Can Brains Point the Way?

Evolution can be simple or complex, depending on how far down the explanatory hierarchy you are forced to go. The chart shows the hierarchy (upper left corner) and the decision chart that offers an explanation for how a population gets from generation M to generation M+1.

Just while I have been struggling to understand the relationship between the Baldwin Effect and cultural/linguistic evolution, along comes a study about birds reporting that bigger brains lead to greater diversity of species. The authors claim that their research provides the “first general support for the importance of behavioral drive in evolution.” (Daniel Sol & Trevor D. Price, “Brain Size and Diversification of Body Size in Birds” in The American Naturalist; abstract here)

“Behavioral drive in evolution” sounds like something out of Lamarck whose biological theory of common descent proposed that changes in behavior led to changes in species. The idea was scorned by many at the time as insufficiently “scientific” (i.e., not a mechanical explanation, and no good at all for explaining plant evolution) and is rejected today on the grounds that we inherit genes, not behavior. So it is startling to find a mathematically precise account of the role of behavior in speciation. Remote and technical as it sounds, if the study holds it has important implications for speech origins.

The thesis is simple: bigger brains make it easier to expand one’s range and survive in new niches. Once a new niche has been penetrated, adaptation via natural selection is almost inevitable as the members of the smart population compete among themselves for the niche’s benefits. Sol and Price call this process “behavioral drive,” but it seems identical to the Baldwin Effect described by Terrence Deacon and discussed on this blog a few weeks ago. (See: Did the Baldwin Effect Give Us Language?)

An example of behavior associated with bigger brains is stealing food from others (“kleptoparasitism”). It is easy to see how this behavior can begin with smarts. An animal is pushed into a new range where it has few adaptive advantages but is smart enough to recognize the opportunity to simply take the food from a more able hunter. Even though this activity begins as an opportunistic behavior, evolution will favor the descendants who are best built for thieving. Looking at the decision chart heading this post, we can see how the process can be explained:

Is one trait more adaptive than another? Yes. Eating is more adaptive than starving, so we can rule out genetic drift as an explanation for the kleptoparasitism.

Has an environmental change made a trait more adaptive? Again, yes. The relevant change is the presence of a hunting species whose food is there for the taking. Thus, we can rule out simple natural selection that merely optimizes an already established situation.

Did a behavioral change produce the environmental change? Yes once more. The birds figured out the feeding-by-stealing method. Three yeses in a row leads to evolution via the Baldwin Effect.

As for speech origins, there is a general point—the Baldwin Effect really does occur in nature and can be understood as Darwinian, not Lamarckian evolution—and a hint about why, in my previous post on the Baldwin Effect, I found that simpler explanations usually seem sufficient to account for the appearance of steps leading up to speech. The Sol/Price paper states as a general comment that “those [behaviors] associated with the use of new resources or environments are likely to be particularly important” in Baldwinian evolution. [p. 175] Speech surely started as part of an optimizing process once the human lineage was transformed from something egocentric and social into something cooperative and communal.

But once begun, speech itself was a critical new, part of the environment and the Baldwin Effect could come into play. For example, if you have two individuals in a speaking community and one is able to control its speech more effectively and efficiently than the other, that distinction should be an advantage. Efficient control is not neutral (no, genetic drift); the adaptive value is a reflection of the new linguistic environment (no mere optimizing of a trait); yet the speech itself is itself behavioral rather than genetic. Thus, control of the tongue and lips could well be a result of Baldwinian evolution.

Does that mean that the Baldwin Effect has been important to human evolution ever since speech began? I’m skeptical and suspect that there was a window when what Sol/Price call “behavioral drive” was most important in human evolution. For one thing, even though our lineage’s brain grew enormously during the past 3 million years, there was plenty more speciation at the lineage’s beginning than there is now. If the Sol/Price research is correct, shouldn’t it be the other way around?

The early speciation is not much of a mystery. Our brains today are very large, but even five million years ago our ancestors were relatively big brained. So as the African forest retreated, the apes of that time were smart enough to penetrate a variety of woodland niches and then adapt to them. Later, as woodlands gave way to grasslands, other species and adaptations appeared. Notably, however, once the lineage’s brain began to grow still more there was no matching increase in speciation. This paradox is less problematic if you keep in mind one of the limits on the Baldwin Effect: If a population’s behavior keeps changing, it can outpace natural selection’s ability to respond.

The modern world’s rate of change is obviously too rapid for biology to keep up. Earlier cultures were far more stable, of course, but perhaps not as stable as we might think, especially in locale. Thus, Homo erectus maintained the same basic tool kit for a million years, all the while expanding its range enormously. Very likely an erectus individual roamed through a variety of niches during a lifetime, making biological adaptation to any one counterproductive.

A second impediment to speciation in big brained Homo is our technology. Clothes and tools make it easy to adapt to unusual niches without changing our anatomy. And finally, language itself provides a third block to speciation despite behavioral changes. Language makes teaching so much easier, increasing the speed with which non-genetic adaptation can spread through a population. These observations suggest there is a window in which the Baldwin Effect works: too dumb, and animal behavior is too mechanical to contribute much toward evolution; too smart, and behavior is too flexible for evolution to keep pace.

When considering human origins we have to remember there was a period when the human lineage was no longer an ape but not yet us. The details of how that period worked are the hardest to discover.

Comments

[JanetK]

I am trying to get my head around the exact nature of the Baldwin Effect. I had always thought of behaviour in the following way. If an animal is in a stable environment then it is likely to evolve towards fixing its behaviour genetically so that it is more reliable. When the environment changes, there is pressure to unfix the behaviour so that it is easier to take advantage of new niches in the new environment. As soon as the animal is ‘in’ a new niche then the pressure to fix the behaviour genetically returns. So in the transition from one niche to another (one species to another), there is a pattern of: less genetic control of behaviour, changes to genes controlling anatomy and physiology, increase genetic control of the changed behaviour. It seems like a larger brain would make survival without fixed behaviour easier and therefore would make the evolution of new species easier. Is the Baldwin Effect another way of saying this or something different?
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BLOGGER: I think you are in the ballpark, but keep in mind the Baldwin Effect's reversal of the expected direction of causality.

Imagine an insect evolving a new behavior. Assuming insects are as unimaginative as I believe them to be, a new behavior reflects, at every step of the way, changes in insect physiology that are themselves the result of changes in the genes. Changes in genes result directly in changes in behavior.

With the Baldwin Effect, changes in behavior lead to changes in genes.

[Michael]

The concept of a "behavioral drive" according to which "episodes of innovation and cultural transmission are more frequent in large-brained species, leading these animals to exploit the environment in new ways and so exposing them to novel selection pressures" was, I think, coined by the Biochemist Allan C. Wilson in the 80ies.

You might be interested in the the work of Simon Reader and Kevin Laland, who have applied the concept of behavioral drive to hominid evolution.

Reader, S.M. and K.N. Laland. 2002. “Social Intelligence, innovation, and enhanced brain size in primates” PNAS 99: 4436-4441
http://www.pnas.org/content/99/7/4436.abstract
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BLOGGER: Thanks for that link.

The Sol/Price paper attributes the behavioral drive idea to: Wyles, J. S., J. G. Kunkel, and A. C. Wilson. 1983. Birds, behavior and anatomical evolution. Proceedings of the National Academy of Sciences of the USA 80:4394–4397.