Is the Human Animal Still Evolving?

Yes, but it’s complicated. And it might be accelerating.

Darwin first proposed his Theory of Evolution in 1859 in his ground-breaking On the Origin of Species. Based on decades of analysis and observations while on his famous voyage on the HMS Beagle, he explained all species are derived from lower species through the process of natural selection, making life a complex tree, of which humans are a distant, tiny branch.

However, some argue we have hindered or stopped our evolution because we no longer allow natural selection to run its course. They claim medicine, birth control, compassion, war, our ability to drastically alter our surroundings, etc. makes it possible for almost everyone to pass on their genes without selection and prevents those with the fittest genes from passing them on more than others.

Author Robert Black agreed when he said “Human beings have evolved so fast, relative to other life on Earth, and this has never been properly explained, but now there are signs that the human race has burned out in evolutionary terms, and perhaps it is our time to devolve.”

Black and others who agree with him, though, have underestimated Mother Nature. Evolution is a powerful, primordial force that even the human animal can’t stop, despite our best efforts.

The Birds and the Bees

Evolution is about struggle, survival, sex, and death.

Evolution happens through natural selection, in which nature chooses which members of a population are allowed to pass on their genes based simply on which can to survive and reproduce. The fittest naturally produce more offspring, thus passing on more of their genes. Therefore, across generations, the gene pool of a species is stripped of genes that hinder survival and reproduction and is filled with those that help it.

For example, imagine a population of insects on the white trunk of a tree. Those insects which are more obvious to predators have less chance of survival, and those that blend in have a greater chance of survival. The insects with the genes for light colors will survive and reproduce far more than those that have the genes for dark colors. Therefore, in this case, nature selects for light colors, and the population’s gene pool will have far more of them than dark colors.

Now imagine the trunk switched to black. The genes that encode dark colors would now be beneficial, while those that encode light colors would make the insects vulnerable to predators. Over multiple generations, the population of insects would become darker, as light color genes would not get passed on nearly as much as dark ones because those with light ones would die at a higher rate.

Although this example is simple, it demonstrates that the fitness of a gene is relative to a specific environment. If the environment changes, then so does the definition of fitness.

Now imagine half the insect population relocated to another continent, with different climate, predators, etc. The genes selected for will be radically different from the original population due to a radical change in the environment. Fast forward a hundred years and the two populations will have diverged substantially. Fast forward long enough and they will have diverged enough to be genetically incompatible, meaning they can no longer produce offspring, making them a new species.

If the original population continued to subdivide and relocate to different areas with different obstacles to their survival and reproduction, then the original population would be the origin of numerous species. Therefore, all species share a common ancestor at some point in their history.

Furthermore, gene mutations accelerate evolution. Due to damage or errors in replication, DNA is frequently altered. For the most part, not much happens, but some of these alterations can give an organism an evolutionary advantage or disadvantage, thus altering rates of survival and reproduction. If a mutation provides a benefit, it will get passed along more than others and become common in the gene pool. Overtime, the gene pool will become inundated with beneficial mutations, thus changing the genetic makeup of a population very quickly.

Therefore, starting some 4.5 billion years ago, the process of natural selection has turned simple microorganisms into a vast tree of both the simple and complex life forms we see today, including us.

“Evolution is adventitious and not foresighted. Only through the deaths of an immense number of slightly maladapted organisms are we, brains and all, here today.” –Carl Sagan, Dragons of Eden: Speculations on the Evolution of Human Intelligence

Our Recent Adaptations

Adults can drink milk. It’s strange for adult mammals to drink milk. After childhood, all other mammals lose the ability to create lactase, an enzyme needed to process lactose. However, humans have evolved the ability to continue lactase production throughout their lives. This characteristics is thought to have arisen around the same we started large scale animal husbandry, which makes sense as being able to consume nutrient-dense milk would give an evolutionary advantage.

“The first time that we see the lactase persistence allele in Europe arising is around 5,000 years BP [before present] in southern Europe, and then it starts to kick in in central Europe around 3,000 years ago,” claimed professor Laure Ségurel.

Our brains are shrinking. Our brains are noticeably larger than our evolutionary cousins, yet they have been shrinking since the stone age. Some estimate that they’ve shrunk 10 percent. Why this has happened is anyone’s guess, but some of the suggested reasons are loss of body weight due to climate fluctuations, less of a need to store information internally due to external methods such as cave drawings and writing, and mate selection such as Brian Hare’s “Survival of the Friendliest.”

Our wisdom teeth are disappearing. Our ancestors had large molars, likely to help them process tough foods, such as uncooked roots and meat. But as we evolved into the Homo genus, our molars began to shift in the other direction. Using a new mathematical model published in Nature, researchers have shown that our teeth evolve in a predictable pattern based on a handful of simple rules. Not only does this model explain the jaws and teeth found in the fossil record, it predicts our wisdom teeth will become a thing of the past.

Our immune systems are always in flux. Humans have always been in an arms race with pathogens. As pathogens evolved, so did our immune system. As we migrated to new locations, our immune systems had to change to compensate for new threats. Even when we domesticated animals, living in such close proximity put serious stress on our immune systems. Therefore, overtime, we evolved to defend ourselves against the unique threats in a given location. However, due to globalization and interbreeding, we have shared beneficial genes and exposed each other to new threats.

“The migration fluxes and the admixture of different populations are reaching unprecedented levels, allowing faster expansion of advantageous alleles,” said Domínguez-Andrés and Netea.

We are getting colder. Some studies have shown that the average body temperature has been steadily decreasing for the last 200 years. This is possibly the result of a more sedentary life-style, dietary changes, or a response to a warming climate.

The authors of one study found that “the body temperature of men born in the early to mid-1990s is on average 1.06 F lower than that of men born in the early 1800s. Similarly, they determined that the body temperature of women born in the early to mid-1990s is on average 0.58 F lower than that of women born in the 1890s.”

Future of the Human Animal

Human evolution is about to get faster and weirder.

1. Climate change is already drastically altering our environment, forcing us to adapt at an ever accelerating pace. The planet is getting hotter, global diversity is plummeting, crop yields are falling, and some have suggested it could make us more susceptible to pandemics.
2. Gene editing will allow us to decide which genes we want and which we don’t, taking nature out of the equation.
3. Genetic screening in fetuses will allow us to deselect for certain genes, such as those that may cause complications or health risks, again removing nature.
4. Living on extraterrestrial bodies such as the Moon or Mars will expose us to unpredictable obstacles, forcing us to adapt to a radically new environment. Plans for both a Moon colony and a Mars colony are underway, yet we are not sure how humans will adapt to either.
5. Externalizing information will continue to accelerate with technology, perhaps shrinking our brains even further. This is not necessarily a bad thing, as it is thought that this simply makes them more efficient.
6. Brain implants like Elon Musk’s Neuralink will change human evolution unpredictably. There’s no telling what the long-term impacts of something like will be.

No body can say for sure how the human animal will continue to involve, as we have done something no other species could: take evolution into our own hands. Let’s just hope it’ll be positive.

“It is our ultimate purpose to continually evolve as a species both physically and emotionally, as change is the mechanism for growth and development, and if we fear change we stunt our own growth and with it, human evolution.” -Kat Lahr, Anatomy Of Illumination

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