Evidence for evolution–rapid human evolution

One of the most amusing (amongst so many) from the evolution denialist crowd, lead by Ken Ham and his creationist zombies, is that evolution has never been observed.  According to Answers in Genesis

Macroevolution is a term used by evolutionists to describe the alleged, unobservable change of one kind of organism to another kind by natural selection acting on the accumulation of mutations over vast periods of time.

If you take a genetics course in any reasonable university (not one run by anti-evolutionists), you use fruit flies (Drosophila) to select for or against certain features, evolving a population rather quickly.  Some anti-evolutions say that this is “microevolution,” which to a scientist is no different than “macroevolution.”  The problem with the evolution denialist viewpoint is that fruit flies have a very short lifespan, so generations upon generations can be studied over a few weeks or months.  If humans lived only 2 days, then we could observe evolution in humans.

Of course, wouldn’t it be interesting if we could observe evolution in a historical time frame in humans.  Since evolution doesn’t happen in just a few generations, it would take thousands of years to find evidence of change in a population, which would presume to support the rather simplistic arguments of the creationists.  Oh wait, it might be possible.

In an article in the New England Journal of Medicine,  A Novel Protective Prion Protein Variant that Colocalizes with Kuru Exposure, by Mead et al., human evolution is observed over 200 years, give or take.  Until recently (when cannibalism was outlawed), the Fore people of Papau New Guinea honored their dead by eating their organs, including the brains.  Unfortunately for these people, kuru, a neurological disorder caused by prions and related to other transmissible spongiform encephalopathies, such as Creutzfeldt-Jakob Disease.  This disease is similar to the popularly known “mad cow disease,” or Bovine spongiform encephalopathy

Prions are a particularly nasty infectious agent, which are merely folded proteins.  No nucleic acids, which are necessary for replication even in simple organisms like viruses.  When the prion enters an organism, it forces it to produce misfolded proteins.   This is particularly nasty for the brain, and there is no known cure.  In fact, there is no known prevention other than not eating infected meats, because cooking doesn’t necessarily destroy the prion.

Mead et al. determined that a subgroup of Fore people were resistant to the disease because of Codon 129 heterozygosity in the human genome.  This simple mutation (an exchange of just one nucleic acid in the sequence) caused the protein that was affected by the prion to become resistant and not repeat the misfold.  According to Rosa Rubicondior: Rapid Human Evolution

This mutation arose about 200 years ago by accident in a single individual and was inherited by his or her descendants so that, about 100 years ago when the kuru epidemic was at its height, there were just a couple of families who were carriers of the mutant gene. They and their descendants survived whilst many of the non-carriers died, so, under intense selection pressure, the frequency of the mutant allele increased hugely in the gene pool in just a few generations.

If cannibalism wasn’t outlawed by the government, the tradition would have continued, and more resistant individuals would pass the genes onto the next generations, and in a few generations, honoring their dead relatives would have not had any negative effects, except for a few that didn’t career the mutant gene.

According to Simon Mead, the principle investigator,  “I hope it will become a textbook example of how evolution happens. It’s a striking and timely example, given the 150th anniversary of the publication of Darwin’s Origin of Species.”

So yes, we can observe evolution, even in long-living species like humans.  And not all mutations are detrimental to the organisms.  Oh, yeah, that’s another creationist myth that “mutations really don’t help evolutionary theory at all.”  Wrong again.

In another post, from Rosa Rubicondior: More Rapid Human Evolution, she discusses the humans that live in the Tibetan plateau, which is about 4000-5000 meters above sea level (about 12-15000 feet).  The oxygen levels are about 40% of sea level, which makes it harder for oxygen to cross the membranes from the lungs into the bloodstream.  Sea level dwelling humans have a hard time living at such a height because the body’s response to lower oxygen is to produce more red blood cells.  Unfortunately, this is problematic, because more blood cells makes the blood “thicker”, causing higher blood pressures, more clotting, and other problems, which are sometimes grouped together as “altitude sickness.”

Amazingly, and as a rather nice example of how evolution can work counter-intuitively, two of the mutations found (in Tibetans) normally cause low haemoglobin levels. So, one might expect adaptation to high altitude to involve making more red blood cells with haemoglobin in them, not less. However, a long-tern effect of more red blood cells is that the blood is thicker, so blood pressure tends to rise to push it around the body. This causes ‘altitude sickness’ in non-adapted people, one effect of which is reduced fertility and higher infant mortality. Han Chinese living in Tibet have an infant mortality rate three times that of Tibetans. So, coupled with other changes which allow their bodies to use oxygen more efficiently, these mutations counter the tendency to make more haemoglobin, so avoiding altitude sickness, while still being able to live with 40% less oxygen.

Wow.  So lower fitness (in the sense of producing the next generation) selects against higher red blood cell levels, while the environmental pressures (lower oxygen level) select for other mutations or normal physiological processes that allow their bodies to live with the 40% less oxygen.

So we see in this example how humans can adapt to new environmenrts by a simple process of Darwinian Evolution by natural selection acting on variations in the genome and, when the conditions are right and selection pressure is high, how this can take place over a very short period of time. It also demonstrates that a mechanism clearly evolved for short-term emergency situations like blood loss and temporary high altitude, such as might well have occurred in a nomadic hunter-gatherer, is not always suitable for a permanent solution and may actually create a long-term problem which needs to be countered. In this situation, a mutation which would normally be disadvantageous because it would prevent this short-term solution, is actually an advantage.

This response to the environment was relatively quick (at least with respect to evolutionary change) and observable, once again demolishing another anti-evolution myth.  

Remember, fighting the anti-evolutionists is a moving target.  You close down one logical fallacy, another one pops up.  The list of crazy discarded anti-evolution arguments is quite long, and we get to add this one as another.

 

The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!