Why do dogs have floppy ears?

Last week, I installed the latest version of OS X on my Mac: Lion.

Bear with me, this will make sense. Eventually.

This update has upset some power users, because it introduces features intended to make your computer easier to use, some aimed at novice users, some aimed at all users. These include a system that automatically saves documents, in a way that is transparent to the user and no longer requires them to remember to save every five minutes, and eliminates the danger of accidentally pressing “don’t save” and losing all of your work. Basically, it works just like your iPod Touch – leave an app at any time you like, and don’t worry about losing your data or the state of the app: it’ll still be there when you come back.

Though this doesn’t hurt power users at all (in fact, this will make their lives much better, too), and makes computers much less intimidating for normal people, tech-savvy people sometimes still get upset about this – computers aren’t supposed to be easy, and people who don’t understand how their computers work are just idiots! Yes, sadly, this kind of contempt for non-enthusiasts and for ease-of-use runs strong in some segments of the technologically inclined; I remember, as a kid in the 90′s having arguments with my Windows-using friends, with a major point against the Macintosh being that it was “too easy to use.”

Incidentally, that was the same argument that some nut job at one of my high school jobs used against the metric system.

But anyway, the point here is not to rag on technology enthusiasts, but to observe that this is actually a common thread running through communities of experts and enthusiasts – contempt, or at least disregard for, the needs or abilities of the non-expert. For example, car enthusiasts who don’t understand why anyone would want to drive an automatic instead of a manual car (or, for that matter, why someone wouldn’t even know how to drive a manual car), or how someone could not know how to change their own oil or rotate their own tires. That last one led to an interesting conversation when I was trying to sell my manual car a few months back – when I mentioned to the guy I was showing it to that I was planning to replace it with an automatic, he said that I was “turning in my man card.” Gender essentialism and sexism aside, he was clearly making different calculations about what he wanted from a car.

I experience this feeling too, as an evolutionary biologist, when evolution is discussed in popular culture. From my position as – compared to any lay person – an expert on evolution, the misconceptions and just plain wrong-headed ways that people think about evolution are enough to make me crazy at times. It takes some effort to step back and at least be grateful that people are accepting of the theory of evolution at all, but when their misconceptions are used to justify sexist, racist, homophobic and just plain stupid ideas, it starts to grate again.

There are a number of common misconceptions that I could put under the microscope here, but let’s focus on a common one: teleology.

In evolutionary biology, teleological thinking is, essentially, the belief that every feature of an organism must have a purpose, and therefore must have been selected for by evolution. For example, why do dogs have floppy ears? A teleological explanation accepts as its premise that floppy ears must have an evolutionary advantage over non-floppy ears, and attempt from there to explain what this advantage is. This is a relatively intuitive and understandable lay view of evolution; every first-year biology student is a teleologist. So too, unfortunately, are many experienced cell and molecular biologists. It’s understandable because it took about one hundred years after the publication of Origin of Species for even evolutionary biologists to mostly abandon teleological thinking. But it still sets my teeth on edge.

As it turns out, we do have a pretty good idea about why dogs have floppy ears: because it comes with the behavioral traits associated with domestication. You may have heard of the long-running domestication experiment on the Siberian silver fox, in which researchers selected for non-aggression and other domestic traits over many generations, from a population of silver foxes originally taken from the wild. Eventually, as you would expect, these foxes became much like domestic dogs in their behavior and dispositions. Surprisingly, though, they also took on much of the appearance and traits of domestic dogs – floppy ears, multi-colored coats, wagging tails and so on. For some reason, these traits are inextricably linked with domesticated behaviors.

Of course, people don’t need to interact with evolutionary biology in the same way that they must interact with cars or computers to get things done, and there’s no way to make any advanced science less complicated for a lay person. But the point is that we can’t know everything about everything, or indeed, everything about anything. We all need to rely on experts for subjects about which we don’t have perfect knowledge, be it computer science, climate science or how to replace a fuel pump. That’s as it should be, and often times we experts need to just get out of the way, or better yet, find some ways to make the parts of people’s lives where they interact with the objects of our expertise easy and even enlightening, rather than frustrating.

Are men necessary?

Well, yes, strictly speaking – that is, if you want to reproduce. Mammals and most other vertebrates, at any rate, require a male at some point in the process to produce some gametes – sperm, specifically – which must make their way to an egg and fuse with it to make a zygote. This is usually achieved by the delightfully biological processes of copulation, ejaculation and insemination, though some aquatic vertebrates make use of the decidedly less titillating (although less risky, in some ways) method of external fertilization. That particular practice is even more widespread when we consider sex in invertebrates, though internal fertilization is still popular among insects and other large groups.

We, as humans, have a more recreational approach to sex than most species, which is why we’ve devised a number of means by which we can engage in it whilst avoiding some of the more unpleasant potential side effects (horrible diseases, babies, etc. etc.). So, for most of us, the question “Why sex?” seems misguided, at best.

We'll always have dumb questions.

But, scientifically speaking, it’s a stumper. There are a number of objections to engaging in sex, but the major issue is that sex generally requires, as we have established already, males (am I right, ladies?). The problem with males is that those lazy, selfish bastards don’t produce offspring of their own, which cuts the potential rate of reproduction of a typical sexual population in half. That’s bad news if you’re competing with asexual populations that don’t face this particular handicap – they’ll outproduce you in no time at all, and then it’s curtains, Charlie. That should lead us to expect that most species will be asexual, but in fact, most multicellular eukaryotes (in particular, animals, fungi and higher plants) are sexual at least part of the time, and doing just fine. That’s pretty strong evidence to suggest that sex is actually enormously advantageous for these kinds of organisms. Determining what about it is advantageous has been the pursuit of some of the best minds in evolutionary biology over the last four decades or so.

We’ve done pretty well at coming up with theoretical explanations that account for sex. Keep in mind that “theory” means something pretty specific in evolutionary biology, and that is mathematical modeling of the problems and potential solutions; so this is sophisticated, sometimes mind-bending stuff, not vague hand-waving. So, here’s a short list of theoretical advantages to engaging in sex:

Fighting off parasites (and, from the parasites’ perspective, attacking hosts): sex facilitates rapid coevolution; an evolutionary “arms race.” This is the Red Queen hypothesis.

Adaptation: sex produces a wide variety of offspring genotypes, increasing the odds of adapting to a changing environment.

Protection from mutations: without sex, nasty mutations stack up in your genome, ultimately hurting your fitness, quite severely under some theories.

Complementation: sex can prevent deleterious mutations from negatively affecting the phenotype much of the time (i.e., we have recessive deleterious alleles).

There are dozens more. What has proved more difficult than generating theories has been gathering empirical evidence to support or refute them. Happily, that side of the science of sex has been gathering steam over the last few years, and there is increasing evidence to support some of these theories. For example, we now have definitive evidence that asexual species often do accumulate mutations at a more rapid pace than sexual species, although the consequences for fitness are harder to establish. And now, this month, an elegant study released in the journal Science provides clear evidence in favor of the Red Queen hypothesis: sex is good because it gives you an advantage in fighting off parasites.

The inimitable Carl Zimmer posted about this study on his blog earlier this month, and I certainly won’t try to imitate him; I strongly recommend reading his post, it’s a short and clear description of the study. But if you don’t want to click through: sexual and asexual populations of nematode worms were reared in environments with and without parasites, and the asexual worms clearly did worse in the presence of parasites, ultimately being wiped out.

What I have to say about this is that it’s tremendously exciting to be able to demonstrate the predictions that we make coming true in actual organisms, and it’s mildly astonishing that this study has not been done before. Many of the theories for the advantages of sex have only become practically testable in the last ten years or so as we have become able to very cheaply get lots and lots of DNA sequence data, but this is a pretty old-school experiment. Evolutionary science definitely has a people-power issue – only so many people are working on these problems. That can make it both a wonderful area in which to do research, due to relatively low risk of being “scooped” by competitors, but also a frustrating one when your realize that there are gaps in your knowledge of a system that no one can fill, because no one has worked on it. So this is good news. To be clear, this doesn’t prove that parasites are THE reason for sex; chances are that it is one of a number of contributing factors, some of which are undoubtedly listed above. It sure is nice to have solid evidence that it is part of the picture, though.

Is that virus alive?

A time-honored method used by teachers to provoke discussion among young biology students at all levels is the question, “Are viruses alive?” If you have been fortunate enough to have any kind of comprehensive science education in your life, you’ve probably heard this question at least once, and if you’re the kind of weirdo that takes a biology course in college, or graduates with a degree in biology – or weirder yet, if you then go on and enter a post-graduate program in biology – then you’ve probably heard it more times than you may really want to think about. And there’s a good reason for that, because viruses are weird – they are big chunks of the basic genetic building blocks of life, DNA or RNA, often encapsulated in a protective protein jacket, occasionally not, and written in those chunks of DNA or RNA are functional genes. But that’s all they are – making those genes actually do anything requires them to piggyback on a functional cell, which almost always doesn’t go well for that cell. So viruses occupy a strange middle ground, having the same genetic material as cellular life as we know it, but unable to do anything with it by themselves.

As in all things, familiarity breeds contempt and we get sick of hearing this one after awhile, especially once we have all drawn our lines in the sand and taken a firm stance that viruses are not alive, or that they are. Discussions on down the line often just rehash these old arguments without further intellectual engagement with the question, which is too bad because it’s actually a very good question – not just on its own merits, but for deeper reasons as well.

To explain, the argument against viruses being alive typically hinges on their lack of cellular metabolism or structure – they cannot harvest energy from the environment, they cannot reproduce by themselves and they assemble spontaneously from component molecules within a host cell rather than dividing. This is a pretty convincing argument if you think that cellular processes are the defining features of life. That’s where I dug in my heels somewhere around the end of high school or early in college, and that’s where I stuck. But this argument deserves some reconsideration, because it is founded upon the idea that there is some fundamental, qualitative distinction between the biochemistry of a cell and the biochemistry of a virus that makes cells something different and special that we can call life.

We have spent the majority of human history convinced of our own specialness, and we’ve turned out to be wrong every time our specialness is put to the test. That’s not really our fault, because of the way our brains work, but it does mean that we’ve accumulated a long history of embarrassing errors about our place in nature. In the time of Shakespeare, we were the “paragon of animals;” unique, distinct from the dumb and mundane menagerie of the rest of the animal kingdom. But as we developed scientific systems for classifying organisms and identifying their relationships, we began a slow descent into banality. First we were primates – but special primates, distinct from the rest. And then it became clear that, really, we looked a lot like apes. That caused a fuss, but eventually it was accepted that we were apes, but still special, unique apes. Eventually, we had to accept that we were in fact another great ape, but chimpanzees, gorillas and orangutans were obviously a lot more similar to each other than to us, so we could live with that – until it became clear that, no, in fact we are much more closely related to chimpanzees than anything else. And worst of all, that means that chimanzees are more closely related to us than they are to anything else! The study of biology and taxonomy has destroyed our specialness.

Cosmology and astrophysics haven’t helped either, first destroying the geocentric solar system, then the heliocentric universe, and then making the universe so outrageously enormous that the presence of humans on this one little planet turns out to be far, far less than a rounding error.

The point is that science destroys specialness and obliterates the ego. For a lot of us, that’s part of what makes science so wonderful – the universe is an unbelievably vast place, where we are unbelievably unimportant, and that means that we’re unlikely to run out of things to do or learn. But it’s also very threatening. Biology and astrophysics say, “So, you think you’re pretty special, huh? What’s so special about you anyway?” And the answer turns out to be, well, pretty much nothing.

“Are viruses alive?” gets at the same question, but at a larger scale than mere human existence – it demands that we contemplate the specialness of being made of cells, and of life itself. What is special about cells? There are 15 times as many viruses in the oceans as there are prokaryotic cells – that seems to be enough metabolism to go around for all of the biotic particles in the world. Is there something fundamentally different about the biochemistry of a cell and the biochemistry of a virus?

It turns out that I don’t have as good an answer to this question as I thought I did. Humans, after all, are just another animal. Animals are nothing special, either – just a tiny proportion of the living organisms out there. And life itself is, after all, just chemistry.

Obviously, there comes a point where it gets impossible to function without drawing the line somewhere. Humans are obviously not the same as chimpanzees. Viruses are obviously not the same as cells. But reality doesn’t exist in discrete little boxes. It’s fine to have a line between categories, but at least we should know that we put that line down, and why we did so. I don’t think that’s where most students take this question, nor that educators intend them to do so. That’s what it makes it a perfect question to keep coming back to. The best questions, to me, are the ones with real depth. All of us, students, teachers, lay people, scientists, gain something from contemplating them.