Challenges to reflex darwinian explanation...are they conveniently overlooked?

Darwin loosed much upon the world, with his systematic documentation of the idea that life evolved as an historical process of divergence from a common ancestral source, and that complex traits could arise by differential survival of inherited factors that construct organisms' traits.

No current explanation competes with this one.  Its realization had tremendous explanatory power.  It also had tremendous power to affect human society, and not always for the good.  It became an ideology: not only were some traits the result of natural selection, but essentially all were.  Natural selection was seen as a ubiquitous, highly focused and precise 'force'.  That led to the idea of value judgments: that we as intelligent products of this process could now help it along, by assessing what selection has liked or what was 'better' and say thus that such traits should be favored, by our giving the law of Nature a helping hand.

There are all sorts of logical problems with such reasoning, but it led people seen as authorities to define what was good and bad in this context and to make policy assertions about society in that context.  The eugenic era (the word basically meaning to help) led to many presumptuous abuses based on this sort of thinking that we know what Nature wants or what would be biologically better for our species.  The idea seems OK in principle, but we know that it led to awful abuses, and after the lessons learned by the Nazi policies based on rationales using academic advice of this sort, there was a revulsion against such genetic determinism.  It  may have gone too far in the denial direction, but it was based on an understanding of how an ideology can go terribly sour.

But now it's creeping back on little cat feet.  What is essentially strongly genetic determinism, driven by new genomic technologies, has led to a fervent belief that, so to speak, everything is determined by our genes.  A trait is explained by finding the selective factors responsible for it--that is, for finding those genetic variants (or assuming their existence) that lead to the most successful individuals.  It's an ideology, we would say, because it is too unquestioned, and there are many instances where we think that can be seen.

We discussed aspects of the relevance of this problem to issues of human race and racial variation on May 19.  That had to do with the dystopic uses of darwinian determinism.  But here are a couple of examples that show the issue in a different way.

Playboy bunny bodies and the Darwinian drool
There all sorts of theories about the traits involved in mate choice. It's a very sexy topic, so naturally it attracts a lot of 'scientific' interest.  It is all about sexual selection, an idea Darwin carefully documented from his point of view (mainly in non-humans).  But how deep is the thinking?

Lots of studies now and in the past have looked at purportedly representative samples of our species (that is, local middle-class 20 year-old college students) to see what gets them, er, excited.  How the face looks, the timbre of the voice, where the curvey parts or beefy muscles are. 

Mate choice would seem like the sincerest compliment, so close to evolutionary fitness (that is, reproductive success) that it can be a very strong molder of a healthy, hale, 'fit' and advancing species.  If you don't get chosen, well, bye-bye babies!  So one would expect that our ancestors had pretty much wrung all the variation out of such traits over the millions of years of our ancestry as humans.

We once heard a speaker, a licensed academic, say that the human ideal was the Playboy bunny type (this was, you'll have guessed, a male analyst).  This seems rather like the kind of assertion that is so wrong as to be laughable on the face of it.  After so many years of bunny behavior, at the heart of strong natural selection, we should all look like Hefner's dreams!  But any visit to a local mall or anywhere people gather shows how ineffective, that is, untrue, this assertion about sexual selection must be.  Not only are we not all like Playboy bunnies, but we're not even close.  Yet these aberrantly shaped people are having children!  Indeed, the actual rarity of this supposed Darwinian ideal is why there can be bunnies!

Still, pat selectionist explanations have such apparent appeal that this problem seems so easy to overlook.  And a story in the May 18 NY Times Weekly Review section reports a study that shows even more directly than a simple observation of human variation in the supposedly sexy traits, that these physical attractants, the immediate cues that a Darwinian viewpoint would argue are the flags of fitness, are not what has drawn people together who actually marry and stay (and have children) together.  Instead, those immediate sexy lures pale relative to compatible modes of interaction--getting along, shared interests, and so on. These traits are largely culture-specific, not driven by a  narrow set of highly adapted and selected genotypes. 

But, does a story that give any pause at all to the advocates of adaptive determinism via mate choice? 

There is a huge wealth of anthropologically well-known reasons why not all human males choose bunnies as mates (or, to be fair, bunnies choose football players), and why the widely asserted ideas of a prescriptively genetic basis for mate choice simply don't work.  The evidence against narrowly Darwinian accounts of human mating patterns is simply overwhelming, and yet somehow it seems very easy to conveniently ignore if you just don't want to see it.

The persistent sickness of the (ugh!) lower classes
We routinely see stories warning of the devastating potential of some current or impending epidemic of infectious disease among the poor people in the world.  We know that now and historically, the wealthy were spared much of the carnage of past epidemics.  They live in cleaner environments, are less crowded, with better nutrition, medical care, and the ability to get out of town when the epidemic comes.  The poor, well, since time immemorial they have been documented to suffer the mass deaths of plagues.

The evolutionary dynamics of infectious disease are widely studied, and again there are all sorts of very sophisticated selection-adaptation arguments for how the pathogen and the host (that is, people) co-evolve.  A massive epidemic leads to the survival of resistant people, just as massive use of antibiotics leads to resistant bacteria.  This is classic Darwinian selection and adaptation. 

But why, then, is it still the case that the poor are so vulnerable?  Given the heavy selective whammo of the long history of plagues, or cholera, or whatever, with some among the poor surviving while cart-loads of their peers ended up in pauper's graves, why aren't the poor as hardy as Superman?  Shouldn't we expect the rich to be the feeble, wobbly ones who are most delicately vulnerable, and doesn't what we actually see raise questions about how cogent are our models?

Of course, if you're a committed adaptationist, you can always make sure that the facts can be fitted to the narrow Darwinian view, by post-hoc arguments, selective use of data, and other tactics to defend a belief system against contrary facts.

We see the same sort of thing today more generally, in which assumed genetic causation of a tractably simple kind is at the core of much of the biomedical belief system.  Beliefs are treated as axioms--assumed truths--rather than ideas to be tested.  Once that's done, every fact is fitted to the assumption.  Studies generally are not designed to falsify our notions, as we self-flatteringly so often proclaim, but are in most ways designed to prove what we want to prove.

This message is not anti-Darwinian
We write often on this general problem.  But we are not at all anti-Darwinian.  Darwin's insight that life has evolved its diversity from a common simple origin through strictly historical processes was transformational.  Organized traits exist and must be explained in light of these facts.  The issue for us, as exemplified by the above examples is not whether sexual selection or infectious disease dynamics are potentially important, nor whether genomic variation related to individuals' traits or evolutionary process take place.  The issue is the tendency of the strength of commitment to lead investigators to force pat explanations onto a world that isn't so pat.

In principle, the questions could be posed in perhaps a more productive, less ideological way.  We do, after all, have shapely bodies, different color hair and eyes, curvy organs and protuberances, and so on. Epidemics surely affect those most susceptible who are exposed.  If these traits are not involved in fitness, then why do we have them?  This is a legitimate question, actually a lot more interesting and deserving of more serious consideration than the simple declarative explanations. 

Likewise there is the important issue of what studies to believe and what ones to dismiss.  That the Times reports a study saying that sexual body traits don't actually determine mate patterns may or may not be a good study, just as claims of Playboy mate choice may be based on weak evidence.  The issue is one of a more dispassionate evaluation of evidence and a more assumption-neutral way of designing studies.

When science is really making advances, you start to see committed devotees of some theory begin to accept that it may not be so after all.  But, the way humans cling to beliefs, even in science as in other belief-based areas, don't hold your breath.

The sexy scent of a mate.....in flies!

There are many wonders in nature and it is tempting to look at ourselves and believe that while we are conscious, intelligent beings, the rest of living nature is made up mainly of molecular robots, that respond much like thermostats and little more than that.  But that arrogance may be badly misplaced.  Not only do simple, lowly creatures have complex decision-based lives, but they often do things in ways similar to what we do--often using evolutionarily similar genetic mechanisms.

A new report of mate choice in the fruit fly Drosophila melanogaster, in the Proceedings of the Royal Society (part B, Biology),  shows this sort of thing in what seems to be a very interesting way, assuming lab flies reflect what's going on right now in your nearby dumpster.

"How great to meet again!"  (From: 2D Fly Tracker Analysis webpage at Tufts.)

Sight and smell (at least)
The investigators first produced a line of red-eyed flies unable to smell (flies with a loss-of-function Orca allele).  They then performed three different experiments to test novelty vs. familiarity.  They mated a virgin male with a virgin female, then placed each male into a test tube with two females, the one he'd mated with and one novel; females were distinguished by eye color.  The second experiment was the same except that females were either marked on the thorax with paint or left unmarked, and in the third experiment, the male was presented with familiar and novel females that had been decapitated and pinned to the mating chamber.  The idea was to eliminate any effects of female behavior on male mate choice.  Investigators collected courtship counts, mating latency, mating duration and mating success. 

To test female mating choice, they introduced a female to two males, one that she'd previously mated with and one that had mated with a different female, and recorded rejection behavior toward each male.  Sex-specific responses for collected for flies with Orca mutant alleles, that is, that couldn't smell, and those without.


Drosophila can mate more than once during their lives.  Populations tend to stay rather local (say, around the dumpster behind a fruit market, where the banana  peels are particularly savory).  After they've had their first 'experience', does this affect their later choices?  Do they form personal attachments, or are they strictly promiscuous?  And how do they know, or do they know, which they're doing?

This study found different patterns of response in male and female flies in terms of potential mates' traits, both in behavior and 'smell'.  Males in this study tended to prefer femals that were very different from their previous mate, while females more often preferred males similar to their previous mate, though results were much weaker for flies with the Orca mutation.  The authors speculate on the evolutionary reasons and origins, but that is beyond our expertise and the point, here.  What attracted our interest was the complexity of flies' lives and behaviors: how do they perceive the incoming information and integrate it into "Oooh, yes!" or "Thanks, but no thanks"?

To see whether the flies were using olfactory (odor) cues, part of the experiments involved flies engineered to have a non-functioning Orco gene, a gene that is required for them to express their odorant detection gene system (see below).  Changes in behavior that resulted would suggest that smell was important in the decision-making behavior.

Olfactory biology
Olfaction is a complex process and flies use very similar mechanisms as we do.  There are a group of olfactory receptor (OR) genes, that are expressed on the cell membranes of olfactory organs (smell-cells, so to speak).  Part of the OR protein (coded by a single OR gene) sticks out of the cell and can detect the presence of odorant molecules that pass by and are attracted to the binding-pocket of the OR.  There is  high variability in the binding pockets of each of a given fly's set of about 60 different OR genes.  The binding of the odorant molecules to an OR protein triggers a neural signal to the fly's brain.  The combination of such signals is used by the fly to identify (and remember) what the odorant is.  This is very similar to the way our own olfactory systems work (though we have many hundreds of different OR genes).

If each fly gives off a different set of odorant molecules--that is, molecules that ORs can detect--then it is no surprise that a fly can tell one fly from another (unless one thinks of flies as being very stupid automatons).  Likewise, the authors found that, statistically, at least, close relatives to a former mate are among preferred subsequent mates.  This is plausible given the specificity of the OR-recognition system and the fact that close relatives--human or flies--resemble each other genetically.

This gene families related to olfactory responses are evolutionarily very old, and elaborated differently and independently in various animal lineages.  Each species has a lot of differences in the details, but the nature of the receptor-specificity 

Of sex..and feeling?
The authors described ideas that might account for what they observed, in evolutionary terms, that is, of natural selection.  That's very speculative (the authors don't claim otherwise), and may be difficult to identify with any convincing precision.  Even more interesting (to us) would be the question as to whether some flies are sexier than others, or what the feeling is like when a fly sees an exciting new potential mate or when having a reunion with a former partner.  Does the latter experience have an existential component, a qualia, like 'warmth'?  Does it resemble how we feel in such situations?  At present, that is very interesting but truly speculative by any stretch (except of the imagination!).

This study was just one and in just one kind of fly.  But there is every reason to think that similar complexities, even if differing in their details, will apply across the insect world....and beyond.

Whether we are 'alone' in the Universe or not, we have plenty of behavioral company right here at home.