Are humans still evolving?

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Perplexing, isn’t it? Homo sapiens, as a species, have made it. There are now over 7 billion of us swarming across the planet, going about our daily business and often forgetting our humble origins. Indeed, often forgetting that we are a bunch of bald apes with enormous heads, doing weird things like watching football matches and hoovering and writing blogs. If evolution is all about survival of the fittest, where those organisms with the greatest reproductive success increase their gene frequencies and are ‘evolutionarily successful’ then why aren’t we all focussing on just having sex? Let’s face it; something incredibly weird has happened to human evolution.

Only 0.1% of the human genome exhibits variation, in other words we are 99.9% genetically identical. Compare any two humans, ANY two humans, and they are vastly more similar genetically than, say, a Western and Central African Chimpanzee. Despite this, ever mounting datasets from projects such as the 1000 genomes project and the HapMap project allow scientists to unpick signatures in our genetic ancestry, and identify startlingly recent instances of human evolution.

Between 8,500 and 2,500 years ago, humans started behaving differently. Many were abandoning their hunter-gatherer way of life for a more sedentary one in which they had fixed homes and farmed the land. This period is known as the Neolithic revolution. Changes in culture during the Neolithic revolution hugely altered the selective pressures which would guide the natural selection of human individuals.

Many adaptive genes increased in frequency during the Neolithic revolution, due to the drastic changes in diet. AMY1 gene, for example, currently exists in the human genome at between 2 and 15 copies, depending on the individual. AMY1 is a gene which codes for amylase, an enzyme that breaks down starchy food like bread into glucose, which can then be used to fuel respiration. So if you have a higher copy number of AMY1 in your genome, you can break down proportionately more starch. Interestingly, individuals with a higher copy number AMY1 are associated with regions where starchy food was (and still is) a key staple of the diet. So in Japan, Europe and the USA, where starch has historically been essential to the diet, AMY1 levels are higher, whereas the Mbuti and Biaka people of Africa (who live primarily by hunting and gathering) have comparatively lower AMY1 copy number.

As society has progressed and western culture has emerged, diet has not only changed but also our living standards. It is safe to say that in western culture many people are obsessed with cleanliness and as such alienate themselves from parasites and bacteria. For natural selection to be directive, a selective pressure needs to be present so if many humans live in a very hygienic environment, there is little evolutionary incentive for the species to continue to evolve immune defences to parasites and bacteria.

This ‘Hygiene Hypothesis’ goes further and says that intense cleanliness has meant that humans are slowly losing some of their ability to respond to infection. And this sounds feasible, since in this day and age even if you are genetically unhealthy, you have a plethora of antibiotics available, and so may still live to a ripe old age and have babies. Infectious diseases have fallen since the advent of medicine but immune disorders such as Coeliac disease, asthma and Crohn’s disease are on the rise. The Hygiene Hypothesis suggests that as we move beyond how our lives were in the ancestral state, we become increasingly ill-adapted to our environment.

The incredibly debilitating disorder Crohn’s disease, where patients experience life-long abdominal pain, vomiting and diarrhoea, provides a fascinating example of how our pre-historic environment once supplemented disease. In this modern age, those with Crohn’s disease are at the whim of modern medicine. Interestingly, treatment with an age-old parasite, the tapeworm, alleviates many of the symptoms of Crohn’s.

The parasites and bacteria our ancestors faced not only helped them develop, but drove the evolution of human resistance to infectious disease. To some extent, this aspect of evolution may be stalling.

So great! We have definitely evolved in the last 8,500 years. But are we evolving NOW? The inevitable and slightly boring answer is a resounding yes. Evolution is defined as the change in gene variant frequency over time within a population. Given that we all have genes, and some of us are having children, evolution must be occurring. The more interesting question is: in which direction is evolution taking us, if any?

We have established that a selection pressure imposed by the environment drives the direction of natural selection and thus morphs the future population. So, what can we say of our selective pressures?

Well in fact, more than any organism ever on this planet, humans are now creating their own selective pressures.

Here I would like to introduce the concept of the ‘Extended Phenotype’, a beautiful concept developed by Richard Dawkins. A phenotype is an observable trait of an organism. So my red hair, or your height or my brothers blood type, are all phenotypes. The extended phenotype takes a step further. Not only is my red hair a phenotype (incidentally; dyed red hair, but then again did not my genes, development and environment not compel me to decide to dye it red?) but so too is anything that I build or create. Just as much as a bee’s hive, or a beaver’s dam, is an extended phenotype, so too is human society, built by and lived in by humans.

So why am I talking about this? I am trying to point out a fascinating and also incredibly worrying loop in the course of our own evolution. As our extended phenotype becomes ever more convoluted and complex, it extensively defines our environment. So much so that we are in fact now being subject to the selective pressures that we ourselves have created. As more and more human generations are born, the very fabric of our nature weakens. Our biology becomes hyper-dependent on our environment, an environment which we (the products of our biology and environment) have ourselves created.

So what for the future of our species?

One thing is for sure: our species is changing. In particular, as our society becomes ever more complex, it is perhaps also becoming increasingly fragile. As we become adapted to an ever more artificial environment, we can only become more vulnerable – and what will happen when that artificial environment ceases to exist? Only time will tell.

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19 thoughts on “Are humans still evolving?

  1. A very interesting blog.
    I like to take a more optimistic view of our genetic future though:
    As our knowledge of the genome grows, we’ll become more and more able to directly intervene. It’s already happening with gene therapy for cystic fibrosis. Eventually we’ll be able to tease out and model the phenotypic effects and interactions of every single base pair of our genome, and change them routinely.
    At this point we’ll have to decide exactly what we want humanity to be, and then we can allow natural evolution to give way to a sort of intelligent design, with ourselves as the designer.

  2. Hey Tim! Thanks for your comment! I don’t know if you know about ENCODE, but they’ve generated vast amount of data on the human genome. The problem is, the epigenetic state of our genome turns out to be insanely complicated and often has unpredictable effects. I often feel that we really know hardly anything about our genome.. Modelling the effects of altering base pairs on phenotype also could be a long way away, the number of interactions would be unimaginably large (due to epistatic and additive effects etc). So first we need to think about building a computer to hold that kind of data.
    Certainly, we now understand the vast majority of the genetics underpinning Mendelian diseases such as CF, but as far as I am aware we are still a long way away from successful gene therapy and even further away from understanding complex disease such as T2 diabetes.
    As to your last comment, you will recall that evolution isn’t predictive – and even if it was can you really see humans achieving this? There would be no benefit for hundreds of generations (if ever a benefit), and it could mean a return to primitive living..
    Very interesting thought experiments! Definitely room for a more optimistic attitude towards our genome, perhaps I will talk about it in future blogs..

  3. Wow! Charlotte you have really opened my eyes to the human condition from a genetics standpoint. I never thought I’d find something like this interesting! You’ve converted me! I’ll definitely be taking biology A level now!

  4. Hey Clarissa! I discussed human evolution a lot in Cambridge with the very brilliant zoologist Dr Matthew Wilkinson and my uni peers. Also I’ve learned a lot about it from my undergraduate lectures and reading papers and books like Richard Dawkin’s ‘The Extended Phenotype’. Basically from being a massive nerd and thinking about evolution a lot!

    Charlotte

  5. Every time I hear “man,” or “human” made enviroments such as “man made lakes, or that humans are causing global warming to incresse faster or something like I think, well man IS nature. We as humas aren’t above any other factor that changes the earth and the world we a live. People will argue or give the excuse that humas can think and therefore “know better” as to not to harm or change the environment. I argue that. Even though we know certin things we do can or will harm the enviroment we do them anyway. It is in our genes. Of course there are some that believe if they act or do differently they can make a change or preserve things that it will prevent harm to the earth, but the percentage of humas that actually do that is a pitance compared tho the population of the world. So “man made”. No such thing! If a giant meteriote colided with earth today like they have in the past, the earth and everything natural or “man made” will vaporize and disapate. The earth would be a molten ball. When the earth cooled down and recovered everything would start over. In 3 billion years and if the sun has not died, and humans evolved again there would be no evidence that there was any living, or man made thing before the melt down on earth that the earlest fosils they found would indicate.

  6. Every time I hear “man,” or “human” made environments such as buildings, cities, factories, “man made” lakes etc, or that humans are causing global warming to increase faster, or humans are destroying the environment, I think, well, man IS nature! We came from the earth the same as any entity on it. We as humans aren’t above any other factor that changes the earth, environment, and the world we a live. People will argue or give the excuse that humans can think and therefore “know better” as to not to harm or change the environment. I argue that. Even though we know certain things we do can, or will harm the environment, we do them anyway. It is in our genes. Of course there are some that believe if they act or do differently they can make a change or preserve things that it will prevent harm to the earth, but the percentage of humans that actually do that is a pittance compared the population of the world. So “man made”. No such thing! If a giant meteorite collided with earth today like they have in the past, the earth and everything natural or “man made” will vaporize and disappear. The earth would be a molten ball. When the earth cooled down and recovered everything would start over. In 3 billion years and if the sun has not died, and humans evolved again there would be no evidence that there was any living, or man made thing before the melt down on earth that the earliest fossils they might find would indicate.

  7. Yes I agree that man is part of nature, and by extension, you could define our actions and creations as natural. However, how useful is this argument? We need a way of referring to the pollutants that humans produce, as these pollutants are incredibly different to the ones other animals can make. We are able to pull enormous amounts of carbon out of the Earth and pump it into the sky, to make incredibly stable polymers, to slaughter entire species.

    As to your argument that this destructive behaviour is ‘in our genes’, I’m afraid as a geneticist I entirely disagree. Genes codes for RNA codes for proteins. Genes do not code for things like environmental disregard. We are fortunate to have evolved into existence with a large, complex and plastic brain. We are able to learn. We can either use our brains to stop wreaking havoc on our planet, or we can ignore the whole situation and let millions of eco-systems slip away.

    To me, the argument you postulate provides an easy way for people to ‘get out of’ caring about their actions, it is a dangerous argument in the hands of people who don’t understand genetics are a looking for an excuse to make their actions justified.

    As to your meteorite argument, I am not sure how big an asteroid would need to be to turn our planet into a fireball. But if this did happen, most geologists agree that complex life could not evolve again. Our sun is too old.

    Thanks for your post – really thought provoking.
    Charlotte

  8. You certainly gave me a new way to view evolution. I thank you for that.

    What drew me here was thinking about why we don’t see more change in the existing human population.

    If you consider for a moment that we are approximately 7 Billion strong, and that over evolutionary time we were probably numbering in the low tens of thousands to hundreds of thousands; a few things come to mind immediately. One, in any given generation, you would expect a certain fraction “X” to have genetic variations, and a certain subset “Y” to have viable variations that would yield an advantage.

    Therefore, we should be seeing massive genetic variation at mankind’s current population size. Anywhere from 10,000 to 700,000 times the X and Y values for genetic variation seen over previous evolutionary time when our population numbers were much lower. The only assumption, and a quite reasonable one, is that the rate of genetic variation, i.e., mistakes, has not changed over time.

    I’ve never seen anyone address this problem. Have you? If so, send me a reference.

    It’s a problem because it makes me doubt evolution. I don’t believe in religion either, however, I would like to see a more rational explanation for evolution. The lack of massive current genetic variation in present day mankind is distressing – if evolutionary theory is to hold true.

    Addressing the self directed evolution one of your commenters mentioned: I think he is spot on. You mention that “it is still a long way off”. I remind you that we are talking about evolution and hence evolutionary time scales. So, we will one day self direct our evolution in precisely the way that commenter mentioned. Further, if our more advanced descendants were to see the end of their technologically advanced race on the horizon, they could easily engineer the subsequent generation of man to be tree and jungle ready for “the end of technology”.

  9. I realized after posting my comment that you blog was in part an attempt at answer my very question. However, here are the flaws in your argument (despite it being potentially partially true and highly thought provoking):

    1) The relaxation of “pressure” is extremely recent. Only over that last one hundred years has man actually pulled himself out of the rudest of environments and then, only in pockets: America and Western Europe. Further, only in the last 30 years have the BRICs matched that as well.

    2) Even if we exclude the time since the discovery of American, we still have an estimate of 300 Million people in China one thousand years ago. This reduced number would still demand a much faster evolutionary rate than what was seen in over evolutionary time for each generation.

    You might argue that China was advanced and that would be true, to a small degree. I would think not enough to justify such a low evolutionary rate.

  10. Hey Derek,

    Your first argument where you argue ‘we should be seeing massive genetic variation at mankind’s current population size’ – I would direct you to any good evolution textbook. When I was an undergraduate I used EVOLUTION by Nicholas H. Barton, Derek E.G. Briggs and Jonathan A. Eisen. Essentially:

    – the vast majority of mutations have a negative selective coefficient (they are bad for the organism)
    – mating is not random
    – the human population passed through a bottle neck of around 10 000 individuals around 500,000 years ago so there is not much raw variation in human populations

    You also might like to read about epigenetics, which explains how there is heritable genetic variation without any differences in the basic DNA code.

    I’m not sure that it would ‘easy’ to prepare a single generation for life in the jungle. Tribes alive today rely on thousands of years of inherited knowledge. But who knows, it is a matter of opinion. In my opinion, a human population trying to direct their own evolution would be unsuccessful. This is because this would equate to a system without evolutionarily stable strategy. Basically, individuals would ‘cheat’. http://en.wikipedia.org/wiki/Evolutionarily_stable_strategy

    Relaxation of selection pressures is evolutionarily recent as you say, but this does not mean it has not effected the genetic structure of human populations. Potentially millions of individuals alive today would not be passing on their genes if it were not for modern medicine, even in developing countries. And millions of individuals are not being born due to contraception.

    I’m afraid I don’t understand your point about China.

    Interesting ideas!
    Charlotte

  11. hey Charlotte Mykura,
    I really liked your blog and i do agree with you on some points, but what i suppose is that the evolution that is taking place is in the form of technology, we say we adapt to our surroundings and thats what we do.

    For a comfortable life or for example to adapt/live in a hot area like say las vegas we developed an air conditioner so that we can live comfortably. Evolution is all about adapting.

    And we are adapting through the use of technology.
    and now that our body is aware that we have developed the technology to live like this, then why should we evolve genetically.

    Another example:- a boy named sam has got dry skin and feels uncomfortable, though his genes have not evolved to give him a moist skin, now that is because his cell nucleus thinks that we have developed the technology so why should we work, so the boy uses a cream called vaseline.

    i am sorry if i may sound dumb, i am in 8th grade, and thats what i believe. 😛
    please correct me,

  12. Heya Vikram! You don’t sound dumb at all! It’s the smartest people that ask the questions.

    It’s important to remember that evolution is about the survival of the fittest; put another way, this is also ‘the death of the weakest’, or more so, ‘the failure of the weakest to reproduce’ (‘strong’ and ‘weak’ here used in an evolutionarily and not literal sense).

    Having dry skin probably isn’t something that selection would act strongly on, because it doesn’t really effect reproductive capacity. But let’s say it did, and I will continue with your example.

    Before vaseline was invented, a boy born with very dry skin (so dry that none of the girls fancied him or would go near him) would not be able to moisturise. He would die without ever having had any children, and his dry skin gene(s) would be removed from the population.

    However nowadays, the boy could visit a doctor, get his skin sorted and have babies that also carry his ‘dry skin gene’.

    Thus, deleterious genes now persist at higher frequencies in the population whereas in before the age of modern medicine they had more chance of being removed. Remember, evolution is simply change over time. Gene frequencies will always change over time, so we will always evolve. We are in a sense becoming better adapted to our technological environment, which also means that deleterious genes can be passed down to the next generation with greater ease.

    I’ve been to Vegas, and when I was outside I collapsed from heat stroke. If there hadn’t of been an air conditioned room for me to sit in afterwards I might have died and then my genes for being bad a coping with heat stress would be removed from the population.

    However, these examples are complicated by the fact that our bodies do develop in accordance with our lifestyle. If I had lived in the desert my whole life, I would be better at coping with heat, and if the boy had never used moisturiser, his skin might never have become dry in the first place.

    This evolutionary dynamic is more easy to understand if we talk about genetic disorders like cystic fibrosis.

    Thanks for your post,

    Charlotte

  13. Forget the physical – its spiritual /emotional evolution that is important for humans. Try reading Teilhard de Chardin – difficult but stick at it!

  14. Thank you so much for this inspirational blog Charlotte Mykura. I am currently at a wall with a university assignment and this has really helped and gave me some other aspects to consider. Could you please suggest some places to search for more information on recent human evolution. 🙂

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