Jun 08 2021

Evolutionary Compromises

Evolution if one of the most fascinating scientific phenomena because it is so complex and operates over such varying and long timescales. It’s a real challenge to wrap one’s head around. There is therefore a tendency to settle on overly  simplistic evolutionary narratives. This is not a criticism, we all do this in an attempt to grapple with evolutionary thinking. The challenge is to recognize this fact, and be open to a deeper, more complex and nuanced understanding of evolutionary processes. It’s a great example of what should be a general intellectual posture – recognize the limits of our current understanding (wherever that may be on the spectrum) and not only be open to, but seek out new information and concepts to keep incrementally pushing our understanding forward.

In that spirit, here is a study on the evolution of broad-horned flour-beetles that illustrates some of evolution’s complexity. The male broad-horned has exaggeratedly large mandibles, which is uses to compete with other males for mating access to females. This is an example of sexual selection, when a feature specifically increases mating success but is not necessarily broadly adaptable. The go-to example of this is the peacock’s tail feathers – a garish display meant to attract females, but an evolutionary burden in many other aspects. This sets up an evolutionary tug-of-war, where a feature may be advantageous in one respect but disadvantageous in another. Evolutionary processes are fairly efficient at balancing such conflicting forces.

As an aside, the balances tend to be only metastable. They can alter with changes in the environment or behavior. Even different individuals within a species can adopt different survival strategies that result in a different balance of traits. If a population within a species does this it may even eventually lead to a speciation event. For example, it has been documented that within some primate species dominant males will have access to females due to their alpha status, while others gain access by currying favor with the alpha, and still others gain access by gaining favor with the females and sneaking behind the alpha’s back. Still others may act as a “wing man” to a close kin, promoting their genes into the next generation by proxy. The lesson here is – no one strategy captures the wide diversity of behavior even within a single species.

Back to the beetles – there a second important evolutionary principle at work here as well, intralocus sexual conflict. This occurs when genes are active in both sexes, but what is optimal for one sex is not for the other because they have different needs. Again, the go-to example of this is pelvis size in humans. Males need narrow hips which are optimized for bipedalism, while females need wide hips for birthing large-brained babies. Hormonally determined developmental processes allow for sexual dimorphism, but it is constrained by their shared genes. Evolutionary forces have reached a compromise where neither sex has the optimized pelvis but both work well enough.

The broad-horned flour-beetles have a similar sexual conflict. They share genes for their mandibles, and therefore the size of one affects the others. While the female mandibles are much smaller, larger male mandibles will drag female mandibles to become a little larger as well (so-called masculinized phenotype). Larger mandibles, in turn, require a larger head and a smaller abdomen. A smaller abdomen reduces the number of eggs a female can carry. So again, an evolutionary compromise is struck.

To test all this researchers exposed a population of broad-horned flour-beetles to a predator that targets males with larger mandibles. This turns up the dial on selective pressures against a large male mandibles, resulting in a new metastable balance of evolutionary forces. After several generations the size of mandibles for both males and females was reduced (supporting intralocus sexual conflict for this trait in this species). Further, the female beetles were able to lay 20% more eggs, showing that they benefited from the smaller mandibles.

The deeper lesson here is – don’t fall for simplistic evolutionary just-so stories. Not even natural selection is the only force at work. Brute force and competition are also not the only survival strategies. Species do not only engage in a single survival strategy – predators sometimes scavenge.  The “5th grader” version of evolution is just a starting point, but unfortunately for many it is also an ending point. I also find that evolution deniers are stuck in this overly simplistic strawman version of evolution (for them it’s a feature not a bug).

This principle also applies to knowledge in general. A good rule of thumb is that it (anything) is always more complicated than it seems. At least this is a good first assumption. Certainly every time I do a “deep dive” on a topic I find hidden depths that I did not anticipate. Sometimes even answering simple questions reveals incredible complexity. The trick is striking a functional balance. Acknowledge the complexity and be comfortable with it. It’s OK to have simple summaries (like schematics of reality), but know that is what they are – it’s a useful approximation, not a complete picture. At the same time don’t be overwhelmed by the complexity into inaction. You can “bottom line” a topic so as to make a necessary decision.

For example, vaccines are generally safe and effective, with benefits far in excess of risk. Books can be written on this topic, years spent in study and acquiring expertise, but that quick summary is sufficient to decide whether or not to get vaccinated. It’s great to deepen your knowledge, to understand how vaccines work, what the different kinds of vaccines are, what the rare side effects might be, etc. Just don’t confuse a moderately deeper level of knowledge with true expertise. This middle zone is where, I think, many people get lost. They confuse a little bit of knowledge with expertise, or they fail to recognize that a biased set of facts and conclusions can be curated by vested or ideological interests, to give the false illusion of deep knowledge. We see this, for example, with the anti-GMO movement. Those with the most anti-GMO attitudes think they know the most about genetics, when objectively they know the least. They have been deceived by the illusion of knowledge.

This illusion is exactly what I am talking about, circling back to the evolution example. That illusion can come from many sources, so be wary of it, and don’t let it stop your quest for deeper understanding.

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