First of all, comparing the meaning of the “costs” (and presumably the “benefits”) of “intelligence” in fruit flies, early hominids and modern humans is to compare savanna grasses with pre-cultivation tomatoes and then genetically-modified anti-freeze tomato of the mid-80s. (I know this is imperfect but its better than the apples, oranges and tangelos I started out with.)

In addition to the staggeringly problematic move of comparing the “costs” of “intelligence” to species as wildly different in their biogenetic make-up and sociality as insects, hominids and humans, and as folks with sociobiological tendencies oh-so-often do, this approach tends to abstract single or straightforward mutations and assume they relate to single rather than the uneven aggregation of traits and that these mutations and traits occur in straightforwardly bounded time outside of any relationship(s) with other “environmental” or “structural” factors whether, genetic, developmental, ecological or multi-trophic.

Secondly, as sociobiologists are again so wont to do – and as Mr. Zimmer has uncritically reported in the NYTimes – it treats pregnancy and “unaided” childbirth as competitive and inherently and highly dangerous, while focusing on nutrient “competition” and skull/pelvic size. There is no question giving birth presents risks to mother and child. At the same time, there are overwhelming volumes of evidence-based medical research that show that the “aid” modern, masculinist medicine has provided women and babies has increased the dangers in childbirth rather than decreased them. Historically, well-fed, active and strong women – aided by other women – gave birth to children with what, by comparison to modern rates of complications, are “surprisingly” low complication, tearing and death rates (but note the stress on well-fed, active and strong women since our “modern” diets and lifestyles have, for at least two hundred years, produced large numbers of variously mal-nourished, physically pacified and weakened women.)

Lastly, it is only if you take an asocial, reductionist and unsophisticated approach to the complexity of competition, predation, mutualism and commensualism (where symbioses can be facultative, obligate, oligophilic or polyphilic) that the issue of “costs” can be made so primary when it comes to the coevolution of human biology, sociality and transformation. Here, respectful or not, responding to the idealist and textual reductionism of creationists with the hyper-realist and economistic reductionism of modern biologism does science, its richness, its material complexity and its beauty few favors… or at least that’s how I see it.

Sorry for the screed.

Thanks for clear expositions of intriguing hypotheses.

But I’m still of the opinion that there’s a larger mystery in this question (and no, I’m not setting up for a supernatural non-explanation).

Apologies in advance for the late-night inelegance of my phrasing here, as well as for my raising a question probably sliced up and composted in the typical Paleontology 101 class.

My response to both of your proposals: consider two groups of hominids, functionally identical except that one has a tendency toward larger-brained offspring. Members of the latter group may have an edge in terms of tying knots, more elaborate group interactions, etc: fairly subtle advantages, but the sort of thing that natural selection can work wonders with.

However, the former group loses fewer females (and usually their infants as well) in giving birth – a rather unsubtle advantage, one that will lead to outcompeting the bigger-brained bunch by sheer population size in short order (assuming both groups start with at least an average primate level of social and physical skills).

I.o.w: what (evolutionary) good is it for (say) a male to have a 1% advantage in attracting females, if his offspring have a 1.1% greater probability of killing their mothers and themselves at parturition?

There aren’t enough fossils to put any kind of reliable numbers into this scenario, but the evident fact that women’s pelvises and birth canals are still so narrow that unaided birth can be highly dangerous suggests to me that the relevant prehistoric selection factors must have been intense, prolonged and unusual. (The pelvic-width issue in turn brings up the questions of our ancestral transition to bipedalism, a roughly contemporary process to that of brain growth and thus probably involving the same environmental conditions.)

Indeed there must be considerable variation in this effect across species. Research with humans suggests an opposite relationship, with greater learning and memory ability (as defined by IQ) corresponding with a longer lifespan. Specifically, Deary and Der (2005) showed that having a lower IQ significantly correlates with an earlier death, even controlling for education, social class, and smoking. However, this relationship becomes non-significant when controlling for reaction time. The authors argue that this is evidence that efficiency of information processing in the nervous system mediates the link between mental ability and lifespan.

Given other research suggesting that intelligent human brains are also fuel efficient brains, perhaps there’s an opposite effect in flies, whereby an intelligent fly is a less fuel efficient one. This would seem to explain one of the larval competitive ability (LCA) results, whereby high and low learning flies did not differ in LCA when plenty of food was available. However, when less food was available, the high learning flies showed an LCA disadvantage.

So being an intelligent fly might mean a “brighter” fly that burns out faster, whereas the opposite effect might occur for humans (if you exclude the stereotypical troubled artistic genius).

Reference

Deary, I.J., & Der, G. (2005). Reaction time explains IQ’s association with death. Psychological Science, 16, 64-69.

For example, in the first experiment Carl writes about, the quinine experiment, how do the researchers know that the adaptation is necessarily learning? Is it possible that the flies developed better “quinine detectors” (i.e. could it have been some kind of physiological adaptation to their sensory organs and not necessarily to their nervous system)?

http://www.sciencemag.org/cgi/content/full/320/5874/362

However something like ~97% of genes show measurable decreases in fitness following loss under more difficult environments.

In fruit flies, the laboratory environment used was so simple, no predators, no wind, no temperature extremes that intelligence and learning doesn’t significantly aid survival or reproduction. There may be other interpretations.

From the Abstract:
Schizophrenia poses an evolutionary-genetic paradox because it exhibits strongly negative fitness effects and high heritability, yet it persists at a prevalence of approximately 1% across all human cultures. Recent theory has proposed a resolution: that genetic liability to schizophrenia has evolved as a secondary consequence of selection for human cognitive traits. This hypothesis predicts that genes increasing the risk of this disorder have been subject to positive selection in the evolutionary history of humans and other primates.

The link:
http://journals.royalsociety.org/content/6215831652282576/

Add this to the costs of painful, dangerous delivery and our large brains seem a mixed blessing.

That’s true: in environments that are more variable, insects are more likely to have winged morphs. If the place you’re in right now sucks, you just fly somewhere else that’s better. Intelligence allows you to stay put but alter your environment so that it doesn’t suck so bad anymore (boiling poisonous plants, etc.).

It’s like how some predators track prey by following electromagnetic gradients, others use chemical gradients, and others use motion-detectors and stereoscopic vision. They all get the job done, each probably being under strong phylogenetic constraint once it gets going. That could be why insects aren’t very smart: they’ve already gone so far down the path of “winged migration” as the solution to a variable environment.