We will now explore the ways in which humans have impacted evolution - both our own evolution and the evolution of other organisms. The influence we have had on our planet and its many creatures in such a short amount of time is, frankly, quite frightening and a little disturbing. Let's discuss just some of the changes humans have made to the process of evolution.
The impact of humans on our own evolution
It is no big secret that as a species, we have impacted our own evolution in a number of ways, particularly since the development of modern medicines. Without going into specific examples, these technological developments have all achieved the same general effect on human evolution - reducing selection pressures. In the past, several selection pressures acted on humanity's ancestors to produce modern-day humans, but this is no longer the case - at the least not nearly to the same extent. Let me explain using a relatively basic example. During the evolution process which led to modern humans, individuals with superior hunting and foraging abilities had greater genetic fitness, as those who were more easily able to obtain food and vital nutrients were more likely to survive long enough to reproduce. One genetic factor which would have influenced an individual's ability to better obtain food is their eyesight. Individuals with superior eyesight would have had superior aim when hunting prey and a better chance of finding nutritious berries and roots when foraging. As such, the environment would have selected against individuals with impeded vision, and they would not have survived long enough to reproduce. Nowadays, we are not faced with this issue. You need only look around to see the vast percentage of individuals who rely on glasses and contact lenses to go about their every day business. We even have things like macular surgery to address issues with vision, thus allowing individuals with the "defective" alleles for impeded vision to survive long enough to reproduce, and hence pass on this trait to their offspring. This same model applies to many other areas too. In nature, individuals born with significant physical or mental disabilities would be selected against, purely due to their comparatively low genetic fitness. But now, with the help of a combination of technologies, such as wheelchairs, this selection pressure has been diminished. Societal values arising from cultural evolution may also play a role in this, as we have evolved to become accepting of those born with such disabilities, rather than isolating them in the way other animals do. Other examples of humans abolishing their own selection pressures include the development of antibiotics and vaccines. These have allowed humans to dodge death in many ways, with both of these technologies allowing for the control of disease, and in some cases (e.g. smallpox) eradicating them entirely. |
The impact of humans on the evolution of other organisms
As well as influencing our own evolution, humans are having significant impacts on the evolution of other organisms too. From destroying habitats through deforestation and pollution to using biotechnology to physically alter organisms, humans are meddling in all sorts of 'unnatural' when it comes to our fellow creatures. Let's discuss some of this in more detail... First of all, the most primitive style of genetic modification exists in the form of artificial selection, or selective breeding. Despite not knowing the genetic basis for this in the past, humans have been using this technique for centuries! Most of us know that all modern dogs are descended from the grey wolf, but did you know that this divergence only occurred because humans wanted it to? Humans bred wolves based on temperament for generations in order to produce the fluffy pooches we know and love today. In other words, humans acted as the selection pressure, rather than environmental conditions, causing speciation to occur. This has been repeated with cows, horses, cats and even several crop species such as bananas and corn. In addition to selective breeding, humans have also cross bred plants and animals to create new species altogether. Modern technology has allowed us to go even further, and create transgenic organisms, splicing desirable genes into the existing genomes of organisms, such as inserting the green fluorescent protein in jellyfish into other organisms into the genomes of mice. As well as artificially influencing allele frequencies and the actual genomes of organisms, humans also have a severe impact on habitats leading to behavioural adaptations in organisms. One bizarre instance of a behavioural adaptation directly caused by humans is that of birds using cigarette butts to construct their nests. The nicotine from cigarettes acts as an insecticide, and hence is used by the bird to ward off dangerous parasites. This behavioural adaptation, along with several others, is one of the direct impacts of humans on the organisms around them. Other, more devastating impacts are the extinction of species due to complete loss of habitat through deforestation and pollution or over-hunting. If you're interested in which species humans have driven to extinction in the past two centuries, click here to learn more. |
Figure 5.1 Human intervention in evolution has led to positive outcomes, such as the development of Golden Rice, enhanced with beta-carotene to help combat malnutrition in developing countries.
|
Figure 5.2 A double muscled cow. Often, humanity's own greed has driven us to modify organisms in ways not necessarily in their best interest.
|
So, humans have had a pretty significant impact in our short time on this Earth. But the question has to be asked - where do we draw the line? Is the notion of transgenic organisms acceptable to the community, or are these 'Frankenstein' organisms too much for society to handle? How far do we let modern medicine go? Individual opinions differ so much on the ethics of biotechnology to the extent where I doubt the true possibilities of this area will ever be fully explored.