In 2002, a debate at Edinburgh University entitled ‘Is Evolution Over?’ sparked controversy when a group of scientists proposed that, because of Western lifestyles, human evolution is over. But is this true and how can it be proven?
If you could go back in time, you would see humans evolve from tree dwelling hominids, to cave men discovering the wonder of fire, to Homo sapiens moving out of Africa to conquer the world. But is this the end? It can be theorised that humans’ evolved intelligence is helping avoid the selective pressures of changing environments, separating sex and procreation and helping to create medicine to avoid disease, but are humans simply being exposed to more subtle pressures, and could evolution just be moving more slowly?
Darwin’s theory of natural selection states that favourable traits become more common in successive generations of a population while unfavourable traits become less common. This process of ‘survival of the fittest’ works on the idea that genetic selection stops all bad or faulty genes from making it into the next generation.
Professor Steve Jones, of University College London, argues that today almost all our genes are making it to the next generation, free from selective pressures. He argues that our growing intelligence, resources and technology may have circumvented natural selection. However, could it not simply be that the pace of evolution is constantly oscillating; that we are presently going through a slow patch?
Jones feels that with more people travelling, and breaking through what were previously evolutionary barriers, to settle in places far from their own places of birth, genes are blending and becoming more uniform. Nevertheless, could this sharing and mixing of genes that would normally be continents apart, simply be another stage in evolution. Is our inquisitiveness for our surroundings one reason for humans evolving a higher intelligence?
In days gone by, death rates usually equalled birth rates mainly as a result of poor hygiene and ravaging diseases, but this is literally a thing of the past. Today most children will live past twenty five years, not just as a result of good genes, but also due to medicine and other artificial aids. Perhaps the evolution of a larger brain could also be our downfall. Does a greater intelligence mean a weaker human race?
Jones feels that today, perhaps with the exception of a few rock stars, we are far more monogamous than we were in the past, when it was common practice for a dominant male to fight in order to mate with many females, which ensured that his genes were passed on. In turn it was strong females who could ‘handle’ these strong males, resulting in a real survival of the fittest.
Despite these arguments, I cannot help but feel that most of them only have a basis in the developed world where we have surrounded ourselves with so many creature comforts, created excellent healthcare and strive towards careers.
In the less developing areas of the world evolution may still be more apparent simply because the barriers of technology and medicine are simply not as prevalent. For example, the selection on genes in response to disease can be seen more readily in areas of the world with less advanced health care.
The blood disease sickle-cell anaemia is not thought of as a desirable trait, but in many parts of Africa evolutionary forces have chosen to select it as one. Those individuals with the disease have a faulty gene that results in one wrong amino acid in the haemoglobin in their red blood cells. This mutated haemoglobin cannot effectively transport oxygen around the body and causes red blood cells to appear sickle-cell shaped.
For the majority of the world population the normal haemoglobin gene far outnumbers the faulty gene as it holds no benefit to have a gene that can cause, amongst other symptoms, spleen damage, heart failure and paralysis. However, in Malaria besieged areas of Africa, almost 1 in 10 individuals are heterozygous (possessing one faulty and one normal gene) for sickle-cell anaemia. The malaria parasite spends some of its life cycle inside our red blood cells but it finds the sickle-cell shaped cells highly inhospitable. So if you live side by side with malaria carrying mosquitoes you have a better chance of survival if you carry a gene with the sickle-cell trait. It would be interesting to see the effects of anti-malarial programmes upon sickle-cell anaemia in the future and its affects, if any, on a specific cultural group’s evolution.
This modern day example of evolution is not so common in the more developed areas of Africa and the rest of the world. In the ‘developed world’ are we now only seeing a strong selective pressure on diseases where there is very little medication or hope of a cure, such as AIDS.
Certainly humans have not reached a state of perfection, far from it. The human body itself is very much flawed with joints that wear, highly fallible spinal discs, and bones that lose minerals from as early as the age of thirty. The simple truth is that we were not designed to live this long and perhaps the next stage in evolution is for our bodies to be able to stand better the test of time.
In the past, evolution may have been punctuated; humans may simply be at a plateau awaiting the next environmental stress to come, be it a major climate change shift or a natural disaster.
For the moment, perhaps evolution has been slowed by our expanding knowledge, changing priorities and eagerness to explore the world around us, but we are looking at a very small fraction of time, buried in over hundreds of thousands of years of evolution. So how can we even say for sure what the future will hold for the human race?
Humans have created comfortable barriers that help shield them from the harsh environment. Healthcare means we can all be free of common diseases, irrelevant of what disease fighting genes we have. Visual aids mean poor eye sight no longer puts people at a disadvantage and we can even separate sex from procreation. So what selection pressures are we being exposed to?
Researchers at the Department of Anthropology in the University of Wisconsin-Madison believe that such changes in technology, disease and even diet have in fact increased the forces of selection. Led by Assistant Professor John Hawks, the team found their evidence in the International HapMap Project (haplotypes map http://www.hapmap.org/) where they studied the prevalence of single nucleotide polymorphisms (SNPs), the variations in the smallest units of DNA and genes.
These variations are associated with diversity within populations, for example susceptibility to diseases. However, over time natural selection would deselect many of these SNPs. When Hawks and his team analysed the human genome, they discovered that the level of variation is still high even today, leading to speculation that humans are still evolving so fast that these SNPs have not had time to be deselected.
The findings are excellent, although the conclusions drawn from them are debatable. Hawks argues that the rate of evolution is speeding up and thus the effects of natural selection are still present. But, would a lack of selective pressure not result in more genetic variability due to more genotypes being passed to the next generations? Yes, it is likely that these SNPs are the result of a rapid change in the lifestyle of modern Homo sapiens; our exposure to new diseases, climate and diet as we moved out of Africa. However, the barriers to natural selection that are being debated are far more recent (e.g. the industrial and medical revolutions). Is it possible to see more recent adaptive mutations?
To believe humans are at a stand-still evolutionally is difficult to believe when we can even see cases of evolution in perceived reverse mode. Dollo’s Law states that evolution cannot run backwards and is irreversible. Any unused genes are not always lost; instead they are silenced by the accumulation of random mutations. However there is evidence of these ‘silent genes’ being reactivated, producing traits that resemble evolutionary throw backs. An example of this is webbed hands or feet, a common birth defect that can mend itself over time, which occurs when the ends of our limbs fail to divide into five fingers or toes. The conception of twins or triplets is also theorised to be an evolutionary throwback to when mammals had larger litters. Perhaps silenced genes can be reactivated if they offer a selective advantage? If the worlds’ population was to drop dramatically would having genes that make you predisposed to having twins be a selective advantage?
Humans could be at an evolutionary plateau, a supposition that is corroborated by the theory of punctuated equilibrium: ‘evolution proceeds relatively rapidly during the formation of species, but between these events the population remains relatively static’. I believe our gene pool is still being exposed to selective pressures, although perhaps more subtly. Humans have evolved over hundreds of thousands of years through Hominid evolution, dominating the world by evolving the ability to walk upright, having a larger brain capacity and creating a social culture.
But the human body, in all its marvel and complexity, is far from perfect. When we complain that our every day appliances never last long enough, how often do we consider that our own bodies are not built to stand the test of time? Many of our flaws include eyes that are connected back to front, with our light sensitive cells sitting behind the nerve cells rather that in front, a result of vertebrate eyes evolving from an infolding of the brain; our lungs have very delicate alveolar walls meaning lung diseases such as emphysemas are common; and even at the molecular level some of our DNA polymerases -the machinery that replicates and mends our DNA- is far from accurate creating as many errors as 1 base per 100 copied.
But is evolution designed, as many idealise, to create perfection? It is most likely natural selection only requires something to work with less selection for genes that benefit you later in life; logical when you remember that survival of the fittest only requires you survive long enough to pass on your traits to the next generation.
In 1963, Theodore Dobzhansky wrote the potentialities for rapid evolution of the human species have not been depleted, since the environment continues to change and the genetic variance remains plentiful. Mankind assuredly continues to evolve, both culturally and biologically. Have our evolved brains enabled us to create cultures, which in turn produce their own biologically selective forces?
In recent decades our diets have changed with more varied and exotic food becoming available, as it is shipped around the world. So perhaps the genes that govern food metabolism are under selective pressure? The gene for Leptin encodes a hormone, which is involved in the regulation of food intake and the storage of fat in our bodies. Could a gene like this be selected for a world where humans are consuming more and more fattier convenience foods?
Ray Kurzweil, author and futurologist, recently described the technological revolution as an outgrowthand a continuation of biological evolution. He agrees with those that feel evolution is increasing and at an exponential rate. I agree that we need to anticipate future evolutionary trends and realise that rates of change are not constant. However, I feel that his idea can still coincide with punctuated equilibrium; periods of exponential evolutionary change can be interspersed with periods of slower genetic drift. If today we are under less selective pressures then we could be at a plateau, where our gene pool is increasing in variation and complexity, ready for an event that will drive the next change in Homo sapiens.
In order to prove if selection pressures are changing us today will require a study of gene banks and SNPs across hundreds of different genes across hundreds of different cultures and countries. Uncovering modern selective pressures and their effects is already becoming a popular area of research, but for the moment it seems we are left with more questions than we started with. The answers are in our genes, but evolution is still writing its story.
In the words of Benjamin Franklin – When you’re finished changing, you’re finished.
