Natural selection for humans has been driven by a world of threats. Most of which have now been eliminated. In The Story of the Human Body, Daniel Lieberman studies the insidious feedback loops that progress has set in place.
1- Our expanding brainpower was an evolutionary adaptation allowing us to think and co-operate better; its cost was energy consumption. Industrial food production and labor-saving technology are cultural innovations with huge benefits; they also come with costs.
2- Mismatch diseases, which are your most likely cause of death, are the result of those costs. Some, like scurvy, were easily solved. Others, like diabetes, tooth cavities, many cancers, and heart disease, are not.
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This blog post is part of a series I am making called Reading For The Aspirational Self. Don’t think of this as book summaries – I’m not doing that. Instead, I’m drawing out specific lessons that I find particularly interesting. And which I think could act, together, to help people who share my aspirations. If you, too, want to be present, family-centric, intrinsically motivated and polymathic, I can help.
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- The series is also on YouTube in the form of 7-12 minute videos. Here’s the channel link – the video and transcript are below.
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If you want to know more about The Story Of The Human Body you can check out Lieberman’s full lecture here.
This week’s video
What are we adapted for as human beings? That’s a very complicated question. The story of the human body gives a clear account of what we know so far and particularly focuses on how the last 15,000 years and how, how we live now is challenging the bodies that we have evolved.
In this video I’ll firstly, give a quick overview of how evolutionary biology works. Then I’ll identify two ways in which our species stands out. We use a lot of energy in our brains to cooperate better than other mammals. And finally, I’ll explain what a mismatch diseases is and talk a little bit about obesity in particular.
Our selection, like that of any of the species has been driven by a world of threats. So the most able to survive in a particular in clot environment, the fittest for that environment is the one who passes on their genes to their descendants and those genes spread. So when we’re examining what we’re adapted for as humans, that’s the world.
It’s a world of threats. Most of which have now disappeared. And what those threats gave us was a common human evolution. So all of us who descended from people in Africa about two or 300,000 years ago, which isn’t that long in evolutionary terms.
But what the evolutionary biologists like Lieberman do is try and work out, which parts of our bodies are meaningful adaptations to an environment that we don’t live in anymore. And which part of our parts of our bodies are just chance. So something like a third of our genes have no discernible purpose, as far as geneticists have worked out so far.
And even those that do have a discernible purpose, aren’t necessarily beneficial to us in the broader context, not just of how we live now, but also the rest of our body. Lieberman is refreshing to be honest about how complicated the work of evolutionary biology is and how simplistic claims that our body is adapted to do X and therefore we should do X as people nowadays are generally very misleading.
And so that’s why I use this as an example of evolutionary biology when I’m talking to you. And that’s the true value of this book is that honesty and complexity that it brings, which makes it quite hard to talk about in a fairly short form.
(section – thinking and collaboration)
There were two things that homo-sapiens, all of us are adapted for more than any other mammal. Thinking and cooperating in groups. So both our brains and particularly our vocal system allows us to cooperate in groups in a more complex way than any other mammal that we’ve studied.
This is reflected in the fact that both our brains and our guts, each consumer around 15% of our energy needs with most of the mammals, the guts, the kind of digestive system as a whole are around four times as energy intensive as the brains. With us it’s, it’s about equal and that’s quite a marked change over the course of a few hundred thousand years that has, has given us a greater intelligence in a lot of ways.
We see this in brain size too. So our brains are about three times larger than they should be. Most of the mammals are kind of on the line where the bigger the body, the bigger the brain. We’re about three times higher than we should be by that metric.
And that is a costly adaptation. So that intelligence that we have gained has a cost. So when you’re at rest, somewhere between 20 and 25% of your energy is used by your brain and any absence of energy, any moment in which blood sugar drops too low and the brain doesn’t have energy of another kind is incredibly costly.
And as a result, we have various adaptations to our body, both our digestive system, and particularly the way that our hormones work in terms of insulin that adapt us to store fat when there is surplus energy available, that’s a kind of adaptation that for Lieberman is a consequence of our brains.
We need to store that fat to make sure that we can always break it down and use it as sugars in the brain.
There are two things that make the human brain somewhat unique. One is the size of our neocortex. So the neocortex roughly correlates with group size. So as, as the mammals neocortex gets bigger, the group in which that mammal lives get bigger as a general rule and humans are adapted by that measure.
There’s a bit of controversy around this. But by that measure, humans are adapted to live in a group somewhere between 100 and 230 people. That’s the number of individual people that we can meaningfully distinguish from another, as far as neocortex size is concerned. Like I said, there’s a bit of dispute there.
And the other area that is markedly different is our parietal lobe are also bigger, which is for things like symbols, math, and mental maps.
But the main co-operative adaptation, isn’t actually in our brains. It’s in our speech. So we’re about 10 times as effective at vocalizing as chimpanzees. Due to a variety of adaptations, which Lieberman and goes into great detail on if you’re interested in reading the book.
But it includes things like the way we can move our tongue our mouth shape our jaw shape, the vocal tract, the way that air actually moves up and down through our trachea enables us to give a more precise sound than any of the species out there in the mammalian world.
There were many other adaptations and coincidental changes in the human body that Lieberman talks about, but I won’t go into that now.
What I will say is that our bodies are still pretty much the same as they were 15,000 years ago, before the invention of farming. So our bodies are in many ways, still the same as Hunter gatherers. There were a few changes. And so things like lactose tolerance, things like malaria, partial resistance for some populations, things like our body shape and our skin color have all of that changed slightly.
But most of our internal workings, most of our hardware is still the same as it was before farming. Our environment is of course, very different.
Progress in the last 15,000 years or so has largely eliminated the threat of food scarcity. For the people who live in your area and the area of most people who spend time on YouTube food scarcity is not an issue now. And hasn’t been for a good couple of generations at least. It became less of an issue in the were more abundant calories on many measures, um, throughout the, the farming revolution.
But even more so since industrial food has, has become the norm across the Western world and much of the rest of the world now, too. So we have abundant food supplies. We have an abundance of an ability to provide shelter for ourselves. Climactic change doesn’t have to impact those of us who are reasonably wealthy immediately. It might later, but it doesn’t now.
This abundance and the cultural changes that have come about in tandem with that abundance not caused by, but in tandem with that abundance have set in place what Lieberman calls an insidious feedback loop. And those insidious feedback loops lead to what he terms mismatched diseases.
So our body adapted for life 15,000 years ago, before we had farming, let alone industrialized food production, and has not kept up with the rate of cultural change that humans because of their co-operative nature have been able to cause over the past 15,000 years.
This is notable in the fact that you’re most likely to die of a mismatched disease, something that was basically insignificant 15,000 years ago. Some mismatch diseases are, or were, easily solved, like scurvy.
Other mismatch diseases like cavities are not. It turns out the tooth cavities are remarkably rare in the preserved remains of people before farming. And Lieberman attributes that to the growth of starch in diets since farming.
Starch is one of the things that encourages the bacteria to grow on your teeth. Because we eat so much more starch than we used to, cavities in a way of the price that we pay for cheap calories.
Other mismatch diseases that have become more prevalent in recent years include things like heart disease. Many of the cancers that have become more common over the recent decades and, and diabetes, which is one of the greatest problems going forward.
All of these are contributed to, by the way that food producers can now produce what people have wanted forever cheaply. So, they can produce fat, which as I say, we crave, it’s kind of in-built thing. We crave fat in order to keep our brains healthy and make sure that we have a constant energy supply, sugar, starch, cheap calories, and salt is another thing that was quite rare back when we were living together as, but can now be added to food and is one of the only things that’s almost universally added to food. But in excess is a problem for us.
One of the problems is that while we’re consuming more foods that include starches and sugars, we’re consuming less foods that include a broader range of the nutritional inputs that we need. And when you look in particular processed food, which is how the food is delivered to people, in affluent countries nowadays by and large. Processed foods contain even less nutrition than just the kind of simple foodstuffs that you might consume now.
And they also contain much less fiber. And fiber is particularly important because it slows your digestive system down, which allows your body to balance itself out over time.
And at the same time as our food stuffs have become slightly less nutritious and far more calorific or, or cheaper for the same amount of calories. Our energy expenditure has dropped quite markedly. So most people who are watching this probably spend the majority of their day sitting at a desk. And various labor saving devices have reduced our energy expenditure across everything that we do from transport to escalators and elevators instead of stairs.
We do less. We have to intentionally exercise now rather than live, if you believe fitness magazines and things like that. But an interesting, just aside is that simply standing instead of sitting at seven or 8% to your energy consumption, when you’re doing something like office work. So simply by standing, instead of sitting, you can burn something like 175,000 calories over your working year, which is the equivalent of about 20 kilos of fat.
So what’s really interesting about the way Lieberman presents this work is that whether we’re dealing with natural adaptations, such as our increased brain size, which comes at the cost of increased energy expenditure and a need for fat, or we’re dealing with cultural innovations. Like, the agricultural revolution and then the industrial food revolution, which has allowed more calories to be delivered to more people than ever before, which comes at the cost of nutrition and fiber. Adaptations come with both cost and benefits.
That’s the real yakeaway from most of this and an awareness of those costs is important when you’re thinking about how we might live as people in the future, the kind of consumption that we should encourage both in ourselves and in our children and at a political level as well. He talks a little bit about how regulations in different countries can interact to make the world a better place.