Courtesy- Image by Gerd Altmann from  Pixabay

Author: Abhishek Kumar,The Fourth year, Integrated MSc.School of Biological Sciences,  National Institute of Science Education and Research(NISER)

 

I believe that human beings are evolving and that too in  very fast rate. Evolution is defined as the change
in the traits of a population over several generations due to mutations, natural selection and genetic drift. In recent times the notion that human evolution has ended has become more and more prevalent. This misconception is due to the belief that the selective forces for natural selection are no longer operational due to the long post-reproductive phase and low competition for food. This is true for less than 10% of the world population living in developed and ultra-rich communities. Rest of the world has populations living in poverty, malnutrition, infectious diseases and war zones. Even in western countries, there are people living in poverty. Bains, in his editorial of bioscience hypothesis 2009 very aptly explained that even the countries with western affluence have selection happening in at least three levels of pre-reproductive mortality, reproductive dynamics and reproductive success. [1]

Evolution is a sedate phenomenon; we can observe manifestations of evolutionary effects only after a number of generations. Evolutionary effects are not always morphological changes rather evolutionary effects may appear as changes in cognitive abilities too. There has been a lot of work on the cognitive evolution of humans. A number of scientific publications have helped to establish that there has been a very significant evolution in the cognitive abilities of humans over the last 10000 years. [2] Archaeological data and fossils provide clues of anatomical and morphological evolution in humans. This development seems to be driven by both genes and environment. [3] We have gained abilities to process vast amounts of information, solve complex problems, we are able to cooperate in large numbers and understand abstract ideas. Higher cognitive functions in humans are due to specific genetic components which appear since the divergence from Neanderthals i.e. recent evolutionary processes. [4]

Even in the apparent absence of natural selection the forces of mutations and genetic drift are still in play. One can argue that with the increase in pollution, smoking, electronics, electromagnetic radiation, ozone depletion etc. there should be an increase in the number of mutations which could be inherited. The accumulation of these mutations in subsequent generations will lead to change in characteristics. Cochran and Harpending claim that the evolution is now 100 times faster than it was 10000 years ago. [5] Cultural evolution of humans do not eliminate adaptive evolution via natural selection, it only increases adaptive evolution. Agriculture altered the human environment and caused an increase in the numbers and local population densities. Agriculture is labour intensive, the crops require constant protection and care. As a result, even early agricultural fields caused a large increase in local human densities.

This new population structure became an ideal breeding ground for numerous infectious diseases which are still in the 21 st century a major cause of death of farmers in developing and under-developed countries. A number of case studies show that in sub-Saharan Africa there was an extensive positive selection for heterozygous sickle cell allele at haemoglobin β-locus, which confers resistance to malaria. In addition to sickle cell anemia, thalassemia and glucose-6-phosphate-dehydrogenase deficiency alleles appear to be naturally selected due to similar reasons. [6,7]

Moreover, the overgrowing human population and influence have altered our environment by intruding upon the habitats of other species. These culturally induced changes created a whole new niche of cross -species infectious agents which can affect humans with just a few mutations. Not only the infectious diseases there has been an increase in systematic diseases like diabetes, heart diseases and neurodegenerative disorders. The increase so rapid that evolution cannot be the sole culprit rather the cultural and environmental changes have increased the occurrence of these diseases. [8] Humans will continue to evolve until they are reproducing. Evolution is said to be slowing down when there is a decrease in reproductive success. This would lead to a loss in genetic variation and severe depletion of the overall population in a few generations. However, the opposite is happening in humans. The human population is now very huge and hence, has a very high evolutionary potential. Even if the cultural evolution has limited the selection for particular traits they can be still selected as a correlated response to the selection of some other trait like sickle cell anaemia due to selection for malaria resistance. [9]

So, the evolution of human beings has not stopped rather it is faster than ever before. I would like to just point out one simple thought at the end isn’t it more reasonable that we have evolved in last 40000 years and will keep on evolving rather than the idea that we have remained same in last 40000 years with no change i.e. the humans of 21st century are same as the hunter-gatherers of 40000 years ago.

References:

  1. Bains, W. 2009. Evolution, hypotheses, and the question of whether humans are still evolving. Bioscience hypotheses 2(4) 193-197.

  2. Heyes, C., and Huber, L. 2000. The evolution of cognition. Vienna Series in Theoretical Biology. Cambridge, MA: MIT Press.

  3. Gunz, P., Neubauer, S., Maureille, B. and Hublin, J.-J. 2010. Brain development after birth differs between Neanderthals and modern humans. Current Biology 20, R921–R922.

  4. Srinivasan, S., et al. 2018. Enrichment of genetic markers of recent human evolution in educational and cognitive traits. Scientific Reports volume 8, 12585.

  5. Cochran G, Harpending H. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. New York.

  6. Wiesenfeld SL. 1967. Sickle-cell trait in human biological and cultural evolution: Development of agriculture causing increased malaria is bound to gene-pool changes causing malaria reduction. Science 157, 1134-40.

  7. Templeton AR. 2006. Population Genetics and Microevo-lutionary Theory. Hoboken, New Jersey: John Wi-ley & Sons

  8. Kolb H, Mandrup-Poulsen T. 2010. The global diabetes epidemic as a consequence of lifestyle-induced low-grade inflammation. Diabetologia 53:10-20.

  9. Templeton AR. 2010. Has Human Evolution Stopped? Rambam Maimonides Med J. Jul; 1(1).