Are Humans still evolving?

 

Natural selection is a process that causes species to become better adapted to survive in their environments and results in evolution – changes in allele frequency over many generations in a population. (Estruch, 2020) Human anatomy and behaviour have not changed drastically over the past 65,000 years. Due to a lack of selection pressures because of constantly improving healthcare systems and better availability of food and shelter, rate of evolution in humans might be decreasing. (Stock, 2008)

 

Research published in a 2014 paper suggested that Aboriginal Australians have adapted to remain cooler in some of the hottest climates of the world over the last 10,000 years. Typically, the body releases thyroxine, a hormone that increases metabolic activity and regulates heart rate, in increasing temperatures. Too high of a concentration of thyroxine in the body in extremely hot conditions can be dangerous. Approximately 40% of the Aboriginal Australians in the study were found to have changes in the gene that controls the release of thyroxine, and these alleles are associated with lower temperature associated release of thyroxine. Scientists believe that this might be helping in maintaining lower body temperature in warming climates. (SciShow, 2020)

 

Over the last 3000 years, another adaptation that has arisen is larger spleens in the Bajau people of South-east Asia which allows them to hold their breath for over 15 minutes and swim to depths of 70m and above. Scientists have found that this adaption allows more oxygen to be made available in their blood when diving as the spleen contains a large amount of oxygenated red blood cells. This feature has been found in both non-divers and divers in the Bajau community and this suggested that this enlargement was not just a result of regular diving. Scientists found that a change in the PDE10A gene correlated with larger spleen size, and it was theorised that this gene variant was most likely introduced into modern humans through introgression. Due to natural selection, this gene is now prevalent in the Bajau people. (Rincon, 2018)

 

Similarly, the Tibetan people have adapted to live at higher altitudes. The Tibetan people have low levels of haemoglobin in their blood and lack the barrel-shaped chests of the Andean people who also live at extremely high altitudes. These low levels of haemoglobin in blood are beneficial because it reduces the viscosity of blood, reducing damage to blood vessels and therefore the risk of Chronic Mountain Sickness. Tibetans also exhale more nitric oxide than the Andeans which leads to increased vasodilation. Tibetan babies also have greater birthweights and have higher oxidation concentrations at birth. All these adaptions occur due to mutation in the EPAS and EGLN genes and it is suspected that this gene was inherited from Denisovans, a different species, which through natural selection is now prevalent in the Tibetan people. (Riley, 2017)

 

In conclusion, although the rate of human evolution may decrease because of a lack of selection pressures, there are other factors that affect rate of evolution other than natural selection. Modern medicine can cause evolution via genetic drift where genetic differences vary randomly within a population, by not eliminating harmful mutations. Adaptations can also arise through epigenetic modification, where there are changes to whether genes are expressed at all, therefore meaning that humans are still evolving and will continue to evolve in the future.

(TED-Ed, 2020)

 

Works Cited

Estruch, 2020. MissEstruchBiology - YouTube. [Online] 
Available at: https://www.youtube.com/watch?v=0W__hCcXjYA
[Accessed 03 2022].

Riley, 2017. How Tibetans survive life on the ‘roof of the world. [Online] 
Available at: https://www.bbc.com/future/article/20170227-how-tibetans-survive-life-on-the-roof-of-the-world
[Accessed 03 2022].

Rincon, 2018. Bajau people 'evolved bigger spleens' for free-diving. [Online] 
Available at: https://www.bbc.co.uk/news/science-environment-43823885
[Accessed 03 2022].

SciShow, 2020. Are humans still evolving?. [Online] 
Available at: https://www.youtube.com/watch?v=oCjAAVk7Uis
[Accessed 03 2022].

Stock, 2008. NCBI. [Online] 
Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327538/
[Accessed 03 2022].

TED-Ed, 2020. Is human evolution speeding up or slowing down? - Laurence Hurst. [Online] 
Available at: https://www.youtube.com/watch?v=NTeOhj6dxsU
[Accessed 03 2022].