Vestigial Structures

Vestigial Structures

Evolution can leave recognizable traces of a species’ ancestry.

It’s a misconception that organisms are perfectly formed and adapted to their environments. We can see the traces of natural selection, a slow and imperfect process, in vestigial structures. These are traits whose ancestral function has been reduced or lost. They may still serve other functions. Vestigial structures may only be present during the embryonic stage or they may be a permanent feature. In the past, they served an important purpose that helped a species survive.

For example, an ostrich’s wings no longer enable flight, though they retain other uses, including display and balance. The human goosebump reaction to stress or fear is a vestigial response, based on how our ancestors would have fluffed up their fur to look bigger when confronted with a predator. Some snakes have the remnants of a pelvis from the time when they had legs, as do whales. The presence or absence of pelvic remains is one way we classify snake species. Pigs have smaller side toes that normally sit above the ground but are not simply useless. The malaria parasite retains a plastid derived from a photosynthetic ancestor; the organelle still performs essential functions. Some burrowing mammals have greatly reduced eyes, but moles are not uniformly blind. These examples show why reduced structures must be examined rather than assumed to have no value.

So why don’t vestigial structures just go away? It all comes down to natural selection. Natural selection acts on differences that affect reproductive success, including effects on survival. If a vestigial structure confers no benefit but causes no harm, there is no reason for it to disappear. Getting goosebumps during a horror movie isn’t likely to reduce an individual’s chances of reproducing, nor does it require enough energy to be a meaningful hindrance. So goosebumps will probably stick around for a good while longer unless random mutations eliminate the response or it becomes detrimental.

Even when vestigial structures do go away, it happens gradually over many generations. At a certain point, they cease to be relevant to the process of natural selection. There are even instances when further shrinking or eliminating a vestigial structure would be more detrimental than leaving it in a diminished form, so it remains. For them to disappear completely may require overall structural changes in an organism which are not feasible, or not important enough to exert selective pressure. Scientists are always learning more and sometimes a feature that seems to serve no purpose has one we haven’t discovered yet. Vestigial structures can be helpful for learning about evolution and determining if species have a common ancestor.

Success is measured by persistence.

— Geerat Vermeij

One of the interesting problems for humans is that the pressures we face from each other are not isolated and often require a complex response. We are not just trying to run faster than an antelope. We are trying to be better in so many ways that we often feel like we are failing at everything. So we burn out or give up.

However, similar to velocity, the “speed of adaptation is not the same thing as effective adaptation.…The point is that what matters is not the speed of adaptation, but what problems it helps you solve and what problems arise as a result of an enemy’s adaptations.”

An adaptation is useful in a particular environment. It can also involve tradeoffs: an advantage in one respect may come with costs elsewhere. Humans have big brains. A benefit is unmatched problem-solving ability. We can survive in a wide variety of situations for which we have no direct experience. Large brains also bring costs, including demands on birth and development. Human young remain dependent for many years.

Adaptations are further constrained by the fact that an organism must be viable at all stages of the adaptation process. What this means on the human life timescale is that if you are compromising your physical health or your sanity, you are not adapting. You are instead weakening your ability to successfully respond to changes in your environment.

Adaptations are about being successful in your environment, so it becomes critical to define success. For animals it means living long enough to pass on your genetics and, depending on your species, getting your young through the early vulnerable stages. In many mammals, parental care also helps young survive and learn to navigate their environment.

But beyond our biology, there is no universal definition of success that all humans would agree to. For some it’s about power and recognition, for others it’s about the freedom of choice, and others still would emphasize spiritual enlightenment and peace. However, a fundamental component of success must be that it involves benefit. You gain when you succeed. Anything that compromises your ability to succeed is not justified by this model. Running as fast as you can to stay in place is not a euphemism for 16-hour workdays. It should not be the reason you don’t see your children or be used to justify ignoring the needs of your body or soul.

« No innovation comes into existence perfectly hewn. Error is thus necessary for the generation of variation. »

Geerat Vermeij