It is difficult to explain the origin of life on earth. Presumably, inorganic molecules at some point made the transition to organic molecules, allowing for self-replication. The state of the earth at some time and place must have been conducive to this event, while it wasn’t before and elsewhere. Even if life on earth was seeded by organic materials arriving on meteors, these seeds must themselves have had an inorganic origin somewhere else in the universe. This is admitted to be a difficult problem. But there is another problem in this neighborhood that is equally difficult: why did life on earth arise only once? Evidently, conditions on earth made life possible at a certain time, but why didn’t those same conditions lead to life at other times? We are told that life arose at a particular place and time, so that everything now living traces back to this singular origin, but why is this so—why didn’t it arise many times once the appropriate conditions obtained? Why the singularity? It is as if the switch went on once but then the earth forgot how to switch it on again. The events of the universe are mainly repetition, but in this case we have a one-off event—a completely unique occurrence. Once life arose from non-life, why didn’t it keep on so arising? The conditions were conducive, so why didn’t they conduce more often?

Suppose you travel to a distant planet and find life there. You investigate this life and determine that it arose n billion years ago: but it arose not just once but multiple times. It has kept on arising, perhaps millions of times, since the conditions for life persisted after the initial rising; there are thus a great many chains of living things that trace back to these many points of origin. There is nothing physically impossible about this; indeed, it is what you would expect given the conditions on this planet. So why isn’t earth more like that? Why the stinginess? Life on earth is all about repetition–organisms duplicate, cells divide into copies of themselves, the same kinds of biological events occur over and over—so why is the origin of life on earth a singularity? This fact cries out for explanation, but no explanation is forthcoming. Something special must have happened–but what? And how could anything that happened at life’s inception be so special? The singularity seems inexplicable, strange, mysterious. Imagine if life on earth had evolved three times, or seventeen times, but then stopped evolving: wouldn’t that be peculiar, calling for explanation? One time seems no less arbitrary, no less improbable. It might be more explicable if life had evolved by a huge cosmic accident—say, a fully formed pair of tigers, male and female, are created from inorganic materials by chance: that is not likely to happen again! But this isn’t how life on earth began: the process was incremental, with only bacteria at the early stages, preceded by organisms yet more simple. There is nothing intrinsically chancy about the earliest forms of life; yet they arose only once. It’s like a mountain arising only once or rain falling only once.[1]

I rehearse these points in order to draw an analogy I have not seen drawn: between life and language. The origins of language are notoriously problematic and subject to much controversy, but less often noted is the problem of singularity: why did language evolve only once? That is, why did language with the properties possessed by human language arise only once? I don’t mean communication systems in general, such as are possessed by whales, dolphins, bees, and ants; I mean the kind of grammatically complex systems possessed by humans. Clearly, the human language faculty has a tremendous adaptive advantage—some say it is the key to our dominance—so it must be a question why it has not evolved several times.[2] Other highly adaptive traits have evolved many times, as in so-called convergent evolution, but in the case of language this is not the case; we don’t find a plethora of species speaking a language like ours. In particular, we are the only hominid species with a language faculty: it is as if we were the only such species with eyes or ears. According to modern conceptions, the language faculty is an autonomous organ grounded in the genes, analogous to other organs; but it is an organ that appears only in our species.[3] Why? Its existence is a singularity, like life, but this is puzzling. One might expect that such a useful organ should have evolved many times, especially in our nearest relatives, but evidently not: we are its sole proud possessor. It arose at a certain late point of human evolution and only in us, but it has proven its worth a hundredfold, so why isn’t it more common. Like life, it is a strange singularity. You might suggest it is like the Mona Lisa—a sublime work of art, understandably rare—but that is very unconvincing: the Mona Lisa is not that unique among works of art, and is anyway a human product of creative genius. The language faculty, by contrast, is a biological organ evolving by mutation and natural selection just like other biological organs; so its occurrence should be governed by the same laws—hence its uniqueness is perplexing. On other planets there may be many speaking species—it may be the norm—but on our planet language is confined to a single species and arising at a specific time. If its origin is a mystery, so is its uniqueness. And if the mystery of origin is resolved, that will only intensify the mystery of uniqueness, since it will explain how natural processes of a non-mysterious sort account for the origin of language. An explanation of the origin of infinite recursive productivity, for example, will accentuate the question of why this property is not found elsewhere. It is as if no eyes ever evolved for billions of years, despite favorable conditions, and then a single species suddenly evolved them, never to appear again. Maybe language will evolve again in the distant future—as life may conceivably evolve again on planet earth—but heretofore we have a marked absence of both recurrences. Why is nature behaving so sparingly, so miserly? Life and language are now everywhere on the planet, but they refuse to evolve afresh as they once did. They seem determined to belong to an elite club of one. Why the exclusiveness?

It might be replied that appearances are misleading: life and language have come into existence many times, by chemical concatenation or genetic mutation, but they have not been selected for, and hence do not exist in full form in multiple cases. But there is no evidence for this, and anyway it just raises the original question in a revised form–namely, why has there been no natural selection for these common uprisings? Obviously there was selection in the case of the life and language we see around us, so why not for these other alleged fledging cases? Nor, of course, would it be remotely plausible to suggest that life and language have arisen many times and been selected for but we have just not noticed it: where might these elusive realities be hiding—at the center of the earth maybe?  No, both have arisen only once, puzzlingly so. We have here two “mysteries of singularity”: not why did they arise at all but why did they arise so sparsely. It almost seems as if there is some force preventing them from arising more than once. I have no idea how to answer this question and I doubt that anyone else does either, but the question is clearly worth asking. It reveals a serious limitation in our understanding of natural history.

[1] We might compare the origin of life with the origin of the universe. The big bang was a singularity too—a major event that has not been repeated. We haven’t had a series of big bangs (in our universe) since that initial one. Why? What explains the uniqueness? If there is a multiverse each with its own big bang, then we have a plurality of cosmic origins; but that doesn’t account for why our universe has only experienced one big bang. Is it because the nature of the universe was so changed by the big bang that the laws of nature ruled out a recurrence thereafter? That kind of explanation would clearly not apply to the origin of life—or of language (see below).

[2] I would speculate that consciousness (sentience, awareness) has arisen independently many times: it does not all trace back to a single evolutionary origin. Consciousness in humans and consciousness in the octopus are cases of convergent evolution. This is because consciousness is very widespread, unlike language. If consciousness were confined to a single species, that would be very surprising and cry out for explanation. Language is the outlier, not the conscious mind in general.

[3] It has struck many people as strange that more animals don’t speak—hence those fantasies about speaking animals. It is as if they lack an obvious ability, unaccountably granted to us. Speaking seems natural, only to be expected. What if language had evolved in monkeys instead of us? We might still have high general intelligence, while theirs might be inferior to ours (compare young children who can speak well but aren’t all that bright). That would seem very strange: if they have it, why don’t we? Isn’t it just anthropocentrism that makes us think that we alone are sophisticated enough to speak? What is really surprising is that monkeys don’t speak, given that there was nothing preventing them from evolving the capacity. Why should we be the chosen ones?