Over the last 150 years, Homo Sapiens have largely stepped down from their celestial pedestal and taken their rightful place alongside their organismal brethren. But this step was taken not in the publishing of Darwin’s magnum opus, On the Origin of Species, where he in fact shied away from human evolution, worried about the predicted disgust from society towards being lumped with the pigs and plants. We had to wait for his second great book, The Descent of Man, before such ideas were revealed. But while Darwin showed that we are very much a product of natural forces, what of our current state? The question of whether or not humans are still subject to evolution has become hotly contested ever since the publication of Darwin’s book, leading to debates over the very nature of evolution itself.
It is easy to follow the argument that humans are no longer subject to evolution. At its base, evolution describes the process where the variation in the reproductive success of organisms within a population leads to the spread of some characters that are well adapted to the environment, and the extinction of others which are less well adapted. With the advent of human society, and by extension medicine, the majority of individuals that are born in developed societies today survive to reproductive maturity. We are no longer looking over our shoulders for lions in the dark, or terrified that every cut or scratch could lead to infection and eventual death.
The invention of the vaccine is a modern miracle: we are now able to combat and sometimes even eliminate infectious disease. If someone who, ten thousand years ago, would have fallen prey to the natural world in childhood can now survive well into their eighties, is it right to say that we have truly broken free of evolution’s chains?
Well, unfortunately evolution has never been that simple.
The women living in the small town of Framingham, Massachusetts were the subject of a long-term study that collected complete medical histories, centred around the function of their heart. First conducted in 1948, it was the longest running study of its kind, with data overlapping multiple generations of women. Utilising this information, evolutionary biologist Stephen Stearns found that each generation was in fact shorter and plumper than the previous, as smaller, heavier women on average had more children. These changes in height and weight were accompanied by lower cholesterol levels and systolic blood pressure. Despite the fact that the rate of evolution is slower due to the stability of the environment, character frequencies still change in response to differences in reproductive rates between the individuals involved, however minor.
Though our evolution in a physical sense has weakened, we are not in biological stasis. Our societies are unique because we possess culture, which can be defined as social behaviour that can be shared between individuals through learning. Humanity is unique even among other animals that have a form of culture. Our culture is cumulative: each generation is able to build upon the achievements of the last, gradually improving the design and allowing the ‘brainpower’ of many individuals to contribute. With this, we are capable of rapid technological evolution, changing our genetic makeup even within a single generation. For example, when new methods of travel are invented, populations separated by previously insurmountable distances are able to intermix, introducing new adaptations into novel populations. This can result in new traits appearing.
In a study between fathers and children, the possession of a nicotine receptor allele that makes it more difficult to stop smoking has been correlated with early mortality in fathers. In the 1950s, a pack-a-day smoking habit was the norm, meaning that possession of the gene could effectively be considered a death sentence for a smoker. In the modern day, smoking habits have changed and been reduced, after societal realisation that smoking kills. The selection pressure has changed with changes in culture.
Though it is impossible to say the direction in which human evolution is moving (the predictions from Disney’s WALL-E of overweight, technology-dependent humans are so far unverifiable) we can at least say that it is happening. Culture is progressively shaping our biology and will continue to do so in ever-accelerating rates as our species becomes more genetically mixed and interconnected.