Survival of the fittest... to die

One of these days a friend of mine reminded me of that wonder or nation called babirusa. For those of you who have not had the fortune of making its acquaintance, it is a kind of Indonesian wild pig with the peculiarity that its tusks, both the upper and the lower, sprout up (because of its looks it is often called the deer-pig or the deer-boar). The bottom ones are less problematic, but the upper ones curve backwards and in some cases they eventually pierce the skin, the skull and even the brain, with the amount of pain that such a perforation foreseeably entails.

One could wonder how is it possible that nature has allowed this to happen. The answer to this question reveals an aspect of evolution that is often overseen: evolution is not teleological, it has no objectives or goals, it has no ideas on how to "change" a species and it does not aim to "improve" them. Consequently, humans are not the "final product", but just another one in the long chain of evolution. It is true that we are very powerful, way more than any other species before us (by some accounts we might have exterminated competing species of hominids back in the day), but in the end we just obey one beautifully simple (and somewhat cruel) rule: if it survives, it stands, and the better it survives the long it will endure. Mosquitoes, nasty as they are, survive because they have figured out a way to reproduce faster than (technically exactly as fast as) they are killed by bird or cold weather. And if the conditions in an ecosystem became such that they cannot keep up with their death rate they will die out in that ecosystem, possibly until the conditions are reestablished and they spread from a neighboring region where they have managed to survive.

 

Photo: PxHere

For the babirusa, cases of self-injuring are common but not the norm. In most cases the males (the only bearers of these appendices) end up breaking their tusks in fights with other males, which ins probably the reason why they keep growing: if a strand were to come out with the peculiarity that their tusks stop growing after a certain age it would happen that in case they broke in a fight they would never again have a chance to win one, so they would have less offspring than their endlessly-growing counterparts and the feature would eventually be wiped out of the gene pool.

Conversely, if another strand appeared withe double the speed of tusk growth it could happen that they just do not have enough fights to ensure that the teeth break before skewering their brains, so they would probably tend to die younger than their normal-growth counterparts, have less offspring and, once again, the trait would be erased form the gene pool. (I have to clarify that this is just a mental exercise without any rigor, not a report that this has happened or a theory that it might happen anytime soon.)

At any rate these Indonesian pigs are not the only ones displaying this peculiarity. Many rodents also show tooth growth through their entire lifetime to compensate for the wear and tear that their feeding and living habits cause on their teeth. In fact for domesticated mice, hamsters and Guinea pigs it is always advisable to provide hard objects for them to gnaw on, lest their teeth grow out of control and end up hurting their jaw.

In the case of insects it is very common that some individuals sacrifice their lives for the survival of the colony (think of the raft-building ability of the fire ants), but even those who do not live in groups often find a violent deat at the hands (or claws) of their own kind. Praying mantises are one of these examples, where the female bites off the head of the male during the copulation and, once the fertilization of the eggs is done, feeds on the remains of the partner. This strategy probably ensures a full fertilization (preventing the male from "running away" halfway through the process) and helps the female to make up for the energy required to mate and lay the eggs. I am going to speculate that this strategy works best when the male-to-female birth ratio is significantly above 1 (or if females only spawn once in their lifetimes). In any case, it seems to work well, since mantises have been around  for the last 100 million years.

Contrary to the process of natural selection, where the best adaptation to the environment survives at the expense of the other not-so-well-adapted, human selective breeding is teleological: we created dogs and the modern breeds of cereal by allowing the reproduction of the friendliest cub in the wolf pack, the corn with the biggest cobs and the wheat with the shortest stalk, because that is what we wanted. The drawback of this process is that it is impossible to know what else we are "buying" in the same package as the feature we desire. As an example, many of the current types of apples look wonderful on the selves of the supermarket but they have no taste once we bite into them at home.

There is yet another method of evolution that is, ironically, a hybrid: natural selection under artificially created conditions. As I mentioned before, when sheep were initially domesticated they had significantly bigger brains, which also meant they were probably more resourceful when it came to escaping their enclosure. This creates a selective pressure in favor of the dumb sheep: the adventurous one might never be found by the shepherd to be brought back, but the meekest ones will stay in the herd and reproduce happily, making the "meek gene" more prevalent in the population. Over hundreds of generations modern sheep have a brain half as big as comparable wild variants. A similar process happened with the northern European pastoral societies, where those who could digest milk into their adulthood survived better in the cold north, so this trait was retained there.

Luckily, there have been very few (and widely condemned) attempts at breeding humans selectively, but still we are not exempt from this kind of pressures. For instance, African Americans are descendants for a particular subset of the original African populations: only those who seamed physically suited for the plantation work were shipped over by the slave trade and consequently, even if many generations have passed, African Americans still today have, as a group, an above-average physical strength.

One case of natural evolution in artificially conditioned environments that is particularly interesting to me is the potential influence of obstetric technology: for the most part of human history, cesarean section was an emergency procedure whose outcome was uncertain at best and to which many women did not have access. This meant in practical terms that women with wide hips had a priori better chances of surviving several pregnancies and provide healthy children than those with narrow hips (there is of course a lot of variability, but it was a good proxy). IN the last decades the improvement in the health systems around the world means that C-section is now of very limited risk and, at the same time, easily accessible to a big fraction of pregnant women. In my view these advances have removed some of the selective pressure for wide hips: women who would have had a hard time to bear children (or would have sadly died giving birth to the first one) are now having even more than one, all through cesarean section. (Do not get me wrong, it is great that all these women survive childbirth now.) If we compound that removal of the pressure with the fashion trend that slim women are considered preferable mates it is not beyond the imaginable that, by the end of this century, a big majority of births will be surgical as the hips of women continue to get narrower.

Where does evolution end? It never does. As long as there is life there will be changing conditions and every change is an opportunity for one subset of individuals to have a tiny reproductive advantage over the rest. If there is a gene for "digital aptitude" it will probably become widespread within a few generations. In the meantime there is still a lot of work to be done to detect and possibly correct genetically-induced diseases. Fortunately we do not have biological pressures to die early, so the improvements in health care are likely to translate in longer and happier lives. Have a nice evening.