Humans Are Still Evolving. Here Is How…

Dan Bennison

In his 1895 novel, The Time Machine, H.G. Wells describes a world in which subterranean and forest-dwelling subspecies of humans coexist. To a distant relative of Homo sapiens, the concept of modern humans was likely as foreign as Wells’ world is to us. Still, there is no doubt in the mind of scientists that humans are still evolving.

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Image Credit: Pixabay

The main driving forces of evolution are known as selection pressures. How well an individual can overcome these pressures, like predators and diseases, will determine how long it survives and whether it reproduces. By evolving, and passing on genes considered ‘successful’, a species can develop features to help overcome these selection pressures and live longer, reproduce more and ultimately become better suited to the environment in which it lives.

The major advantage we humans possess is the ability and the intelligence to alter our environment, while other species must adapt to better survive within theirs. Farming, healthcare, and lack of predators remove most selection pressures towards humans, and can lead to changes that may well be mistaken for evolution. Is the increasing human lifespan due to evolution or healthcare? We can’t say for sure.

Saying that, there are certain physiological changes that are definitely evolutionary. If wisdom teeth have been as painful a problem for you as for me, you might be glad to know that humans are predicted to lose them altogether. Our jaws are becoming smaller and more bullet-shaped, as cooking and utensils have reduced the need for large, strong jaws with extra teeth for eating tough food.

In addition, our brains are getting smaller, but are being ‘rewired’ to become faster and more efficient. The number of blue-eyed individuals worldwide is increasing. This is thought to be because blue eyes, fair hair and pale skin are linked, and allow greater vitamin D production is low-light environments such as northern Europe. Dark eyes, hair and skin provide more protection from harmful UV rays in hotter regions such as Africa and the Caribbean.

The environment in which human populations live is a major factor when considering evolution, predominantly due to food availability and disease. Seeing as different diseases are more or less common in different areas in the world, humans have evolved different mechanisms to survive.

A huge selective pressure on humans is malaria, a disease transmitted by mosquitos between the tropics of Capricorn and Cancer. In these regions, multiple types of resistance have evolved (and are evolving) separately, such as the sickle cell trait and a type of anaemia called thalassemia. Both of which alter the red blood cells – where the malaria parasite grows in humans. Some mechanisms that have evolved, such as Pyruvate Kinase deficiency, would not be beneficial in malaria-free regions. PKD means your cells cannot make enough energy, leading to many serious health problems. But these health problems are less severe than malaria, so these mutations are beneficial (a type of bet-hedging).

In remote Papua New Guinea, the Fore tribe are the only population of humans that are commonly infected with Kuru, a rare neurodegenerative disease caused by misfolded prion proteins in the brain. Within this tribe, a change in this protein grants resistance to Kuru, and is found nowhere else in nature. Studying human resistance to disease shows how selection pressure has directed mutations within an isolated population.

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A map of where different heritable genetic resistances to malaria can be found, the majority of which coincide with the malaria belt. Image Credit: Wikicommons

In terms of how far evolution can go, if you’re hoping that humans will suddenly sprout wings and take to the skies, then I’m sorry to disappoint. It is far more likely that subtle changes will take place to help us better suit the environment in which we live. In rural, developing countries, this may include resistance to diseases to compensate for less effective medical options. However, in more technology-driven communities, eye size is likely to increase and become more efficient in low-light. Facial features are likely to become more objectively appealing, with perfect left:right symmetry.

On a worldwide scale, gene flow as a result of genetic mixing between ethnicities may lead to a future in which humans look extremely similar, with many of the differences between races being lost – a human ‘standard’ of darker skin, large heads and large eyes. The global nature of the modern world, ease of transportation and even social media make this convergence increasingly likely.

Another more alarming possibility is the increase in less favourable traits that become widespread as a result of the modern lifestyle. For example, celiac disease (gluten intolerance), is becoming increasingly common. 50 years ago, it is estimated that 0.2% of people had this disease in the U.S., compared to one in 100 people today. With global trade, humans are becoming less reliant on staples such as grains and wheat, meaning the selection pressure of having celiac disease is less of an issue and individuals can eat enough to survive – increasing the number of people with this disease. Within developing countries where staples are still essential, celiac disease is much rarer.

This is also occurring in type one diabetes, with insulin therapy so effective that patients can live near normal lives, with normal lifespans, and potentially pass the condition onto their children. Furthermore, the battering of our perfectly adapted gut bacteria with prescription antibiotics reduces much innate resistance to disease, and may also affect individual traits such as weight gain and digestive health.

Of course, the possibility of editing human embryos is still a possibility. But it remains to be seen whether this technology is ever routinely used in practice. All in all, the impact of selection has been reduced in humans because of our own intelligence. Evolution will never cease, but just continue adapting humanity to the ever-changing conditions in which we live, with each major change or event providing more ground for evolution to work with.

Who Were The Neanderthals?

Christopher Butler

The Neanderthal (Homo neanderthalensis) was humans’ closest relative. We are so incredibly similar that scientists have considered grouping modern humans and Neanderthals together under one subspecies– I challenge you to distinguish between a Siberian and a Bengal tiger, which is an equivalent relationship. No doubt we too looked and acted very similar to a Neanderthal. Recent evidence points towards their ability to utilise fire, build tools and perhaps most impressively – bury their dead. It seems only a shame that Neanderthals are now extinct.

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Sub-Species: The Bengal tiger (1) and the Siberian tiger (2) are an example of a subspecies. So may be Homo sapiens (3) and Homo neanderthalensis (4).

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Image Credit: Pexabay, Wikimedia commons

It is believed that the last resting place of H. neanderthalensis was on the island of Gibraltar, where they feasibly became extinct as recently as 28,000 years ago. Their decline coincides with a time in which humans were migrating out of Africa. Many scientists conclude that our ancestors simply outcompeted our close relatives. But what attributes did H.sapiens possess which Neanderthals lacked during this evolutionary arms race? Professor Chris Stringer; who works for the Natural History Museum London, believes he has found the answer. Analysis of skull properties has indicated how Neanderthals have larger eye sockets, which presumably allowed them to see during our gloomy European winters. Conversely H. sapiens; which originate in sunny Africa, could afford to have significantly smaller eye sockets. Stringer argues how this anatomical set up may have allowed H. sapiens to develop large frontal lobes; areas of the brain associated with “high level processing”. This allowed our ancestors to develop complex speech patterns giving them the ability to organise themselves into efficient social groups. Essentially, Stringer believes that H.sapiens were able to out-think and therefore out-compete the Neanderthals. Underlying Stringers’ theory is a more universal message: working together is usually a more successful strategy than working alone.

Events in human history which occurred earlier than the Neanderthal Extinction (~28,000 years ago):
  • The invention of the flute.
  • The invention of a bow and arrow, replacing spears as a method of hunting food.
  • The domestication of dogs
  • Cremation acts during rituals
  • H. sapiens had migrated out of Africa and had already settled in far reaching locations; such as Sydney, Australia.

It’s important to note that we did not evolve from Neanderthals, but we both evolved from a common ancestor. Whilst Neanderthals may be extinct now, for many years they coexisted with our ancestors. This period of time lead to genomic introgression: essentially genetic material from Neanderthals was transferred to H. sapiens and visa versa through sex. As a result, the current global human population carries approximately a fifth of the Neanderthal genome, which makes up around 1-3% of our genome. What genes are Neanderthal in origin but currently reside in modern humans? And are these genes considered a hindrance or an advantage when considering our modern way of life?

  1. Straight hair. Genetic analysis has revealed that the mutation which allows keratin to form straight, thick hair is Neanderthal in origin. This makes sense – as modern humans migrated out of Africa we needed to adapt to colder environments. Straight hair is typically oilier and therefore more insulating.
  2. Freckles. The gene BNC2 is Neanderthal in origin and causes its owner to develop freckles and paler skin. Fair skin is of benefit of populations where light levels are limiting as it allows more efficient production of vitamin D.
  3. Red hair. The gene which causes ginger hair is Neanderthal in origin.
  4. Blood clotting. A gene variant that speeds up the process of blood clotting is considered Neanderthal in origin. Whilst this trait is largely adaptive in preventing infections, it does have further complications amongst modern humans such as increasing stroke vulnerability.

There have been lots of other human traits which have been proposed as Neanderthal in their origin. Some of the more bizarre include vulnerability to depression and nicotine addiction. These findings always bring about great excitement amongst the scientific community and the general public alike. There is something curious about studying our closest set of ancestors. This is only heightened in the case of the Neanderthal because they have long been extinct, living on in our own DNA.