Evolution Is the Greatest Show on Earth - Issue 85: Reopening

Science can be a peculiar source of joy—the joy, largely unique to human beings, of understanding the universe in which we live. For some, the joys of science are readily accessible; they get hooked on it as children, then get to enjoy a regular fix of science for the rest of their lives. For others, though, it’s not so easy. Many people could get hooked on science, but for one reason or another don’t take to it immediately and never acquire the taste. They recognize how useful science is, of course, but they’re closed off to the pleasures of its discoveries.

As a result, science educators like myself are always trying to find ways to turn people on to science. One way that I suspect has gone relatively unnoticed is using memes and viral YouTube clips as a gateway drug to science. And one area where this may be particularly effective is in the science of animal behavior. Many viral animal clips—of gorillas and gazelles, weird birds and bees—look like frivolous fun on the surface, but turn out to hold important lessons about the evolution of our “cousins in fur and feathers” … and about our own evolution. 

Here are some of my favorites. Enjoy!

Behavior Evolves

The first lesson in the science of animal behavior is this: Natural selection doesn’t just create anatomical adaptations, like eyes and wings and teeth and claws; it creates behavioral adaptations as well. Behavior, in other words, evolves. More precisely, the motivations and neural circuitry underpinning behavior evolve. No less than eyes and claws, these things are adaptations designed ultimately to pass on the genes giving rise to them.

To kick off with a simple example, consider this industrious little spider, diligently weaving her web.

The precise sequence of bodily movements required to accomplish this were crafted by natural selection, just as surely as the spider’s eight legs, eight eyes, and exoskeleton. (The web itself was also crafted by natural selection, but that’s another story.)

Now, the spider presumably doesn’t have a mental image of the completed web in its little spider mind, in the way that a human architect or engineer would. Even so, it’s amazing that natural selection can engineer such intricately patterned instincts, and amazing that it can squeeze so much behavioral complexity into such a tiny brain. Imagine how hard it would be to build a spider-sized robot that could do this!

Natural Selection Is a Gifted Engineer

This is just one example of a very general trend, namely that natural selection routinely builds mechanisms that human engineers still struggle to match. Here’s another example: the neural structures underpinning head stabilization in this hawk.

Head stabilization is common in the animal world, and especially common in birds. It has the same function as image stabilization in cameras: to maintain a steady view despite motion. The main evolutionary payoff of this is that it helps the animal get a stable fix on prey: all the better for making a kill.

Evolutionary Arms Races

Hunting is a crucial adaptive task for many animals, and natural selection has built various adaptations to facilitate it. But as soon as you’ve got hunters, you’ve also got huntees—and it’s not in the interests of the huntees to end up in a hunter’s belly. Thus, hunters create a selection pressure on prey for adaptations to defend against the hunters. These adaptations in turn ratchet up the selection pressure on hunters for effective hunting abilities, which then further amplify the selection pressure on prey for effective anti-predator technology—and so on, and so on. The net result is that predator and prey evolve more and more sophisticated adaptations, with no overall advantage to either side. Biologists call this an evolutionary arms race, and it’s a major spur to evolutionary change.

In this clip, we see the fruits of one such arms race, as one amazing product of natural selection narrowly escapes the clutches of another amazing product of natural selection. This time…

(The stars of the show, by the way, are a kangaroo rat and a rattlesnake.)

Playing Dead

Snakes are often cast as the bad guys in this kind of story. But snakes can be prey as well as predators, victims as well as victimizers. Consequently, like so many other animals, snakes have evolved a suite of behavioral adaptations designed to thwart would-be predators. Here’s a great example: a hognose snake faking its own death in response to an apparent threat. Little guy could be up for an Oscar …

Collective Behavior

The kangaroo rat and the hognose snake were working alone against the hostile forces of nature. Often, though, animals work together to defeat predators and other dangers. Curiously, some of the most impressive examples of this are found not in big-brained, clever animals like ourselves, but in tiny, small-brained animals like insects.

For example, in this clip, we see hundreds of honeybees performing their collective threat display. Known as “shimmering,” the display is similar to a wave in a sports stadium, and is designed to scare off wasps and other predators. Gotta say, I think it would work on me.

Getting Frisky

All the adaptations we’ve looked at so far evolved to help their owners survive. But natural selection isn’t just about survival. Even if an organism were to live for a thousand years, if it didn’t produce any offspring in that time, its genes would be expunged from the gene pool the moment it died, just as surely as if it had only lived for a day. With rare exceptions, if you want your genes to persist, you have to have offspring. And in sexually reproducing species, that means finding a mate.

This brings us to an important subtype of natural selection, known as sexual selection. Sexual selection is selection for traits that increase one’s reproductive success, as opposed to one’s survival or longevity. Sometimes this means traits that help one get the best of same-sex rivals—think male deer locking horns, fighting for access to females. Often, though, it means traits that help their owners catch the eye of potential sexual partners.

The classic example is the peacock’s tail. This unwieldy appendage evolved not to boost the peacock’s survival prospects—if anything, it does the reverse—but to attract the sexual attention of any passing female. The peacock’s tail is such a well-worn example of sexual selection that it’s easy to forget how amazing and bizarre it is. Here’s a quick reminder:

Weird and Weirder

Although the peacock’s tail is the best-known example of sexual selection, it’s really just the tip of the sexual-selection iceberg. In a diverse array of species, sexual selection has turned the males—and sometimes the females too—into living sexual ornaments, equipped with colorful head crests, crazy dances, and a thousand other wonders.

Take, for example, this bizarre creature: the long-wattled umbrellabird …

The wattle hanging from his chest is a sexual display: the umbrellabird equivalent of the peacock’s tail. Ditto the Elvis quiff. (Sexual selection really went to town on birds.)

Evolutionary Trade-Offs

Adaptations are never perfect; they always involve a mix of benefits and costs, with selection favoring the variant with the least-bad benefit-cost ratio available at the time. More precisely, selection favors the variant with the least-bad benefit-cost ratio on average. Thus, on average, the benefits of sporting a sexy tail, or fighting rivals for mates, outweigh the costs—if they didn’t, these things would never have evolved. But that doesn’t mean that the benefits outweigh the costs for every individual or in every single instance.  Here’s a case where natural selection for survival trumps sexual selection …

Parental Care

Mating is crucial in evolution. For many species, though, it’s just the beginning. In mammals and birds in particular, the young often can’t survive on their own. As a result, natural selection has crafted a new kind of behavior: parental care.

Here’s a great example: a mother bird refusing to abandon her eggs in the face of a significant threat.

Why does she risk her neck like this? The answer is that any genes giving rise to the tendency have a good chance of being located as well in her offspring. In effect, those genes are looking after copies of themselves located in other bodies.

Of course, the mother bird isn’t thinking about preserving her genes; she’s just protecting her young because she wants to. But why does she want to? Simple: Because mother birds in the past that didn’t want to protect their young had fewer surviving offspring than those that did, and therefore the desire to protect one’s young became more and more common with each passing generation.

Don’t get me wrong: Mother birds don’t always protect their young; sometimes, they cut their losses in order to have more offspring later on. But the fact that they protect their young most of the time—and the psychological mechanisms underpinning the decision to protect or cut their losses—are behavioral adaptations put in place by natural selection.

It’s Not Just Mom

In most parental species, it’s the females that care for young, while the males are deadbeat dads. As with almost everything in biology, however, there are many exceptions to the rule. In some species, for instance, the males are the primary caregivers, whereas in others both sexes help care for their offspring. (This shouldn’t come as too much of a surprise; after all, we ourselves belong to one of the latter species.) Here’s a nice example of a male pulling his weight: a silverback gorilla standing guard as his family crosses the road.

Altruism Beyond the Family

Parental care is the most widespread example of an extremely deep trend in the living world, namely that organisms tend to care more for genetic relatives than for unrelated individuals. This tendency is found not only across the length and the breadth of the animal kingdom, but also in plants, bacteria, and even viruses.

However, altruism in the living world doesn’t always stop at the boundaries of the family. In some species—most notably our own—individuals also often cooperate with and come to the aid of non-relatives. And sometimes, occasionally, our kindness and cooperativeness extend even further than that.

This final clip captures this nicely. And it reminds me of one of my favorite quotes from the guy who got the ball rolling on this whole area of inquiry, Charles Darwin: “The love for all living creatures is the most noble attribute of man.” Couldn’t agree more!

Steve Stewart-Williams is author of The Ape That Understood the Universe: How the Mind and Culture Evolve (2018. Cambridge University Press). Follow Steve on Twitter.

Lead image: Drop of Light / Shutterstock