Book Club: Darwin’s Unfinished Symphony, 2, it’s all about copying, isn’t it?

Human copying behavior

Human copying behavior: Ken Laland’s son imitates his father

I have recently began a series of posts to discuss my colleague Kevin Laland’s recent book on cultural evolution, Darwin’s Unfinished Symphony: How Culture Made the Human Mind. Last time we talked about just how different — quantitatively, for sure — human cognition is from anything else known in the animal world. This doesn’t make us the result of magic, of course, but it does mean that biologists, anthropologists, and cognitive scientists are faced with a rather unique challenge if they really want to understand what makes us humans.

Chapters 2 and 3 of the book, with which this post is concerned, deal with a widespread mechanism by which both humans and other species learn: copying other members of the same species. Chapter 2 aims at establishing that copying is, indeed, a very common learning strategy, while chapter 3 deals with the basic question of why, and under what circumstances, copying is an adaptive strategy (it isn’t always, so this is not a trivial question). There is far too much material for me to do a section-by-section commentary, so I will focus on a number of things that struck me as particularly interesting.

Rattus norvegicus, the brown rat, is not Norwegian, but of Chinese origins. It is also one of the animal species best adapted at living with humans, despite our systematic attempts to exterminate what we regard as a pest. Already Darwin had noted that the brown rat is so successful because it is very good at copying what works from other members of its species, as well as at avoiding behaviors that turn out to be lethal. Interestingly, rats have been able to adapt, both genetically, but — more importantly for our purposes here — behaviorally, even to new poisons that act slowly, designed to stretch the time between cause and effect, thus, in theory, precluding other rats from learning to stay away from poisoned foods.

Turns out, however, that the strategy adopted by these rodents is rather more canny: they don’t avoid dangerous foodstuff, they actively seek the sort of foods eaten by fellow rats who thrive. In other words, populations of Rattus norvegicus have developed “dietary traditions” in order to stay a step or two ahead of their human nemesis.

Rats are certainly not the only animals to have developed cultural traditions of sorts. Laland details several studies that, beginning back in the 1970s and ‘80s, have clearly shown the phenomenon to be common among apes and monkeys. Interestingly, we don’t really understand the adaptive value — if any — of some of these behaviors. For instance, at least three populations of orangutans are known to blow raspberries as they go to sleep. Nobody knows why. Or consider this: in the Lomas Barbudas reserve, in Costa Rica, pairs of monkeys simultaneously insert their fingers into each other’s nostrils, remaining in such odd position and swaying as if in trance, for several minutes. Go figure.

Learning from your social environment can be maladaptive, if one does not pay attention. For instance, blue tits and great tits birds often forage in mixed species groups. However, the blue tits eat twigs that are high on trees, while great tits feed mostly on the ground or on lower branches. Experimenters shifted things around so that young birds of one species would be reared by parents of the other. They observed that the animals adopted the foraging behavior of the rearing species, which sometimes was not exactly a great idea: some great tits attempted to forage hanging upside down from branches, in the manner typical of blue tits. And they kept falling off!

In order to copy, apparently, one does not have to be particular bright:

“The ubiquitous influence of social learning in nature is beautifully illustrated by the example of mate-choice copying, where an animal’s choice of partner is shaped by the mating decisions of other, same-sex individuals. This form of copying is extremely widespread, with examples known among insects, fishes, birds, and mammals, including humans. The fact that animals do not require a big brain to copy could not be more clearly demonstrated than by the tendency of tiny female fruit flies to select male flies that other females have chosen as mates.” (p. 41)

Another area where copying is fundamental is anti-predator behavior. Obviously, learning by trial and error in that case could easily be fatal, so animals tend to learn predator avoidance by watching what their conspecifics do. Interestingly, at least in some cases, fear of predators does not seem to be innate, but acquired, as demonstrated by the fact that rhesus monkeys reared in captivity are not afraid of snakes, while they wild counterparts certainly are. It’s also fascinating that experiments show that fear of predators is learned very quickly and lasts for a long time, while monkeys tend not to develop long lasting fears in response to stimuli that are not actually threatening. This, as Kevin puts it, is not only efficient in terms of predator avoidance, but also precludes the acquisition of potentially time wasting “superstitions,” i.e., fears of things that are not dangerous. If only humans were as good at avoiding superstition as monkeys…

So, copying as a learning strategy is widespread, and does not require large brains, only a cognitive system sophisticated enough to be capable of associative learning.

That said, for a long time biologists have struggled with why, exactly, copying is so widespread in nature. Even though the answer seems intuitive, mathematical models have repeatedly faced researchers with what is known as Rogers’ paradox, named after University of Utah anthropologist Alan Rogers: such models seem to show that copying is just as likely to lead to learning maladaptive, or outmoded, behaviors as adaptive ones. What gives? That is the topic of chapter 3 of the book.

Other animals aren’t the only ones engaging in copying, humans do it too. Experiments and observations in developmental psychology clearly show that children copy behaviors, especially from their care takers, from very early on. Their propensity to do so varies over time, peaks around age four, but never quite disappears. But they don’t copy indiscriminately, instinctively paying attention to behaviors that seem functional, and rapidly discarding others.

Obviously, members of a species cannot learn only by copying each other, or no innovation would ever be introduced, and any significant change in the environment would pose a threat of population extinction. Mathematical models, therefore, predict a mixed evolutionarily stable strategy, where learning by trial and error is in equilibrium with learning by copying. Except for the above mentioned problem posed by Rogers’ paradox. I will skip other fascinating bits of chapter 3 of Kevin’s book in order to focus on how he and his team managed to solve the paradox: by organizing a competition among different learning strategies, implemented by way of computer programs battling each other.

The idea isn’t new. It was successfully implemented, as Laland explains, back in the 1970s by economist Robert Axelrod to solve another famous biological puzzle: the evolution of cooperation. Axelrod organized a competition for the best program to solve the so-called iterative prisoner’s dilemma, a classical situation in game theory where agents have a strong incentive to cheat, even though cooperating would actually be the overall best strategy. Famously, the winning strategy in cooperation games is known as tit-for-tat, and was developed by Anatol Rapaport, a psychologist then at the University of Toronto. The strategy is as simple as it is efficient: when encountering a new agent, act cooperatively on the first round, then do what he does. If he cooperates, keep cooperating; if he cheats, beat the crap out of him. Cooperation, then, becomes a matter of so-called reciprocal altruism: I’m nice to you if you are nice to me, and so long as you will keep being nice to me.

Kevin goes into some detail on how his team — inspired by Axelrod’s success — organized a similar tournament to solve Rogers’ paradox and make progress on the issue of social vs asocial (i.e., solitary) learning. The result was indeed very insightful.

The tournament was structured so that players (i.e., computer program), in each round could implement a mixed strategy composed of three possible moves: INNOVATE (introduce a new behavior), OBSERVE (engage in social learning), or EXPLOIT (implement a previously learned behavior). Obviously, no pure strategy based on a single one of these moves would be adaptive, but which combination turned out to be the winner?

“The first finding that jumped out at us was that it is possible to learn too much! In the tournament, investing lots of time in learning was not at all effective. In fact, we found a strong negative correlation between the proportion of a strategy’s moves that were INNOVATE or OBSERVE, as opposed to EXPLOIT, and how well the strategy performed. Successful strategies spent only a small fraction of their time (5–10%) learning, and the bulk of their time caching in on what they had learned, through playing EXPLOIT.” (p. 66)

Moreover:

“Among the top-performing strategies that progressed to the melee, by and large, the more the strategy learned through OBSERVE rather than INNOVATE, the better it did. However, among the poorer performing strategies we actually witnessed the reverse relationship — the more they copied the worse they did. That told us something very interesting — copying was not universally beneficial. Copying only paid if it was done efficiently.” (p. 67)

Which was a very good clue toward the solution of the riddle posed by Rogers’ paradox. The winning strategy turned out to be one called DISCOUNTMACHINE by its authors, Dan Cownden and Tim Lillicrap, two graduate students from Queens University in Ontario. DISCOUNTMACHINE is so named because it discounts information according to how old it is: the older a behavior is, the more likely it is to be out of step with the always changing environment, and less likely therefore it is to be useful to the agent.

Also, both DISCOUNTMACHINE and all the other top strategies relied mostly on social learning. Indeed, when Kevin and colleagues introduced a “mutant” of the winning strategy that relied solely on innovation, its performance plummeted. Also, the researchers found that learning asocially is a viable strategy — perhaps not surprisingly — only under very extreme circumstances, when the environment changes drastically and rapidly, obviously because no previously developed behavior is then adaptive. Finally, and perhaps a bit more surprisingly, mostly copying was still the winning strategy even when the error rate was very high, up to 70%, further demonstrating the superiority of even badly executed social learning over the asocial option.

“Simple, poorly implemented, and inflexible social learning does not increment biological fitness, but smart, sophisticated, and flexible social learning does.” (p. 72)

One of the conclusions of the study was that, while copying obviously does not discover and introduce new behaviors, it preserves adaptive behaviors beyond the death of the individual that produced the original innovation. This is the first, widespread, step that makes cultural evolution possible.

Advertisements


Categories: Book Club, Philosophy of Science

Tags:

48 replies

  1. Hi Massimo,

    I have found this book very interesting. I’m up to chapter 7 where Hannah Lewis’s simulation is introduced. Laland kindly sent me their paper about the simulation.

    It inspired me to create my own analytical model using the algebraic program Maple to deal with the difficult integrals. The analytic model does not have the full flexibility of the simulation. It does produce some interesting affects – e.g., a ‘singularity’ in learned trait accumulation when there exist some rate of combining ‘cultural traits’ with a low enough loss of trait loss rate.

    I may post it to this blog, but I’ll wait till we get to chapter 7.

    Like

  2. Massimo,

    Sorry, I tend to think of scale in terms of multiplication, not addition. Like hurricanes and earthquakes, each step isn’t a fraction, but an order of magnitude.

    What are the terms in biology and the cultural extensions? Obviously it is not linear steps from fruit flies to people, because each cell, neuron and associated linkages multiply the number of potential relationships in the network.

    Though my original observation is that the same, essential binary decision making process is at work. Which is also multiplied untold times.

    Like

  3. Traps:

    My daughter once had some kind of rodents as pets. I forget what they were called. They were from somewhere like the Gobi. They are illegal in California, but we lived in Ithaca at the time.

    They were very bright. They loved to get out of their cage and were damned hard to catch. You basically had to wait till they were hungry enough to go home.

    We tried making a trap, by setting up a box set on a stick with a string attached and baited it with lettuce (they loved lettuce).

    As long as you sat with the string in your hand and your eye on the box, they would not go in it. If you became distracted, they would dash in, grab the lettuce, and run back out, before you could react.

    How the hell did they figure that out? I don’t recall the trap working even once!

    In the end they died from gnawing on plastic pop bottles we stupidly left in their cage. I would guess rats have long since learned not to do that.

    Liked by 1 person

  4. Arthur,

    So their desire to explore and acquire information is second only to their desire to acquire food and energy?

    Maybe, on a cultural level, that is why banks rule.

    Like

  5. Okay, so non-social mammals like bears have dietary habits, but brown rats have dietary traditions?

    I’m really not trying to be argumentative, but I’m lost, particularly when pondering the interplay of genetic to environmental to behavioristic to cultural adaptations and/or evolution. It seems we are pretty much bracketing the topic around social animals and doing some pre-staging before Leland makes the case for the uniqueness of human cultural evolution. That’s not a major problem for me since as yet bears have not created cartoons of humans acting like bears while the opposite is in fact the case.

    I think I’ll just shut up and wait for your next OP on Leland’s book.

    Like

  6. Thomas:

    Both bears and rats have dietary habits, however it makes no sense to talk of dietary traditions in non social animals. The issue isn’t really that important as all Laland is trying to show is the wide variety of ways that rats transmit dietary preferences. Bears do this too from parents to offspring, but rats have more complex mechanisms because of their social organisation.

    I think (I haven’t read very far ahead) Laland is constructing the thesis that social learning is the foundation of cumulative culture, and that copying behaviour is the basis of social learning. As such, there is no point for him to study non social animals.

    Liked by 1 person

  7. Synred,

    Glad you are enjoying the book, but yes, let’s wait to discuss the material ahead once I get there.

    Brodix,

    Again, I’m not sure what you mean “from fruit flies to people.” Those species have evolved along completely different trajectories, so there is no “from … to” to speak of.

    Obviously fruit flies are developmentally, behaviorally, and neurologically far less complex than humans, but to compare them on some sort of scale is to compare, well, apples with oranges (actually, that would be less of a far fetched comparison).

    Like

  8. One thing I can’t find much on is the mechanisms involved in learning behaviour – either neural or genetic. How developed is the research on this? The complexity of rat approaches to learning the behaviour of other rats appears quite high, and yet fruit flies can learn by copying too. Is there a universal mechanism for learning by copying, or is it something of an umbrella term for a mixture of mechanisms that change from species to species?

    Like

  9. Bunsen,

    My guess is that there will be variation across phylogenetic clades, depending on the specifics of the genetic-developmental system. That’s a good example of how mechanistic explanations are semi-detached from adaptive ones: from the point of view of natural selection it doesn’t matter how a certain behavior comes about, so long as it is advantageous.

    Like

  10. Massimo,

    Obviously flies and people have evolved separately for a billion plus years. The fact remains that some organisms have developed more complex relationships with each other and their environment.
    The issue I am trying to raise is the essential binary nature of the cognitive process! The basic impulse of attraction/rejection.
    Consider the political polarization in this country, as an obvious example of how it can really bubble up through all the complex factors of give and take.

    Like

  11. Brodix,

    There is nothing binary I can see in the cognitive process.

    Like

  12. Once again let me thank Massimo for his great summary, and everyone for their insights.

    In response to comments, I’d like to discuss the extent to which we can think of animal culture as an independent inheritance system, or whether acquired knowledge is under genetic control. Monkeys that appear predisposed to acquire a fear of snakes were mentioned. This form of learning is known as observational conditioning – animals learn what they should be frightened of through observing fear responses in other animals. Experiments conducted in the 1970s-80s found that it was easier to condition monkeys in this way to be frightened of snake-shaped objects than flower pots. The experiments have become citation classics in the behavioural and evolutionary literatures. They seemingly imply that selection biases learning – including social learning – towards what is adaptive.

    Well, it does, but it turns out that this impression is nonetheless misleading, as such biases are the exception rather than the rule. Experiments have established that the observational conditioning mechanism through which the monkeys acquire their fear of snakes is both very general in facilitating the acquisition of fear responses to a wide variety of objects, and taxonomically widespread across vertebrates. The particular salience of snakes to rhesus macaques is seemingly a derived character: the ancestral condition was no learning bias, and the bias to learn readily about snakes evolved subsequently in some monkeys to enhance their avoidance of dangerous predators. Blackbirds, which also have been shown to learn socially to recognize predators, in this instance by attending to the stimuli mobbed by conspecifics, can be conditioned to acquire a fear of arbitrary objects such as plastic bottles. They seemingly have not (yet) undergone a similar genetic adaptation.

    What this, and other, data is telling us is that the capability for cultural learning is reliant on some very general processes (e.g. associative learning) that we can surely regard as adaptations, but that natural selection has not favored genes specifying the precise content of cultural behaviors. For instance, the ability of a rat to learn what is safe to eat (e.g. by attending to cues on the breadth of other rats, or preferentially feeding at food sites marked by the excretory deposits of other rats), almost certainly is an adaptation. What the rat eats, however, is not under tight genetic control, and varies from one colony to the next. Selection has furnished animals with an ability to acquire certain kinds of adaptive knowledge, without dictating what it should be in any instance.

    This has implications for how we think about evolution. Cultural transmission, which is widespread in animals, can both generate novel phenotypes (e.g. novel diets), and modify the pattern of selection acting on the population (e.g. impose selection favouring specific digestive enzymes). Animal culture is a source of phenotypic plasticity – a means by which many animals adapt to their environments. Plasticity currently receives unprecedented attention from evolutionary biologists (in no small part as a consequence of Massimo’s work on this topic). Potentially, animal culture provides extensive data in support of this ‘plasticity-first’ (i.e. phenotypic change precedes genetic adaptation) hypothesis, yet these literatures are poorly integrated. As we get to later chapters, you will see that culture as a driver of genetic evolution becomes a central theme. The truly extraordinary aspects of humanity – our language, our creativity, our intelligence – appear to have evolved as adaptive responses to our ancestors’ cultural activities.

    Liked by 6 people

  13. Hi Kevin,

    What the rat eats, however, is not under tight genetic control, and varies from one colony to the next. Selection has furnished animals with an ability to acquire certain kinds of adaptive knowledge, without dictating what it should be in any instance.

    So the genetic bit will be: “there will be dangers that you need to learn about”, which is then coupled with: “what they are in your local environment you’ll learn about culturally from others”.

    That sounds about right to me. That would enable an animal to cope with a wider range of environments than if the genes specified the particular threats.

    Liked by 1 person

  14. Massimo,

    I frequently find myself attracted to, or repelled by lots of things, before my thought process comes along to complicate things. Yet even if I have to decide among, say eight different options, that still amounts to one yes and seven no’s.
    Survival of the fittest is a binary. You live, or die. Religion and culture are largely about do’s and don’ts. Even the aforementioned monkeys are learning snakes are bad.
    I’m not saying I’m right, but it would be interesting to know why you think I’m wrong, that our thought process is not like computation; a multitude of binary decisions.

    Like

  15. Kevin, I’m interested in seeing your ideas play out with language, and how this plasticity affected brain development, which then in turn sent linguistic development down certain pathways, narrowing, but not too narrowing, of course. And, I know we may only be able to tell so much on this.

    Ditto on creativity as a possible driver of the religious impulse.

    Like

  16. >One of the conclusions of the study was that, while copying obviously does not discover and introduce new behaviors, it preserves adaptive behaviors beyond the death of the individual that produced the original innovation. This is the first, widespread, step that makes cultural evolution possible.

    murder, he found the beast occupying his own bed-room, into which it had broken from a closet adjoining, where it had been, as was thought, securely confined. Razor in hand, and fully lathered, it was sitting before a looking-glass, attempting the operation of shaving, in which it had no doubt previously watched its master through the key-hole of the closet. Terrified at the sight of so dangerous a weapon in the possession of an animal so ferocious, and so well able to use it, the man, for some moments, was at a loss what to do.

    Poe, Edgar Allan. The Murders in the Rue Morgue (Kindle Locations 549-552). Vook, Inc.. Kindle Edition.

    So did Poe know primates where inclined to copy? And the ‘Ourang-Outang’ recognizes itself in a mirror too! </:-_)

    One of the conclusions of the study was that, while copying obviously does not discover and introduce new behaviors, it preserves adaptive behaviors beyond the death of the individual that produced the original innovation. This is the first, widespread, step that makes cultural evolution possible.

    Like

  17. I can find a reference to the imitative faculty of primates in an Americam newspaper in 1789, so yes Poe could have known about it.

    Liked by 3 people

  18. A factoid on Poe is that he is credited with first supposing space and time as one, in the essay Eureka.

    What I consider as interesting about that is that Poe is a professional storyteller and so it is his purpose to distill and construct linear narratives out of events. Often the analogy used for time as dimensional, is of a book, or movie, where the sequence of events exists on that temporal dimension and our sense of now is circumstantial.

    To tie this back to the subject of culture, it is that culture rises from history, which rises from narrative. It is our ability to escape the present moment, which truly rises us up from plants and other animals. That we not only remember our individual past, backed by genetic instinct, but that through language and learning, pass this through multitudes of generations and can build on the many lessons learned.

    Liked by 1 person

%d bloggers like this: