Natural Selection Ain't Survival of the Fittest: Recent Selection and Technology

In ancient times half our children would have died by the age of twenty. Now, in the Western world, 98 per cent of them are surviving to the age of 21. Our life expectancy is now so good that eliminating all accidents and infectious diseases would only raise it by a further two years. Natural selection no longer has death as a handy tool.-Prof. Jones [1]





In October of 2008 a geneticist, Professor Steve Jones of the Department of Genetics, Evolution and Environment at University College London, announced that human evolution was at an end at least in the western world[1]. He makes the common mistake of assuming that natural selection is survival of the fittest; it is an easy idea to fall into, but it is wrong. We are currently undergoing evolution and we have gone through many genetic changes since the rise of agriculture in recent history and will continue to undergo further changes in the future. There are four evolutionary forces: geneflow, genetic drift, natural selection and mutation. Professor Jones whittles this list down to, three conflating genetic drift and gene flow[1], and as the above quotation shows misunderstands the concept of natural selection. Natural selection is differing reproduction rates, no more and no less. A human who lives to be a thousand but produces no children is less fit than a human who lives to be 20 and reproduces. While Professor Jones may have stated something that many people would agree with, he is quite wrong.


Humans are not immune or beyond natural selection. Our ever-growing technologies and growing population actually increases the amount of selection possible and the amount of variation inherent in the population. Evolution is not stopping or slowing down, if anything changing fitness landscapes and the growing population makes evolutionary forces stronger than ever in humans. It can not be stressed enough that technology does not completely flatten the fitness landscape, rather it modifies the landscape.


The size of the human population is a key component in the rapidity of human evolution[2]. An illustrative example of the role that population size plays in evolution can be seen in flies. Scientists have been studying mutations in flies for many decades. When exposed to radiation, mutations do occur, but these mutations are often incompletely passed on and have fitness costs[2]. Pesticides give a counter example of what can occur over large populations where a perhaps rare mutation can arise and become fixed in a very short amount of time when under heavy selection pressure[2]. Human population is much larger than it has ever been in the history of our species. For a given species the amount of variation directly related to the population[2]. Interestingly, Professor Jones argues that the relative earlier average age for human males' reproduction actually decreases variability[1]. Whatever effect that has is surely swamped by the vast numbers of humans. The average age could be 50 percent less and it would still have an impact that was orders of magnitude less than the increase in variability from large population sizes.


One trait that is highly derived in humans in brain size, humans have incredibly large brains in relation to their body mass. Large brains are common in primates, of course, and brain growth in the hominin lineage has a long history. However, it is also a recent mutation. The gene ASPM, (abnormal spindle-like microcephaly associated), is a regulator of brain size and it actually arose 5800 years ago under strong positive selection[3]. A recent studied sampled 90 ethnically diverse people and one chimpanzee; 106 haplotypes were identified[3]. Haplotype 63 was in 22 percent of the individuals which is indicative of strongly positive selection[3]. The researchers identified two groups, haplogroup d and non d, where d is for derived. The variation arose approximately 5800 years ago [3]. This variation probably arose in Eurasia and is still in the process of become fixed in the overall population[3]. It is a clear example of recent evolution[3] and the timing is quite provocative as it coincides with the rise of writing and agriculture. However, are brains larger in people with haplogroup D? Does historical technological advantage correlate with the probably origins of haplogroup D? These questions are not easily answered, as an exact date for the origination of haplogroup D will always remain impossible.


A classic example of natural selection on human populations is malaria. Each year 500 million people suffer from malaria and 2 million people die from the disease[4]. Malaria resistance arises primarily from forms of G6PD or glucose-6-phosphate dehydrogenase, the mutations of G6PD actually result in enzyme deficiencies [4]. G6PD A and A- are found in sub-Saharan Africa and G6PD Med is found in souther Europe, India, and the Middle East[4]. Interestingly, G6PD Med arose later than the African forms and independently of them. G6PD arose quite recently between 1600 and 6640 years ago[4]. This coincides nicely with the rise of agriculture, generally seen as a positive cultural adaptation. Agriculture also means irrigation and lack of tree cover, consequently it creates standing pools of water that humans live near, and mosquitoes breed in. In short, the unforeseen effects of a human technology led to changing the fitness landscape of humans.


Agriculture allowed for larger population densities than hunter-gathering, giving rise to the first towns and cities. This increased population not only gave rise to greater variability as previously mentioned it also meant a changing fitness landscape for humans and viruses that infect humans. HIV is the current scourge of humanity and some people have a strong resistance to HIV infection. Approximately ten percent of European populations have a mutation of the CCR5 chemokine receptor[5]. HIV uses the receptor in infect host cells, in the homozygous state CCR5 32 deletion confers almost complete resistance to HIV infection[5]. There are currently two schools of thought on why this allele is found in so many people of European descent, selection pressure by smallpox or bubonic plague[5]. Given the intermittent nature of the bubonic plague outbreaks, it seems that it could not have resulted in sufficient selective pressure to result in the predominance of the allele[5]. The large populations made it possible for strains of smallpox to more or less continuously be passed between different individuals for hundreds or years, a mutation arose or was preexisting, the CCR5 deletion. Since this allele conferred resistance to smallpox it was heavily selected for, now years later, when smallpox has been all but eradicated the allele still exists and confers resistance.


In addition to specific examples of selection operating on humans, scientists have attempted more large scale examinations of selection. A group of scientists conducted a “probabilistic search for the landscape exhibited by positive Darwinian selection”[6]. Using broad samples now available they discovered hundreds or possible examples of selected alleles[6]. They also found that most groups showed the effects of selective pressure[6]. They propose the interesting question of the relatedness of culture of which technology is one aspect and selection. Ultimately there is no definitive answer as to which leads or follows.


A modern counterintuitive example of selection is poverty. Poor nations have faster growing populations than the developed world. In Darwinian terms, poverty is selected for or being in the developed world is selected against. The developed nations definitely have a different fitness landscape than poorer nations.


Variability is increasing as population increases and selection continues to occur in humans. While I did not discuss sexual selection, it is certainly ongoing as well. Technology has not led to the end of natural selection as people like Professor Jones would claim, rather it has led to changing fitness landscapes. When humans were in small hunter gathering populations different genotypes would be selected for than in an agricultural setting. A modern world has a range of fitness landscapes that simply did not exist for most of human history. So long as there is variability and selection, evolution will continue.









Works Cited

1. Radowitz, J.v., Humans will not evolve further, says geneticist, in The Independent. 2008: London.
2. Hawks, J., Why Human Evolution Accelerated, in John Hawks Weblog: paleoanthropology, genetics, and evolution. 2007.
3. Mekel-Bobrov, N., et al., Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in Homo sapiens. Science, 2005. 309(5741): p. 1720-1722.
4. Tishkoff, S.A., et al., Haplotype Diversity and Linkage Disequilibrium at Human G6PD: Recent Origin of Alleles That Confer Malarial Resistance. Science, 2001. 293(5529): p. 455-462.
5. Galvani, A.P. and M. Slatkin, Evaluating plague and smallpox as historical selective pressures for the CCR5-Δ32 HIV-resistance allele. Proceedings of the National Academy of Sciences of the United States of America, 2003. 100(25): p. 15276-15279.
6. Eric T. Wang, et al., Global landscape of recent inferred Darwinian selection for Homo sapiens. Proceedings of the National Academy of Sciences of the United States of America, 2006. 103(1): p. 135-140.