12.3: Are Humans Still Evolving?
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The mechanisms of inheritance, or genetics, were not understood at the time Charles Darwin and Alfred Russel Wallace were developing their idea of natural selection. But in the1950s genetics and evolution were integrated in what became known as the modern synthesis—the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s and is generally accepted today. In sum, the modern synthesis describes how evolutionary processes, such as natural selection, can affect a population’s genetic makeup, and, in turn, how this can result in the gradual evolution of populations and species. The theory also connects this change of a population over time, called microevolution, with the processes that gave rise to new species and higher taxonomic groups with widely divergent characters, called macroevolution.
Since evolution means change over time, and since evolution is not linear, humans have not stopped evolving, nor are humans the end result of evolution. All living things are influenced by the forces of evolution and therefore continue to evolve.
Examples
Evolution and Flu Vaccines
Every fall, the media start reporting on flu vaccinations and potential outbreaks. Scientists, health experts, and institutions determine recommendations for different parts of the population, predict optimal production and inoculation schedules, create vaccines, and set up clinics to provide inoculations. You may think of the annual flu shot as a lot of media hype, an important health protection, or just a briefly uncomfortable prick in your arm. But do you think of it in terms of evolution?
The media hype of annual flu shots is scientifically grounded in our understanding of evolution. Each year, scientists across the globe strive to predict the flu strains that they anticipate being most widespread and harmful in the coming year. This knowledge is based in how flu strains have evolved over time and over the past few flu seasons. Scientists then work to create the most effective vaccine to combat those selected strains. Hundreds of millions of doses are produced in a short period in order to provide vaccinations to key populations at the optimal time.
Because viruses, like the flu, evolve very quickly (especially in evolutionary time), this poses quite a challenge. Viruses mutate and replicate at a fast rate, so the vaccine developed to protect against last year’s flu strain may not provide the protection needed against the coming year’s strain. Evolution of these viruses means continued adaptions to ensure survival, including adaptations to survive previous vaccines.
Diseases and Mutations
One reason we may think that humans don’t evolve is because an individual cannot evolve—only a population can, and this takes many generations, which is too slow for humans to be able to see in their own species. Another reason is that humans cheat—we don’t live under the laws of natural selection as much as other species do. We are smart and tend to invent our way out of problems (wearing glasses or taking insulin, for example) instead of just dying because of troublesome genes and not passing those down to the next generation. Humans are still evolving. Some examples are the ability for some adults to digest lactose, and the emergence of new “crowd” diseases, with both occurring after the advent of agriculture. Traditionally hominins and humans were hunter-gatherers, who hunted, foraged, and collected animal and plant foods for small, nomadic family groups. Around 10,000 years ago humans switched from hunting and gathering to domestication and agriculture. It is theorized the humans did this because of dwindling population numbers; agriculture produces more food, which allows more humans to be born and survive. In other words, agriculture kept us from going extinct; however, it also had very serious effects on our biology and society (Etheridge-Criswell, 2018)
Mammals become lactose intolerant as part of the weaning process. As adults, humans should not be able to digest lactose. However, two types of mutations happened in history to allow some people to be able to: one was in Africa and one in Europe; both of these were connected to the advent of agriculture and animal domestication. This shows evolution still occurring among humans. Other examples include smaller teeth and teeth crowding and the AIDS epidemic (see below) (Etheridge-Criswell, 2018).