I’ve recently finished reading The Story of the Human Body: Evolution, Health, and Disease, a book from Daniel Lieberman of how the human body evolved over millions of years, that I would recommend all Humans to read. These are are my main takeaways:

Why we are, the way we are

It is all about how energy is used

Us humans and other living beings are essentially organisms that use energy to reproduce and maintain ourselves.

• Natural selection prunes off organisms that don’t use energy in a way that is suited to their conditions and environment.
• Every energy transformation feature / trait has a cost. For example: walking upright allows one to walk using less energy, but lacks the speed of a quadruped.

Long Distance Walking / Running Machines

What drove selection for bipedalism

Hominid bipedalism was likely to have been initially selected to help the first hominids forage and obtain food more effectively in the face of major climate change

Between 10 and 5 million years ago, the earth climate cooled considerably, and overall effect in Africa that caused rainforests to shrink and woodlands to expand. If you were to be in the heart of the rainforest, you likely wouldn’t have noticed much of a difference, but if you were in the margins, this change must have been stressful. As the forest shrinks and becomes woodland, ripe fruits become less abundant, more dispersed and more seasonal. These changes would require you to travel farther to get the same amount of food.

Walking on two legs is more energy efficient for longer routes. Main trade off is less speed, because we could not gallop. We are 3x more efficient moving a distance of 6km than a chimp.

The consequences of bipedalism

Not only was endurance walking useful, but also long distance running was likely selected for scavenging. Running to fresh carcasses, running with food and, persistence hunting, where a big animal is followed by running and walking on sun. They need to find shades and pant, and eventually collapse due to heat stroke.

• We are unique in that we have sweat glands all over the body. Other apes mostly have on the palms of their hands. And we. Don’t have fur, allowing the air to come in contact with sweat and cool your body down. This is essential for long distance running and walking.
  • Other animals have fur that reflects solar radiation, but does it allow body to cool down through sweat

Other features that help us to run effectively. Some of them not specially helpful for walking, like shorter toes:

• Big gluteus maximus muscles, mostly active when running.
• Nuchal ligament is a back neck ligament that connects head to arm that helps stabilize the head while running. It was developed independently in humans and other animals well adapted for running.
• Big semi circular inner ear canals to have more signals to allow for stabilization of our inner systems, such eye actions to compensate for the jiggle.
• Predominance of slow twitch fibers in legs. More endurance, thus compromising speed.
• Narrow waists, wide shoulders, shorter toes.
• Long noses are selected for walking long distances without drying up. Nose humidifies air coming into the lungs, which is necessary, and retains moisture going out. Trade-off is that lungs have to work a bit harder.

All of these walking and running adaptations made us clumsy climbing trees, like shorter toes, but also freed up our hands to interact with the world, create the first tools and throw objects (we are especially good at throwing, having shoulders and upper body that makes it ideal for it), which not only provided some protection, but also allowed us to obtain and process fallback / lower quality foods (which were essential due to scarcity from global cooling climate).

Only mad dogs and Englishmen go out in the midday sun ― Noël Coward

Better dexterity, tools, cognition, less digestive cost, more energy availability

In the average adult human, the brain represents about 2% of the body weight, but accounts to about 20% of total energy consumption.

As the ability to create and use tools allowed the gathering and processing of fallback foods, more usable energy was able to be extracted. Processing foods to smaller chunks, or cooking it, largely increases how much energy can be obtained during digestion, but also requires less intense chewing (we didn’t need as bigger teeth as australopithecus, which resulted in use losing the snout due to less space being needed in the head) and shorter intestines, which reduce energy required for digestion, increases surplus energy to be used by the brain. These factors selected hominids with better manual dexterity and better cognition.

Our manual dexterity, and what it unlocks, plays a big role in our evolution.

Energy hungry brain, and relation with fat

If our brain¹ is deprived of glucose for even 1 minute or two, it causes irreparable damage. This likely selected humans to become unusually fat. 400 to 500 calories daily, are for the brain alone. Extra intense thought only increases hourly usage by 5 calories per hour.

Hunter gatherer mothers have to expend about 2.3k calories for themselves alone to raise kids. Babies are unusually fat. 60 percent of their energy consumption is for the brain. It takes 12M calories to grow a child into a full grown adult. Twice as much as those needed for a chimpanzee.

Our way of living affected the size of our gut so profoundly, that now we are pretty much dependent on cooking to get the caloric intake we need for our body and brain.

Exercise is not great to lose fat (unless you don’t succumb to overeating after exercise) but it’s good to prevent fat gain. It increases muscle (and not fat) sensitivity to insulin and makes the muscles more readily available to store energy, and also increases the number of mitochondria that burn fat and sugar.

• A lean man that doesn’t exercise has twice the risk of dying, compared to obese men that engaged in regular physical activity

High offspring investment

Life is fundamentally a way of using energy to make more life.

• If the environment is risky: quick returns are favored, where little investment is made during life, but a lot during reproduction. Such as spiders, salmon that lay a lot of eggs, hoping that a lucky few will survive
• But when resources are predictable and infant mortality is low, it is feasible to mature slowly and invest a lot in raising the few offspring. This is the strategy of humans, elephants and apes.

Cost of clear speech: choking

What good is it to have a good idea, if you can’t communicate it? One of the main features we developed as humans was our ability to use speech to clearly communicate thoughts, ideas, plans, and other information.

The price is that we are the only mammal that can risk asphyxiation when swallowing something too large or imprecisely², because of the big common space behind the tongue through which food and air both travel to get either into the esophagus or trachea, a consequence of our short and retracted faces and selection of anatomy that favors clear speech. As a result, food sometimes gets lodged on the back of the throat, blocking the airway.

When you are having lunch with friends, consider that you are doing two things: speaking clearly, and swallowing a little dangerously.

Diseases

We’ve created a system that makes people sick through a surplus of energy, and keeps them alive without needing to turn down the energy flow

Lieberman presents the concepts of Mismatch diseases and Dysevolution:

• Mismatch diseases: Diseases that occur because our bodies are poorly or inadequately adapted to environments in which we now live. An example would be eating large amounts of sugar or being very physically inactive leads to problems like diabetes or heart disease that then make us sick
• Dysevolution: Form of cultural evolution where the symptoms of a mismatch disease are treated, but not the cause. One example of this is cavities, which are treated with dentists, and not by removing the sugar from our diet, which is the underlying cause. Lieberman emphasizes that mismatched diseases and their causes must be understood fully to treat the true cause.

Too much energy surplus

Our ancestors ate fruits as sweet as carrots, but as energy dense foods had their availability increased³, more humans moved from subsistence farming and physically strenuous jobs to lower physical effort jobs (in the USA, only 11 per cent are actually factory workers. The rest are in management, services, wealth management and banking services), the same mechanisms that made us effective is storing energy and craving certain foods, are also the ones that have become maladapted to our current environment.

It has been only about 300 generations since we’ve been subsistence farmers, which didn’t give enough time for natural selection and body adaptations to develop.

Sugar and fat absorption mechanisms and effects

Your body can use glucose as energy readily, but fructose can only be worked as fat or in the liver.

• When the liver is flooded with too much fructose, too quickly, it is overwhelmed and converts most of the fructose into fat, triglycerides. Some of this fat fills up the liver and causes inflammation, which blocks the action of insulin in the liver.
• Chain reaction occurs, in that the liver releases stores of glucose into the bloodstream, driving the pancreas to release more insulin, shuttling extra glucose and fat into cells. The rest of fat created by the liver is dumped into the bloodstream, where it ends up in fat cells, your arteries, and other potentially bad places.
  • Visceral fat is more hormone sensitive than other fat cells, resulting that its stores are dumped fat more readily than other fat cells, and since it sits close to the liver, it tends to clog up the liver and constrain its glucagon function when it dumps fat.
• Sugar is 50 percent fructose; fruits also have it. An apple for example has 13g of sugar. 30 percent is glucose, the rest is fructose.

Comparing an apple to a highly processed fruit roll, apart from nutritional differences:

• Fiber covering the apple (the skin) prevents the full absorption of sugar. Fiber makes food stay longer in the stomach, generating signals that release appetite suppressing hormones.
  • Speed of eating and amount of fiber is important. That’s why salads and low glycemic foods should come first in your meal
• An apple gives your pancreas time to realize how much insulin to release. On the other hand, high glycemic, calorie dense foods are easily and quickly absorbed in the digestive process, prompting the pancreas to produce a lot of insulin, which it often overshoots, plunging blood sugar levels, which in turn makes us hungry.

Height as a measure of extra caloric availability and health

• Maximum height is constrained by genes, but available energy will limit actual height. Because if you spend most of your energy fighting diseases and toiling in the fields, then you won’t have extra calories to gain height.
  • It was seen for populations that turned to subsistence farming, like in Asia and America, to have had their height shortened. For example, subsistence farming children spent about 4 or 6 hours working, as compared to children of hunter gatherers that would spend about 1 to 2 hours working in tasks like gathering firewood and helping in domestic tasks.
• Tall people are naturally selected in hot climates, because of higher surface area to release heat. Colder climates select for shorter ones, because they can retain more heat.

Too much Stress

• Stress is an ancient adaptation to save you from dangerous situations, and activates energy reserves when you need them.
  • If a Lion roars nearby, a car nearly runs you over, or if you go for a run, your brain triggers your adrenal glands (which sit on top of your kidneys), to secrete a small dosage of the hormone cortisol.
• Cortisol does not cause stress. It is released when you are stressed.
• One of cortisol’s functions is to cause liver and fat cells (specially visceral fat cells) to release glucose into the bloodstream. It increases heart rate and blood pressure, makes you more alert and prevents sleep, and makes you crave for calorie rich foods.
  • Chain reaction for long bouts of stress: as you crave more energy rich foods and consume them, this increases insulin levels, which inhibits the brain’s response to leptin (fat cells release it to increase satiety), as such, the stressed brain thinks you are starving, so activates reflexes to make you hungry and other reflexes ot make you less active.

Too little Sleep

• Insufficient sleep promotes stress and stress promotes insufficient sleep. Higher income populations get on average more sleep, likely because of having of less challenges of making ends meet and less stress
  • Sleep deprivation is sometimes caused by elevated levels of stress, thus more cortisol.
  • Sleep deprivation elevates the ghrelin hormone, a hunger hormone that stimulates appetite.
• Only until recently did we do start sleeping alone or with a single partner the child detached from parents during sleep, and in stimulus deprived environments
  • On the other hand, hunter gatherers used to sleep in relatively noisy environments, woke up at about 7h, took a one hour nap in the middle of the day, and then went to sleep at 9pm, where they would get two sleeps. Likely an adaptation, that prevented predator under vigilance
  • But now we have entertainment and lights that are able to keep us awake far beyond 9pm, in sensory deprived environments, with less exercise, excess calories, and stress

Too Crowded

Villages, cities, are our human fortresses from the wild. Because we have that fortress, we don’t need to carry arms and be attentive to outer animal threats, like lions. Mostly. There were costs to these though:

• High concentration of humans in low⁴ sanitation⁵ environments facilitated the spread of these diseases, and close contact with animals gave rise to diseases such as influenza, coming from pigs.
• Before the 1900s, the death rates in cities such as London were higher than in rural areas, so they needed a large influx of rural immigrants to keep them going. Which they did, because of a larger scope of opportunities and wealth.
• Cows’ digestive systems were adapted to eat grass, but in the crowded industrial complexes they are fed grains, and as a consequence they have to be constantly medicated with antibiotics, to counter their chronic diarrhea and diseases coming from these crowded, filthy environments.
  • Antibiotics given to industrially raised animals because microbes also consume energy. So this makes them fatter

Cancer

There is a positive correlation between cancer development in reproductive organs and high energy balance.

• Women’s bodies adapted towards delivering as many children as possible, and are maladapted towards having a high energy balance:
  • High exposure to estrogen incentives cell division in breast, ovaries, and uterus, in preparation of a fertilized embryo. Chances to develop cancer in these organs increases substantially from the number of menstrual cycles, and decreases as the number of children the woman bears.
    • During the menstrual cycle the levels of estrogen and progesterone rise significantly
    • While nursing, chances of having cancer go down, as there is less exposure to reproductive hormones, and likely breast feeding aids flushing memory ducts.
  • For women, the incidence of breast cancer was observed to be higher in nuns (hence, the nuns disease)
  • Women in contemporary USA have about 350-400 menstrual cycles, start menstruating at 12, 13, and then stop at early fifties
    • Hunter gatherers have about 150 cycles, and start menstruating at 16. They spent most of their life being pregnant or nursing, while barely having energy to do so.
  • Obese women can have 40 per cent more estrogen, because of the role of fat in the endocrine system. So after menopause being obese is correlated with cancer in women
• For men, higher exposure to testosterone throughout their life is correlated with prostate cancer. But correlation is not as strong as in women.

More exercise results in lower chances of cancer. Likely because the energy spent there is not otherwise spent on reproductive hormones that have these side effects.

• There is compelling evidence that routine physical activity is associated with reductions in the incidence of specific cancers, in particular breast and colon cancer. Physically active men and women exhibited a 30%–40% reduction in the relative risk of colon cancer, and physically active women a 20%–30% reduction in the relative risk of breast cancer compared with their inactive counterparts.

Use it, or lose it; No strain, no gain

Imagine you are tasked with building a robot that is aimed to accomplish a task in the future that is unknown. You can either create a series of specialized robots (e.g. only able to swim, to dig, jump, etc), or a single one that adapts to multiple situations. When you don’t know what the robot will do, the latter works best. That is how animals and plants work. But if you don’t use it, you lose it.

Bone loss

• Bones are a reserve of calcium, an essential component to the body. If there is not enough calcium, osteoclasts start dissolving them at a higher rate.
• Most people will reach their peak bone mass between the ages of 25 and 30, then it keeps going away. Specially struts in spongy bones like vertebrae and joints. They don’t come back.
• Just having a supply of calcium and vitamin D is not enough. You also need to load your bones, otherwise the osteoblasts will not kick in to start building bone.
  • High intensity weight bearing can stop or even moderately reverse some loss.

Teeth problems

If you don’t chew enough when you are young, teeth will become misaligned, and overcrowding happens, leading to issues on wisdom tooth growth for example. The body needs that stress.

Allergies and hygiene hypothesis

Hygiene hypothesis states that early childhood exposure to particular microorganisms (such as the gut flora and helminth parasites) protects against allergies by properly tuning the immune system. In particular, a lack of such exposure is thought to lead to poor immune tolerance. There are two main hypothesis for it:

• First hypothesis is that T helper 1 cells are not busy enough⁶, which increases the number of T helper 2 cells. With more sterilized environments, children’s immune systems are less busy, having more of these T helper 2 cells swimming unemployed, leading to a higher probability that they react to a non-threatening component. First reaction is mild, but the immune system keeps a memory, so the following time that component is detected, it’s devastating.
• Second hypothesis is microbiome destabilization, the “old friends” hypothesis. Microbes have evolved to cohabit with others and us in a cold war kind of environment. Once you start killing several of them with antibiotics and cleaning products, you destabilize their equilibrium
  • There is a case to be made that possible treatments would be to have fezes or filth
  • And it also follows that after antibiotic treatments, that probiotics are taken

We frequently mistake comfort for wellbeing

Hannah Arendt introduced the expression and concept of the banality of evil, where a common person does nefarious actions, since they became accepted and normalized in their society.

Actions that we perceive as normal, such as usage of cancer inducing sodium nitrate in foods (which stems for a trade-off between structural economic gain and health), wearing comfortable shoes, reading and sitting, are in fact not normal when seen through the lenses of long term evolution.

Comfortable shoes

Our feet have adapted for us to efficiently run and walk, but highly cushioned, constraining shoes deform and inhibit our feet from fulfilling their purpose

• Habitual barefoot people have much lower incidence of flat foot, which very likely is due to the high usage of the foot arch, which is restrained on comfortable shoes with arch support, which instead overload the plantar fascia, leading to plantar fasciitis
• A constrained toe box restrains how much stability the foot can provide, and an unbalanced foot leads to an unbalanced knee, hip, body.
• I’ve personally transitioned to using barefoot shoes daily and when hiking, and can only recommend them after using them for more than one year.
  • One common question is if these are appropriate on hard terrain. Turns out that your foot already has a built in mechanism, which is to forefoot / midfoot strike, instead of heel strike. Try to jump to see how your foot automatically lands using the ball of your foot, and how softly you land, when compared to a (dangerous) similar jump landing on your heel.
  • Going barefoot or using minimal shoes, provides you full perception of the terrain and impact, so you’ll adapt towards hitting the ground more softly, and not using heel strikes as much.

Reading

Myopia is a formerly rare evolutionary mismatch that is exacerbated by modern environments. In the USA and Europe, about one third of all children (aged 7 to 17) become nearsighted.

Evidence suggests that being nearsighted used to be very rare: that less than three per cent prevalence amongst hunter gatherers and populations that practices subsistence agriculture. In 1813, it was noted that amongst the Queen’s guards, many were myopic. On the hand, from the 10k foot guard, less than half dozen were myopic.

The mechanisms of how myopia are still not fully understood, but two main causes are suggested:

• Close work, forcing long bouts of close focus. Singapore study found that students who read more than 2 books per week had strong myopia.
• Children spending more time outdoors have lower incidence of myopia. Brightness of light and visual stimuli appear to have a beneficial effect.

Sitting

While sitting in different positions to rest after strenuous activity has been around for much of our species, only until recently have we been multiple hours sitting in a chair, day after day, which is a risk factor towards:

• Muscle atrophy and shortening: calf muscle shortening also happens for high heels usage
• Lower back pain. To prevent this issue, make sure to maintain a strong back via moderate intensity load, but not too much load, like furniture movers.

How to solve these issues

One solution would be to wait for natural selection to sort out these problems, which is very unlikely due to the high rate of change in our societies and environments, in short time windows. As the commander of the Albigensian Crusade said, on a mission to eliminate heretics: “Kill them all; let God sort them out.”

We are all subject to influence by advertising, availability and peer pressure, but we can be nudged to acquire behaviours that benefit us. Daniel Lieberman suggests:

• We should invest in prevention over treatment
• Although adults have the right to get sick, children need guidance. How different is it to restrict fast foods to them, to restricting which movies they are able to attend? Or availability of alcohol to them?
• Just like nature obliged us to do the right thing and evolved our behaviours, government has the right and duty to have information to do rational decisions and nudge or even push us to do so:
  • Question is how much and where and when
  • Government shouldn’t prevent you from smoking, but “you are free to do as wish, as long as I don’t have to pay for it”

Culture does not allow us to transcend biology

Culture is roughly everything we do and monkeys don’t. ― FitzRoy Richard Somerset

Clever as we are, we cannot modify our human bodies any more than superficial ways. And it’s arrogant to think we can engineer body parts any better than nature did. There will be no Pasteur for mismatched diseases.

We should come to terms that:

• We are fat, furless, bipedal primates that crave sugar, salt, fat and starch.
• We crave comfort, but our bodies are endurance athlete machines.
• As Voltaire wrote: “Let us cultivate our garden”. We must cultivate our body.