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Even though we share more than 98% of our DNA with
chimpanzees and bonobos, we still, ya know, look pretty different.
There’s the obvious stuff: our hands and feet, the shape of our faces, the body hair.
But have you ever noticed like how jacked a chimp is?
It can’t be just me noticing this.
Well, it turns out, the difference in our muscle mass is only half of the story.
Humans and our closest great ape relatives also store fat differently.
And that’s probably good news for us in the long term.
Now, the average bonobo is definitely stronger than the average human, especially
in their upper body, where they have much more muscle mass than we do.
But studies have shown that their physical superiority over
humans with similarly sized muscles is actually pretty modest.
When comparing the actual force and velocity of a chimpanzee’s muscle fibers to a
human’s, scientists observed that the chimp’s muscles were a little less than one
and a half times stronger than the human’s.
So even though chimps are definitely stronger than us,
they’re not like “Incredible Hulk” strong by comparison.
But if chimps don't actually possess superhero strength,
why do they look so much brawnier?
Well, it turns out, compared to our primate cousins,
we keep a little more body fat around.
Now you might think that it makes sense that humans
store more fat, just based on our lifestyles.
But it actually is hard to compare humans and apes,
because human cultures have a huge range of nutritional consumption.
Meanwhile, zoo apes have different diets than wild apes, though the diet of
zoo animals is carefully formulated to make sure it meets their needs.
Still, one study has compared human body fat to our ape counterparts.
Researchers performed necropsies, which is the veterinary term for autopsies
of non-human animals, on 13 bonobos who lived in zoos and research
institutions, and died of natural causes.
Despite living in captivity, their body fat percentage was very low
compared to their total weight.
Male and female bonobos had, on average, less body fat
than average adult humans of any gender.
Bonobos clocked in from less than one to a bit over eight percent body fat.
For humans, a healthy range can be anywhere from
around fourteen to thirty percent, on average.
Now, these apes were sedentary, but they were also on
that specialized diet we talked about.
So while it does give us some information about how
much body fat they stored, it’s not the whole picture.
For that, we can turn to something much deeper:
the way our DNA is packaged.
You see, mammals actually have a couple of different kinds of fat cells.
The ones we’re going to talk about here are white adipose tissue,
or white fat, and brown adipose tissue, or brown fat.
Both white and brown fat cells function by storing fat, but it’s much
easier for brown fat cells to tap into fat as an energy source.
This is because they have a lot more mitochondria than white fat cells,
and mitochondria are the cellular structure responsible for
converting things like fat into chemical energy.
So, the more white fat cells an animal has,
the greater their ability to store fat, and the more brown fat cells it has,
the more rapidly it can turn that fat into a fuel source.
Now the cool thing is, white fat cells can actually become brown-ish,
turning into a type of cell that is literally called beige fat cells.
That makes it easier for the animal to convert all this stored fat into energy.
And the instructions for how to change from a white fat cell into a
beige fat cell is stored in our DNA.
But there is a catch.
There’s so much DNA inside your cells that there’s no way it could exist as these
long, unruly strands. It has to be folded just right to fit inside the nucleus of the cell.
The long strands of DNA are wrapped and folded around proteins called histones.
Scientists call this complex of DNA folded up with proteins chromatin.
Exactly how tightly packed a particular stretch of DNA
is affects how easily the cell can get to it.
Densely packed regions mean that bit of genetic code is hard
for the cell to get to and use. While more loosely packed areas are more active.
And according to a 2019 study, it’s the overall accessibility of
the chromatin in our fat cells that may be at least partially
behind the difference in chimp and human body fat percentage.
In chimps, the region of DNA that holds the instructions for white fat cells to convert
to brown fat is pretty easy for the cellular machinery that reads DNA to get to.
But in human fat cells, the chromatin is folded and packaged in
such a way that these instructions are kind of buried.
The end result is that humans end up with more white fat
cells than chimps, thereby storing way more fat.
And that fat, turns out, is good news for humans.
Some scientists hypothesize that our enhanced ability to
store fat might be one of the factors that allowed us to develop such large brains.
Gram for gram, our brains require more energy than almost any other tissue.
So it’s easy to imagine how our ancestors, roughing it out on the savanna,
had a survival advantage with a little extra fat around
to feed those energy-hungry thinking machines.
Which means that we may have our enhanced fat storage
to thank for our big, beautiful brains. And that’s pretty neat.
Thank you for watching this episode of SciShow,
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