Are we still evolving?

You know, the spleen is an organ that often goes unrecognized for its remarkable functions. It serves as a vital oxygen reservoir by storing red blood cells, which are responsible for carrying oxygen throughout the body. A larger spleen allows for a greater amount of oxygen to be released into the bloodstream, even during moments between breaths. Interestingly, certain diving mammals like whales and seals also possess enlarged spleens to optimize their diving capabilities.

However, unlike these diving mammals, we cannot simply strengthen our spleens through repetitive diving. Evolution does not work in such a direct manner. The Bajau divers, who have inhabited aquatic environments for thousands of years, experienced a genetic change along their evolutionary path, resulting in individuals with larger spleens. This adaptation allowed them to consume more resources and consequently increased their chances of survival. Over numerous generations, this genetic advantage became more prevalent in the population. This process exemplifies natural selection, where a gene becomes more widespread over time as individuals carrying that gene are better equipped to withstand environmental pressures.

Since the emergence of our species, humans have thrived in diverse environments across the globe. Our ancestors encountered countless environmental challenges, such as varying food sources, climates, and, as we settled into larger communities, the spread of diseases through domesticated plants and animals. Throughout history, our survival hinged on the presence of new and improved versions of genes that offered advantages in combating these challenges.

For instance, Himalayan populations developed the ability to breathe air with significantly lower oxygen levels compared to the majority of humans. In certain parts of Africa, individuals exhibit enhanced resistance to the germ responsible for Lassa fever. Populations that migrated closer to the poles developed lighter skin, allowing them to efficiently absorb sunlight at high latitudes, where sunlight is less intense. This adaptation was crucial since our bodies require sunlight to synthesize vitamin D.

Now, let's shift gears and discuss another topic—dairy products. I must say, many of us have a fondness for them. Calcium found in milk plays a role in vitamin D synthesis. However, as animals mature, many of them lose the ability to digest milk effectively. Well, that's unfortunate for them. Thankfully, some of us underwent a genetic change that allowed us to maintain the ability to drink milk throughout our lives. As milk provides a reliable source of protein and calories, the ability to digest it evolved independently in various regions.

These changes, along with countless others that have shaped our species, have occurred through the process of natural selection. Genes become more prevalent because they confer advantages for survival. However, the present times are different. Humans have invented numerous tools, developed medicines, implemented sanitation practices, and created environmentally controlled living spaces. We have access to an abundance of food, to the extent that we often don't know what to do with it all. When was the last time you thought you might be attacked by a tiger while going out for lunch? The truth is, people are not dying as frequently as before. Human life expectancy has more than doubled in the past couple of centuries.

Now that the majority of individuals survive past the age of reproductive capability, does that mean natural selection no longer applies to us? Are we living in a post-Darwin era of humanity, in a hyper-technological trans-human utopia where evolution has ceased? The answer is no. Natural selection is not the sole driver of evolution, my friends. Some genetic changes become common purely due to random chance.

Allow me to illustrate this concept. Here, I have a jar filled with M&M candies. Each bag of M&Ms represents a population with a specific genetic makeup. However, this particular population of M&Ms differs significantly from the original one, and so will the future population. This change occurred due to a chance event when I randomly grabbed a handful.

Delicious, isn't it? If I were to repeat this process multiple times, I would obtain different results with each attempt. The same principle applies to genes. Random events can determine which genes survive and become more prevalent, rather than solely relying on environmental factors. This phenomenon is called genetic drift, as opposed to natural selection.

Now, imagine a group of highly advanced life forms inhabiting a particular region. Suddenly, a meteor strikes, leading to the survival of only a few individuals by random chance. Over time, the population will look remarkably different from its original composition. Alternatively, through a series of unfortunate events, a small group may end up on a secluded island. The characteristics of this new population will depend on the individuals who founded it. Similar processes can occur within human populations as well. If you have European ancestry, there's a high probability, around 90% or more, that you have wet, sticky earwax. On the other hand, if you're of Native American or East Asian descent, there's about a 90% chance that you have dry, flaky earwax. This difference is influenced by two distinct versions of a single gene. However, the type of earwax one possesses doesn't necessarily provide a survival advantage. The prevalence of each version in specific regions likely resulted from the gene versions carried by the initial humans who migrated there. Are you following along? It's genetic drift at play.

However, the impact of chance events in genetic drift is more significant in small, isolated populations. And as for humans, well, we're not quite like that. We move around, share cultures, and as we do so more than ever, our genes mix too. This has led to decreased genetic differences among human populations as a whole. When rare gene variants do arise, they are more likely to be diluted out through this mixing process. The fact that humans are living longer and experiencing reduced mortality rates, thanks to our incredible inventions, might also diminish the influence of natural selection. Furthermore, our mobility and extensive intermingling may reduce the effects of genetic drift. As a result, extraordinary adaptations like the Bajau's super spleens will probably become less common in the future. When you consider all these factors, it becomes clear that the notion of humans becoming increasingly similar as Darwin's ideas fade away and we mix ourselves up is quite inaccurate. Even characteristics such as skin color or eye color involve complex interactions among numerous genes in various combinations. Just look at the vast range of physical appearances we observe today in individuals with mixed ancestry. People will always exhibit considerable diversity.

However, there is one more process that can influence our evolution apart from natural selection, and it relates to how babies are conceived. You can ask your parents about that one. Genes don't randomly find each other; individuals have the choice of whom they mate with. If someone is attracted to individuals with the largest, most impressive antlers in a herd, this preference can lead to offspring with fancier antlers, even if having fancy antler genes doesn't necessarily enhance survival in their environment. This phenomenon is known as sexual selection, where the genes that persist are connected to the choices individuals make regarding their mates. The impact of sexual selection on the future of human evolution is a topic of ongoing debate. For instance, if the traits we find attractive today are correlated with intelligence (which many scientists believe to be the case), it could mean that future humans will possess traits associated with intelligence, such as larger brains or genetic predispositions. Once again, we're not discussing genes that aid our survival against germs or adapt to our environment, but genes that may simply enhance our attractiveness. Now, this final aspect might evoke mixed feelings depending on one's perspective. Thanks to our tools, the future of human evolution might be partly under our control, or at least subject to our attempts at control. As a species, we already rely on machines to thrive and flourish, and our dependence on them will only grow stronger in the future. This process gradually diminishes the role of natural selection.

Furthermore, we won't just rely on machines for assistance; eventually, we may achieve physical or neural integration with them. The consequences of such integration on our genes, and which genes become more or less common, remain unknown. With the advent of genetic engineering, we now possess the ability to insert customized genetic sequences into living organisms, including ourselves. We might even have the power to select and shape the genes we desire for our offspring. This form of evolution is unparalleled in any other species.

The extent to which these future forces will impact our species is also within our purview, but their influence will undoubtedly be significant. Evolution is a process of change, and it never ceases—for our species or any other. While natural selection may have less dominance in determining our future due to our impressive intellect, change remains constant.

It's intriguing to contemplate that we may be the only species on Earth with the power to shape our future to some extent. However, this power comes with great responsibility. And hopefully, it also comes with a refreshing glass of milk and an Oreo.

Stay curious.

Hey, what's up, guys? I'm currently in Florida working on our upcoming episode. Before you go, I have some exciting news for all the history buffs out there. PBS has just launched a brand new YouTube channel called PBS Origins, focusing on history. It will be home to a variety of fantastic new shows. Right now, you can check out "Historian's Take," which explores history through the lens of pop culture and delves into what ancient civilizations can teach us about our own and our future.