Science Advocacy
Science Advocacy
Welcome to Ask a Scientist, where we answer questions from our readers on a wide range of scientific topics. Got a scientific question? Drop us a line.
Q: Are humans still evolving? B.N. Bernalillo, NM
This is a fantastic question, B.N! A solid argument can be made that humans are no longer evolving because of our advanced healthcare and medicine. Sir David Attenburough, who has done more for science then UYBFS ever will, and has been knighted for his efforts, has suggested that he thinks humans are no longer evolving based on this reasoning, saying:
“We stopped natural selection as soon as we started being able to rear 95–99 per cent of our babies that are born.”
Say a child is stricken with juvenile diabetes on his 10th birthday. Prior to the invention of modern medicine, this was a death sentence – the child would have died from hyperglycemia and diabetic ketoacidosis within a short period of time, effectively eliminating his genes from the population. However, scientists were able to determine that a loss of insulin production in the pancreas is the cause of this form of diabetes, and since 1922, insulin (first from animals, now produced in bacteria) has been available to treat these children. Today, while the effects of juvenile diabetes can still be quite severe, if the child can maintain his blood glucose levels appropriately, he or she can expect to live a relatively normal life, certainly one that will be long enough to reproduce if that is their desire.
So in this case, science and modern medicine has enabled the spread of genes responsible for (or predisposing people to) juvenile diabetes. The successful treatment of any life-threatening childhood disease with a genetic component (cancer, cystic fibrosis, severe asthma) will have the same effect. On top of this, our ability to successfully treat or prevent potentially deadly infectious diseases in children (measles, rubella, pneumonia, diphtheria, etc) will, in theory, lead to an increased number of people who are more susceptible to these diseases over time.
Since evolution is driven by the passage of genetic material, the treatment of any medical condition that could impair an individuals ability to reproduce would have a similar effect. A great example of this is the treatment of infertility. The use of artificial insemination techniques, in vitro fertilization, and hormone therapies now allow people who would have had zero chance to pass along their genes to do so at a rate very similar to unaffected persons. The same would be true for women who are genetically predisposed to complications during labor, like those who require a C-section in order to deliver a healthy child. Before modern medicine, these women would not have been able to reproduce, and many may have died during attempted childbirth.
Finally, if you look at the issue from a population genetics perspective, any human intervention for a condition that increases the likelihood of a gene being passed on in a population as a whole would have a similar effect. For instance, while cancer strikes most adults after they have reproduced, over time it likely affects enough people of reproductive age that the ability to treat it, even if only to delay death long enough to reproduce, is likely to impact human genetics over many generations. The same can be said for non-medical modern human advancements. For instance, in the not so distance past, people in small populations who were considered less desirable by the opposite sex stood very little chance of reproducing. In contrast, in modern society, the opportunities to find mate are greatly increased by larger populations and global (or at least large regional) communication methods, like the internet.
Taken together, this paints a picture of a human population that is slowly becoming dependent on modern medicine, and this is undoubtedly true to some degree. So, does that mean we are no longer evolving?
With apologizes to Sir David Attenborough, it does not.
First of all natural selection and evolution are not the same thing. Natural selection is a process that “selects” for advantageous traits while putting less useful traits at a disadvantage genetically. Evolution is the actual change in traits of a species over time. Natural selection is not the only thing that drives evolution – random chance plays a big part as well. In addition, Sir David is assuming that natural selection needs to be “natural” or at least not man-made, but the term “natural” in this context just refers to a process that isn’t consciously driven by the premeditated decisions of humans. The process of natural section and evolution is alive and well in the human population, even if it looks a bit different than in most animals.
Perhaps the easiest example of modern human evolution is that of the disparate reproductive rates between developing and developing societies. In the countries like Angola, Niger, Mali, & Uganda, mothers typically have 6-7 children over the course of their lives. In the United states, that number is 1.9 kids, and in Japan it’s just 1.4. Even with a higher infant mortality rate in these developing countries, they are contributing to the human gene pool far more than the United States and Japan. Over time, this will lead to a population with more traits carried by persons from these developing countries – humans will evolve to be more like them.
On a smaller scale, height is being selected for in the Netherlands, the country with the tallest people in the world, because it’s women tend to prefer tall men, and the frequency of genes allowing adults to digest lactose is increasing as people across the globe continue to eat dairy products into adulthood.
While it may seem like we are allowing some disease-causing genes to pass on in today’s society, a recent study found a number of disease-causing genes that are reducing in frequency over time, including those that predispose people to Alzheimer’s Disease (potentially due to the “grandmother effect“). This same study also found that genes for blood hair and blue eyes are increasing (likely because of selection by potential mates), as are genes that make it harder for people to quit smoking, likely due to high mortality rates in this population.
Before we wrap up, it’s important to note that the idea of controlling our own evolution has taken our species to some morally calamitous destinations in the past. The two most terrifying examples being the Nazi attempts to “purify” their gene pool and the ethical quagmire of eugenics. Humans are still evolving, but attempts to control evolution by replacing natural selection with human selection are fraught with ethical and moral consequences that we as a species have demonstrated time and time again we are unable to handle.
Our evolution may be different from other animals because of our ability to preserve some disease-causing genes with our modern medicine, but it continues nonetheless. Humans are likely to look very different in 1,000 years and beyond. Many scientists agree that the our skins will get darker as the earth heats up from global warming, and we are likely to continue our trend towards becoming taller. It is also possible that we will all have red eyes, incorporate nano-robots into our blood, or just start to engineer ourselves. That is, as long as the machines don’t rise up against us.
