Why, among the myriad species of social animals on this planet do we humans, uniquely (as far as we know), have culture? Half a million years ago early hominids would have lived in social groups much as we observe higher primates, chimpanzee in particular, now. Then something must have happened to trigger the transition from social to cultural. What was that trigger and what were the processes and mechanisms of the transition? How did the earliest proto-cultural behaviours emerge and take hold, and what were those behaviours?

These are deep questions that are extremely difficult to answer, not least because the archaeological record tells us almost nothing of the processes and mechanisms of the emergence of culture. But why and how do we have culture? is surely a Big Question. A question that notably transcends discipline boundaries. An answer would profoundly deepen understanding of our origins as a cultural species, and therefore the human condition, and - if the processes by which culture emerges turn out to be generalisable to other species - we would have an insight into how we might recognise culture in non-human species, including aliens and robots.

Theories of cultural evolution broadly fit into two camps: one holds that culture is merely an adaptation and that genes will always, as E.O. Wilson put it "hold culture on a leash". The other and more controversial Memetic theory of cultural evolution holds that culture is not an adaptation but instead an accidental by-product of humans' capacity for imitation that has, according to S.J. Blackmore's The Meme Machine, taken off on its own evolutionary trajectory and is now more-or-less independent of genes. The culture-is-just-an-adaptation theory is, for me at least, the less interesting and persuasive of the two; in saying this I - a fully paid-up disciple of Ockam - am acutely aware that the memetic theory is the less ontologically parsimonious. But sometimes the right explanation is not simplest and, tantalisingly, the memetic theory may turn out to be testable.

In a nutshell, the memetic theory goes something like this.

1. Early hominids evolved the ability to imitate each other. It is reasonable to speculate that imitation has strong survival value since if you are a good imitator then you can copy someone else's learned behaviour and therefore save yourself the effort of learning that behaviour from scratch. The important distinction here is between social learning (and imitation is one way to do social learning), and individual learning; social learning costs much less effort than individual learning. The thing-that-is-imitated and hence passed from the originator to the copier is called a meme. (Note that imitation doesn't necessarily imply cooperation.)

2. As soon as the imitation skill is sufficiently refined and widespread, then memes are able to persist in the population. In fact, memes will experience (a) mutation, since it's more or less impossible to copy something perfectly, (b) selection, since the meme imitators will selectively copy some memes over others, and (c) heredity, since a single meme could be copied, then the copy may be in turn copied over multiple (meme) generations. Thus, as soon as the society of meme originators and meme copiers has collectively reached some minimum threshold of imitation skill (including sufficient fidelity of imitation), then memes will evolve in that society according to Darwinian processes of natural selection, except that this is now memetic evolution.

3. When the society reaches this stage then an important transition has been crossed. Up until that point those early hominids evolved only by means of genetic evolution. But as soon as memes are able to persist and evolve then there are two parallel evolutionary processes: genetic and memetic; this is so called meme-gene co-evolution. After this transition, the theory argues, being an effective meme copier confers a premium in the game of sexual selection. Any genetic mutation that improves imitation skill will be differentially selected, giving rise to a richer environment for memes to evolve, which in turn improves the likelihood of meme copiers mating and - it is conjectured - a runaway cycle of meme-gene co-evolution resulted in big-brained hominids that are exquisitely skilled and artful imitators. Since the imitation skill can imitate anything, and since the most compelling memes will gain a strong foothold, then culture can now emerge with all of its kaleidoscopic variety: art, music and dance, ritual and religion, language and technology.

According to the memetic theory imitation is a prerequisite behaviour necessary for the evolution of culture. But what other prerequisites are needed? One, arguably, is communication. Language clearly has a pivotal role in human culture, but is language an outcome of the evolution of culture, or a prerequisite? Many social animals communicate, even animals with very small brains (relative to mammals); think of bees communicating the location of pollen. And primates appear to have a complex repertoire of calls which, in the case of chimpanzee combine with body language and facial expression to allow the sophisticated communication of emotional states. Since imitation need not involve communication, or indeed cooperation, it's not at all clear whether communication is a necessary prerequisite or an extraordinary beneficiary; my own view is that some minimal level of communication is a prerequisite (turn taking and attention seeking or giving, for instance) but that the co-evolution of high fidelity imitation and memes provided the springboard for the language instinct in humans.

Another prerequisite perhaps, is theory of mind: the ability of one individual to build a internal model of another's intentions. It's well known that chimpanzee have sophisticated social behaviours which demonstrate so called Machiavellian intelligence; the matriarchal Bonobo are a remarkable example. One individual might for instance become friends with another not because they want to be friends, but in order to gain social advantage; the fraudulently befriended might have friends that they really want to get to know. Success in these complex social interactions requires an individual to have an internal model of not just one but a number of other members of the group and, at some level, be able to ask 'what if' questions: "What if I make friends with...?"; "Should I be assertive or passive?", "How should I respond if s/he tries to make friends with me?". My view is that theory of mind - in the sense of Machiavellian intelligence - is not a prerequisite for culture (but that may just be because I can't figure out how and where it might fit into the co-evolutionary processes). Of course you could also argue that imitation is itself a simple form of theory of mind, because the very act of imitation implies that the copier confers agency to the copied and of course requires that the copier builds some kind of representation of the meme in its brain.

When discussing prerequisites we must not overlook the environment. It's hard to imagine that environmental factors like climate change, predators, competitors or disease wouldn't play a part in triggering or catalysing the transition from social to cultural; some trauma that provided additional evolutionary pressures which differentially favoured imitation and innovation. Perhaps forest dwelling hominids with abundant food and no predators (as gorilla would be if it were not for man) had to be evicted - as it were - by environmental pressures from their evolutionary garden of eden to trigger the transition to culture.

Returning to the question that forms the title of this essay, the answer to the question Why, is I believe, easier. My own view is that the reason we humans have culture is, quite simply, because we can. The fact that we have culture is of course, in itself, an existence proof that culture can emerge in social animals. The reason that it did, in our species, is - I would argue - because of an entirely contingent (and probably rather unlikely) combination of circumstances. In other words the right behavioural and environmental prerequisites were present over a sufficiently long time period to allow the engine of memetic evolution to splutter into life. The question How remains a big and unanswered question.

Postscript: An answer to the question How is currently being attempted. A research project in the UK is attempting to build a society of robots, create the conditions (prerequisites), and then free-run that artificial society in the hope that proto-cultural behaviours will emerge. The project is extremely challenging for several reasons. The first, already discussed above, is to determine the initial conditions: the behavioural and environmental prerequisites. The second challenge is to programme the robots with the prerequisite behaviours and create an artificial environment for the robot society. The third and perhaps greatest challenge is, when this artificial society is free-run will anything interesting emerge at all and, if it does, will it be recognisable and robustly interpretable as evidence for culture, given that it will of course be robot-, not human-culture. The methodological starting point for this project is the memetic theory of cultural evolution and the project therefore offers the possibility, for the first time, of experimental validation of that theory

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