Predicting Future Evolution (Spring 2019)

One of the activities that I regularly have my students complete in my Evolution course is called “Future Evolution“. The activity sends students on what most evolutionary biologists consider a fool’s errand: to try to predict the future evolution of some particular trait in some particular species. Making such predictions is really difficult for these basic reasons:

• So much of evolutionary change relies on random mutations, and predicting where or how new mutations might arise is nearly impossible;
• All future genetic changes will occur in the context of the existing genetic architecture of each organism, and although we are getting better at understanding this architecture we are a long ways off from being able to predict what’s possible to change in traits by making genetic changes; and
• Although there are some very clear environmental changes occurring now — most of them caused by human activities — it is difficult to know if these changes will be sustained for long enough to lead to changes in the traits of particular species.

Why send students off to make predictions when most evolutionary biologists would be loathe to make such predictions themselves? Well, as a thought exercise making these predictions is actually really valuable.

A skill that I try to teach to all of my students is to “tell an evolutionary story”. I want students to be able to explain what kinds of changes to existing traits would be required for a new trait to evolve, how the resulting trait variant might provide advantage in a particular environment and therefore increase in prevalence due to some form of selection, and explain how that overall evolutionary process would produce this new trait as an adaptation of a particular species. When we look retrospectively at traits that have already evolved, the goal is to verbalize a reasonable scenario under which this trait evolved. When we make predictions about the evolution of novel traits, the goal is to predict the evolution of a trait in a particular species that feasibly might occur given what we know about recent changes to some aspect of that species’ environment. The prediction doesn’t necessarily have to be likely to come true — even most reasonable evolutionary predictions are still low-probability outcomes — it just has to be feasible. Making these feasible predictions requires a strong understanding of how evolution works, which is why we do this exercise in our final class session.

Every semester I get some really fun, interesting, provocative, and off-the-wall predictions. Below are some highlights from one section of this semester’s class…

Prediction: Human hands will evolve a shape that better allows us to use our phones

Ah, the power of cell phone technology! We often overestimate the evolutionary impact of the here and now, and no prediction better illustrates this than various “cell phone prophecies” that seem to always come up during this exercise. The first problem with this prediction is that our devices are themselves evolving way too fast to be a sustained force of natural selection. Human generation time is about twenty years; in that time, cell phone designs have completely changed. It’s impossible for long-lived and slow-developing humans to evolve genetically in response to such a rapidly-moving cultural environment. And then there’s the question of reproductive advantage: exactly what would be the reproductive fitness benefit of being able to better use a cell phone? Do we think that the most evolutionarily-successful humans are the ones who send texts the fastest? (And by the way, if you still send texts with your hands, you are behind the times). Although not perfect, cell phones are also designed with the existing (ages old) evolved shape of the human hand in mind, suggesting that there might not be much selection for modifying this anatomy.

Prediction: Humans will lose their hearing due to listening to loud music on their headphones

Wow, how Lamarckian! Lucky for our offspring that not all the unhealthy things that we do to our bodies actually get passed on. You can’t damage the genes you have that allow for the development of hearing by listening to your headphones (no matter how loud), so your offspring will be fine… even if you can’t hear what they are saying.

Prediction: Human body size will decrease in response to limited resources, decreased space, and cultural norms/sexual selection

It’s tempting to think about overcrowding in human populations and to imagine that the smaller among us might be more likely to survive. After all, this is what seems to have happened to both certain populations of humans as well as populations of other species such as elephants. But the issue here is whether the factors that may have caused the evolution of smaller stature would be present in the future. The idea that we are “running out of space and resources” is not really valid in this context; despite increasing population densities, we enjoy unprecedented access to resources.

The question of cultural norms and sexual selection is an interesting one. Unless there is some advantage in choosing a shorter mate, it is hard to be confident that shorter stature will be the sexually-selected trait of the future. There’s even some evidence that there is sexual selection for average height!

Prediction: Humans will gradually evolve to have less body hair due to a combination of rising temperatures and hair removal in response to cultural norms

This prediction is a double-whammy of evolutionary misconceptions. The first misconception is that we are not already pretty well evolved to dissipate heat. We are essentially still a tropical ape, notwithstanding some variation in how hirsute each of us may be. Even the hairiest among us retains the fundamental adaptations of our Savanna-dwelling African ancestors: a body with minimal hair and the ability to efficiently remove excess body heat via perspiration. This is not to say that the health risks of rising temperatures are not real: I am just skeptical that minor variations in amount of body hair are going to determine who does and not survive the climate change heat waves of the future. Plus, in most of the world we currently rely on clothing to maintain optimal body temperature; most of the population will be able to just take off a layer of clothing as temperatures warm.

And what about the hair removal dues to cultural norms? Well obviously we are not talking about genetic evolution if hair removal is a cultural norm. And can we count on cultural norms staying the same for long periods of time? History suggests not… beauty standards oscillate pretty wildly across periods of evolutionary time.

Prediction: Humans will evolve to lose their pinky toe due to continued bipedalism

This is just silly. Have you ever injured your pinkie toe? If you have, you know it helps maintain your balance as you walk. And we have been bipedal for a long, long time… why would the pinkie toe suddenly become a disadvantage?

A lot of these evolutionary predictions are kind of on the border. Maybe they could be
feasible, but we just don’t know enough to accurately assess their feasibility.
Below are some examples of these “marginal” predictions.

Prediction: Humans will evolve the ability to tolerate more small particle air pollution and be less susceptible to the health problems caused by these particulates

The appeal of this prediction is pretty obvious: the air quality is really bad in many places across the globe, with levels of particulate matter (PM) pollution causing premature death and other health problems. This would make one think that any person with a mutation that lowered their sensitivity to PM would be more evolutionarily successful. Whether or not that is true really depends on when the impacts of PM set in and how severe they are. One interesting — and depressing — aspect of PM is that it can increase rates of asthma in young children. If these health effects really prevent a sizeable fraction of young people from reaching adulthood, they could select for tolerance of PM.

The other unknown in this prediction has to do with the prevalence and persistance of the environment that could foster these genetic changes. While a lot of people are exposed to PM pollution, we don’t know if that number will increase or decrease in the future. If enough countries reduce PM pollution, there won’t be sufficient selection for this prediction to come true… which would certainly be better for overall human quality of life (usually, the conditions that cause selection for genetic changes in human are pretty unpleasant).

Prediction: Domesticated cows will become larger and meatier due to genetic modification by humans

We can, but will we? That seems like the major unanswered question lurking behind this question. Our powers of artificial selection have been augmented by the ability to directly edit the genome of the organisms we have domesticated, making this prediction seem more “when” than “if” in terms of feasibility. So the real question is not one of capability, but one of motivation: is there any reason why humans would need larger and meatier cows? Perhaps we are actually heading, culturally/technologically-speaking, towards synthetic meat. If the technologies for producing protein-rich meat without raising live cows can progress far enough, perhaps we will abandon our mutualism with cows (at least at the industrial scale). The unpredictability of human cultural technologies and preferences makes this prediction a bit hard to assess.

Prediction: Raccoons will evolve an increased capacity to use tools in human-dominated environments

Whether this prediction will come true depends on a lot of factors that are not easy to ascertain. But it is premised on an idea that at least has merit: increasingly, at least some populations of raccoons are highly dependent on gathering food from human-created environments. We also tend to prefer that raccoons are not hanging around our homes, so we are locked in a coevolutionary battle with the raccoons: we invent new cultural technologies to prevent them from raiding our garbage and other sources of food, and they are either learning or perhaps even genetically evolving to become better at obtaining the food we try to hide away. And it is that last concept that’s critical to this prediction: if raccoons are going to genetically evolve, they have to not just learn how to defeat human cultural technologies, they actually have to evolve to be better learners and inventors of technology. Whether this actually happens is partially a matter of chance (Will some raccoons accumulate mutations that change the way they learn?) but also an ecological question (Is getting food in human settlements really so challenging that tool use would be an advantage?).

Looking at all the “wrong” and “marginal” predictions above, you would think that it is
pretty hard to make a feasible evolutionary prediction. And it is, but below
are a few feasible predictions created by this semester’s class.

Prediction: Polar bears will lose some density of their fur and fat-layer insulation due to a warming climate

This seems like a reasonable and rather obvious prediction given how extreme climate changes are in the Arctic. I suppose the only question is whether this would actually require a genetic change, potentially leading to actual evolution. Like many mammals, polar bears already maintain the ability to respond to their environment, which leads to the question Would changes in polar bear fur and fat be in response to the environment or an actual evolved change in the genetic basis of this trait? Perhaps given the food limitations polar bears now face, it might be the case the individuals that are less genetically-predisposed to put on insulative fat would fare better. Such a change would represent a shift in the response of polar bears to their environment; such genetic set-points are likely to evolve in response to changes in climate.

Prediction: The ability of humans to “self-navigate” from place to place will decline

This is an interesting prediction because humans are not like many migratory birds: we are not born with the biological capacity to navigate. The only genetically-mediated capacity we have to navigate through our environment is our ability to learn, and over the course of recent human history we must have learned a big variety of strategies for navigating. In recent time, that learning has to do with how we employ tools — maps, compasses, sextants, and of course now GPS-enabled devices — to get from one place to another. So I don’t think that this prediction, if feasible, is about genetic evolution. The only way that it could be a prediction about genetic evolution would be if we actually have a particular genetic capacity to learn how to navigate… which seems pretty unlikely. I guess if there were differences in the genetic potential of different people to learn navigation, one could argue that our current devices “release” us from that selection. But it is also not clear for how long we might have already been released from that sort of selection.

What’s more likely in this scenario is that this prediction would be true for our cultural evolution. There are still many people across the globe whose cultural traditions include strategies for navigating across the landscape using only environmental cues (such as the movement of the sun and the position of landmarks). But the number of people who are passing on those traditions may be in decline as more and more of the human population gains access to technologies that require a different kind of learning (how to navigate a cell phone, how to search for a desired location). Like a lot of other cultural innovations, the ability to use these new technologies will supercede the use of older navigational practices so long as our environment is one that contains GPS devices and GPS satellites. It’s interesting to ponder how dependent we all are on these large-scale social technologies, but this dependence would only be maladaptive if somehow our large-scale civilizations collapse (in other words, if you like navigating using GPS, make sure that we don’t destroy large-scale civilization by allowing climate change and other large-scale environmental impacts to get too out of hand).