I have been rather skeptical of the so-called Gaia Hypothesis, the notion that planet Earth is one large, self-regulating organism, as opposed to the environment in which a number of ecosystems have evolved. The notion was first proposed by independent scientist James Lovelock in the 1970s, and co-developed by the controversial biologist Lynn Margulis, famous for having proposed that some cellular organelles, such as mitochondria and chloroplasts, initially evolved as endosymbionts, i.e., as functionally integrated organisms within organisms.
A few years ago I wrote an article for Skeptical Inquirer in which I strongly criticized the Gaia Hypothesis, characterizing it as essentially pseudoscientific, as it is based on a radical misconception, in my mind, of what a living organism is and how evolution works. It is, moreover, entirely untestable empirically. I am not the only critic of Gaia, another one being W. Ford Dootlittle, an evolutionary and molecular biologist, now Professor Emeritus at Dalhousie University in Halifax (Nova Scotia). Ford (we are on a first name basis) has done important work on cyanobacteria, among other things finding convincing evidence that — as predicted by Margulis — chloroplasts, the plant organelles where photosynthesis takes place, originated as endosymbionts.
Imagine my surprise, then, when a few weeks ago I read an article in Aeon, written by Ford, in which he announced that he had changed his mind about Gaia, and that he hoped that more of his colleagues would reconsider the idea. So, here I am, reconsidering it, on the basis of Ford’s arguments.
Ford begins with a problematic statement right off the bat. He notes, correctly, that ecosystems have some self-regulatory abilities, meaning that when they are perturbed by environmental changes they are capable of reorganizing themselves and keep going. Equally correctly, if a bit trivially, he reminds us that we wouldn’t be here today if our planet hadn’t maintained conditions suitable for life for the past four billion years.
Immediately thereafter, however, Ford sets up a false dichotomy. He claims that there are two interpretations of the above mentioned facts: on the one hand there are people who think there is a planet-wide natural equilibrium, the Gaia Hypothesis; on the other hand there are those who reject such possibility as nonsense on the grounds that “organisms are ‘selfish,’ and evolution isn’t cooperative but rather a brutish Darwinian competition that selects individual organisms based on their ability to survive and reproduce.”
The problem is that the second option Ford gives is seriously outdated. Even Darwin rejected the notion that evolution is “red in tooth and claws,” allowing for cooperation being one of a number of strategies for survival and reproduction favored by evolution. Think social insects, or social primates. Or the very kinds of endosymbionts Ford has studied during his career. Moreover, the “selfish gene” metaphor has long been dead, pace the still many fans of Richard Dawkins (and, to be fair, it was only a metaphor in the first place). Contemporary evolutionary biologists realize that evolution by natural selection occurs at various levels of complexity, from the gene to the organism, to groups of organisms to — possibly — entire species. The technical term is multi-level selection theory.
Ford then reminds us of Lovelock’s original Gaia Hypothesis, according to which, for instance, algal mats have evolved so as to control global temperatures, and Australia’s Great Reef Barrier is a “partly finished project for an evaporation lagoon” with the purpose of controlling oceanic salinity. This language should immediately sound suspicious: who, exactly, carried out such projects? How does a biological structure have a “purpose”? We know Lovelock did not believe in intelligent design creationism, but his highly anthropomorphized terminology was sloppy and alienated a number of professional biologists, for good reason. It did not help that Gaia became very popular with New Age types, who are notoriously anti-scientific.
Ford admits that he was an early critic of Gaia, but he says that he has now spent some time in an attempt to “Darwinise” the notion, and that he sees cooperation as widespread in the biological world, possibly extending to the planetary level. (For another article on the problems with too much emphasis on cooperation in biology see here.) Ford writes that he can see several paths by which a Darwinian — such as myself — might accept that planet Earth as a whole has evolved “biosphere-level adaptations, selected by nature for their stability-promoting functions.”
Well, frankly, I don’t see any such path, for the simple reason that natural selection works on the basis of a number of factors that are just not present “at the biosphere level.” In a landmark paper, the evolutionary geneticist Richard Lewontin (a major inspiration for my own career as a biologist) formalized the three principles necessary to articulate the theory of natural selection:
1. Phenotypic variation: different individuals in a population have different morphologies, physiologies, and behaviors.
2. Differential fitness: different phenotypes have different rates of survival and reproduction in different environments.
3. Heritability of fitness: there is a correlation between parents and offspring in the contribution of each to future generations.
Any population, regardless of how constituted, in which these three principles hold will undergo evolution by natural selection. (Modifications and improvements to Lewontin’s scheme have been proposed, but they are rather technical and we don’t need to consider them here.)
It should be immediately clear why Gaia is in trouble: there is no “population” to be considered if we look at the scale of the entire planet. We’ve got one planet, which has no phenotypic variation, no differential fitness (whatever “fitness” would mean at that scale), and — a fortiori — no heritability of such fitness.
Ford, of course, is aware of Lewontin’s conditions, and he paraphrases them in his article. He is also aware of the above mentioned multi-level selection theory. Which is why he admits that Lovelock’s original hypothesis “goes many steps too far.” He even quotes my former CUNY colleague, Peter Godfrey-Smith, who reviewed a more recent book by Lovelock, A Rough Ride to the Future:
“Feedback between different living things is indeed ubiquitous, and some kinds of feedback help life to continue. But those benefits to life as a whole are byproducts — they’re accidental. The interactions between species are consequences of the traits and behaviors that evolutionary processes within those species give rise to, and those processes are driven by reproductive competition within each species. … From the fact that life still exists, we can tell that traits too antagonistic to life itself, however beneficial to the organisms that bear them, must not have arisen. If they had, we wouldn’t be around to discuss the matter. But that isn’t what kept those traits at bay.”
Exactly. But Ford wants “something more,” a mechanism “by which selection at the level of the biosphere would be likely to produce stability,” adding “I’d hope that Darwin, were he alive today, wouldn’t balk at the non-traditional steps I’m about to take.” I think Darwin would balk, and for good reasons.
Ford’s first step is, in my mind, a non-starter. He says that we should accept that mere persistence should be regarded as a legitimate mechanism of natural selection. His example is illuminating: he asks us to imagine 1,000 radioactive atoms in the process of decaying. The atoms remaining after the process has gone on for a while have the same properties as the initial group, so their “survival” of the decay process is a result of luck. But, continues Ford, if there were “mutations” that somehow gave atoms the ability to “resist” decay, then — obviously — the atoms left at the end would be more likely to carry those mutations.
The problem with this hypothetical scenario is that Ford has simply conjured a highly unlikely version of Lewontin’s conditions, assuming that the atomic “mutations” were heritable. But constructing imaginary scenarios proves nothing. The question is: do planetary ecosystems have the three properties necessary for evolution by natural selection? And the answer is a very clear no.
Ford acknowledges that it is “highly unlikely” that whole biospheres could acquire stabilizing mutations, but, he insists, it is possible that they might. No, it is not. Or at least, there is no known mechanism by which they could, so the burden of (unmet) proof is squarely on Ford’s shoulders. And let me remind you that there is a crucial difference between the 1,000 atoms and the one Earth biosphere. There is no “population” when the relevant number is one, which means that Lewontin’s conditions cannot be met by a biosphere.
A bit later on in the article Ford attempts to get around this lethal objection by positing that there were multiple LUCAs (Last Universal Common Ancestors) shortly after the origin of life on Earth. He goes from there to claim that this “means Dawkins’s objection that Gaia is not part of a population of competitors on many planets becomes irrelevant: there were enough such competitors on this planet, possibly even in the same ‘warm little pond’: it’s just that they were less persistent than Gaia, and are now all gone.”
This is astonishing for a variety of reasons. First off, we don’t have any empirical evidence for multiple LUCAs. There may or may not have been, we don’t know. That’s a really bad starting point for an ambitious theory that pretends to revolutionize the way we look at the biosphere. Second, even if there were multiple LUCAs, we don’t know that all but one went extinct because of competition, as Ford postulates. The process might have been random. Third, and most important of all, LUCAs are not biospheres, unless we assume that a given clade (i.e., group of phylogenetically related species) living in the same environment thereby counts as a separate biosphere. But why we would do that, other than to artificially rescue Gaia?
Ford then attempts a second approach to make Gaia palatable to evolutionary biologists, and this, I’m afraid, gets pretty technical. Bear with me, I’ll do my best. Ford invokes a schema articulated by philosopher of science David Hull, according to which we should think of the living world as made of two kinds of entities: replicators and interactors. A replicator is an entity that passes on its structure directly via replication, say DNA, for instance. An interactor is an entity that interacts as a cohesive whole with its environment in a way that replication becomes differential (i.e., some interactors leave progeny and others don’t). Living organisms are interactors. Specifically, you are an interactor, and so are your kids. Your DNA, by contrast, is a replicator.
Why all this complication? Because according to Hull — whose schema, by the way, has been criticized in philosophy of science — selection can then be understood as a process in which differential proliferation (and death) of interactors causes the differential perpetuation of the replicators produced by such interactors. That is, the fact that you have more kids than your neighbor, say, means that more copies of your DNA get passed down to the next generation compared to his copies.
What does that have to do with Gaia? Well, according to Ford, if we “sometimes” substitute “reproducer” for “replicator” and “persistence” for “reproduction” we might get an evolving Gaia. As he puts it: “Modified in this way, we could say that the ‘differential extinction and proliferation of interactors’ (at any level of the hierarchy of life) causes the ‘differential perpetuation of the replicators that produced them’ — the term ‘perpetuation’ understood to embrace both reproduction and persistence.”
Gaia, in Ford’s modified scheme, is a persister and an interactor. But this makes little sense. For one thing, persistence is not the same thing as reproduction. When they talk about differential persistence — for instance in the case of species or clades — biologists use the term “sorting” rather than selection. That’s because the resulting dynamics are very different. And unlike all levels of biological complexity below the planetary one we, again, have only one entity, not a population. Again, evolution happens to population, not individuals. Also, Gaia cannot be an interactor, because it has no “environment” to interact with.
Finally, Ford tries a third route to rescue Gaia. This one too is inspired by a philosopher, in this case Andrew Inkpen. The theory is known as “it’s the song, not the singers’” (ITSNTS is the horrible resulting acronym) because of an analogy used to describe it. Consider a particularly popular song, like “Happy Birthday.” It recurs because of the stability of the song, not because the same singers sing it over and over. The song is perpetuated via periodic performances, carried out by different performers.
Ford here invokes memetic theory, saying that it “encourages us to believe that songs that are more singable, and ‘mutations’ of existing songs that make them so, could evolve by natural selection.” Unfortunately, memetic theory itself has long been a dead end, and arguably never really arose above the level of simple metaphor, much like Gaia itself (see here). But this doesn’t stop Ford, who goes even further on a limb by suggesting that “when it comes to Gaia, perhaps the relevant unit of selection is the process that multiple and redundant species implement — not the collective made up of those species itself. According to ITSNTS, interaction patterns or metabolic processes are re-produced whenever species capable of performing the steps are present: because there are singers, there’s a song.”
Setting aside well founded skepticism about memetics, this doesn’t come anywhere near being a scientific theory that (a) makes sense on the basis of what we know of biology on Earth and (b) is empirically testable. Ford is aware of some serious issues raised by his proposal, since he writes: “A problem here might lie in the implication that processes or patterns of interaction, which are arguably not material things, can cause the evolution of species, which are.” Yes, that is a problem! Cleverly, he tries to diffuse it by citing the very anti-Gaia Dawkins, who considered genes to be not physical strands of DNA, but eternal immaterial entities instantiated in particular strands of DNA. Too bad for Dawkins and his strange form of Platonism, I’d say.
But the biggest problem I have with Ford’s attempt at rehabilitating Gaia comes in the last paragraph of his article: “Beyond the benefit to science, ‘Darwinising Gaia’ would also have some political benefits. It might encourage us to look at nature as a coherent whole, with an evolutionary trajectory that we can foster or deflect as we choose.” No, science should never be pressed in the service of political goals, regardless of how commendable they may be. Science is supposed to provide us with facts and interpretations concerning how the world works. What we wish to do with such facts and interpretations depends on our values and our ability to reason. If we begin to make up scientific hypotheses because they are politically useful we enter a dangerous territory fraught with distortions and rationalizations, and in the process we lose both science and our ability to act reasonably on what science actually says.