Thursday, April 17, 2014

Is Cultural Evolution a Darwinian Process?

March 19, 2013Print This Post         

by Massimo Pigliucci

The “Darwinian” theory of evolution is here to stay. I used the scare quotes to refer to it in the previous sentence because the current incarnation, known as the Modern Synthesis (and incorrectly referred to as “neo-Darwinism,” which actually was an even earlier version) is significantly more sophisticated and encompassing than the original insight by Darwin. Indeed, my opinion — which is certainly not universally shared — is that evolutionary biology is currently undergoing another gradual but significant change, referred to as the Extended Synthesis, that will expand its domain of application and explanatory tools even further.

But will it expand them to the point of providing us also with a coherent theory of cultural evolution? Chris Buskes, in a recent paper published in Philosophia and entitled “Darwinism Extended: A Survey of How the Idea of Cultural Evolution Evolved” seems to have no doubt that the answer is in the affirmative. I am not so sure.

Buskes’ paper is worth reading in its entirety, as it is a lucid survey of a number of ideas attempting to connect Darwinism and cultural evolution, including concepts like niche construction, gene-culture co-evolution and, of course, memetics.
The basic argument advanced by Buskes is that cultural evolution is best thought of as a Darwinian process because it shares the fundamental elements of Darwinian processes. These elements have been laid out in a famous paper by geneticist Richard Lewontin back in 1970. The list looks like this:

* Variation: members of a population that evolves in a Darwinian fashion show some degree of phenotypic differences in a number of traits.
* Selection: some individuals are more successful than others at surviving and reproducing, because of their phenotypic characteristics.
* Inheritance (which Buskes calls “replication”): there is a statistical correlation (regardless of specific mechanism) between the fitness-enhancing characteristics of the parental generation and those of its offspring.

While this basic summary — which Buskes refers to as “Darwin’s formula” (though, as such, it’s really Lewontin’s formula) — has been criticized for being actually too bare-bones (see, for instance, the discussion in Okasha’s excellent book on multi-level selection theory). As we shall see, my problem with Buskes’ conclusion is in part a result of the excessive minimalism of the formula.

Of course, people have proposed before that Darwinian evolution is “substrate neutral” and that its principles can be universalized. Dawkins’ and Dennett’s ideas about memetics (which do enter, with caution, into Buskes’ considerations) are an obvious example. More recently, even chemists like Addy Pross and physicists like Lee Smolin have gotten into the fray, proposing extensions of Darwinism to chemistry and cosmology respectively (here and here is why I disagree).

Let’s take a quick look at the building blocks of Buskes’ argument, focusing in the end on why I think he got close, but eventually missed the mark.

After introducing “Darwin’s formula” Buskes move on to make the point that human beings are highly cultural animals, very different in this from pretty much any other species on earth (he refers to culture as a “major transition in evolution,” a popular term these days, though one that has a bit too much of a teleological flavor for my taste). Which means that there really is something to explain above and beyond the basic biology of being human. No argument from me there. The problems begin when Buskes makes the move of declaring (plausibly, but with scant hard evidence) culture to be a “complex adaptation,” immediately making the evolutionary psychology-like leap that it therefore could have happened only by way of Darwinian selection. This, in my book, counts as a pretty massive begging of the question.

Buskes’ next move is to introduce the concept of niche construction (from evolutionary ecology) and to present it as a way to understand cultural evolution. Niche construction is a way to think about repeated gene-environment interactions going beyond the simple standard model that sees environments as posing a “problem” for the organism that evolution “solves” by mutation and natural selection. The classic example of niche construction is beavers’ dams (also an example of what Dawkins called an “extended phenotype”), structures that dynamically alter the environment not just of beavers but also of other species in the local ecological community, thereby introducing new selective pressures, which in turn act also on beavers’ phenotypes and behaviors, and so on. As interesting as these ideas are, it isn’t at all clear what work the concept of niche construction actually does — other than as an interesting metaphor — in explaining the transition from straight biology to culture in human beings.

Indeed, it is here that the weaknesses of Buskes’ approach begin to appear evident to the attentive reader. This is the section in which he cites the now classic work of people like Cavalli-Sforza, Feldman and others on gene-culture co-evolution. The thing is, if we are meant to take that (interesting, pioneering) work as a way to theorize about cultural evolution, we are at a dead end. Most of those papers are from the 1970s and ‘80s, with very little having been done since. That approach looks increasingly like what philosopher of science Imre Lakatos famously called a “degenerative” research program, i.e. an approach that seemed once fruitful but that has since ceased to bear fruits.

Buskes then moves to an interesting analysis of how biological and cultural evolution might be connected. He examines two broad frameworks, neither of which he finds entirely satisfying. First, there is the sociobiology / evopsych inspired model according to which — as E.O. Wilson once famously put it — biology keeps culture “on a leash.” Here the locus of explanation is the pre-modern (for some reason, largely Pleistocene) evolution of Homo sapiens, with modern human behavior explained either as still adaptive but rooted in the past, or as recently turned into a maladaptation because of the sudden decoupling of culture and biology in post-Pleistocene times. Second, we have the memetic model of extensive decoupling of culture from biology, where new entities (the “memes”) compete for space in our brains, regardless of their effects on the fitness of their “hosts” (i.e., us).

Buskes is sympathetic to aspects of both models, but is also aware of many of the criticisms they have received. Frankly, I don’t think he goes far enough on his critical path on either count. It would take too much space (and it would bring us significantly off course) to rehash my problems with both evopsych and memetics, but you can find a summary here and here, respectively.

[On memes, however, I can’t resist two of my favorite quotations. The first one is by my colleague and sometime antagonist, evolutionary biologist Jerry Coyne, who aptly said: “{Memetics is} completely tautological, unable to explain why a meme spreads except by asserting, post facto, that it had qualities enabling it to spread.” The other one, even more damning, is by biologist Jeffrey Schloss: “It is not entirely clear how it is that positing unseen and undefined entities that infect human minds by unassessed processes involving the entities’ own quest for transmission and that cause people to do things that transcend their genetic imperatives is fundamentally different from medieval demonology or, in any case, qualifies as an empirically grounded explanation in terms of natural causes.” Ouch.]

We finally get to the crux of my disagreement with Buskes, which comes into focus when he gets around discussing the two most common (and interrelated) objections to thinking of cultural evolution as a Darwinian phenomenon: the apparent “directedness” of cultural evolution and its “Lamarckian” character.

In terms of directedness, the idea is obviously not that the outcome of cumulative cultural evolution looks teleonomic, as the appearance of teleonomy is typical of Darwinian biological evolution too. The eye, to pick on the standard example, appears to have been designed for the purpose of seeing. In reality, there was no such longstanding design or pre-ordained tendency, only a large number of haphazard mutation-selection cycles, which however did bring about the function of the eye as we currently understand it. In fact, years ago I have used this sort of insight to argue that evolutionary biology maps conceptually very well onto the famous four Aristotelian causes, including the so-called “final” cause, which answers the question “What is X for?” The answer is, of course, different from the one Aristotle would have provided, but such is progress in human understanding.

So, the issue here is not one of directedness of the outcome of evolution, but of the source of variation. Contra Buskes, a cardinal tenet of the Modern Synthesis (and indeed of the original Darwinism) is that mutations — the ultimate source of novelty in evolution — are random with respect to fitness outcomes. It is important to understand this point. Molecular biologists have long discovered that mutations are not random in the sense that they all appear with the same frequencies, regardless of genomic localization. There are “hot spots” along different chromosomes in different species, and some structural changes in DNA are more likely than others to occur because of the three-dimensional conformation of DNA. But — despite the occasional claim to the contrary — there is no convincing evidence that favorable mutations (in a given environment) are more likely to occur than unfavorable ones. Should the exceptional claims ever be confirmed and widely accepted that would amount to a rejection of Darwinism, though not, crucially, of the more encompassing idea of evolution (so creationists need not rejoice).
Now, cultural evolution is directed not just in outcome, which would be compatible with a Darwinian explanation, but also at the source. We direct it by consciously focusing on one problem or another, deciding to work on one solution or another. I am not, obviously, suggesting that all human cognition is conscious, we know better by now. But even if a relatively small fraction is (i.e., unless you belong to the “it’s all an illusion” school of non-conscious thought) then cultural evolution departs in a major way from its biological equivalent.

The second objection to a Darwinian model of cultural evolution raised (and quickly dismissed) by Buskes is connected to the dreaded L-word. Lamarckism is a really, really bad word in evolutionary circles, arguably undeservedly so. Lamarck, after all, was a pioneer of the field, one of the first modern thinkers to explore the idea of a naturalistic explanation for the history and complexity of the biological world. Yes, he got major details wrong, but that’s the way science works and makes progress. Moreover, let’s not forget that Darwin himself — who died without figuring out a mechanism to account for the origin of biological variation so crucial to his theory — flirted with Lamarckism and tried to incorporate it into his own view of biology. (Mendel, a contemporary of Darwin, had figured it out, but Darwin never read Mendel’s paper, even though he apparently received a reprint of it.)

It isn’t even clear, really, what Lamarck actually said. I have never read the original text (and, I guarantee you, neither have the overwhelming majority of people who have no qualms pontificating about it), but I understand that his famous notion of the inheritance of acquired characteristics — because of which the L-word has enduring negative connotations — was a relatively minor part of his overall theory.
Indeed, the major component of Lamarckism, according to my colleague Eva Jablonka, who has thought a lot about this stuff (and has read Lamarck!), was the idea that organisms react actively to environmental challenges, as opposed to the more “passive” process of natural selection postulated by Darwin. So, really, the chief Lamarckian idea has more to do with directedness, the topic we discussed above, than with the inheritance of acquired characteristics.

Nonetheless, the latter is there too, and it applies beautifully to cultural evolution. As Buskes himself readily acknowledges, biological evolution works (mostly, there are exceptions, especially but not only in the bacterial world) by way of vertical transmission of information, from the parental to the offspring generations. Cultural evolution does incorporate vertical transmission (you can and should teach stuff to your kids!), but also rampant horizontal transmission (peer-to-peer, so to speak), and even “oblique” transmission (as in from a teacher who belongs to the previous generation to students who belong to the next one).

To recap then, take a look at the figure below, which summarizes what I think are the differences between biological (Darwinian) and cultural (Lamarckian) evolution:

I think the divergence between the two is clear enough. Of course, we are still talking about evolution, and not just in the sense of “change over time” (as in the evolution of the universe, for instance). This is cumulative evolution that brings about complexification and adaptedness (though plenty of both biological and cultural structures/artifacts are not at all “adaptive,” and of course the fitness currency is much more clear in the case of biological evolution than in the cultural instance — there is quite a bit more work to do here!).

The conclusion that biological and cultural evolution are different also nicely accounts for the fact that cultural evolution is so much more dynamic (it happens much faster) and unpredictable than its biological counterpart. If we think of both as instances of Darwinism that difference becomes more puzzling.

All of the above said, we already know that Darwinian evolution is not confined to biological systems: computer programmers have worked with “genetic algorithms” for a long time now, in the process independently rediscovering many of the basic ideas of (biological) population genetic theory. At the moment, though, we don’t have any example of Lamarckian evolution outside of humanity. If we ever succeed in producing truly artificial intelligence, that would likely count as a second example on this planet (other than our own), and of course it may be that there are many other cultures scattered throughout the universe. Hopefully, we shall see about that at some point in our future.

Piece crossposted with Rationally Speaking | Creative Commons License

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