Explanations of Life

Suppose we encounter life forms on another planet unrelated to ours and possibly quite unlike ours. Still, there is evident adaptive complexity, so that the laws of physics and chance cannot explain what we observe. What possible explanation might be given for this complexity? How might it have come to be?

One possibility is intelligent design—not by God, to be sure, but by scientifically advanced aliens. These organisms might have been synthesized on a Life Production Machine. They are in effect artifacts of another civilization, so the explanation of their existence matches the explanation for the existence of artifacts in our civilization: intentional intelligent design. We can’t rule this explanation out; it is a matter of empirical fact whether it is true (just as it is for life on earth). We might well gather further information that rules out the hypothesis (there is no such advanced civilization in the vicinity), but as a matter of principle the hypothesis is a theoretical possibility—it cannot be excluded a priori. Alternatively, the life forms might have arisen by ordinary natural selection with no intelligent intervention. But there are also mixed cases: the organisms might have been subjected to guided breeding after a period of natural evolution, or they might be genetically engineered and then left to natural selection. Conceivably they might be selectively bred from an initial batch of bacteria, so partly the result of natural design and partly of intelligent design. There is an indefinite range of possible combinations of natural evolution and guided evolution, varying between species and planetary fauna—for instance, the mammals have been left to natural selection while the reptiles have been intensively bred for intelligence or strength. Maybe elsewhere in the universe all the possibilities have been tried—as is partially the case on earth where humans have artificially bred certain species but not others.

The traditional theoretical dichotomy between intelligent design and natural selection may be quite parochial where advanced civilizations have developed, because there is ample scope for partial intervention into the process of generating life. Selective breeding and genetic engineering can certainly speed up the evolutionary process considerably, taking decades to achieve what natural selection would take millions of years to achieve. When intelligent life forms take evolution into their own hands the sky is the limit. Naturally evolved life might be the most primitive form of life, vastly outclassed by the kind of life created by life itself, i.e. designed by life forms with the intelligence to change the course of evolution. No need to wait for that lucky chance mutation; just create whatever mutation looks promising and then subject the result to rigorous test. Just as bacteria look very primitive in the light of later evolutionary developments, so naturally evolved life might look very primitive compared to the kind of life that intelligent designers can contrive. If the secret to the origin of life is ever discovered, it could be used to re-start the entire process, producing untold wonders by creative intervention. All of life could come to be intelligently designed.

Interestingly, the possibility of intelligent design depends upon antecedent natural design: not every life form in history could be the result of intelligent design, since an intelligent life form has to come from somewhere. No universe could create intelligent life ab initio: the long and painful process of natural selection has to create the first form of intelligence, since intelligence cannot depend upon other intelligence all the way down. But once a form of intelligence has evolved that is capable of selective breeding and guided evolution, it can produce new life forms without reliance on the old machinery of blind random mutation and natural selection. Then the explanation for the design of organisms will involve intelligent design not natural design. Most of the life in the universe might be of this kind: whole galaxies could be inhabited by intelligently designed organisms. Geological time is vast but cosmological time is much vaster, so the possibility of intelligently designed life coming to dominate the universe can’t be ruled out. We might be just at the beginning of the history of life—the short initial period in which life evolved naturally. Already we are beginning to change the course of evolution; genetic engineering could accelerate this process enormously. Other intelligent species elsewhere might be much further along in imposing their will on nature.

If a Charles Darwin is born on a planet that has been subject to intelligent design, he will hit upon the correct theory of evolution for that planet, namely evolution by intelligent design.[1] Maybe life was seeded naturally by the accidental arrival of bacteria, but then intelligent creatures stepped in to guide the course of evolution, creating whatever organisms took their fancy. A rival theorist who hypothesized natural selection as the explanation would be mistaken; there was, on this planet, an intelligent designer responsible for the adaptive complexity on display. Natural evolution could have ended millions of years ago, with all life now the result of intentional intervention. The traditional Darwinian theory used to be true, but it is no more: everything is now carefully monitored and cultivated. This is what is taught in biology classes these days, and it is entirely correct. All genetic alteration is brought about by scientific intervention, so that nothing is left to chance; then certain strains are chosen for reproduction and others rejected. It is as if the old religious creationist story were true, only it is not a divine being calling the shots but a super-alien. On our planet now Darwin’s theory is the true theory, but on other planets the theory of intelligent design may be the true theory (and may come to be the true theory on our planet). There might come a time when none of the species inhabiting the galaxies evolved by natural selection. That was just the early phase in the history of life, and destined to be superseded by intelligent design. Evolution will cease to be blind.[2]

C

[1] His book On the Origin of Species defends the view that all life results from the intentional actions of a mighty intelligent designer. This Darwin might not know the identity of the designer—that was not discovered until space travel became a possibility centuries later—but he was brilliant enough to see that no other explanation could be true given the facts. Organisms were just too well designed for this to be a matter of blind variation and mindless selection! He considered the alternative theory but found it wanting—and he was entirely right in his conclusions and reasoning.

[2] Just to be scrupulously clear, this essay is not intended to provide succor for creationists about life as it evolved on planet Earth; I am speaking of imaginary plants and imaginary ways of shaping life.

Why Did Sex Evolve?

Some reproduction is sexual and some is asexual. There is no biological necessity about sexual reproduction, despite its prevalence. How could there be any such necessity, given that the basic principle of evolutionary biology is just that organisms are designed to maximize the presence of their genes in later generations? This says nothing about mixing genes or about a division between the sexes. Why not reproduce purely by cloning? Why isn’t all genesis parthenogenesis? This seems perfectly possible, much simpler, and evidently how reproduction began on planet earth. So why did sex evolve from non-sex?

The problem is not just that no obvious adaptive rationale for sex seems to suggest itself; there are positive reasons why the existence of sex seems to violate basic principles of evolutionary biology. The most obvious point is what might be called “gene dilution”: instead of passing down a hundred percent of one’s genes, one passes down only fifty percent. In parthenogenesis a hundred percent are inherited, so surely an organism would prefer that figure to a mere fifty per cent. Genes that build bodies that pass on only a fraction of themselves will not be as frequent in later populations as genes that pass on a hundred per cent of themselves. Sexual reproduction appears to thwart the prime directive governing genes: maximization. Second, in sexual reproduction it is necessary to find a suitable sexual partner, whereas in cloning you can go it alone. That requires expenditure of energy and risk of failure: why take such a hard road when parthenogenesis enables one to stay home alone and get on with the job without going out in search of unreliable mates? Third, from the female’s point of view sexual reproduction looks a lot like altruism: she is providing a service to the male by passing on his genes, using her own energy resources, for which she does not seem adequately recompensed. She seems to be doing the male a favor, but organisms built by selfish genes don’t do each other favors. The role of female looks unacceptably altruistic. We need to show what is in it for her genetic prospects. Why tolerate males at all? Why aren’t all organisms female?

Sex thus appears biologically paradoxical—inconsistent with even the most basic principles of evolution. We must find a way to explain its origin and persistence that comports with basic biology. Many theories have been proposed, which I won’t discuss here. I intend to propose, as economically as possible, another theory, which respects the game-theoretic selfish gene perspective now prevalent in the field. I call this the “genetic parasite theory”.

Imagine a population of single-celled eukaryotic organisms (ones with a sheathed nucleus containing DNA) and suppose their mode of reproduction to be asexual. They are all, in effect, female, and reproduce by cell division, transmitting one hundred percent of their genes into each offspring. Now, life being what it is, opportunities for parasitism will arise: some of these cells may adapt to exploit the resources of other cells in the population, without killing them. Let us suppose that they attach themselves to the surface of host cells and siphon off nutrition found in the host. The host will resist such nutritional theft, but it may persist nevertheless, possibly following an arms race between parasite and host. Being a parasite is always a highly attractive option for any evolved creature, having all the benefits of theft over honest toil, and is not easily foiled (it is really just a kind of non-fatal predation). But suppose that some cells are more ambitious: they seek not just food but also reproductive assistance—they want to use other cells to pass on their genes, sparing themselves the expense and trouble. They therefore evolve a pointy organ that can penetrate the surface membrane of other cells and transfer their own DNA into the nucleus of the host cell, where it can enjoy the resources of the host cell in getting itself reproduced. These cells are not nutritional parasites but genetic parasites. They might even be able to replace entirely the DNA of the host cell, by inserting all their own DNA into the nucleus. That would mean that none of the host’s genes are transmitted and all of theirs are. By the laws of gene selection such a host would soon go extinct; its offspring would be copies of the parasitic cell. We would thus expect that counter-measures to the genetic infiltration would evolve, and an arms race would develop. The host cell might develop ways of poisoning the parasite or dissolving its genetic residue once inside or blunting its pointy organ. Let us suppose that an equilibrium point is reached in which fifty percent of the parasite’s DNA is permitted inside the host’s nucleus and fifty percent of the host’s DNA remains. Perhaps if the host accepts this amount less damage is done to it by the invasive cell, which will limit its aggressive incursions if the host cooperates to some extent (otherwise it will fight to the death). Still, this is a highly unsatisfactory outcome for the host, because of gene dilution. How might it adapt to this state of affairs? It needs to find a way to get something out of the new arrangement—some sort of genetic payoff.

Some of the genetic parasites will contain better genes than others. If poor quality genes are mixed with the host’s genes, then the result will be less advantageous than if good quality genes are mixed. Given that the host is losing fifty percent of her genes in the new arrangement, it would clearly be better if she were to have good quality alien genes than poor quality ones, since the whole package will then do better, which is good for her genes. So she begins to favor parasitic genes that are better than others—she exercises quality control with respect to her genetic parasites. She becomes selective in her resistance. She is still not as well off genetically as she was before all this happened, when she reproduced by solitary cloning, since she is still suffering from gene dilution. But there is little she can do about it given the aggressive parasites she has to contend with. It is always better to have no parasites than some, but it can be better to have some parasites rather than others. You want the ones that can do you a favor in return, if that is at all feasible. Thus our host will want to select the best genes she can from her would-be parasites, because these will aid her own genes better than other parasitic genes will. The situation is still unstable, however, because there will be selective pressure to revert to the pre-parasite state of things, where all of her genes get perpetuated. She will want to resist the genetic parasites as much as possible, consistently with the arms race and the costs of resistance. How can things be made more palatable to her?

Suppose that among her “suitors” a select few have genes with the following property: if they are combined with hers they will actually increase the chances of her own genes surviving into the future, relative to their chances without such combination. Given genetic variation in the population, some cells will be more viable than others—and these are the best ones to “mate” with. In other words, the optimal strategy for an invaded host cell is to select a parasite that will improve her genetic prospects—not just relative to other potential parasites but also relative to her chances without such parasites. If she mates with such a fine specimen, then her genes will actually be better off than if she reproduced all on her own. True, there will be fewer of her genes in the next generation, but by combining with genes superior to her own she will ensure that more of her genes will eventually survive and reproduce. The result of this kind of upgrade combination is a “leg up” in terms of genetic survival, compared to the way things used to be. This, then, is how sexual reproduction evolved as a stable mode of reproduction: genetic parasitism combined with genetic selection that provides a “leg up”. What started as straight parasitism, with the usual arms race and compromise, turned into a kind of symbiosis, when the female improved her genes’ chances by selecting high quality “male” genes. Now there was something in it for her, beyond simply minimizing the bad effects of determined parasites. If she could have won the arms race against the parasites, reverting to her untroubled asexual mode of reproduction, that would have been quite satisfactory; but it is even better to find a way to exploit the parasite by selecting only parasites that serve her own genetic interests better than the old regime. And if she could not win the arms race anyway, it is better to turn a fait accompli into an unexpected triumph: the female cells that are better at selecting the male genetic parasites with the best genes will do better than those that are not so good at this. Thus we get competition among males to be selected and competition among females for the best males.

Here are a couple of analogies to bring out the logic of the situation. Suppose there was a parasitic worm that could actually affect the DNA of its host: it secretes a chemical into the DNA and changes its composition, producing new genes. Suppose some of these worms produced worse DNA and some produced better DNA. Clearly it is to the advantage of the host organism that it selects the worms that improve its DNA, since these will then have a better chance of being passed on. It might be better to have no such worm, but given that this is unavoidable, natural selection will favor the “good” worms over the “bad”. And maybe there are some worms so good that it is better to have them than to have no worms at all—since they can build organisms greatly superior to any built by the host’s original genetic composition. These super-worms produce simply outstanding children for the host. Similarly, alien DNA (deriving from a “male”) might so improve the female’s gene complex that the necessary genetic dilution is acceptable, according to the genetic calculations. Fifty per cent of my genes surviving for a thousand generations is a lot better than one hundred percept surviving for only ten generations. It is like five of my ten children living to be a hundred with the other five dying in childbirth, compared to all of them living only to the age of three. A worm that re-tooled your genes to make them substantially better at surviving would pay its way in the unforgiving genetic arithmetic. Genes for tolerating such a worm would be more likely to be passed on.

The second analogy concerns coalitions. If someone comes to you to form a coalition in order to secure some future benefit, you must ask yourself a simple question: am I better of with her or without her? If I can secure the benefit without the coalition, I do well to decline her offer, since I would then have to share the benefit. But if I judge that I cannot achieve the end without her help, then I should join with her in a coalition, since I will get nothing otherwise. Sexual reproduction has the same logic: if my genes go it alone they have a certain probability of surviving to reproductive age (maybe zero), but if I combine them with someone else’s genes (losing fifty per cent of them, say), then there is a different probability of their survival. If the latter exceeds the former, then I am rational to choose the latter over the former. A potential mate is like someone offering you a coalition: if you mate with me I assure you the chances of genetic happiness are high, compared to the chances if you mate with someone else or just decide to go it alone. Suppose you happen to have both means of reproduction available to you, sexual and asexual. You have to choose which to employ. You compute the payoffs by multiplying the number of your genes that will get passed on by the probability of their survival (over, say, the next million years). If a hundred per cent get passed on by the asexual method, but there is a low probability of their long term survival, you might opt for the sexual method where fewer get passed on but the probability of survival is much higher—but only if you believe the “donor” genes have this kind of survival power. In the same way, your coalition mate has to be good enough to warrant dividing the spoils with her later, or else you will choose to go it alone and keep all the spoils for yourself. Sex arises from genetic coalitions, possibly preceded by genetic parasitism. This is better for both parties, because there is something in it for the host and the parasite benefits because its incursions are no longer resisted. Thus we move from resistance to consent: the male benefits but so does the female. This solves the problem we started out with, which was to explain how sexual reproduction could make sense given that asexual reproduction seems so much more sensible biologically. The answer is that it results from a strategy for dealing with genetic parasitism.

Let me restate the point in less abstract terms. Why should a female mammal allow her womb to be colonized by a male mammal with a different set of DNA? Why should her energy resources be diverted into generating his child? He should take care of it himself! He is just freeloading off her womb and energy resources. The suggested answer is that she is gambling that the influx of his genes will improve the prospects of her genes. Given that the male would just parasitize her womb anyway, it is better to be selective about mates and try to improve her own chances in the genetic lottery. In the payoff matrix that describes all the options, with their various costs and benefits, sexual reproduction seems the best choice—the best compromise, we might say. Asexual reproduction makes perfect biological sense—it is how a well-meaning Creator might have arranged things—but given the rough and tumble of evolution, with the ever-present threat of unscrupulous parasites, sex has emerged as a kind of game-theoretic solution to an inevitable problem: namely, what to do about those pesky genetic parasites. The parasites are with us always, given the attraction of that line of work; the question is what can be done about them. And the answer in one word is: compromise. Sex is a kind of accommodation to the harsh reality of biological existence—ultimately, access to energy.

If this explanation is on the right lines, what might we expect to characterize animals and their sexual behavior? One point has already been mentioned: we would expect male competition for females, selectivity from females, and competition within females for outstanding males. Of course, these are all abundant features of animal behavior. Correspondingly, we would expect female sexual anatomy to conform to the general theoretical picture: it should not be too easy to impregnate the female, which would impair her ability to be selective. Her consent to copulation should be required for copulation to be feasible for the male. Rape should be, at least, difficult and potentially hazardous. At the same time, copulation should not be so difficult that a suitable male is just not up to the task: hence difficult but not too difficult. We might also expect sex to be somewhat predatory, given that the male is always essentially exploiting the female, in order to spare himself the effort of gestating offspring; and the female will always be wary and choosy, wondering if this suitor is really “the one”. She is giving up a lot to incubate his progeny, in terms of energy and commitment; so she has to be sure there is something in it for her (i.e. her genes). The genes of the female must move her in such a way that their interests are respected, even though only fifty per cent of them will end up in the next generation. The genes of the male have no such concerns, given that he is not called upon to act as incubator; and he can spread those genes around ad libitum. The underlying logic of sex predicts these kinds of phenotypic facts, and they are evident enough in animal behavior. Fundamentally, the male is still the aggressive parasite and the female the reluctant host trying to make the best of a bad job. Of course, once the sexual machinery is in place and the female has no other reproductive option, she will act with enthusiasm and commitment; but the genesis of sexual reproduction is still written into the underlying structure of the sexual relationship.

A less obvious consequence concerns sexual selection. The female exercises quality control: she evaluates her potential mates by formulating hypotheses about their genetic fitness, based on what she can observe. She cannot peer directly into the suitor’s genes but must go by outward appearance. Thus she espies the peacock’s lavish tail and infers genetic superiority within. This causes males to improve their appearance so that females will evaluate them highly: but to improve their appearance they have to improve their reality. They have to be bigger and stronger, less infested with parasites, and more able to sustain pointless bits of flamboyance. So there is selective pressure on males to improve. Thus sex leads to sexual selection, which leads to improvement. That is, sex is what powers evolution to produce ever more complex and accomplished animals, via sexual selection. But asexual reproduction has no such consequence: the organism just reproduces itself according to its original design. There is no sexual selection when reproduction is asexual, and hence no motor to drive biological progress. The result is likely to be stasis, uniformity, and dullness. You don’t get complex beautiful animals when the method of reproduction is asexual. It is not, of course, that anyone is aiming for such complex beauty; it is just that the mechanism for producing it does not exist in a world without sexual reproduction. We owe it to sex to kick start evolution into a higher gear; before sex the pressures for change were minimal. It was when females started to be choosy, as a way of making the best out of living in a world of genetic parasites, that sexual selection triggered the kind of evolutionary changes that we see. Without sex Earth might never have got beyond boring bacteria floating in nondescript oceans. We owe it to the parasites among them to have initiated a process that led to the impressive variety of animal life that now exists.

Here is one final point–a kind of theorem: a genetically perfect female has no rationale for engaging in sex in a world in which she is subject to genetic parasitism. If she cannot improve her genetic fitness by merging her genes with those of a male, then she has no motive to permit her body to be used as incubator. For her, all genetic mixing is genetic degradation. She therefore has every reason to fight off all male incursions. But the same is not true of a genetically perfect male: he still has every reason to reproduce sexually, since he can thereby produce more copies of his genes than by solitary cloning. He just has to deposit them in as many willing (or unwilling) female bodies as possible. There is a huge logical asymmetry between being the one with the incubating body and being the one who uses someone else’s body as incubator. That asymmetry is the real basis of sexual reproduction (and indeed ultimately defines the difference between the sexes). Genetic perfection in the female leads naturally to frigidity, but genetic perfection in the male entails no diminution of sexual appetite. In other words, the genes see no point in sexual reproduction for the genetically perfect female, but they see a lot of point in it for the genetically perfect male. Of course, there is no such thing as genetic perfection in the real biological world–but I am making a purely logical point.

Colin McGinn

Evolutionary Causation

Evolution is a causal process. But it is a causal process unlike any other. It is a causal process in which the effect vastly exceeds the cause, and indeed (in a loose sense) contradicts the cause. The most obvious point is that the effect is much more complex than the cause: from natural selection operating over simple entities, ever more complex entities evolve. At the origin of the causal chain leading to humans we have simple bacteria; and there is no infusion of complexity from outside, except that provided by genetic mutation and natural selection. The evolutionary causal process takes us from simplicity to complexity, dramatically so. Evolution also takes us from mindlessness to minds—from matter to consciousness. Nothing psychological directs the evolutionary process, but something psychological emerges from it. The effect is mind, but the cause is mindless. It is the same with purpose: there is no purpose to evolution by mutation and natural selection (despite the misleading connotations of that phrase), but the result is animals endowed with purpose. Teleology is caused by non-teleology; efficient causes produce final causes. Animals desire and intend things, but evolution does not. Similarly, animals—some of them—have foresight and plan ahead, avoiding future catastrophe; but evolution has no foresight and is not deterred by future catastrophe. Evolution could drive all animals to extinction and not lift a finger to avert that consequence—just as it has driven countless species extinct (nor does it lament those vanished species, as we might). Evolution is blind in its operations, but it produces animals that are not. Evolution is also amoral, wasteful, cruel, and indifferent; but it produces at least one species with a moral sense (and maybe more). Indeed, it produces moral beings that deplore the very process that led to them: we would change nature’s methods if we could. We recoil at the very process that leads to our ability to recoil. Our moral nature is not nature’s nature, but the opposite of it. Finally, evolution has no comprehension of anything–no understanding or intelligence or insight–yet it causes creatures that have comprehension of many things, including the evolutionary process and its lack of comprehension. Thus we can say that animals (especially humans) are caused by a process alien to themselves: animals have characteristics that are not found in their (remote) evolutionary causes, and which are at variance with their causes. The causality is a kind of paradoxical causality—as if it gives rise to things opposite to itself.

The same can be said of embryological causality, which is in many ways just like evolutionary causality. The embryological process takes us from the simple, mindless, purposeless, blind, amoral, and uncomprehending to the opposite of these traits—to a being with the negation of each of them. The process itself is one of mechanical self-assembly, guided by nothing, not even a blueprint, purely local in its methods of protein synthesis; yet it produces a being endowed with a rich set of traits. The causality is again paradoxical, anomalous, surprising, hard to believe, miraculous-seeming. It has the look of creating something from nothing. But it is entirely natural, governed by the laws of physics and chemistry, just like evolution.

No such paradoxical causality is assumed in creationist models of evolution or embryogenesis. According to those theories, the cause of creatures with the traits listed is another creature with the traits listed: God is precisely a being with complexity, mind, purpose, foresight, morals, and comprehension. Creationist causation is non-paradoxical (paradoxically!), since the cause has the very traits found in the effect. But that theory is known to be false, while evolution by natural selection is known to be true—so we are saddled with the kind of causation it involves. And notice that it is not just that the causation is emergent or generative; it actually involves negating the defining features of the cause—that is, producing traits that are at variance with the nature of the cause. It is just as if nature were contradicting herself.

It might be said that evolutionary (and embryological) causation is not as special as I am making out. Isn’t the early history of the universe likewise causally “peculiar”? After all, the universe was once all dispersed gas and only gradually did gravity create solid discrete bodies—stars, planets, galaxies, etc. Didn’t physical causality produce the solid and massive from the vaporous and weightless? Well, no, it didn’t, because all that gas was simply dispersed matter, with the standard properties of matter—mass, volume, electric charge, and gravity.[1] The universe never went from non-mass to mass or non-gravity to gravity. There was no paradoxical emergence, no something from nothing, just the working out of what already existed—basically, material aggregation by gravitational force. Even the production of the elements inside stars proceeded by the pre-existing laws (gravitational compression). It is only when we get to the evolution of life that the surprising kind of causality kicks in; then the universe discovers a new kind of causal process, with vastly greater generative power. Mutation and natural selection, genes and self-replication, prove to introduce a new kind of causation, capable of far more impressive feats than any observed hitherto—even if they are far more local and parochial, as well as less physically powerful (it takes only sunlight to fuel the whole process). The causation involved in the expanding universe operates on a much larger and more general scale than the expanding of life on earth, but it is far less impressive than evolutionary causation in its innovative power. The cause-effect mismatch of the latter is not mirrored in the former. Evolution is causally prodigious.

It would be good to have a label for the two types of causation, but none currently exists. We might borrow from Kant’s discussion of the analytic-synthetic distinction and press into service “ampliative” and “augmentative”. Thus non-evolutionary causation might be described as “ampliative causation” because it merely spells out what was already present: it adds nothing essentially new, though it can yield non-trivial transformations in the universe (stars, elements, black holes, etc). By contrast, we have “augmentative causation” in which radical innovations occur, even the kind of oppositions I have described. Evolution and embryogenesis involve augmentative causation—as a synthetic judgment for Kant involves going beyond the content of the subject in the predicate. Or we could speak of “conservative causation” versus “creative causation”, or “easy causation” versus “hard causation, or “mechanical causation” versus “innovative causation”. Of course, it might be maintained that the two types of causation really collapse into each other, because what I am calling a special type of causation really reduces to the other type. Either the evolved traits I listed do not really exist (“eliminativism”) or they can be reduced to properties that obey the ampliative type of causation (“reductionism”). I have not claimed to refute such a position here; my point has been that evolutionary causation is special on the assumption that the traits in question exist and cannot be reduced away to properties found in the evolutionary causes that don’t presuppose them. That is, I have assumed that mammals, for example, instantiate a range of traits not found in bacteria (mind, purpose, morals, etc). Given that, we need to recognize two basic kinds of causation in the universe (though they may be interwoven in complex ways).

I strongly suspect that this distinction lies behind an historical puzzle concerning the discovery of the theory of evolution (indeed I formulated the distinction while trying to solve that puzzle). It wasn’t until the nineteenth century that Darwin (as well as others) came up with the correct theory, though there was nothing to prevent earlier thinkers from discovering it, even going back to the ancient Greeks. The question was how to explain biological adaptation, and the answer is blindingly obvious once formulated; yet no one thought of it. It was quite possible to come up with the theory from the armchair by a priori reasoning, and it is not the kind of counterintuitive and difficult theory that (say) quantum theory and relativity theory are. All we need are the notions of chance variation and differential survival. The theory really could have been invented by Aristotle or Descartes well before Darwin’s time—so why wasn’t it? In fact, Darwin himself did not endorse it from the armchair but had to amass huge amounts of empirical data before he could accept the theory—the data forced the theory on him. Why the reluctance to accept what seems so blindingly obvious? (Selective breeding alone should have given the game away long before.) Something seems to have been blocking people from seeing it—and more than just piety and tradition.

My suggestion is that it was the nature of the causation involved that made the theory invisible for so long: people just assumed that the cause of animal (and human) existence had to conform to the usual kind of conservative ampliative causation. Hence the easy attraction of the creationist picture: it didn’t involve counterintuitive paradoxical-looking causation, but just regular causation in which cause and effect match each other. It turns out that this view of causation was too restrictive, as we now understand, but it is not surprising that there would be resistance to it at a gut level. The production of life had to be a causal process of some sort, but the kinds with which we are familiar respect the conservative principle, so it had to be that kind of causal process. We have certainly never observed the kind of creative causation manifest in the evolutionary process, simply because it takes place over such a long span of time. The idea that things like humans, with their distinctive traits, could be caused by a blind mechanical amoral process, originating in things like bacteria, was just too much of an affront to habitual assumptions about how causality works. And indeed it is still difficult to make sense of the causal process involved, precisely because it seems to entail getting something remarkable from nothing very much. It is thus very surprising that Darwin’s theory is true—something to marvel over (mind from mindlessness, morality from amorality). This explains why it was so hard for Darwin and others to recognize its truth. If someone had come up with the basic idea centuries earlier, it would have struck them as preposterous: how could chance variation in mindless entities, combined with blind natural selection, have caused the creatures we see today? We have found out, however, that the impossible is actually true—if I may exaggerate a bit. So it is not inexplicable that Darwin’s theory lay hidden for so long, despite its simplicity and a priori availability—unlike Newton’s theory that required enormous feats of mathematical reasoning and pure genius. No one came up with Darwin’s theory for so long because it seemed causally impossible—quite unlike the traditional creationist story (despite its falsity). Even today I suspect that many people resist Darwinism simply because of their habitual intuitions about causality, formed by ordinary observation, not because of any immovable religious commitment. People came round to the heliocentric hypothesis much more easily, because it did not challenge their intuitive notions of causality. But if what I am suggesting here is right, it is much harder to persuade people of evolution because of the causal picture it implies. To put it more positively, in order to overcome resistance we need to address ourselves directly to the question of causality and face it head on. The theory should be advertised as empirically correct but causally counterintuitive, or at least causally surprising. Simply passing over the causal question in silence, without facing it squarely, leaves people uneasy and perplexed. We need to accept that when species evolved a new species of causation evolved.[2]

[1] An exception might be made for the instant of the big bang in which it is said that matter, space, and time came to exist with extreme rapidity. Putting aside the question of whether that is the right thing to say, my comment is that if this is indeed so then causation at this early stage had the kind of innovative power I am attributing to evolutionary causation. Thereafter, however, physical causation followed a far more conservative trajectory.

[2] This is not to deny that evolutionary causation is grounded in ordinary physical causation (compare mental causation); it is just to say that the macro causal process of evolution involves the production of kinds of entities not present before. Teeming life comes from monotonous non-life—animals from atoms, men from molecules.