Ranchi, 23 December 2012 :: Are Humans Still Evolving?
“Do you think that humans are still evolving”? This was a question that was posed to high school students and university Professors attending a symposium on evolution held earlier this year in Montreal, Canada.
About 80% of the audience attending the symposium answered “No”.
It was not surprising, as most people believe that the human race has made so much progress on the social, racial, cultural and technological fronts that they have managed to free themselves from the pressures of what Darwin called natural selection.
Recent findings, however, show otherwise – that instead of becoming immune to the selection pressure, humans have actually created new ones.
It has taken several million years to evolve from the apes to humans, through changes in the useful information stored in the genetic building blocks, otherwise known as DNA. At first, this evolutionary change proceeded mainly by natural selection, arising from random mutations in the DNA sequence, and produced humans who developed language for exchanging information.
One of the best known examples of recent human evolution is the development of resistance to malaria as there was strong pressure to evolve defenses against it – for giving descendents a chance to have offspring.
A case in point is the sickle cell anemia, the red blood cell disorder that impairs blood flow, is one of the best known examples of defense against malaria. Apparently, people who have this blood disorder are resistant to malaria as the parasites are unable to infest their blood cells.
Sickle cell anemia is quite prevalent in Africa (ranging between 10% and 40% of the population in some areas), and is also found among the people with origin in the Mediterranean and Saudi Arabia (WHO Report, 2006). Interestingly, in the USA, where malaria is not endemic, the prevalence of sickle cell anemia is much less among the Black Americans (about 0.25%), whose forefathers came from Africa.
In addition to the African, Mediterranean and Saudi Arabian variants, there is also an Indian-Pakistani variant of sickle cells (about 10-15% population affected). Scientists believe that these different variants evolved separately, probably in the last three to four thousand years.
Another example of a recent evolutionary change in humans is lactose tolerance. Most adults are unable to digest lactose, a complex sugar found in the milk, and show signs of intolerance (e.g., stomach upset) after consuming milk. However, population who bred animals and consumed milk as the nutritious food source, developed tolerance for lactose by having prevalence of genes that helped in lactose digestion. Scientists think that the lactose tolerance probably developed about 7,500 years ago.
A recent study by the evolutionary biologist Professor Stephen Stearns and his colleagues, based on extensive analysis of data (economic status, births, deaths and marriages) found from church records and national health registries, strongly support the idea that Darwin’s natural selection theory is still operating on contemporary humans. An interesting observation that came out of this study was that strict adherence to monogamy was not a limiting factor for natural selection.
Recent evidences also suggest that the evolution process is becoming rapid – its effect becoming visible as quickly as within few generations instead of occurring in a Darwinian time scale.
Thus, as people learned to rely more on agricultural products as a food source for sustenance – which was a major shift from their animal hunting days – they developed a way to produce more copies of a gene for a salivary protein, known as amylase, which helps in digesting starch.
According to the noted Physicist Professor Stephen Hawkins, humans have entered into a new phase of evolution that is driven by “external record, in books, and other long lasting forms of storage,” and he called it “an external transmission phase” as opposed to the “internal transmission phase” that is handed down to succeeding generations through genetic material.
Professor Hawkins believes that this new phase will allow us to change and improve our DNA through “self-designed evolution”. According to him, initially these changes would be “confined to the repair of genetic defects, like cystic fibrosis, and muscular dystrophy” – these diseases would be indentified fairly easily and corrected, because they are “controlled by single genes”. However, “qualities, such as intelligence, are probably controlled by a large number of genes”, and hence, it would be “much more difficult to find them, and work out the relations between them”. Nevertheless, he believes that “people will discover how to modify both intelligence, and instincts like aggression” during the next century.
Professor Hawkins also believes that intelligent machines, rather than macromolecules will be involved in this human race redesign, which could eventually replace DNA-based life, as we know it now, “in the same manner DNA may have replaced an earlier form of life”.
(Sources: BBC News, New Straits Times, Belfast Telegraph and Life in the Universe lecture by Professor Stephen Hawkins, 2009)
Dr. Hemanta K. Sarkar
Education – Ph.D. (Biochemistry)
Profession & Working Place – Knowledge-Based Service Provider (Biotech Consultant & Science Editor/Writer).