Tuesday, March 23, 2010

Modern evolution in humans

On page 218, Jerry Coyne asks the question "Are we still evolving?". Many types of natural selection are no longer existent because of modern nutrition, sanitation, and medical care. Are humans moving past natural selection with the use of technology? Are humans actually getting smarter and stronger or are we on a continuous path? Also, Coyne discusses how many genes have come full circle, genes that once were helpful to us are now hurting us in our modern world. So could this possibly mean that humans are backtracking, or "de-evolving" (219)?


  1. Many argue that evolutionary factors are no longer at work since most people are capable of living long enough to reproduce. However, evolution is very likely still at work and maintaining the continuity and change of the human race. Although these forces can not necessarily be seen in a few generations, genetic recombination still assures some will be more likely to reproduce than others. Steven Stearns of Yale University led a study testing the fertility of about 14,000 Massachusetts women. They found that "sout, slightly plump (but not obese)" women tended to have more children. This is because very thin women tend not to ovulate. Since it is a selective advantage to be slightly shorter and heavier, women over time will attain these characteristics. The slight changes in women's stature unveils the slow continuity and change of modern evolution.
    The most interesting debate of modern evolution is the rate at which it occurs. Steve Jones at University College London argues that male fertility controls adaptation rates. He claims that sperm are more likely to mutate than eggs, especially in older men. Since men tend to have less children and at a younger age, there is less genetic variability. Thus, the evolutionary process is drastically slower.
    On the contrary, the Hawks-Cochran study at the University of Madison claims evolution is occurring more rapidly. By studying skulls throughout time, they found that many features, such as size and shape, have morphed more drastically in recent years than ever before. Although the rate at which evolution unfolds is debated, most agree that the forces are, and always will be, at work.


  2. I think that humans are still evolving today but evolution may not be as fast as it was in the past. With better sanitation and medical technology, people who would have died in the past are now able to live longer. Modern society slows down natural selection by allowing those who are less fit to survive. Even though natural selection may not have such a great role in making humans smarter and stronger, humans are becoming smarter and stronger on their own due to both education and medical knowledge improving drastically in the past centuries.
    Going along with what Dani said, there still is evidence that evolution is occurring today. According to National Geographic News, scientists have recently found over 700 regions in the human DNA that show strong selection at work. Genes that were affected by selection the strongest include those that deal with skin color, bone formation, and the metabolism of foods. According to Are We Still Evolving?, a gene called CCR5-32 which offers some protection against HIV appears to be increasing in some populations in Africa. This discovery shows evolution at work since a gene that allows a person protection to a disease would be a selective advantage, especially in a country where that disease is widespread. These examples show evolution occurring today in regards to human DNA. While some genes appear to hurt us today more than they once did, this does not necessarily mean we are de-evolving. These genes were a selective advantage at one point, leading to them being passed on to descendants. Over time, these genes became less of a selective advantage but remained in the DNA of humans because they were not detrimental enough to lead to natural selection deleting these genes in the whole population.
    Sources: http://news.nationalgeographic.com/news/2006/03/0308_060308_evolution.html

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  4. Humans definitely aren’t moving past natural selection just because of effective medicinal aid. It is true that the effects of technology in helping reduce mortality rates has allowed for less advantageous characteristics to become pronounced in each developing generation, such as heart problems being a hereditary trait, but a recent study done by Stephen Stearns of Yale University concluded that humans are still undergoing constant evolution, and even thought it’s slow and gradual, the results show that the predicted rates of evolution in humans are the same with those of plants and animals. Taking advantage of data collected as part of a 60-year study of more than 2000 North American women in the Framingham Heart Study, researchers analyzed a handful of traits important to human health. By measuring the effects of these traits on the number of children the women had over their lifetime, the researchers were able to estimate the strength of selection and make short-term predictions about how each trait might evolve in the future. After adjusting for factors such as education and smoking, their models predict that the descendents of these women will be slightly shorter and heavier, will have lower blood pressure and cholesterol, will have their first child at a younger age, and will reach menopause later in life. Therefore, I believe that natural selection remains, for the most part, unaffected by the presence of modern nutrition, sanitation, and medical care.
    Regarding the second part of the prompt, where Coyne discusses human backtracking, or “de-evolution,” I believe that gradual evolution is constantly in progress. If by de-evolution, you mean that we take away parts of the anatomy that prove to be leading causes of illness or degenerative effects, then it is true that humans are in fact de-evolving, because, for example, studies have proven the shrinking of the appendix over time. However, this can also be seen as forward evolution, in which the body recognizes the presence of the appendix as harmful and thus begins its eradication. Therefore, I believe that backtracking is present in humans, but it’s for increasing the chance of survival and should thus be labeled as forward evolution.

    Sources: http://mybroadband.co.za/vb/showthread.php?220969-Are-Humans-De-Evolving&s=c85c2adb457ec0a439759c1d13c79a72&p=3710847#post3710847

  5. Quite an argument could be made for the absence of evolution in humans. Modern technology such as medicine, surgery, sanitation etc. has interfered with the deaths of numerous people. About 250 million people alone in the US receive medical care. (CBO) Vitamin and mineral pills are also available for all those who care to purchase them. The streets and public areas are also kept very clean and sanitized. With technology such as soap and hand sanitizer, it helps stop the spread of disease and infections before they happen. This makes it so that many of those who would have died from illness, malnutrition, or disease live on with medical assistance. Many people survive to sexual maturity, and who would have died still live to pass on their genes, which counters evolution, and may in fact, induce de-evolution.
    Humans also learn to make our own tools. With the lack of natural weapons such as sharp claws or a menacing set of jaws, we have learned to make our own non-biological weapons, such as guns. If humans were constantly under duress from other animals and had to fight back, surely we would have gained some sort of biological weapon we could use against other predators or prey. However, with such weapons, our bodies do not need any biological adaptations. This means that we are limiting our potential to evolve into a more advanced species by making our own tools since we do not need the natural adaptations. Natural adaptations are substituted by artificial ones that we create ourselves.
    However interesting this case may be, studies still suggest that “Human evolution hasn't ground to a halt. In fact, we're likely to evolve at roughly the same rates as other living things.” (Stearn) He has studied human evolution and conducted a 60-year study that comes to the conclusion that women that are slightly heavier and shorter tend to have an evolutionary advantage as those who are skinny tend to not ovulate. This will also help women have lower cholesterol and blood pressure. Along with these benefits, they will also have their first child at a younger and reach menopause later in life, which allows them to produce more offspring in their life. (ScienceDaily) Even if his studies are ludicrous, as some could argue that taller and skinnier women may have the sexual selection advantage, it has been argued that we as a species are slowly getting smarter. Either way, our species are still changing.

    CBO: http://www.cbo.gov/doc.cfm?index=4210&type=0
    Science Daily: http://www.sciencedaily.com/releases/2009/10/091019162933.htm