Hopeful Monsters and Hopeful Models

A hopeful monster is a mutant born with a genetically determined and large novel trait (compared to its parents) which confers enhanced fitness on that individual. This enhanced fitness increases the likelihood that the new mutant gene that determines this trait will be passed on and spread throughout the evolving population, so in a single generation a rapid process of speciation is initiated. For example, a fish with a mutation that causes both its eyes to grow on one side of its head could become the flounder of a new generation of flatfish. Well, just for the halibut, it might be fun to further examine this notion.

The hopeful monster idea is attractive for three reasons. First, we already know that some of the most profound differences between larger scale taxonomic groups (like the phyla) are about aspects of body plan that are controlled by early stages in embryonic development. So, if a simple mutation in one of those stages can cause a taxon that has a certain number of limbs to give rise to a new species with a totally different number of limbs, then that would be cool. The second reason is that the fossil record seems to have the property whereby many species stay roughly similar for long periods of time, then suddenly, there is lots of evolutionary change. You've heard of this, it's called "punctuated equilibrium." If hopeful monsters ... also called saltational (dancing, leaping) evolution ... occurred generally, we might postulate that these moments of dramatic change, these punctuations, are periods in time where for some reason a lot of hopeful-monstering was going on all at once. That would be cool. The third reason that this is an attractive idea is just that it would be cool, especially if you are the guy who discovers the next hopeful monster.

Olivia Judson recently wrote a column talking about the Hopeful Monster idea. She proposes that the idea, which has been mostly discredited and put aside as not possible, or at least, so unlikely as to not be a factor in explaining overall patterns in evolution, is coming back. Her column, "The Monster is back, and its Hopeful" ... is here.

The article is interesting, but she does not really provide any new information that would lead one to suspect that we should be rethinking the unlikelihood of hopeful monstering. She gives a few examples of single, possibly small genetic changes that have huge (perhaps) phenotypic effects, within populations, that she suggests could be analogs for hopeful monster events. One of these I want to discuss in more detail in a moment is the loss of feathers on a chicken over the neck and head. This, she suggests, is analogous to vultures having naked heads and necks (a presumed adaptation). So, a population of carrion eating eagles could give rise to a hopeful monster gene that produces a carrion eating vulture.

Olivia Judson's article has been read and taken to task by Jerry Coyne, a blogless curmudgeon who happens to be an expert on this topic, and who is friends of Carl Zimmer. Zimmer has given Coyne a spot on The Loom (Zimmer's Blog) to respond to Judson. This post is here.

Coyne explains how Judson is totally wrong. The hopeful monster idea has been thrown out, and in fact its debunking happened some time ago. Nobody believes this crazy idea now, and what the heck is she doing bringing this up again.

I want to say a couple of things about both bits of writing, but especially Coyne's.

First, I think Judson's column is unconvincing and very fluffy, and I agree with Coyne's critique that this kind of looks like a journalist getting readers more than the heralding of a new way of looking at evolution. However, it is a column in a newspaper and Judson is acting as a journalist, so maybe this approach can be forgiven. Regarding Judson's examples, I think they are all reasonable examples of a genetic mutation that could indeed arise and spread in a population, but they are not species- or (and this is very important) higher taxa-determining differences. A vulture is different from an eagle for a very large number of reasons, and the naked head is only one of them, perhaps not even the most important. If a population of naked-headed eagles arose, then we'd have a subspecies of "truly bald" instead of "looks bald" eagles. They would not really be hopeful monsters.

On the other hand, I think that Coyne's treatment of Judsons's paper is a bit heavy handed and rather sanctimonious. And given this holier than thou attitude (which may well be justified, but I'm just sayin....) it is appropriate to hold him to a very high standard of perfection.

Coyne mentions that the naked-necked chickens are an example of a mutation in a domestic animal (true) and that mutations occur in domestic populations with great frequency compared to wild populations (maybe) and that these mutations only persist because the animals are coddled in their domestic setting.

This last part may often be true, and I think I agree with that. But not for the naked necked chickens. Naked necked chickens are common in the African tropical rain forest. They are not coddled. They are not kept in coops, they are not provided with water, they are not fed. Maybe they are kept from predators, but in fact, that is hard to argue since they are often eaten by eagles, hawks, snakes, civets, wild cats, and so on. It is even possible that in that setting, where they do eat some carrion, and where there is a high parasite load, that the naked neck and head are adaptive (though I'm not advocating for that idea .... it is merely a tenable hypothesis).

So, I agree with Judson that the naked necked chicken .. .a simple genetic mutation ... may be a good example of a one-shot trait that need not have arisen feather by feather over generations of time. But I disagree that a naked necked chicken is a hopeful monster. As hopeful as such a trait may be, it just isn't that monstrous.

Now, if you try eating one of these chickens, that that is a different story. They are as tough as buffalo hide. Truly monstrous, as cuisine.