When we think of evolution, we think of legendary scientists such as Darwin, Lamarck, Woese and others. We are the beautiful products of millions of years of selection and mutations, developed into one super organism, but are we correct to think that we are the end of it all? What if we are merely an intermediate species that will evolve to be something completely different in a thousand years, or have we made ourselves an environment free of selection pressures that drive evolution?
Genes and evolution
There are many studies currently examining humans’ capability to respond to new conditions. Scientists believe these adaptations can be seen in our genes. By tracking allele frequencies, scientists can determine the selection pressures on genes in the general population.
Every person has two copies of each gene, called alleles, and they can vary between individuals. A mutation in one of the copies can lead to an increase or decrease in a certain physical trait, or feature, that the gene codes for. If the environment a person is living in (i.e., climate, food and water availability) is more favourable for one of the two mutations, then people with that mutation will pass on their genes. The result would lead to the selected mutation becoming more prevalent in the population than a non-beneficial mutation.
This is the basis of genomic data that looks for evolutionary shifts in a population. Looking at populations from around the world we can see variations in the human species by observing different physical traits; however, it is important to note that there are many variations that we may not be able to see with our eyes. All of these genes in collective tell a story as to how the species or population got to where they are today. At some point in the life time of a population, there must have been selection for the traits they exhibit now.
What does evolution look like today?
Just a quick look around will show the many human traits we have inherited via evolution. In fact, there are many genes scientists have shown to only be present in humans less that 40,000 years old. This shows direct proof that humans are still inheriting new mutations based on their environment. For example, the introduction of city living drastically changed the sectional pressures on humans and changed the gene variants being selected for in populations.
Our immune systems have also adapted to fight off HIV infection. Different combinations of immune proteins can be more effective in clearing the infection than others. Since proteins are coded in DNA, variations of the DNA can change the combinations of proteins present. These can then be inherited by generations to come, creating a population that is immune to the disease. For example, HIV is far less common in Western Europe than in Africa. Coincidentally, 13% of European populations were shown to contain a variation in the gene coding for a co-receptor of HIV; this allowed them to be completely immune to the disease.
We have also developed many other traits thanks to evolution, such as our ability to drink milk. Typically, the gene that digests the lactose in milk is turned off after the mother has finished breast feeding. This means everyone older than an infant should lose the ability to drink milk, but this clearly isn’t the case. Following the domestication of sheep, cows and goats, there was a nutritional advantage to digesting lactose, and those who did so were more likely to pass this trait on to their children. Therefore, in areas where milk evolved to become a large source of nutrition, there were selection pressures that gave an advantage to those who could continue to digest milk after infancy. This is why today, more than 95% of Northern European descendants carry this gene.
Mutations have also caused blue eyes and other traits that are now slowly being lost, such as the reduced prevalence of wisdom teeth due to our reduced jaw size. Features such as these have left us clues into the discovery of evolution in a modern context; it is because of these reduced features that some scientists also believe evolution is not only still occurring, but is actually occurring at a rate much faster than what has previously been observed.
On the contrary, Professor Steven Jones, a geneticist from the University College London, states “natural selection, if it hasn’t stopped, has at least slowed down”. He further argues that through technology and inventions, we have been able to alter the course of evolution acting on us. This also accounts for an increase in the longevity of human lives.
We have previously been at the mercy of our genetic makeup and how we would react to our environment, but today we are able to transcend these boundaries though medical and technological interventions. Almost everyone survives to an adult age to pass on their genes, regardless of the “strength” of their genes. Further, there is no correlation between genetics and the number of children one has. In fact, many choose to not have children at all.
Stephen Stearns, a Professor of Ecology and Evolutionary Biology at Yale University, explains the shift in the method of gene transference to subsequent generations has to do with our dependence moving away from mortality as an evolutionary mechanism. We are beginning to see more variation in fertility causing changes in evolution, rather than mortality. Evolution's mechanisms are changing!
What will evolution look like in the future?
So if evolution is still happening, how is it going to change the world we know today?
Any time there is variation in reproductive success, we have evolution. Stearns argues evolution “cannot be stopped", and if we knew how to, then we would be able to stop the evolution of things such as antibiotic resistance; however, these types of mechanisms do not exist.
Ultimately, Stearns believes it is difficult for us to “wrap our heads around processes that are so much bigger and more moving than [us]; evolution takes time, and most of us can’t step outside ourselves and see a population gradually changing”. Evolution is occurring every day at rates that are difficult for us to fathom or see, but this does not mean it is not real. Stearns argues scientists have collected data for years showing evolution happening right before our eyes; we only need to trust the process as it occurs in the future.
Scientists like Steven Jones and anthropologist Ian Tattersall of New York’s American Museum of Natural History, however, believe the contrary. Tattersall states “because we have evolved, it’s natural to imagine that we will continue to do so, but I think that’s wrong”.
Tattersall's premise is when genetic mutations are passed down from generation to generation, it is because it benefits the species to inherit the mutation. If the mutation serves no purpose in the population, it would not be passed on at a higher frequency than any other mutation. Further, Tattersall explains, “genetic innovations are only likely to become fixed in small, isolated populations”, such as in Darwin’s famous Galapagos Islands. Jones follows up by stating “Darwin’s machine has lost its power… The fact that everybody stays alive, at least until they’re sexually mature, means [survival of the fittest has] got nothing to work with.”
Cultural evolution vs biological evolution
Stearns believes the largest misconception about evolution today derives from the confusion between biological evolution, involving our genetics, and cultural evolution, involving physical and mental traits, such as reading and learning. Both happen in parallel and produce different results, and with culture changing rapidly, evolutionary outcomes are difficult to predict.
Alongside this expansion of cultural evolution, we also see sexual selection through our choice of mates. This is required in order for one to succeed economically and to raise children, according to Geoffrey Miller, an evolutionary psychologist at the University of New Mexico. He also explains “the more advanced the technology gets, the greater an effect general intelligence will have on each individual’s economic and social success, because technology gets more complex, you need more intelligence to master it.”
These sexual selection pressures will likely see a rise in correlative traits involved in physical attractiveness, such as height, muscularity and energy levels, as well as health. Miller notes this has the potential to create a divide in the population between the upper and lower-classes, due to the “rich and powerful” keeping artificial selection for themselves. Artificial selection would allow parents the ability to choose the genetic contributions in their baby. Most of these would select for physical and mental traits. Miller believes, however, due to the profitability of these types of genetic technologies, it is quite possible that these technologies will be affordable and available to both the rich and poor.
A new world of evolution
Evolution has made us who we are today, but the world has changed immensely since the first microorganism inhabited our planet, and our future is much less defined. Just as Stearns has pointed out, we cannot predict cultural evolution, just as those before us would never have imagined the lives we live and the technologies we have now.
Therefore, there is large importance in being able to recognize evolution does not look the same as it did in the past. Biological evolution and cultural evolution are still occurring, just at different rates, and our advances in culture have reduced our biological evolution, which is why scientists like Jones and Tattersall believe evolution has stopped. As Stearns states, however, our cultural evolution is alive and well! It is acting on us every day, and physical and mental traits are being selected to allow us to survive in the advanced world we live in!