Are humans still evolving on Earth? The short answer to this biology question is yes. Human evolution continues to affect people, and natural selection is still working.
If you talk to an evolutionary biologist, you will learn that modern humans are changing and evolving all over the world, from Europe, Asia and Africa to North America, South America and Oceania.
A Short History of Evolution
In the middle of the 1800s, Charles Darwin and Alfred Russel Wallace proposed similar theories for evolution. After observing animal and plant life on the Galapagos Islands, Darwin developed the idea that evolution happens through gradual and small changes over long periods of time.
Wallace came to a similar conclusion after studying animals in South America and Asia. Their work raised the question of whether humans are still evolving today, and there is evidence to show that it is happening, reported in science news every day.
Definitions of Evolution and Natural Selection
Darwin's definition of evolution was descent with modification. This means organisms change and adapt over time because of inherited physical or behavioral characteristics that are passed down from the parents to the offspring. Organisms share a common ancestor, and evolution happens because of natural selection.
One of the mechanisms that drive evolution is natural selection, which means certain traits or characteristics are favored by the environment. This causes those organisms to survive, reproduce and pass on the favorable traits. It also eliminates organisms that do not have those desirable traits. Genetic mutations, migration and genetic drift are additional factors that are responsible for evolution.
It is fairly easy to see natural selection in action. For example, imagine a population of butterflies with distinct genetic variants. A mutation leads to a genetic change, so some butterflies have brown wings while others have white wings.
The brown wings make it easier for the butterflies in this area to hide from predators like birds, so more of them survive and pass on their genes. Natural selection makes brown wings a favorable environmental and genetic trait. Over time, gene frequencies change in the population, and brown wings outnumber white wings.
Are Humans Still Evolving Today?
Although some argue that people can overcome natural selection through technology, medical advances and other methods, human populations are not above natural selection.
Improvements in health care do allow individuals who may be less fit to survive and reproduce. However, humans are never truly isolated, which means that genetic drift and evolution caused by isolation rarely occurs.
Evidence That Humans Are Still Evolving
Although the human species has overcome certain obstacles and things that would kill them without technology, it does not mean that changes to the gene pool have stopped. The human genome is not unchangeable.
For instance, certain countries and areas have higher birth rates, which mean they supply more of their genes to the human species than other areas. Different environments make it easier or harder for people to survive. There are gene variants and mutations that can lead to new advantageous traits that will be passed on.
Evolution and Infectious Diseases
An infectious disease can wipe out an entire group of people. However, natural selection for resistance against certain diseases can help individuals survive. For example, a new disease may appear and kill some people while others stay alive. This leads to natural selection for those who overcome the disease.
Lassa fever and malaria show how natural selection in humans is pushing the gene pool to select for people with resistance to these diseases.
Certain traits, such as red blood cell disorders like sickle cell anemia, provide some protection from malaria. Regions like Africa that have many mosquitoes carrying malaria also have more people with sickle cell anemia. People who lacked that sickle cell trait were less likely to survive a bout of malaria; since they didn't survive, they didn't pass on their genes.
Certain genes may have also helped people survive the black plague. The plague left survivors with specific immune system genes, which continue to affect Europeans today and explain why they are more likely to have autoimmune disorders.
Their immune system genes coded for proteins that helped the body fight harmful bacteria. However, the same genes also appear to increase the inflammatory response from the immune system.
Evolution and the Environment
Humans can adapt and evolve to live better in certain environments.
For instance, people with darker skin and more melanin have better protection from the sun in areas closer to the equator. People with lighter skin in areas with less sun are able to get more vitamin D. Over time, gene mutations and variants have also been selected to allow certain groups to survive better at higher altitudes.
Those who live in the Andes Mountains have evolved to handle the lower oxygen amounts in the air. This adaptation to a higher altitude can be seen in people who can carry more oxygen in their red blood cells despite the air being thinner; they have more hemoglobin proteins in the blood to carry oxygen. This allows them to move oxygen more effectively throughout the body and survive in the mountains.
Evolution can affect groups of people in different ways. One example of this is how people in Tibet adapted to higher altitudes. Unlike those in the Andes, people in Tibet take in more breaths per minute instead of having more hemoglobin. This provides their bodies with enough oxygen to survive. They are also able to expand their blood vessels more, so the oxygen can travel better.
Evolution and High-Fat Diets
Sometimes the type of food that is available for humans to eat can affect evolution. The Inuit population has adapted to a high-fat diet through natural selection for genes that allow them to thrive on this type of food that they can get in their environment naturally.
In Greenland, the Inuit evolved to cope with a diet filled with high levels of omega-3 polyunsaturated fatty acids from seafood. Fatty meat is one of the few food options in the Arctic because vegetables and fruits do not grow in the harsh environment.
Despite eating a high-fat diet, the Inuit have lower rates of cardiovascular diseases and diabetes. Researchers believe their bodies have adapted to the fatty food through genetic modifications over time. Their bodies make less omega-3s and omega-6s because so much fat comes from their diet. Their genes also lower the level of LDL cholesterol, which is the bad type of cholesterol.
It is important to note that modern Inuit who do not eat the traditional high-fat diet have higher rates of diabetes. Researchers believe that those who have switched to the typical, high-carb diet that is common today are not adapted to it.
Evolution and Milk
You can see evolution by studying milk digestion in humans. Certain populations have genes that allow them to digest milk better. For most people, the ability to digest the lactose sugar in milk fades as they get older. However, some groups, especially Europeans, continue to be able to digest milk despite aging.
Northern European populations have genes that determine the activity of the lactase enzyme, which is responsible for digesting milk. Researchers have found that these groups continue to have active lactase enzymes as they get older. They also believe that this was the result of recent natural selection, within the past 5,000 to 10,000 years, because of the rise of dairy farming.
- Scientific American: Are Human Beings Still Evolving?
- JSTOR Daily: Humans Are Still Evolving
- Khan Academy: Introducing Darwin and Natural Selection
- UC Berkeley: Understanding Evolution: Natural Selection
- Encyclopaedia Britannica: Natural Selection
- YourGenome.org: What Is Evolution?
- Science: Black Death Left a Mark on Human Genome
- Science: Greenlandic Inuit Show Genetic Signatures of Diet and Climate Adaptation