# How big advantage had a trait have to bring to evolve in the human evolution?

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Yes, I've heard that we have evolved from the common ancestor with primates as intesively, as the chimpanzees. Sometimes I read about some enormously complex traits, evolutionary psychologists think have evolved in humans, such like religion, night owls or art (which don't seem to require a specific complex mutation). On the other hand we still grow many unnecessary organs, so I really wonder: What is the percentage advantage a trait had to provide to humans (so that no other species share it) to actually evolve continuously?

OR (I'm not sure if it can be calculated generally) I can get by with this question: What is the correct formula how to calculate the average probability of survival a trait had to increase to preserve over some time (with the gene expression calculated in it)?

I think a clear way to rephrase this question would be "How beneficial a mutation needs to be to behave really differently from neutral mutations?". I am answering to this question.

Neutral mutations and nearly neutral mutations

The probability of fixation of a new neutral mutation is \$P_{neutral}=frac{1}{2N}\$, where \$N\$ is the population size. An intuitive way to understand why this is true is that, after an infinite amount of time (constant population size and in absence of speciation), the whole population will necessarily descend from a single individual. In absence of selection pressure every single individual has the same probability to be the ancestor. As a fraction of \$frac{1}{2N}\$ of the population is carrying the mutant allele when it first occur, then the probability that his allele reaches fixation is \$frac{1}{2N}\$. In fact, this result can be generalize to say that the probability of fixation of a neutral mutation present at frequency \$p\$ at a given time in the population has a probability \$P_{neutral}=p\$ to get fixed.

Given the selection coefficient \$s\$, a good approximation is that whenever \$2Ns<<1\$, then the probability of fixation is essentially not different from \$P_{neutral}\$.

This qualitative boundary (\$2Ns<<1\$ or \$2Ns>>1\$) is the boundary you were interested in. In your post you talk about "percentage advantage". This percentage advantage is just \$scdot 100\$.

Beneficial mutations

For "significantly" beneficial mutations, a good approximation to the probability of fixation of a newly arisen mutation given \$s\$ and \$N\$ is

\$\$frac{1-e^{-s}}{1-e^{-2Ns}}\$\$

Source of information

Your question shows a few misunderstanding and is nested within the field of population genetics. Plus, in absence of good understanding equations and just vague symbols. I recommend that you have a look at an introductory source of information in population genetics. You will find recommendation of books in population genetics here. For a complete and relatively accessible (might still be a bit complicated) introduction to population genetics, I would recommend Gillespie's Population Genetics: A Concise Guide for you. This book will so offer proofs for the equations I gave you above.

## How big advantage had a trait have to bring to evolve in the human evolution? - Biology

Steven Pinker: Evolution of the Mind

Q: Can you talk about our origins in Africa?

A: The genetic evidence suggests that we evolved in Africa. We know that people reached Australia by forty thousand years ago, maybe earlier, which required travelling across sixty miles of open ocean, and it would have required a species with considerable intelligence to put together some kind of canoe or dugout that could have traversed that distance.

Also, probably the longer we look the more we'll find evidence for signs of human creativity and ingenuity in Africa. Europe is where you have a lot of caves, which preserve stuff, and Europe is where you have a lot of archaeologists out looking for human remains, and so I think there's a bit of a bias toward the European landscape. As people get cleverer about finding things in Africa and look longer, I suspect that we will see things beyond the age at which the European artifacts appear.

We also know that a lot of our evolution had to have taken place before the human races diverge because we're pretty much birds of a feather. If you took a bunch of human babies from anywhere around the world -- from Australia, New Guinea, Africa, Europe -- and scrambled the babies at birth and brought them up in any society, they'd all be able to learn the same languages, learn how to count, learn how to use computers, learn how to make and use tools. It suggests that the distinctively human parts of our intelligence were in place before our ancestors split off into the different continents.

So in a sense we're all Africans, and if the first group that budded off from the African population and ended up in Australia did so sixty or seventy thousand years ago, then our evolution had to have been pretty much complete by then, because today's Australians and today's Europeans and today's Asians and Africans are all the same species with pretty much indistinguishable cognitive abilities.

Q: So what happened fifty thousand years ago?

A: Human evolution, at first, seems extraordinary. How could the process that gave rise to slugs and oak trees and fish produce a creature that can fly to the moon and invent the Internet and cross the ocean in boats? Was it some kind of divine spark that made our brains special? Well, I don't think so, because I think that you can understand human evolution in terms of the ordinary process of Darwinian natural selection.

The way to understand how different species evolved is to think about the niches that they fill in an ecosystem -- basically, how they make a living. And how do humans make a living? Well, with their brains. You could think of an ecosystem as a bunch of antagonistic arms races, almost: Everything that an animal depends upon for food is the body part of some other animal or plant who would just as soon keep that body part for itself.

And so all the things that we depend on for food evolve defenses against being eaten. Animals run away, they develop spines or poisons. Plants can't very well defend themselves by their behavior, so they resort to chemical warfare, and plants are saturated with toxins and irritants to deter creatures like us who want to eat them. Now, whenever you have some kind of defensive weapon in nature, you get an offensive weapon, and vice versa. So as the hide gets thicker, the fangs get stronger and sharper, which makes the hides get thicker still, and so on.

This arms race, though, is played out in evolutionary time, and the animal can't will its skin to get thicker in its own lifetime. Now, here's the trick, I think, behind humans: We participate in this arms race -- but in our own lifetime, not in evolutionary time -- by using our brains, by developing a model of how the world works, what causes lead to what effects, and figuring out ways of defeating the defenses of other plants and animals before they can evolve countermeasures in response.

So we invent snares or camouflaged pits, or we coordinate our behavior to drive large animals and stampede them over a cliff, or ways of detoxifying plants by cooking them or fermenting them or soaking them. And because we can figure these things out in our mind's eye by learning how the world works, we can figure out how to use more of the ecosystem to our advantage, and I think that explains why these big-brained creatures became as successful over the planet as they did.

Q: How did evolution, for humans, happen so quickly? We [already] had a big brain, but how did the big brain suddenly start working?

A: Certainly humans didn't evolve to their present state in one instant, in one fell swoop, because we know that our ancestors, the species like Homo erectus and Homo habilis already had a pretty big brain for a primate of that size. They were already using tools. They were almost certainly cooperating with one another. So it's not as if our species was the first to do it it was building on some earlier stepping stones.

And it's unlikely that it happened all at once. You have to remember that not every creature that was evolving left behind its skull or its tools for our convenience tens of thousands of years later. Most bones or most tools rot or get buried and are never found again. So the earliest date at which we find some fossil or artifact is not the point at which the species first appeared it was probably doing its thing for many tens of thousands of years before we were lucky enough to find something that it left behind that lasted to the present day.

Q: Can you talk about the rewiring of the human brain?

A: You have to remember that human intelligence and intelligent behavior don't just come from having a whole bunch of stuff packed into our skull like meatloaf. The actual organization of behavior goes on the level of the individual nerve cells and their connections, and we have a hundred billion nerve cells, probably a hundred trillion connections. It's just mind-boggling to think of all the different ways in which they're arranged in a baby's head. And a lot of our evolution consisted not just in getting more of this stuff, but in wiring it in precise ways to support intelligence.

Q: Does Darwinian evolution allow for such internal rewiring as part of its process?

A: There are lots of ways in which Darwinian natural selection could rewire a brain. There are chemicals that are released in the growing brain that attract nerve cells, encouraging them to grow in certain pathways versus others. There are molecules at the tips of the growing neurons that can engage or not engage some target, like a lock and a key. There are rules for when brain cells die in what part of the brain, so that they might grow in one part, die off in another. All of these are under the control of genes, and as genes evolve, the way they do throughout evolution, the wiring of the brain can change.

Q: So this rewiring pattern happened progressively?

A: Yes. It's very likely that the changes in the brain didn't happen overnight. There wasn't one magical mutation that miraculously allowed us to speak and to walk upright and to cooperate with one another and to figure out how the world works evolution doesn't work that way. It would be staggeringly improbable for one mutation to do all that. Chances are there were lots and lots of mutations over a span of tens, maybe even hundreds of thousands of years, that fine-tuned and sculpted the brain to give it all the magnificent powers that it has today.

I don't think there was a thunderclap or a divine spark that suddenly made one species smart. You can see, in our ancestors, there was a gradual expansion of the brain, there was an expansion of the complexity of tools. Even when our species evolved, it surely was spread out over tens of thousands of years. The fact that we find a whole bunch of artwork or tools in one place just means that that's when they arrived there and left some garbage that survived to the present time. But it's virtually certain that it was extended over many, many generations before that.

Q: What is a "cognitive niche"?

A: Our niche in nature, the "cognitive niche," the ability to understand the world well enough to figure out ways of manipulating it to outsmart other plants and animals. And there's several things that I think evolved at the same time to support this way of life. One of them is cause-and-effect intelligence: How do sticks break, how do rocks roll, how do things fly through the air? A second is social intelligence: How do I coordinate my behavior with other people so that we can bring about effects that one person acting alone, like Robinson Crusoe, could never have done? And I think the third is language: If I learn something, I don't get the benefit of it alone, but I can share it with my friends and relatives, I can exchange it for other kinds of commodities, I can negotiate deals, I can gossip to make sure that I don't get exploited.

So, each one of these abilities -- intelligence about the world, social intelligence, and language -- I think reinforces the other two, and it's very likely that the three of them coevolved like a ratchet, each one setting the stage for the other two to be incremented a bit.

Q: Some scientists think that gossip was the only thing driving language.

A: Gossip is certainly one of the things that language is useful for, because it's always handy to know who needs a favor, who can offer a favor, who's available, who's under the protection of a jealous spouse. And being the first to get a piece of gossip is like engaging in insider trading: You can capitalize on an opportunity before anyone else can.

But language is useful for other things, for exchanging technical know-how -- how do you get poison out of the gland of a toad, what's the best way to make a spear, where are the berries, what's the best time of year to hunt. It's also good for one-on-one negotiations: "If you give me some of your meat, I'll give you some of my fruit" "You and I can gang up on the leader: -- even though he's stronger than either of us, he can't beat the two of us acting together" "If you have sex with me, I'll help bring up the children." There are all kinds of ways that language can be useful. Gossip, I think, is just one of them.

Q: So languages began just about fifty or sixty thousand years ago.

A: We really don't know when language began. It can't be any later than fifty or sixty thousand years ago because that's when the races diverged, and we know that all the races are interchangeable in their language abilities. Bring up an Australian Aborigine in New York, they'll speak English with a New York accent, or vice versa. So it had to be in place before that it couldn't be later than fifty or sixty thousand years ago.

How much earlier? I think considerably earlier, simply because language is complicated. It's like the eyeball or the ear, and complicated organs can't evolve in one fell swoop -- they need too many mutations in order to craft this finely engineered organ. So I think language had to have had a fairly long evolutionary history.

We don't really know why it took us as long to evolve as we did, but I think there's a strong suggestion that language couldn't have evolved before other things were in place. First of all, you have to have something worth saying. What's the use of having long, flowery sentences if you have nothing interesting to communicate? If chickens had language, what would they talk about? Nothing terribly interesting.

And also, you've got to be on speaking terms with someone else. If no one else is interested in what you have to say, or if you tell someone something and they will take advantage of you and you can't expect something in return, there'd be no point in having language. So I think we evolved language when we also evolved something to say and when we also evolved to be on speaking terms with one another.

Language evolved over an extended period of time, but it seems to have coevolved with other things that all came to their present configuration about the same time, somewhere before fifty thousand years ago. Our intelligence, our language, our social interactions, all of them seem to come together at this magic point.

I think human evolution couldn't just have been driven by social completion, by people gossiping and plotting against each other, because that's the equivalent of taking in one another's laundry it doesn't get you anywhere. I think social intelligence coevolved with physical intelligence -- figuring out how the world works. It gives you a reason to hang out together because you can accomplish things that one person couldn't, and it creates an environment in which know-how is that much more worth having because you can share it with your buddies and your kids. And so the costs of a big brain are repaid if everything you know can be multiplied in terms of sharing it with other people.

Q: We're talking about anatomically modern humans -- anatomically modern and behavioral modern are two very different things. Why didn't the others make it and why did this new group make it?

A: It's possible that once the skull had evolved to the present size, there was still more evolving to do. And that might explain the gap between the first anatomically modern human that had the same amount of brain that we had, and the first behaviorally modern human who created art and fine inventions and so on. The difference is that there could have been a lot of evolution going on inside the skull as the brain got rewired.

The actual cause of behavior is not just brain tissue acting en masse like a muscle, but it's the wiring diagram of the hundred billion different brain cells connected by a hundred trillion connections. There are so many ways in which those could be wired and many ways for the genes to bias that in one direction or another that, for a long period of time, there could have been a kind of internal rewiring even if on the outside the skull looked exactly the same.

Q: We always say that we're never going to find the answer to that because the brain doesn't fossilize. Is that true, or do you think we may find the answer?

A: We probably won't find the answer to that in the fossils because the neuron-to-neuron connections certainly don't fossilize. We'll have to be awfully clever about reconstructing it, both from the products that they left behind -- what does a functioning brain do? -- and perhaps also from clever use of genetic evidence, working backwards from the genes that build the brain today to figure out what the genes that built the brain fifty thousand years ago might have looked like. That's science fiction today, but who knows what will happen in ten or twenty or thirty years?

Q: If you look at a Neandertal skull and the skull of the modern human, they're about the same size. One failed and one succeeded. Why?

A: We don't really know why Homo sapiens succeeded and Homo neandertalensis didn't. The brains were the same size, but they may have been wired quite differently, and it could have been that there was wiring in the Homo sapiens brain that supported better language, cleverer know-how, better social coordination, that gave them an advantage. And it didn't have to be a big advantage even an advantage of a couple of percentage points in survival rate could, over a few thousand years, have driven the less well-adapted species to extinction.

A: Certainly, when we look around us and are amazed at all the things that Homo sapiens has wrought -- rockets that go to the moon and the Internet and modern medicine and so on -- that wasn't because our brain evolved to do those things in particular no Robinson Crusoe thinking by himself on a desert island could have invented a rocket. It depends on the accumulation of an enormous number of discoveries that were passed on, not through the genes, but from one person to another through language and other forms of communication.

This is called cultural evolution. Some people call the units of cultural evolution memes -- little units of memory or knowledge -- and we've been accumulating them for tens of thousands of years.

So we figured out how to make nice sharp tools and our jaws and teeth became smaller. We figured out how to use the hides of other animals to stay warm and we got naked. We are now figuring out how to cure diseases, how to build shelters. And for tens of thousands of years the products of the human brain have accumulated in almost a parallel course in evolution to the changes in our bodies and brains.

These memes can be anything from styles that help you fit into a group, like turning a baseball cap around and wearing the peak in the back, to figuring out the cure for some disease or how to grow crops. So the products of the brain that have been transmitted not through the brains but through language have, for many thousands of years, been as important or more important than the actual physical stuff that we're made out of.

A lot of the creations of our brain can make up for physical deficiencies, and could actually change the course of evolution. Thousands of years ago, someone who was severely nearsighted probably wouldn't have had many descendants he would have been eaten or fallen off a cliff a long time ago. But we invented eyeglasses and now being nearsighted has no disadvantage at all.

There are some people who might say, "Well, isn't this interfering with evolution? Wouldn't we be better off letting the diabetics and the nearsighted die an early death to improve the physical vigor of the species?" That really goes against the way that human evolution works, which is that for tens of thousands of years we've depended for our survival on our own inventions, on our own creation, and this is simply extending this process.

Q: How important, in your estimation, is Darwin's theory of evolution by natural selection to the field of biology?

A: Biologists often say that nothing in biology makes sense except in the light of evolution, and, most importantly, Darwin's theory of natural selection explains the appearance of design in living things. You look at living things, and it looks as if they've been engineered. We've got a heart that pumps blood. We've got eyes that have a transparent lens, irises that open and close in response to the light level, and muscles that move them in and out. We've got ears that record vibrations of sound, and lubricated joints in our knees and elbows.

Who put them all together? Until Darwin, it would have been completely reasonable to say, "There has to have been a cosmic engineer." For the same reason that if we see a watch we know that there has to have been a watchmaker, when we see an eyeball or a heart or an elbow, there has to have been something that designed that. Darwin showed why that is not right, that you can get the appearance of engineering in the natural world without invoking a real engineer.

Darwin's theory of natural selection explains how we find signs of engineering or design in the living world why, whenever we look at a plant or animal, we see fantastically complicated machinery.

Q: If Darwin could see the modern world, what would he be most surprised or gratified to understand that we understand?

A: If Darwin were alive today, the discovery of biology that would have pleased him the most would have been modern genetics and DNA, because to the day that he died he was haunted by the worry that his theory wouldn't work because traits of organisms blended when they mated, that anything that was advantageous in an organism would be diluted when it mated with some other organism that didn't also have that trait, and there was no way to get evolution off the ground.

We know now that genes survive intact when organisms mate, that they are particles that don't get blended but survive in their identical form. We know that they have a physical basis, the sequence of bases in the DNA molecule. Those were the missing pieces in the theory of evolution, and that's really what convinced scientists that Darwin's theory was the correct explanation for the evolution of life on earth.

Q: Do you think he would be surprised to know how much dissension there still is around his theory?

A: I think Darwin would be surprised to learn that more than a hundred years after he proposed his theory there are still people who think it's just a theory, who have sincere doubts about it, because the evidence was quite convincing in Darwin's time. And now that the last holes of his theory have been plugged by the discoveries of genetics, by the discovery of the age of the earth, by the discovery of the chemical basis of life, no reasonable person can deny that this is overwhelmingly the best explanation we have for the evolution of life on earth.

Chimpanzees are clearly our close cousins. You cut us both open, you see the same organs. You look at our DNA and we share 98.5 percent of our DNA with chimps. But obviously, we're very different. Chimps are precariously clinging to a few patches of forest in Africa humans have taken over the planet. What could have produced the difference?

Well, there was six million years in which our brains expanded and got rewired in ways that allow us to do completely different things. We can exchange information by making noise as we exhale -- the gift that we call language. We figure out how the world works, we make many different kinds of tools, we coordinate our behavior and exchange information. And all of these changes in cognitive evolution, in the evolution of the powers of the brain, account for why humans are making a film in which they can talk about chimpanzees rather than vice versa.

A friend of mine lived and worked with a chimpanzee for several years, and tells the story of how the chimp loved to imitate things that she did. For example, after she washed the dishes the chimp would wash the dishes, but the chimp's idea of washing the dishes was very different from ours. It went through the same muscle movements it would pick up the sponge, let the warm water roll over his hands, would rub the sponge on the plate, but didn't get the idea that the point of washing the dishes was to get the dishes clean.

It just liked the feel of rubbing a sponge over the plate. It could wash the same dish over and over again, it could rub some of the dirt off and not get all of it off, because what it was imitating was the particular physical sequence. What it didn't think about was what was the goal of the human performing the action. And the ability to guess what other people's goals are is a key part of human intelligence, and it makes us very different from our primate cousins.

## #1: Is there an evolutionary advantage to "being stupid"?

And the #1 blog entry published thus far in 2017 discussed whether there was an evolutionary advantage to being stupid:

As I was looking through the scientific literature the other day, I came across an article published in 1973, "The Evolutionary Advantages of Being Stupid." With a title like that, how could I not read it?

In this article Dr. Eugene D. Robin discussed how larger and more complex brains are associated with greater intelligence, which by evolutionary standards was thought to be related to "superiority." He described how this line of thinking places man at the peak of evolution resulting in our tendency toward an anthropocentric view of the world. Anthropocentrism also leads to interpreting or seeing things in terms of our own experiences or value/belief systems.

Dr. Robin went on to argue that looking at survival of species in hindsight suggests that those which survive have done well whereas those that have died off must have been inferior. Rather, he argues it is important to think dynamically. Meaning that traits evolve continually as does the environment. So a trait that may benefit the species at one point in time might not help at all at if conditions change. He quotes Asimov who posed the question, "Which is the fitter, a man or an oyster?" If Earth were covered in water, clearly oysters would fair better than man.

With regards to intelligence, Dr. Robin also proposed thinking in terms of it being a dynamic trait that could help or handicap a species. Take for example diving mammals. Mammals that are good at diving, have evolved the ability to survive with low levels of oxygen. This ability may also protect them from health conditions associated with low oxygen such as blood loss, heart attacks, strokes, etc. In this example, smaller brains relative to body size are more advantageous as it allows the animal to dive longer (and perhaps have better health). In other words, by presumably sacrificing intelligence, the animals with smaller brains have increased survival. His own research looked at turtles that can dive for more than 1 week. To accomplish this, turtle brains create energy through pathways that do not rely on oxygen and, as a result, have reduced activity while diving. Thus, by anthropocentric standards turtles are relatively "stupid" even though they have survived over 200 million years.

Image of turtles from Lvova Anastasiya (Львова Анастасия, Lvova) (Own work (own foto)) [Public domain], via Wikimedia Commons

Another argument Dr. Robin presents is that dinosaurs were great at hunting because they were big. At the same time, their large size meant they needed to eat a lot and thus were at risk of running out of resources. Compare this to humans, who are more intelligent and thus able to manipulate the environment to produce adequate food (and other resources). What impact have these environmental modifications had? Or consider the modern rise of so-called "superbugs" from the overuse of antibiotics. Is human intelligence thus a lethal trait?

Eugene D. Robin. The evolutionary advantages of being stupid. Perspectives in Biology and Medicine. 16(3): 369-380, 1973. doi: 10.1353/pbm.1973.0060

## Lactose Tolerance and Human Evolution

Anyone who enjoys ice cream can thank evolution. Just 10,000 years ago, no one past infancy could digest milk sugar, called lactose. Babies always made lactase, the enzyme that breaks down this sugar, but after weaning lactase production would stop.

### Related Content

Then along came livestock. Sometime in the past 10,000 years, several different populations—all raising cattle or camels in Northern Europe, East Africa and the Middle East—gained the ability to digest milk for life. Certain gene variants became prevalent that caused lactase production to continue into adulthood.

Lactose tolerance offered these populations a crucial advantage, says anthropologist Henry Harpending, co-author of a recent book called The 10,000-Year Explosion: How Civilization Accelerated Human Evolution. Before the gene variants arose, people had to remove the sugar from of cow or camel milk by fermenting it, but that eliminated between 20 to 50 percent of its calories.  With the ability to digest milk, humans could access this additional energy.

In The 10,000-Year Explosion, Harpending and co-author Gregory Cochran, both at the University of Utah, argue that the ability to digest lactose shaped human history. Lactose-tolerant populations, they claim, could better survive famines, and may also have been better conquerors, aiding the spread of their civilizations and cultures. “The European and maybe Arab expansions that whacked the Byzantine Empire may have been outcomes of this new ability to digest food,” Harpending said in an interview.

The ability to digest lactose is also evidence that humans are still evolving. In those 10,000 years, it arose independently in at least four places around the globe. Today, more than 90 percent of all people have some degree of lactose tolerance. How much tolerance people have depends on which gene variants and the number of copies of those genes they posses. About a third of the population digests lactose imperfectly and experiences some symptoms of lactose intolerance, and some people, mostly of African, Asian or Mediterranean descent, are not able to digest lactose at all.

The rapid selection for lactose tolerance raises an interesting question.  Were people who already had the gene variant motivated to domesticate animals, or were people who domesticated animals more likely to benefit from having a lactase-producing gene variant? “Which came first, the cattle or the mutation, you can’t tell,” Harpending says. “If the mutation had not occurred, there wouldn’t be so much dairying. But if people who could digest lactose didn’t have cattle, the mutation would have had no advantage.”

## Modern times: Excessive sitting, bad posture, and glute atrophy

Through millions of years of life as hunter-gatherers in the Paleolithic, low fitness variations (i.e., a weak and small GM) were slowly taken out of the population. When the Agricultural Revolution spread across the globe, new physical activity patterns characterized by more farm-related work replaced Paleolithic “exercise routines”. Studies suggest that the physical activity levels of early farmers could have been as high – or perhaps even higher – than that of hunter-gatherers (5), but hunting and scavenging were clearly not as important anymore, a transition that might have led to a decline in the amount of stress placed on the GM.

However, this transition is nothing compared to what has happened over the last centuries, as the industrial revolution has spread the globe, desk jobs have become the new norm, and more and more people spend the majority of their day sitting in a chair. Excessive sitting and sedentary living are bad for a number of reasons, one of which being that the glutes aren’t stressed adequately.

Through millions of years of evolution, the large human GM evolved because it improved our ancestors’ ability to survive in environments where running, walking in uneven terrain, and digging were a demanded part of daily life. When we completely abandon this way of life and adopt a lifestyle which the human body – including the glutes – isn’t adequately adapted for, problems occur.

The portion of our genome that determines basic physiology and anatomy has remained relatively unchanged since the Paleolithic era (5, 6), meaning that although we today wear suits and dresses and drive fancy cars, our Stone Age legacy is still with us. There has been too little time for natural selection to adapt the human body to our new living conditions, and as a result, a discordance between genes and environment has occurred, a discordance that sets the stage for a whole host of health problems.

If you take a look at the people around you at the gym or the street you’ll quickly see that glute atrophy, excessive anterior pelvic tilt, and other abnormalities associated with inadequate glute training and excessive sitting are widespread. As every personal trainer, physical therapist, and coach has experienced, these problems aren’t only aesthetically unappealing, but they also set the stage for poor movement patterns in the gym, injuries, and lower back pain.

A person with weak glutes and/or excessive anterior pelvic tilt will often display quad dominant lifting in exercises that are supposed to be hip-dominant, poor recruitment of the posterior chain, and overextension of the back in the squat, deadlift, and many other movements. If he/she simply continues with this exercise technique, faulty movement patterns are ingrained and sometimes exacerbated, good glute development never shows, and an annoying lower back pain might start appearing. In other words, glute atrophy, lower crossed syndrome, and excessive anterior pelvic tilt are serious issues that affect physical performance and health.

The image above showing the evolution of man, from tree-dwelling primates to modern humans hunched over a computer, shows how much our lifestyle has changed. We’re closing the circle in the sense that our new, bent-over position in front of a computer is starting to resemble the posture of our ape ancestors. The important thing to keep in mind is that the transformation from an ape-like creature to a bipedal, big-brained man took millions of years, while the transition from a daily life that involved plenty of walking, standing, and running to a daily life characterized by plenty of sitting, only happened very recently. In other words, we’ve had scant evolutionary time to adapt to our modern lifestyle.

A “large” and strong GM was an adaptive trait in the Paleolithic, but today, the selective pressure working on the human GM has been significantly reduced. Do people with great glute genetics have more kids than those with weak and flabby glutes? It’s possible, but that’s not due to the survival advantage of having a strong and big butt, but rather due to the aesthetics of it…

## Researchers Suggest Big Toe Was Last Part of Foot to Evolve

The earliest hominins split their days between the trees and the ground, alternately adopting ape-like tree-swinging behaviors and human-like bipedalism, or walking upright on two feet—albeit in a crouched position. By the time Lucy and her Australopithecus afarensis relatives arrived on the scene some four million years ago, bipedalism had largely overtaken tree-dwelling, but according to a study published in the Proceedings of the National Academy of Sciences, these human ancestors likely lacked a key evolutionary adaptation: the rigid big toe.

BBC News ’ Angus Davison reports that the new findings suggest the big toe, which enables humans to push off of the ground while walking and running, was one of the last parts of the foot to evolve.

“It might have been last because it was the hardest to change,” lead author Peter Fernandez, a biomedicist at Milwaukee’s Marquette University, tells Davison. “We also think there was a compromise. The big toe could still be used for grasping, as our ancestors spent a fair amount of their time in the trees before becoming fully committed to walking on the ground."

To trace the big toe’s evolution, Fernandez and colleagues created 3D scans of human relatives’ toe bone joints, relying on a combination of living creatures—including apes and monkeys—and fossilized samples. After juxtaposing these scans with ones made of modern humans and mapping the data onto an evolutionary tree, researchers realized that the big toe developed much later than the rest of the foot’s bones. Early hominins’ gait, therefore, had more in common with apes’ than the easy human stride seen today.

According to Live Science’s Jennifer Welsh, differences between human and non-human primate feet come down to purpose. Whereas most primates use their feet to grasp onto tree branches and other objects, humans rely on theirs to navigate life on two legs. For example, arches, which are located on the inside of the foot close to the big toe, make it harder for humans to nimbly climb trees but offer shock absorption when planting one’s feet on the ground.

The human big toe specifically carries 40 percent of the five toes’ collective weight, Corey Binns writes for Scientific American, and it is the last part of the foot to leave the ground when one walks or runs. Comparatively, apes’ big toes are opposable, built for grasping and functioning similarly to the versatile opposable thumb, which allows primates to deftly perform a wide range of motions.

Although early humans such as A. afarensis and the roughly 4.4-million-year-old Ardipithecus ramidus walked upright, BBC News’ Davison notes that the study confirms this bipedalism did not preclude the existence of an opposable, ape-like big toe.

“It was a bit of shock when hominins were found that have a grasping, or opposable, big toe, as this was thought to be incompatible with effective bipedalism,” anatomist Fred Spoor of London’s Natural History Museum tells Davison. “This work shows that different parts of the foot can have different functions. When a big toe is opposable, you can still function properly as a biped."

## Carbs Needed to Evolve Big Brains

Understanding how and why we evolved such large brains is one of the most puzzling issues in the study of human evolution. It is widely accepted that brain size increase is partly linked to changes in diet over the last 3 million years, and increases in meat consumption and the development of cooking have received particular attention from the scientific community. In a new study published in The Quarterly Review of Biology, Dr. Karen Hardy and her team bring together archaeological, anthropological, genetic, physiological and anatomical data to argue that carbohydrate consumption, particularly in the form of starch, was critical for the accelerated expansion of the human brain over the last million years, and coevolved both with copy number variation of the salivary amylase genes and controlled fire use for cooking.

With global increase in obesity and diet-related metabolic diseases, interest has intensified in ancestral or ‘Palaeolithic’ diets, not least because – to a first order of approximation – human physiology should be optimized for the nutritional profiles we have experienced during our evolution. Up until now, there has been a heavy focus on the role of animal protein and cooking in the development of the human brain over the last 2 million years, and the importance of carbohydrate, particular in form of starch-rich plant foods, has been largely overlooked.

Hardy’s team highlights the following observations to build a case for dietary carbohydrate being essential for the evolution of modern big-brained humans:

(1) The human brain uses up to 25% of the body’s energy budget and up to 60% of blood glucose. While synthesis of glucose from other sources is possible, it is not the most efficient way, and these high glucose demands are unlikely to have been met on a low carbohydrate diet

(2) Human pregnancy and lactation place additional demands on the body’s glucose budget and low maternal blood glucose levels compromise the health of both the mother and her offspring

(3) Starches would have been readily available to ancestral human populations in the form of tubers, as well as in seeds and some fruits and nuts

(4) While raw starches are often only poorly digested in humans, when cooked they lose their crystalline structure and become far more easily digested

(5) Salivary amylase genes are usually present in many copies (average

6) in humans, but in only 2 copies in other primates. This increases the amount of salivary amylase produced and so increases the ability to digest starch. The exact date when salivary amylase genes multiplied remains uncertain, but genetic evidence suggests it was at some point in the last 1 million years.

The human brain uses up to 25% of the body’s energy budget and up to 60% of blood glucose. Image is for illustrative purposes only.

Hardy proposes that after cooking became widespread, the co-evolution of cooking and higher copy number of the salivary amylase (and possibly pancreatic amylase) genes increased the availability of pre-formed dietary glucose to the brain and fetus, which in turn, permitted the acceleration in brain size increase which occurred from around 800,000 years ago onwards.

Eating meat may have kick-started the evolution of bigger brains, but cooked starchy foods together with more salivary amylase genes made us smarter still.

Source: Karen Hardy – University of Chicago Press Journals
Image Source: The image is credited to Institute of Physics
Original Research: Full open access research for “The Importance of Dietary Carbohydrate in Human Evolution” by Karen Hardy, Jennie Brand-Miller, Katherine D. Brown, Mark G. Thomas, and Les Copeland in The Quarterly Review of Biology. Published online August 2015 doi:10.1086/682587

## Circular Reasoning

Smith also charges that evo psych engages in “circular” reasoning when “individuating” behaviors. Individuating means identifying specific behaviors based upon their specific effects, functions, or causes. To individuate a behavior based on its effects, “one needs to establish that the contemporary and ancestral causes of the behavior (structures) are strong vertical homologs,” but she explains that evo psych has no mechanism for doing this. To individuate a behavior based on its function entails “circularity,” because it “illegitimately supposes that a behavior was selected for and then uses this supposition as evidence that the behavior was selected for.” To individuate a behavior based on its causes falls into the same trap, because “it relies on the principle that cognitive mechanisms are individuated by the behaviors that they bring about while these behaviors are individuated by the mechanisms that supposedly cause them.”

In light of these difficulties, Smith asks: “Is evolutionary psychology possible?” The answer is no. She concludes: “Evolutionary psychologists simply do not have the methodological resources to justify the claim that the psychological causes of contemporary behaviors are strong vertical homologs of the psychological causes of corresponding behaviors in the EEA.”

It’s remarkable and encouraging to see such clear thinking in a mainstream scientific journal. Even evolutionary biologist P. Z. Myers jumped on this bandwagon, writing about the field of evo psych, “None of their prior claims are valid, and they don’t fit with what we do know about evolution and the brain!” But will these criticisms have any effect on the field itself? Myers concludes that evo psych is too insular for that:

Not that any of this will have any effect on EP at all — that’s a field that relies more on an emotional belief that they can study the past entirely by imposing their desired conclusions on weak data. Smith, on the other hand, has a strong understanding of logic and recognizes where these Evolutionary Psychologists have made a huge leap beyond what the data entails.

## Every 27.5 million years, the Earth’s heart beats catastrophically

Decades of studies have shown parents to be less happy than their childless peers. But are the kids to blame?

• Folk knowledge assumes having children is the key to living a happy, meaningful life however, empirical evidence suggests nonparents are the more cheery bunch.
• The difference is most pronounced in countries like the United States. In countries that support pro-family policies, parents can be just as happy as their child-free peers.
• These findings suggest that we can't rely on folk knowledge to make decisions about parenting, on either the individual or societal levels.

How does one live a happy, meaningful life? For many the answer is, at least in part, raising children. Watching a child grow and learn about the world is a joyous experience, and the time spent providing unconditional love and care offers spiritual dividends. Then in our golden years, children can be a source of palliative comfort.

This view is so entrenched in our culture that many people, especially women, are pressured by friends and family into having children and feel they must justify their reason not to.

As is often the case, social reality proves more complicated than the worldview learned at mother's knee. Decades of research has compared the happiness and well-being of parents to nonparents, and the verdict is in: a lot of parents are less happy than their childless peers. But not all of them.

### The parent trap

A mother soothes her baby child

(Photo by Jenna Norman / Unsplash)

Headlines claiming parents to be more dejected than nonparents certainly grab our attention, but such stories are hardly news. Empirical studies have been tracing out this pattern since the 1970s. Here are three sample papers demonstrating the trend:

A 2011 review by Thomas Hansen, a researcher at Norwegian Social Research, compared our folk understanding on the relationship between parenthood and happiness to the evidence. It found that people believe "the lives of childless people are emptier, less rewarding, and lonelier than the lives of parents," but that the opposite proved true. Children living at home interfered with their parents' well-being.

A meta-analysis by the National Council on Family Relations looked at a more specific metric of happiness: marital satisfaction. It found that couples without children reported more romantic bliss. The difference was most pronounced among mothers of infants, while fathers disclose less satisfaction regardless of the child's age. The authors noted the discrepancy likely resulted from role conflicts and restrictions on freedom.

Finally, a study published in the American Journal of Sociology looked at 22 Organisation for Economic Co-operation and Development (OECD) countries and compared the association between parenthood and happiness. Researchers Jennifer Glass (University of Texas, Austin) and Robin Simon (Wake Forest University) found that nonparents reveal higher levels of well-being in most advanced industrialized societies.

The happiness gap was widest in the United States, where parents were 12 percent less cheerful than childless adults. Fourteen other countries—among them Ireland, Greece, Britain, New Zealand, Switzerland, and Australia—also showed a less-than-sunny outlook for parents, but not to as large a degree as in the U.S.

### Are the kids alright?

A Spanish family sit down together for a meal.

Based on a glance at this research, one could posit that children are a predominant source of unhappiness—and yes, we all know that one kid who is Exhibit A for this statement. But these researchers were careful to note that these effects are correlative, not causative, and there are many factors in the mix beyond progeny.

Hansen's review points out that the parents most susceptible to unhappiness were women, singles, those in lower socioeconomic strata, and those living in less pro-parenthood societies. Meanwhile, the National Council on Family Relations saw the largest decrease in martial satisfaction among the higher socioeconomic groups, likely because their status afforded them greater freedoms before having children.

Glass and Simon found eight countries where parents reported higher levels of happiness than nonparents, including Spain, Norway, and Portugal. Their analysis indicated that countries offering "more generous family policies, particularly paid time off and childcare subsidies, are associated with smaller disparities in happiness between parents and nonparents."

A potential reason? Parents in countries supporting pro-family policies contend with fewer stressors. They can take more parental leave, enjoy expansive subsidized care, and aren't as financially burdened by educational expenses. This is especially true when compared to the U.S., which provides little support for parents compared to the other countries in the study.

Importantly, Glass and Simon also found that such policies had no detrimental effect on the happiness of nonparents. In fact, the presence of strong pro-family policies led to greater happiness for women of all statuses.

### Parental unhappiness is. complicated

A young mother sits with her daughter.

(Photo by Katie Emslie / Unsplash)

Taken together, these three studies suggest a major cause of parental despondency is scarcity. Lower-class parents find it difficult to patch together the money, resources, and social networks necessary to succeed in their own lives while also supporting their children. Even upper-class parents can grow weary if a resource in short supply is traded off, such as time or the freedom to self-actualize.

Countries with pro-family policies can offset these scarcities to help balance the happiness gap between parents and nonparents.

But research in this field casts a wide net. As studies shift their focus, they draw different conclusions to give us a fuller, if more complicated, picture of parenthood's many pitfalls. Taken together with scarcity, all of the following factors likely have some pull on parental happiness, though it is difficult to say to what degree.

Culture of extended families. Countries like Spain and Portugal, where parents report being 3.1 and 8 percent happier than nonparents respectively, culturally center on extended families. The Spanish manage personal problems through family, an approach that extends to child rearing where many hands make light work.

In sharp contrast, the United States culturally centers on a sense of individualism and mobility. Its nuclear family model consists of small family units where parents take near sole responsibility for raising children while the extended family lives in separate domiciles, sometimes hundreds of miles away.

Who becomes a parent. Glass and Robin note that their results could be tempered by parental selectivity. They propose that countries like Spain and Italy, which have low fertility rates, may select toward people who truly desire to have children. The United States, with its much higher fertility rate, could have people not strongly predisposed to parenthood having children nonetheless.

Children in the home. An analysis from the Institute for Family Studies found that men aged 50-70 are happier than their childless peers if their children have left home. However, men who still had children at home reported being less happy than either nonparents or empty nesters. For women of the same age, being an empty nester resulted in a slight decrease in happiness compared to nonparents, but a steep decline if the children lived at home.

Number of children. The same analysis showed that women with only one child were seven percentage points less likely to report being happy than nonparents, while women with three or four children showed no discernible difference. No significant variance emerged for men.

Nicholas H. Wolfinger, the analysis' author, admits these results are counterintuitive and posits two possible explanations. The first is unmet family size preference redounding unhappiness, as many people settle for fewer children than they'd like. The second is a strong sense of familism offsetting parenthood's more negative effects. It is unlikely that family size in-and-of-itself causes a decline in happiness.

Parenting style. The way a parent approaches parenting may have substantial effects on their happiness. Developmental psychologist Alison Gopnik argues in her book The Gardener and the Carpenter that our modern parenting model, in which we view children as material to be molded into a particular type of adult, is not only wrongheaded but also a source of stress and misery for many parents.

"It isn't just that the [current] parenting model isn't the natural model, it's also just not a very productive model," developmental psychologist Alison Gopnik told Big Think. "It hasn't helped parents or children to thrive. It's led to a great deal of anxiety and guilt on a part of parents and a great deal of hovering expectations for children that really aren't necessary and in fact may even be counterproductive if we still want children to innovate and create."

Self-perception. A Pew Research Center survey found that parents who reported being very happy with life also believed they were doing an excellent job as a parent.

We still have much to learn about parenthood, and the results of so much variegated research can sometimes feel in contention. Even so, it should be clear that our folk assumptions about family are in need of a major update, and we must reconsider our views on parenthood, both from an individual perspective and with regard to social policy.

With that said, there are two strong conclusions we can draw from what we do know. For nonparents, your choice to be childfree will not doom you to a sullen, meaningless existence where you'll spend your final days contemplating a life wasted, like some inverse It's a Wonderful Life.

Nor are parents doomed to immolate their happiness on the altar of their child's future. Parenthood can be a source of exuberance, but simply raising a child will not magically bring contentment to your life. If anything, you'll have to work harder for that contentment as many factors, some in your control, some not, dictate parental happiness. Anyone considering parenthood should weight them judiciously before making a decision.

## Is there a reason to have a chin or is simply a trait that evolution didn't select against?

Hopefully the question is clear, I'm wondering if we know of any function of the chin since it seems to me the jaw can be completed from either side in the front without having a protuberance (for some people there doesn't seem to be any anyway).

I took a class on human evolution my freshmen year, and we talked about this briefly. Remember that the way your jaw develops is not as one large bone, but as two bones that meet in the center. Because of this the center of these two jaw bones, ie the chin, is structurally weak compared to the strength of regular bones. To compensate for this the chin grows thicker than the rest of the jaw. This prevents the two halves of the jaw from splitting apart when under stress from chewing.

Interestingly, humans are the only primates with "chins" as we think of them. Other species of primates have what is called a simian shelf, which is a thickening of the mandible, but on the inner side rather than outward. There are some theories that evolution away from the simian shelf and towards the chin is what allowed for speech to develop.

Of course, as with lots of things regarding human evolution, some of this stuff is fairly controversial.

Interestingly, humans are the only primates with "chins" as we think of them.

Not only in primates. We're the only animal out of all animals to have a chin except for, oddly enough, elephants.

One thing to post and it should be posted in response to any question on why something formed.

Evolution is not a ladder. Deevolution does not exist, evolution is simply the change in information generation upon generation. It can be good or bad.

That said, normally beneficial mutations are selected for the most, because they have a higher chance. Neutral changes will also pass on unhindered because they have no negative effects but beneficial still should have the upper hand. Going to negative mutations they are normally selected against, but will still ultimately pass on just at a lower rate.

So any mutation get's passed on no matter what, it's just some mutations depending on the environment have a higher chance.

We bring this up because if someone asks why something exists, they normally phrase the question in such a way they are insinuating it should not of been passed on.

For things like the chin, it could evolve for no reason. It could be a completed negative mutation that keeps developing because nothing is stopping it. If humans begin to stop working out and just use intelligence for the next couple million years they may degrade muscle mass and bone mass and mutate in such a way where we come close to that little "grey alien" type structure, big heads, small everything else. That's NEGATIVE in most aspects, what about fighting physically they are screwed. But nothing selected against it, so it was allowed.

We got intelligent, a chin forming as a negative may never of been a problem, especially because a lot of theories support it is one of the reasons a chin would of been selected for after the fact is simply due to allowing speech to evolve. Your vocal cords rely on the structure of your chin and jawbone for support to make the movements as intricate to produce a wide array of sounds which allows us to communicate. Animals physically can not make the range of sounds we can as humans, that is another huge difference we have. Intelligence and speech, and collective knowledge. Once speech evolves to the point it can record information, a species begins to stop relying on physical characteristics as much, and relies on building of the collective knowledge and standing on the shoulders of giants of the previous generation.

Without speech and recording tools, today we would be the same as 50,000 years ago.

## Conclusion:

While being our best answer, evolution by natural selection is still a theory with arms to be researched.

Darwin’s theory of evolution remains the best model to explain the natural world. It can be broken into many aspects that need to be explained in its own right.

Today we can look with the advantage of retrospect with scientific progress to confirm or direct further understanding.

Each has both factual and philosophical discussions, of which some are open-ended.

Do you think Darwin’s theory explains the natural world today? Leave your answers in the comment section below.