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Due to the advent of social networking and dating sites, it is now possible for almost anyone to find a potential mate. Therefore, there is not as much of a pressure based on physical characteristics or even intelligence anymore. Society does not present the same pressures as was historically present in nature to find food and avoid being killed by predators and potential mating rivals. Almost all alleles regardless of their characteristics are passed on to the next generation through someone or another and attractive traits are no longer chosen above deficient ones. The only exception often being conditions such as dwarfism, Down Syndrome or Parkinson's Disease where the recipients of disadvantageous alleles choose to remove themselves from the gene pool.
Therefore, does this mean that human evolution has been halted due to an absence of natural selection?
My question differs from "Has human medicine stopped humans evolving?" because my post focuses on societal and cultural changes as opposed to medical changes.
Are humans still evolving by Darwin's natural selection?
In 1859, Charles Darwin published On the Origin of Species, a book which transformed our understanding of how life on Earth developed - but ever since then, scientists have wondered whether humans were resourceful enough to remove themselves from the grip of natural selection.
There is no question that humans are unique in the animal world. We have developed technologies that shelter us from the harshness of the environment in a way that no other creatures have managed.
While polar bears evolved thick coats of blubber to insulate them from the Arctic cold, humans could skin that polar bear, and use the pelt as clothing to keep warm.
Does this mean that, at some point, technological advances have stopped us evolving?
Much of the story is in our genes and the sequencing of the human genome has helped unlock the answers.
By comparing the genes of people from all around the world, scientists can see how different we all are, and therefore how much we have evolved apart from each other since our species first appeared.
Skin colour is the most obvious way we have evolved apart, but there are other examples.
"We are living records of our past," says Dr Pardis Sabeti, a geneticist at Harvard University. "And so we can look at the DNA of individuals from today and get a sense of how they all came to be this way."
Another area of recent evolution is how our metabolism has changed to allow us to digest some things that we could not in the past.
The most obvious example of this is lactose, the sugar in milk. Some 10,000 years ago, before humans started farming, no one could digest this beyond a few years of age.
But today, the rate of lactose tolerance in different parts of the world is a clue to the different histories of farming across the globe. While 99% of Irish people are lactose tolerant, in South East Asia, where there is very little tradition of dairy farming, the figure is less than 5%.
So clearly our technology and inventions didn't stop us evolving in the past. But what about today?
Professor Steve Jones, a geneticist at University College London, said: "In Shakespeare's time, only about one English baby in three made it to be 21."
"All those deaths were raw material for natural selection, many of those kids died because of the genes they carried. But now, about 99% of all the babies born make it to that age."
The bulk of medical and other technological developments which protect us from our environment have come in just the past century. So in the developed world today, what is there left for natural selection to act on?
"Natural selection, if it hasn't stopped, has at least slowed down," says Jones.
But although in the developed world today, almost everyone lives long enough to pass on their genes, many of us choose not to.
Some people have three children, and some people have none, so natural selection may be working in a different way.
Humans are still evolving – and scientists don't know why
M odern medicine’s ability to keep us alive makes it tempting to think human evolution may have stopped. Better healthcare disrupts a key driving force of evolution by keeping some people alive longer, making them more likely to pass on their genes. But if we look at the rate of our DNA’s evolution, we can see that human evolution hasn’t stopped – it may even be happening faster than before.
Evolution is a gradual change to the DNA of a species over many generations. It can occur by natural selection, when certain traits created by genetic mutations help an organism survive or reproduce. Such mutations are thus more likely to be passed on to the next generation, so they increase in frequency in a population. Gradually, these mutations and their associated traits become more common among the whole group.
By looking at global studies of our DNA, we can see evidence that natural selection has recently made changes and continues to do so. Though modern healthcare frees us from many causes of death, in countries without access to good healthcare, populations are continuing to evolve. Survivors of infectious disease outbreaks drive natural selection by giving their genetic resistance to offspring. Our DNA shows evidence for recent selection for resistance of killer diseases like Lassa fever and malaria. Selection in response to malaria is still ongoing in regions where the disease remains common.
Humans are also adapting to their environment. Mutations allowing humans to live at high altitudes have become more common in populations in Tibet, Ethiopia, and the Andes. The spread of genetic mutations in Tibet is possibly the fastest evolutionary change in humans, occurring over the past 3,000 years. This rapid surge in frequency of a mutated gene that increases blood oxygen content gives locals a survival advantage in higher altitudes, resulting in more surviving children.
Diet is another source for adaptations. Evidence from Inuit DNA shows a recent adaptation that allows them to thrive on their fat-rich diet of Arctic mammals. Studies also show that natural selection favouring a mutation allowing adults to produce lactase – the enzyme that breaks down milk sugars – is why some groups of people can digest milk after weaning. Over 80 per cent of northwest Europeans can, but in parts of East Asia, where milk is much less commonly drunk, an inability to digest lactose is the norm. Like high altitude adaptation, selection to digest milk has evolved more than once in humans and may be the strongest kind of recent selection.
Realising evolution doesn’t only happen by natural selection makes it clear the process isn’t likely to ever stop
We may well be adapting to unhealthy diets too. One study of family genetic changes in the US during the 20th century found selection for reduced blood pressure and cholesterol levels, both of which can be lethally raised by modern diets.
Yet, despite these changes, natural selection only affects about 8 per cent of our genome. According to the neutral evolution theory, mutations in the rest of the genome may freely change frequency in populations by chance. If natural selection is weakened, mutations it would normally purge aren’t removed as efficiently, which could increase their frequency and so increase the rate of evolution.
Humans Never Stopped Evolving
Aug 1, 2016
© ISTOCK.COM/LEONARDO PATRIZI
N atural selection is tricky to catch in action. As Darwin put it, &ldquoA grain in the balance will determine which individual shall live and which shall die.&rdquo The grain in the balance&mdashthe slightly increased chance that organisms carrying one gene variant will fail in the struggle for existence&mdashis the cost of selection. It is almost invisible, only becoming statistically evident when viewed across thousands of individuals, who may display only subtle differences in the affected character.
In the human population, the toll of natural selection is hidden within millions of deaths and births around the world every year. Everyone dies, many tragically young. And while obvious patterns sometimes emerge from early deaths&mdashcertain diseases, traffic accidents, drug overdoses&mdashthese are often challenging to connect to the action of genes. Likewise, only by comparing the genes of parents with those of childless people, and the genes of.
Six years ago, Yale University’s Stephen Stearns and colleagues took advantage of a long-running study in Framingham, Massachusetts, to assess whether the effects of natural selection could be discerned among the people in the multigenerational study population. Over the last seven decades, public-health researchers have been monitoring the residents of Framingham, noting their vital statistics as well as blood sugar and cholesterol levels to understand the factors that lead to heart disease. As the initial group of research subjects got older, the study started to include their children, and then their grandchildren. The records provide a unique view of the health of a segment of the American population since 1948.
When Stearns and his coworkers analyzed the data, they found lots of evidence that selection was occurring, albeit with many curious patterns. Shorter women had more children than taller women, and heavier women had more children than lighter women. For men, height and weight weren’t as correlated with fecundity. High or low blood-sugar readings in both men and women were associated with fewer offspring, and the age at which individuals had their first child also seemed to influence lifetime reproduction—people who had their first child younger ended up with larger families. 1
The advantage of lactase persistence was enormous, perhaps the strongest known for any RECENT human trait.
The results left scientists frustrated. To what extent are these traits—stature and age at first birth, for example—heritable? What other factors are shaping the population? Age at first birth is surely influenced by cultural factors that can confound the attempt to tease out the contribution of genes.
To get at those kinds of details, we need to combine records of traits with a look at the genes themselves. That kind of research is just now becoming possible.
Last month, for example, Harvard University’s Jonathan Beauchamp published a study in which he compared known gene variants with relative lifetime reproductive success (rLRS)—a proxy for the number of biological offspring an individual has—in people of European descent living in the U.S. and enrolled in the Health and Retirement Study. In this cohort, Beauchamp found evidence that evolution may have selected against educational attainment, while favoring a higher age at menarche for women. Although he notes that cultural and environmental factors may have overridden the effects of natural selection, he makes the case that humans do continue to evolve. 2
In the blood
ED UTHMAN/WIKIMEDIA COMMONS RESISTANT TO MALARIA: Blood disorders and abnormalities such as the sickle cell trait (top) can impede the malaria parasite’s ability to infect red blood cells and are more frequent in regions of the world where malaria was once common. But while these blood differences provided protection against the parasite, they are also associated with health risks, such as cirrhosis of the liver (bottom). NEPHRON/WIKIMEDIA COMMONS The first solid evidence of natural selection in recent human populations was found in blood. Type B blood is common across central Asia, but much rarer in other places. Newly identified blood types outside the ABO system have also been found, and each has a distinctive geographical distribution. One of the most extreme is the Duffy blood type, which has three different versions, or alleles, just like the ABO system. One of these types, Duffy “null,” occurs in up to 95 percent of people in sub-Saharan Africa, but is very rare among people whose ancestry comes from other parts of the world.
In addition to blood type, researchers have investigated the evolution of blood disorders and abnormalities. One of the most interesting is a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD), which helps maintain red blood cells. An insufficient level of this enzyme occasionally causes extreme, even lethal health problems, but is better known for causing a reaction to fava beans in people suffering from the deficiency. Other blood peculiarities include the sickle cell trait, reduced production of hemoglobin (alpha thalassemia), hemolytic anemia (ovalocytosis), and abnormal hemoglobin types (hemo-globin C and hemoglobin E). By examining the frequencies of these conditions, researchers have found that these blood variations coincide with regions where malaria has been common throughout history. Further work revealed how small changes to hemoglobin can impede the malaria parasite’s ability to break into red blood cells. The Duffy null allele, too, helped carriers to resist malaria. 3 The FYA and FYB versions of the gene both result in molecules on the surfaces of red blood cells that function in inflammatory reactions but also provide an avenue of attack for the malaria species Plasmodium vivax. 4 People who lack these molecules may avoid P. vivax infection.
These variations were not without consequences, however. While one sickle cell allele is protective against malaria, most people who carry two copies die young, usually without reproducing. It’s no surprise, then, that malaria-free areas have extremely low rates of the sickle cell trait and other red blood cell variations.
AGRICULTURAL ADAPTATIONS: As human populations began to domesticate animals and consume their milk, they evolved the persistent expression of the lactase gene, which breaks down lactose and is usually only expressed in young animals. © ZACCHIO/SHUTTERSTOCK.COM While the distribution of blood types and abnormalities was the first evolutionary pattern identified among recent human populations, perhaps the most famous is people’s ability to digest milk beyond infancy. Around 30 percent of the calories in milk from humans and all other mammals come from a sugar called lactose, and to make use of the energy stored in lactose, the digestive system must be able to break it down into its two chemical subunits, galactose and glucose. This chemical reaction is catalyzed by the enzyme lactase, the gene for which is shared across all mammals. In most species, however, lactase is only expressed in young prior to weaning, leaving adults unable to digest lactose.
Pre-agricultural humans followed, and many modern humans still follow, this same pattern of lactase expression in infancy only. Regular consumption of milk by an adult can sometimes spur a minimal amount of lactase production, but drinking a large amount of milk or other lactose-containing dairy products can cause severe digestive distress. People from China often have trouble digesting milk, as do many people from southern Europe. Yet in northern Europe and parts of sub-Saharan Africa, more than 95 percent of people produce the lactase enzyme throughout their lives and can thus digest milk as adults without difficulty. A smaller fraction of adults in other populations, such as those in the western half of Eurasia and other parts of sub-Saharan Africa, also have this persistence of lactase.
The persistence is not due to any change to the enzyme itself, but to the short patches of DNA outside the gene that regulate its activity. People from Ireland to India share one mutational change that prompts lactase persistence. In Arabia and sub-Saharan Africa there are four others. At least five times, ancient humans had a chance mutation that spurred lactase activity in adults and began to spread through the population. Not surprisingly, these populations live in precisely the areas where people domesticated cattle, sheep, goats, and camels for the purpose of consistent milk production. That domestication happened only within the last 10,000 years, and cattle became common in sub-Saharan Africa and northern Europe much later than this, placing an upper time limit on these genetic changes.
Lactase persistence is one of the most profound changes in recent human populations, and was one of the first to be investigated by scientists working with DNA directly from ancient skeletal remains, first by Joachim Burger of Johannes Gutenberg University in Germany and colleagues, and later by many others. Before 7,000 years ago, the ancient peoples of Europe lived only by hunting, fishing, and gathering they did not farm or keep domesticated animals. Gene sequences from the remains of these people have never produced any evidence of lactase persistence. Only well after people began to keep cattle—as evidenced by milk residues found in pottery from early farming and herding contexts in Europe and west Asia—did mutations promoting lactase persistence arise. (See “What’s Old Is New Again,” The Scientist, June 2015.)
Once it appeared within these ancient populations, the numbers of people with lactase persistence grew by up to 10 percent per generation. Its advantage was enormous, perhaps the strongest known for any recent human trait. This kind of evolutionary advantage likely resulted from increases in fertility. Women on calorie-restricted diets have lower fertility, and they take longer after the birth of a child to conceive again. If lactase-persistent women could use the extra energy from milk to begin their reproductive lives a couple of years earlier, or could space their children a few months closer together, it would create a huge reproductive advantage.
Indeed, the frequency of lactase persistence has continued to climb substantially in some places even within the past 2,000 years. Just this spring, Stanford University’s Yair Field and colleagues reported on a new study that sampled more than 3,000 human genomes from the United Kingdom to look at the effects of selection on genes. They found that lactase persistence is the largest single change within the British population since Roman times, increasing in frequency more than any other allele across the genome. 5
Not so simple
The lactase example connects human populations and their cultural innovations. But in one important respect it is misleading: it is much too easy to understand. Unlike lactase persistence, most human traits are not the product of a single gene. Rather, they are influenced by many genes, and studying selection on such traits has proven very difficult.
Skin color is a classic example. One of the largest and most obvious physiological differences between populations, skin color is influenced by more than two dozen genes in a pathway that produces the pigment melanin and regulates the amount of this pigment in different tissues. Changes to these genes interrupt the generation of the dark pigment eumelanin, leaving skin with larger amounts of the reddish pigment pheomelanin, leading to various skin tones and patterns of coloration, such as freckles. Despite its complex genetics, skin color shows consistent patterns of evolution across the globe. People whose ancestors lived in the tropics tend to be dark-skinned, while those who lived further north and south tend to be lighter. One of the revelations of the last 15 years is just how recent this pattern really is. According to analyses of ancient DNA, people who lived in northern Europe only 10,000 years ago would not have had the extremely light skin of today’s people in that region.
Other types of human coloration are also evolving. In their recent study, Field and colleagues found several genes related to hair and eye pigmentation that had markedly increased in the ancestors of modern Brits. These traits include one associated with blue eyes and two that are found in people with blond hair. Britain has experienced extensive immigration since Roman times, including the arrivals of Vikings, Anglo-Saxons, and Normans, but the genetic changes seen in this population are not due merely to migration they mark the increase of particular genes above and beyond the contributions of immigrants. The British have become blonder over recent millennia.
Stature is another complex trait that has continued to evolve in recent years. Northern Europeans are a bit taller than southern Europeans, and looking at the genes that differ between them, Field and his colleagues found that the height differences were driven by natural selection for taller stature in the north over the last 2,000 years. This trend is not seen worldwide, however. The Framingham population and other studies in the U.S. have found that shorter women have had a reproductive advantage during the last few decades. On the other hand, a study from one sub-Saharan African nation, Gambia, showed a pattern more in line with the changes seen in Britain’s population: taller women had more children. 6 For men the story is even more mixed. Dutch and Polish men have been under weak selection for taller height over the last several decades, but in other countries a man’s stature seems to make no difference to his lifetime reproduction. 7
Humans across the globe have been living under very different selective pressures since our sub-Saharan roots, and the cultural differences that have emerged appear to have accelerated some kinds of evolutionary changes.
The skeletons of ancient people likewise show physical changes over the past several thousand years. Heads changed shape, becoming broader and a bit smaller over time in many parts of the world. We do not yet know which genes might be connected to such changes, just as we do not know many of the genes that might drive earlier reproduction. As we learn more about the genetics of human biology, studying the pattern of natural selection in genes may help us to uncover the biology of such traits.
Only a few of the recent evolutionary changes are obvious to us. Most are well-hidden, driven by genetic pathways we are still discovering. The record of ancient DNA from Europe is at the moment far more detailed than elsewhere in the world, but this is changing rapidly as ancient DNA samples from the Americas, Ethiopia, India, China, and other areas are coming online. We are already learning about the ancestry of these peoples from single genomes. Soon we will be able to look at past gene frequencies to map the history of adaptations that shaped their recent evolutionary history.
Evolving into the future
If there is one common theme in all this recent selection, it is that much of the human diversity we see around us today arose very recently. More than 90 percent of the heritage of every living human comes from sub-Saharan Africa sometime around 100,000 years ago. Fifteen years ago, many geneticists saw this recent common ancestry as evidence that human evolution had mostly drawn to a close. After diverging from our common chimpanzee and bonobo ancestors some 7 million years ago, hominins underwent massive changes in body size, diet, behavior, and brain size. Huge evolutionary innovations marked the beginning of upright walking, tool use, culture, and language. And those changes all happened before 100,000 years ago. (See “Uniquely Human” here.)
With such a dramatic picture from the fossil record, it is understandable that many scientists assumed that the final phases of human prehistory were fairly boring, at least from the Darwinian point of view. Across most of the genome, humans everywhere in the world are very similar to one another, much more so than to chimpanzees or most other kinds of primates. Modern humans vary profoundly in cultures and languages, but those differences are mostly learned, not coded in our genes.
Nevertheless, humans across the globe have been living under very different selective pressures since our sub-Saharan roots. And, in fact, the cultural differences that have emerged appear to have accelerated some kinds of evolutionary changes. The domestication of animals led to the invention of dairying, for example, a new dietary niche in which lactase persistence provided a huge advantage. Clearing tropical lands for planting domesticated crops and keeping water in pots changed human ecology in more-disturbing ways, making new habitats for mosquito species that afflict human populations with yellow fever and malaria and spurring protective changes in red blood cell morphology. Moving into new ecosystems also demanded new adaptations from the growing human population, from lighter pigmentation at high latitudes to maintain vitamin D production to improved oxygen metabolism in peoples living at high altitude.
Natural selection is fickle. Behavior that ensured survival in our ancestors’ environment may not be as advantageous under modern conditions. (See “Our Inner Caveman” here.) New evidence of how the human genome has changed over the last several thousand years points to a series of massive critical evolutionary changes, setting some aspects of our biology clearly apart from that of our forebears. And we are no doubt continuing to evolve today.
John Hawks is a paleoanthropologist and professor at the University of Wisconsin–Madison.
Why human evolution pretty much stopped about 10,000 years ago
His argument is that human evolution, at least in the western societies, has stopped or slowed down because very few older men in such societies reproduce. Sperm of older men carry many more mutations than those of younger men. Mutations provide the source of genetic variations on which natural selection works. Hence, no older fathers, no genetic mutations, no evolution.
Jones may be right however, I think he is underestimating how long ago human evolution stopped. I think it stopped roughly 10,000 years ago, with the advent of agriculture.
Evolution takes many generations, and so the speed of evolution of a species is relative to how long it takes for individuals of the species to mature sexually and start reproducing (holding constant, for the moment, the other important determinant of the speed of evolution, the strength of selection pressure). Evolution happens faster for fast-maturing species and slower for slow-maturing species. Fruit flies are one of the fastest-maturing species in nature, and humans are one of the slowest. It takes only seven days for fruit flies to mature sexually under ideal conditions, whereas it takes 15 to 20 years for humans. It means that there can be more than 50 generations of fruit flies in one year, before a human baby can even begin to walk. There are more than a thousand generations of fruit flies in one human generation (20 years), for which human need more than 20,000 years. Evolution for fruit flies can happen pretty fast, which is precisely the reason why they are the favorite species for geneticists to study. Human evolution happens much, much more slowly. No human scientists can see it in action the way they can observe fruit fly evolution unfold in the lab.
Natural selection under most circumstances requires a stable, unchanging environment for many, many generations (once again, unless the selection pressure is enormously strong). For example, if the climate is very cold for centuries and millennia, then gradually individuals who have better resistance to cold will be favored by natural selection, and their neighbors who have less resistance to cold (who are more adapted to a hot climate) will die out before they can leave many children. This will happen generation after generation, until one day all humans have great resistance to cold. A new trait – resistance to cold – has now evolved and become part of universal human nature. But this trait could not have evolved if the climate was cold for one century (only five human generations, albeit 5,200 fruit fly generations) and then hot for another century, only to be cold again in the third century. Natural selection would not know who (with which traits) to select.
Since the advent of agriculture about 10,000 years ago and the birth of human civilization which soon followed, humans have not had a stable environment against which natural selection can operate. For example, a mere two centuries (10 generations) ago, the United States and the rest of the Western world were largely agrarian most people were farmers. In the agrarian society, men achieved higher status by being the best farmers those who possessed certain traits that made them good farmers had higher status and thus greater reproductive success than others who didn’t possess such traits.
Then, only a century later, the United States and Europe were predominantly industrial societies most men made their living working for factories. Traits that make men good factory workers (or, better yet, factory owners) may or may not be the same as the traits that make them good farmers. Certain traits – such as intelligence, diligence, and sociability – probably remained important, but others – such as a feel for nature, the soil, and animals, and the ability to work outdoors or forecast weather – ceased to be important, and other traits – such as punctuality, the ability to follow instructions, a feel for machinery or mechanical aptitudes, and the ability to work indoors – suddenly became important.
Now, only one century later, we are in a post-industrial society, where most people work neither as farmers nor factory workers but in the service industry. Computers and other electronic devices become important, and an entirely new set of traits is necessary to be successful. Bill Gates and Sir Richard Branson (and other successful men of today) may not have made particularly successful farmers or factory workers. All of these dramatic changes happened within 10 generations, and there is no telling what the next century will bring and what traits will be necessary to be successful in the 21st century. We live in an unstable, ever-changing environment, and have done so for about 10,000 years.
For hundreds of thousands of years before that, our ancestors lived as hunter-gatherers on the African savanna and elsewhere, in a stable, unchanging environment to which natural selection could respond. That is why all humans today have traits that would have made them good hunter-gatherers in Africa – men’s greater spatiovisual skills, which allowed them to follow animals on a hunting trip for days and for miles without a map or a global positioning device and return home safely and women’s greater object location memory, which allowed them to remember where fruit trees and bushes were and return there every season to harvest, once again without maps or permanent landmarks.
For the last 10,000 years or so, however, our environment has been changing too rapidly for evolution to catch up. Evolution cannot work against moving targets. That’s why humans have not evolved in any predictable direction since about 10,000 years ago.
I hasten to add that certain features of our environment have remained the same – we have always had to get along with other humans, and we have always had to find and keep our mates – so certain traits, like sociability or physical attractiveness, have always been favored by natural and sexual selection. But other features of our environment have changed too rapidly relative to our generation time, in a relatively random fashion – who could have predicted computers and the internet a century ago? – so we have not been able to adapt and evolve against the constantly moving target of the environment.
Can evolution keep pace with climate change?
Rapid evolution has also been recorded in some plants and fish.
Researchers at the University of New South Wales have documented significant morphological modifications in the DNA of South African beach daisies, introduced into Australia in the 1930s.
Supplied: Claire Brandenburger
And Australian scientists studying marine species in both the Antarctic waters of the Southern Ocean and the much warmer coastal environments off South Africa have found increased speciation — the divergence of separate species — caused the isolating effects of variant water temperatures.
Researcher Claire Brandenburger says such revelations help us better understand the evolutionary process.
"What we are learning is that such rapid evolution is much more common than we previously thought," she says.
"More and more evidence is showing that rapid evolution can occur in as little as 10 to 100 years.
"Hopefully this is a little ray of good hope for plants in the face of climate change.
"For plant species that don't move or are only dispersed by their seeds, people are worried that climate change is really going to hit plants hard. And this study gives us hope that perhaps there are some plants that can be able to adapt very quickly."
Luciano Beheregaray, a professor of biodiversity genetics at Flinders University, is less optimistic.
"Climate change is happening very fast in the world's oceans," he says.
"In fact, coastal marine species are shifting their distribution because along many regions the temperature of water is increasing much more rapidly than the average temperature on land.
"Some species might be able to [adapt], but the evidence at the moment suggests that the change in temperature driven by human influences is happening too fast."
His concern is shared by Tim O'Hara, the senior curator of marine invertebrates at Museums Victoria.
"Climate change won't extinguish life, by any means, there will be things that can adapt," he says.
"But to recover that enormous biodiversity that exists on the planet now will take tens of millions of years.
"Antarctica is still responding to an extinction event tens of millions of years later. So, there's really a serious conservation message in this."
Is the human race evolving or devolving?
A similar question was previously answered by Meredith F. Small, associate professor in the anthropology department at Cornell University.
This time we asked Michael J. Dougherty, assistant director and senior staff biologist at Biological Sciences Curriculum Study in Colorado Springs, Colo., to offer his opinion.
From a biological perspective, there is no such thing as devolution. All changes in the gene frequencies of populations--and quite often in the traits those genes influence--are by definition evolutionary changes. The notion that humans might regress or "devolve" presumes that there is a preferred hierarchy of structure and function--say, that legs with feet are better than legs with hooves or that breathing with lungs is better than breathing with gills. But for the organisms possessing those structures, each is a useful adaptation.
Nonetheless, many people evaluate nonhuman organisms according to human anatomy and physiology and mistakenly conclude that humans are the ultimate product, even goal, of evolution. That attitude probably stems from the tendency of humans to think anthropocentrically, but the scholarship of natural theology, which was prominent in 18th-and 19th-century England, codified it even before Lamarck defined biology in the modern sense. Unfortunately, anthropocentric thinking is at the root of many common misconceptions in biology.
Chief among these misconceptions is that species evolve or change because they need to change to adapt to shifting environmental demands biologists refer to this fallacy as teleology. In fact, more than 99 percent of all species that ever lived are extinct, so clearly there is no requirement that species always adapt successfully. As the fossil record demonstrates, extinction is a perfectly natural--and indeed quite common--response to changing environmental conditions. When species do evolve, it is not out of need but rather because their populations contain organisms with variants of traits that offer a reproductive advantage in a changing environment.
Another misconception is that increasing complexity is the necessary outcome of evolution. In fact, decreasing complexity is common in the record of evolution. For example, the lower jaw in vertebrates shows decreasing complexity, as measured by the numbers of bones, from fish to reptiles to mammals. (Evolution adapted the extra jaw bones into ear bones.) Likewise, ancestral horses had several toes on each foot modern horses have a single toe with a hoof.
Has human evolution by natural selection stopped?
Our species' use of increasingly complex tools to shape our environment has changed the selection pressures that created us. Is it reasonable to think that the human body has evolved as far as it can by natural means?
Forgive me if this belongs on r/SpeculativeEvolution. A brief search over there didn't reveal much.
No, and this question gets asked a lot. The basis of the belief that evolution has stopped frequently include: an incorrect view of evolution as being progressive, a lack of awareness of genetic drift, not realizing that large effective population size increases the efficiency of selection, not realizing that migration/gene flow is a mechanism of evolution, not realizing that survival is not the only component of fitness, and not realizing that studies have detected selection in modern human populations.
Here are three studies detecting selection in modern human populations.
Thank you for the thoughtful reply. I was mistakenly thinking too narrowly of outwardly viable characteristics or physical mutations that don't really bestow a survival benefit. I.e. A mutation that gives sharper vision may have been advantageous 3000 years ago when we were hunting or being hunted. Now we go to the store or call the cops, respectively. Thanks for expanding my vision a bit.
No, selection is still acting on humans. For one thing, most of the world's population does not have access to all the medicine and technology that you are implicitly referring to. Also consider that medicine may allow people to live and procreate now that couldn't have done so without medicine, and that of course affects evolution as well.
I appreciate the links. Good food for thought.
Every week, this same question is asked on this sub. Can we put it in the FAQ or something?
Nobody would want to fuck a dude with bad genes, so it still continues to this day.
No. Natural selection will never end on any entity (human animal, animal, social structure, or idea) that reproduces itself, in partial, or in complete.
The selection pressures may change (from, in our human example, the ones that dominated ancient times: large carnivorous predators, diseases and parasites, environmental exposure, environmental inhospitablity leading to starvation, to the ones that dominate modern times in the developed world (although things like disease and starvation still strong affect the developing world): partner sexual selection, some more rare childhood diseases and conditions, human-generated economic competition, etc.), and they may be labeled as different things or as coming from different sources, but they still are selection pressures and they still exist.
Is it reasonable to think that the human body has evolved as far as it can by natural means?
I'm sorry, I'm going to go on a mini rant here.
The word "natural" means almost nothing in biology. Biologists don't use it to refer to any specific thing the way you're probably thing of. It has no widely-agreed upon, well-defined and purposefully-defined definition.
It is very common for people to use the word "natural" when what they really are trying to describe, sometimes without realizing it, is "man-made (technology)" vs. "non-man-made (spontaneous organic occurrence)". However, this is muddied by the fact that sometimes people further mean to describe not just the man-made/non-man-made split, but also "traditional" vs. "contemporary". Like for example, they wouldn't consider a hand axe made from a single stone or a woven basket "non-natural".
Which gets to the real heart of the issue. People often (mis)use the word "natural" when they want to refer to a technology that is sufficiently simple, old, tested, or familiar to them enough for them to understand it (and, from understanding it, accept it into their daily lives).
What you mean to say is not "by natural means". What you mean to say is something like:
"by non-'genetic engineering and cybernetic' means" (the assumed next technological developments in the area of discussion)
Another way of saying what you may be wanting to really get at is the question: "Have selection pressures changed from non-human, environmental ones to human-driven, social ones"?
To which I would say, yes. (Again, in the developed world)
And as to whether the human body has evolved "as far as it can", that's also kind of an ambiguous statement. The human body hasn't stopped changing. For example, one of the fastest (on an evolutionary time scale) ongoing changing parts of our body at an anatomical scale is the little toe, which is disappearing (shrinking). Is that the most significant change (probably what your question was probing at), though? Perhaps not.
Be wary here of assuming that evolution is uni-directional (all beings evolve over time from simple body plans to complex body plans), or one-dimensional (all evolution is towards one goal, instead of being influenced by multi-dimensional, often antagonistic evolutionary pressures).
"Evolution Gone Wrong" author: "I just didn't realize how many things humans are up against"
By Mary Elizabeth Williams
Published May 30, 2021 8:00AM (EDT)
Evolution Gone Wrong by Alexander Bezzerides (Photo illustration by Salon/Hanover Square Press/Kevin Grote)
Okay, humans, if we're so smart, why do our backs hurt so much? Why do we cry? And menstruation, who thought that was a good idea?
Our existence on this planet is the product of chance, timing and a whole lot of evolutionary compromise. Our ability to speak and walk upright and gestate babies with big brains has meant sacrifice and discomfort, and this human condition we've created for ourselves is eternally humbling and idiosyncratic.
Alex Bezzerides knows it well. The Lewis-Clark State College biology professor is fascinated with the imperfect system that is the human body, and he explores and explains it adroitly in his fascinating, funny new book, "Evolution Gone Wrong: The curious Reasons Why Our Bodies Work (Or Don't)." Salon spoke to the author recently about why we are the way we are, and the fallibility of the epiglottis.
I want to begin at the end of the book, because to me there is absolutely nothing stupider or more counterintuitive in the universe than our entire reproductive system. Menstruation, pregnancy, childbirth — they're all ridiculous. Talk to me about this, Alex. Why do we have periods?
That was the hardest chapter for me to write because I went into it really not knowing the answer. That was unique, because most of the other chapters, I at least had an idea of what I was going to write about.
I started reading about the origins and evolution of menstruation, and it got complicated really quickly. I picked up this term, spontaneous decidualization, and I thought, "Oh, my gosh. How am I going to figure out how to translate this to the reader?"
What I came to learn is that the process evolved in a way as a defense for women against these really hyper-aggressive, invasive fetuses humans are. We think that human fetuses are that way because they have to feed this giant, growing, nourishing brain. The only way to do that is to burrow deep inside the woman. The degree of placentation in a human is much, much higher than it is in other mammals.
One idea for why menstruation evolved is that the woman had to start building up her uterine lining and building up this defense even before pregnancy. A big difference in mammals that experience menstruation is they start changing their lining before pregnancy, rather than in response to pregnancy. Then once that uterine lining has changed, if pregnancy doesn't happen, it has to be sloughed. That's one of the big ideas about why it evolved, is that it had to be there as a way to defend the mother against this burrowing human fetus. Kind of a crazy idea.
Just the volume of blood loss is astonishing. Every single month, the amount of blood loss that a woman goes through, it's just an incredible figure. Every little time I get a teeny little cut and I lose a couple milliliters of blood, I think, "A woman can lose 30, 40, 50 milliliters. Some women, a 100 milliliters a month." It's just mind-boggling. You get to the end of this thing, and it's just like, "My God. Why does anybody have kids? How does anybody have kids?" After seeing the whole thing, you feel like there should be like 40 people on earth rather than 7 billion. Like, no way. But it's happened 7 billion times. That's of course for the people that are currently alive. It just doesn't seem possible.
You make a very interesting case that that our big brains are not necessarily the sole metric of our intelligence. From an evolutionary perspective, maybe this isn't the end game, that the smarter we get, the bigger our brains are going to get, the bigger our heads are going to get, and then no one gets born anymore. Talk to me about what evolution might look like.
I think the other piece of the puzzle that has to be talked about any time you talk about the human body and the direction it's gone is the bipedalism aspect. I think that when humans went up on two feet, and it obviously took millions of years for that transition to really fully occur, it just changed so many things about the shape and nature of the body.
One of the things for women is the change of the nature of the birth canal. One of my favorite scientists, that I lean on a lot in the book, is Dartmouth Professor Jeremy DeSilva. He is the foot, and skeletal, and paleoanthropology guy. He and this group found that, even before the brain swelled up to its current huge, ridiculous size, birth was a tight process for hominins and for early ancestors as soon as they basically went bipedal.
That right there set us on this path that made birth difficult. Then, getting into the skeletal chapters, that made our life difficult for our ankles, our feet, our arches, our knees, all these different things. Obviously there are wonderful things that come out of it. There's a whole other book to be written about how amazing evolution has been for us, and our incredible hands and our incredible minds. I thought it was more interesting to write the the darker side of the coin, about all the ways that it's also been difficult.
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This gets back to the overarching story of this book, the trade-offs of evolution.
I thought of the word "trade-offs" throughout the entire book. Like in the throat chapter when I talk about choking and snoring, all these things are trade-offs.
One of my favorite examples of that is where we have this incredible human feature of being able to form words, and speak, and change our vocal production in ways that other animals can't do. But the trade-off of that is that the larynx had to get lower down deep into the throat, and you lost this fail-safe that kept us from being susceptible to choking.
I think about that all the time. Just last night I took a little drink, and my epiglottis didn't quite do its job. I splashed a little water down into my trachea. You kind of sputter for a second. That happens all the time. It's just this great evidence of an evolutionary trade-off in humans. But then the benefit is that I get to talk to you, which is something other animals don't get to do.
We get to talk to each other, but then we also had to cut up our kids' grapes for a really long time.
And my wife has to elbow me to stop me from snoring.
And the reason that we get back pain or the reason that our shoes don't fit is because we learned to walk upright. Walking upright makes you really tired.
It's exhausting. I think about it when I get up in the morning now and I have a little back pain. I just curse the whole curve of my spine, and all the things that are necessary for me to work my way around upright.
Thing that I really enjoyed about this book is that I kept the topics universal and broad enough that you can't talk to anybody that didn't have a tough birth experience, or didn't have back pain, or didn't have three wisdom teeth pulled and one of them was kind of a mess, or something. I find that it relates to everybody, and that's been a really fun.
I had adult orthodontia, but I never made that connection of, "Why don't my stupid teeth fit in my stupid mouth?" Some of these evolutionary problems are also because we're living longer. We've not yet built our bodies to endure for as long as they do, so our backs give out, and our ACLs tear, and our eyesight starts to go.
There are definitely some features in the book that are exacerbated by age. There's no question about that. I tried to focus on things that can fall apart at any point. I think teeth not fitting and eyesight going bad, those are things that can certainly happen at a young age, but it's not helped by the fact that we're all living to be 70, 80, 90, 100, whatever.
I love the part of the book about blinking, and why we blink as opposed to licking our eyeballs, which would be disgusting. When we talk about crying, why do we cry when we're sad, or we're happy, or we're overwhelmed?
There's this connection between our brain and our anatomy that we're just beginning to understand. One of them is this endocrine hormonal balance with things like crying. We have a great understanding of what tears are there for — to keep our eyes moist, and it's necessary. But then these things happen that are tied to our emotions that I don't think we do have as good an understanding of.
The short answer is that those emotional tears have hormones in them (unlike the other types of tears) and one working hypothesis is that those hormones (like prolactin and oxytocin) help to soothe the body. More research is clearly still needed. I like to imagine a whole room of people sitting around watching "The Notebook" as researchers take measurements of all their baseline physiology. I cry at the drop of a hat (for example I cried during an episode of "Kim's Convenience" the other day), so I'll be keeping a wet eye out for any future crying research.
What were the things in the book that surprised you the most or made you take a step back?
The reproductive section, for me. There were a lot of things that caught me off guard with the fertility chapter. I just didn't realize how many things humans are up against when it comes to fertility. People mostly think about fertility issues as a modern problem. Everybody's waiting longer to have kids, and there are all these modern dilemmas related to fertility, and pollution, and incorporation of things in your body that weren't there generations ago.
When I started reading about fertility, you realize that fertility issues have been a thing for as long as people have been around and as people have written about it. There's this whole historical evolutionary perspective of it. A big part of it is the historical mating systems that humans had and the sperm competition that was set up, and how males had to produce overwhelming amounts of sperm in order to compete with other males.
But then females couldn't have an egg fertilized by multiple sperm, so their bodies evolved these defenses to prevent polyspermy, where two sneak in and fertilize an egg. You end up with this reproductive back and forth, just to get over this hurdle of creating a new life. That was something that I didn't really know anything about going into it, the whole evolutionary historical perspective of fertility difficulties. That was really eye-opening.
I remember being at a zoo one time, watching some ungulate when she was giving birth. I didn't grow up on a farm or anything, so I hadn't seen cows being born, or a horse being born, or anything. That was the first time I watched a big mammal being born.
She just gave birth, licked the thing, and then it hopped up shortly thereafter and wobbled around. I was like, "Seriously? That's it? That's ridiculous compared to what we do." It's like days in the hospital and weeks in bed, and then you have to hold a little horrible thing for like a year before it can even do anything. What? [laughs]
You can't leave it around grapes. It's ridiculous.
We have evolved so that other people have to be involved in that process, and we can't do it alone. This feels really important for us to remember as a species, that we are designed to bring children into the world together. Because it's a messy, incredibly painful, incredibly dangerous process.
It is. I don't think people realize just how many women died in the process and still die in the process. Before the advent of antibiotics, it was an incredible number of women that died during childbirth. In parts of the world where they don't have access to antibiotics, because of the incredible trauma, infections are still a huge problem. Many, many women do still die in childbirth.
It's a neat feature of human society and human cultural development, that birth has become such a group and a family process. It almost has to extend beyond birth, too, as an important thing about why human infants are born so helpless, because it's another unique thing about human birth.
This whole idea that Holly Dunsworth has written a lot about, it's because the classic explanation is that they have to come out early or then there's compromise between women's mobility and the shape of their hips, and the size of the baby. The Obstetrical Dilemma just really took off. There's not much evidence for it, and she's come up with this new idea that there is a lot of evidence for, that it's all driven by metabolism. In fact, the baby gets to the point inside the mother where she can no longer nurture its metabolic needs as it grows, and its brain gets so big, the only way to continue to nurture it is outside the mother, and then it's born totally helpless. Not only do you have this birth process where the mother needs a lot of help just to get through the birth, but then, even after that, a lot of help is still needed because there's this super, super altricial infant on her hands that you need a lot of help to be taking care of.
Was there something in the book that really made you marvel? Every part of being human and walking around in these imperfect, breakable systems is kind of remarkable, but was there something in particular that really just takes your breath away?
I think the brain is, in a sense, there, but I'm going to go a different direction. Toward the end of the book, I started reading about the human hand a lot. Obviously I knew primates have different hands, and opposable thumbs were a different thing. But I didn't appreciate how different the human hand was from other primate hands, and what that allows us to do.
I think about that all the time now when I see somebody playing a musical instrument, or doing some incredibly little dexterous craft that no other animal on earth could do. I've started to think of the human hand as as integral to humanness as the brain.
It's also really interesting to me that it came around first. That once we became bipedal our hands freed up, and we went down this path that has allowed us to just create a whole world with our hands. That all happened before our brains kind of exploded. It's a necessary step that the brain took off afterwards, and the way to really effectively use that hand.
Mary Elizabeth Williams
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Has human evolution stopped?
Thinking about current events, I often wonder: Is it possible that our species has entered a stage of devolution, or at least that we stopped evolving thousands of years ago?
I know it’s easy to see humanity in an unflattering light these days, now that the most pea-brained amongst us can impulsively jab dim musings into their phones to share with all the virtual world. But you’re hardly the first to suspect that our species is slaloming downhill into a genetic sewage tank. Barely had the scientific community accepted evolution in the first place when some of its leading lights started worrying that natural selection might cease to affect humans, or even throw us into reverse gear. Their concern, though, was needless — just like yours is.
Let’s back up to review Darwinian theory at its most basic. If you, an organism, are the lucky possessor of some inheritable trait that boosts your relative chances of thriving in the environment you occupy, that trait will tend to be passed along to your fortunate offspring, and to theirs and to theirs. But, the Lees of the world have long worried, what if humans have made our environment so uniquely cozy for ourselves that basically everyone thrives? What if, thanks to advanced medicine and other forms of coddling, all the negative traits that once led to genetic dead ends no longer lower our likelihood of surviving and spawning? Surely that points to a future of sluggish dullards communicating solely in emoji, right?
Hardly. Natural selection is still affecting human development — very slowly. We mammals take our own sweet time evolving compared to fish or lizards, and humans average a leisurely 20 years between generations, Still, even within recent history (evolutionarily speaking), our genes have adapted to our changing circumstances, particularly to the advent of agriculture and animal husbandry, not to mention the discovery of fire. In the past ten millennia, our skulls have rounded, our facial features have thinned, and our jaws, adjusting to the softer food we eat, have shrunk. There have been downsides — the changes in our jaw and larynx structure beginning 300,000 years ago may have led to sleep apnea. But if you can drink a milkshake without doubling over in gut pain, thank natural selection — lactose tolerance is a late addition to humanity’s bag of digestive tricks.
Our brains, it seems, continue to evolve: key variants of two genes that influence brain size, MCPH1 and ASPM, showed up in our pool only about 37,000 and 5,800 years ago respectively, and they continue to spread through humanity. And though “Should I eat this berry?” is hardly the life-or-death question it used to be, other environmental factors remain in play, particularly among specific populations: Tibetans’ lungs and blood have adapted to the low-oxygen atmosphere of the Himalayas, while a genetic resistance to malaria may be developing in sub-Saharan Africa.
In fact, more than two dozen human genes — including ones linked to speech, cognition, and defense against disease<>have been identified as still evolving today. Humans may already be developing resistance to HIV and other viruses. And women may be evolving more significantly than men. Working from almost 60 years of data from a major multigenerational study of cardiovascular disease, the authors of a 2009 paper project that the next generation of women in the study population will be slightly shorter and stouter on average than the preceding cohort, with lower cholesterol levels and systolic blood pressure, and an increased period of fertility — starting about a half a month earlier and ending a month later. Not as flashy as growing wings or tusks, certainly, but remarkable nonetheless.
Our environment hasn’t stopped changing either — much of this our own doing, of course — and it’s sure to pitch us a curveball or two in the coming millennia. Beyond whatever we’ll have to adapt to on a hotter earth, attempts to survive in space or colonize another planet could amp up the evolutionary process. Travelers on space flights are exposed to heightened levels of chromosome-damaging radiation, and without some serious shielding future dwellers on the lunar or Martian surface would receive doses dozens of times greater than the terrestrial going rate. Off-earth life could gradually transform our bodies in other ways too. Despite regular workouts while aloft, astronauts returning from the International Space Station have shown significant bone loss in their femurs it may be that long-term existence in zero gravity would cause our legs to dwindle.
Evolution isn’t the only force at work on how humans develop, though. We’re not just a species that reshapes its environment — through medical science, we’ve also become a species that controls how it adapts to that environment. If we haven’t quite conquered death, we’ve lowered infant mortality rates drastically and continue to extend age expectancy. And every year researchers redraw the frontiers of prosthetic and implant technology: the average healthy denizen of 2316 could well be tricked out with so many nifty cyborg accessories that our current conception of the human body may no longer apply. But I’m confident that doomsayers will still find cause to complain that this new generation of post-humans is the dumbest bunch yet.