspiciously Well-Timed Megafaunal Extinction

who killed the mammoths

So why did the mammoths die out? Many point to the obvious force of climate change, as the glaciers melted and receded, drastically changing the environment and forcing creatures to adapt or go extinct. The end of the ice age certainly took place across a similar timeframe, and mammoths were certainly suited for icy tundras. 

But there’s a little asterisk. The last mammoths didn’t during the ice age swansong. They bit the dust thousands of years later, in their last holdout on Wrangel island, when humans finally found them.

It’s a similar story with the other megafauna, or large animals, that disappeared over the palaeolithic in what became known as the Quaternary extinction event. The Giant ground sloth, the cave bear, the auroch, to name just a few. These animals dominated the landscape for much of the palaeolithic. And they all died out, around the same time as humans migrated to their respective continents. 

The Marsupial lion roamed across Australia, and died out around 35,000 BC, soon after the Aborigines reached the island. The Giant ground sloth was nestled away in South America, the last major continent on the human discovery trail, and it managed to survive till 10,000 BC.

The megafauna had the misfortune of being singled out for special treatment by palaeolithic hunters. And it wasn’t just that they were large, and thereby netted more calories per kill. In the animal kingdom, body fat is positively correlated to size. The megafauna were by far the biggest terrestrial animals, and they also happened to be the fattest. 

A woolly mammoth could hold a staggering 50% body fat. Richly flavoured, calorically dense fat that made it a prime target for wandering tribes. One of those majestic beasts could have kept a group of 50 hunter-gatherers going for several months. And tracking and bringing one down wouldn’t have been as labour-intensive a task as people often make it out to be. 

There was a grassy steppe spanning from Spain, across the Eurasian continent, and over to Canada. This was the biggest biome of the ice age, and it would have been teeming with all manner of plump and fluffy creatures.

Climate change certainly would have had the effect of thinning their numbers and hastening their demise. But hunting was the prime driver of their extinction.

5. Why You Can’t Swap Steak For Rabbit

rabbit starvation myth

At this point you’re hopefully wondering why we couldn’t have just settled for leaner prey, and skipped the mammoth genocide. Early explorers on the American frontier found out the hard way, when they tried to get by on hauls of rabbits and deer. 

They were treated to unpleasant bouts of bloating and diarrhoea, from an acute form of malnutrition known as protein poisoning, or rabbit starvation. They soon realised they needed to take their meat was missing a key ingredient.

There are plenty of accounts of frontier hunters throwing away lean animals despite being in dire need of a good meal. The famous Lewis and Clarke expedition recorded an unsuccessful hunt that netted 40 deer, 3 buffalo, and 16 elk. Another account tells of a party eating five to six pounds of a meat a day, while getting frailer by the day, and continually craving fat.

Unfortunately, the human body is capped at how much protein it can digest and absorb, at somewhere between 35 and 50% of total calories. Beyond that, the liver can’t metabolise and get rid of nitrogen fast enough. A high protein diet is only viable when the calories are further propped up by either fats or carbs.

So if you’re after a bad time, just try the carnivore diet based entirely on grilled chicken breast.

6. The Reason We Went All In On Agriculture

agricultural revolution

This shouldn’t be much of a puzzle at this point. The first agricultural revolution might seem like a terrible idea in hindsight, but our ancestors had their hands forced by a drastic decline in their meal of choice: the megafauna. 

As the palaeolithic stage swung to an end, hunter-gatherers had to deal with their prey getting smaller, and thereby, leaner. The meagre pickings just weren’t enough to sustain wandering tribes. The step into agriculture became a matter of necessity.

The addition of a regular source of carbohydrates counteracted the issue of protein poisoning, allowing them the chance to get away with eating lean meats. Unfortunately, many of them just ended up neglecting meat altogether, hatching up a diet woefully short on nutrition. 

Then there were all the issues that came with living in close quarters with their fellow farm folk. Poverty, disease, and tyranny, to just reel out a few.

As we entered the era of grain states, people who ate meat were often painted as outcasts. In fact, that’s pretty much what the word ‘barbarian’ was used for.

On the bright side, the world has moved along somewhat, and many of us are now in a position to realign with the ancestral diet by bringing copious amounts of steak back to the table.

The Takeaway

Humans aren’t just wired to like fat. We’re built to need it. Fat, and our ability to store it, was critical to our survival over the palaeolithic. And even now that starvation is no longer a worry for many of us, fat is still necessary for our chances of thriving.

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