Not by learning alone

How does a population of any species maintain its behavioural characters? In other words, how do individuals of a species ensure that information about how to survive in the world are passed on from one generation to the next? This can be basically everything that is somehow related to feeding, growing, surviving, and reproducing.

Modes of information transmission

I found this very nice (and short) paper by Bennett Galef Jr. from 1975, where he explains the three mechanisms by which behaviours are passed on to the next generation. Instead of describing the transmission of behaviours I will rather talk about information, as behaviour is also just information. This is:

§1 Information are innate – In this case information are ‘endogenous’ to the individual by being part of its genetical code. The genotype not only influences the phenotype of an organism, but also its propensity for different behaviours (you are less likely to learn how to fly if you were born without wings).

§2 Similar information are gathered by experiencing similar interactions with the (non-social) environment – Individuals of a population that experiences predation by birds of prey might learn very similar avoidance or escape strategies if compared to each other, but likely very different ones compared to individuals of a population that faces predation by snakes. Saying that, it is not all too surprising to find similar behaviours when comparing individuals from different species, which is comparable to convergent evolution where similar environmental conditions and natural selection produce analogous adaptations, like fins in dolphins and penguins.

§3 Information are socially transmitted – In this case individuals gain information by interacting or observing the behaviour of another individual. Because this happens in the context of other individuals it is also called ‘social learning’, which is different from §2 where individuals learn on their own and henceforth called ‘individual learning’. Examples are trial-and-error and insight learning.

As Wakano and Aoki (2006) note, all three modes of information transmission are usually present in a population, they differ, however, in the type of information they carry. If the environment is stable or only slowly changing and information about it keeps valid over a long time it can be innate. If the environment changes moderately social learning is often found, and individual learning becomes inevitable when the world changes quickly. (FYI, that’s what I find in my models as well 😉

Social interaction – sufficient or necessary?

Galef now goes on to discuss social learning (§2) in more detail. Specifically he talks about an aspect I was not aware of before: when is social interaction between individuals sufficient and when is it necessary for learning? What does that mean? The first example Galef gives is based on a study by Harlow and Harlow on Rhesus monkeys from 1965. They found that individuals that grew up without interacting with their mothers or group members never developed a ‘normal’ sexual or maternal behaviour. Therefore, a social interaction is necessary to acquire the ‘normal’, relatively invariant, and species-typical behaviours.

Very different from that example is the case of a study by Galef and Clark from 1971, where adult rats where fed with two types of food: a preferred type with a sub-lethal dose of poison (which will cause nausea but no harm) and less preferred one, which was not altered. Adults learned to eat the less preferred food and avoided the initially preferred food items. Consequently, pups also prefered the initially less preferred food, although they did not even get in contact with the prepared food items, and thus with the adverse stimulus. This is an example where individuals (the pups) could have acquired information on their own (without a social context), by sampling both food types. Here, social interactions are sufficient but not necessary. But let me cite the elegant description by Galef:

Idiosyncratic pattens acquired by the transmitter, as a result of its history of transaction with the environment, may be introduced into a population repertoire, resulting in the establishment of socially transmitted traditions within subpopulations of a species.1

As we see, social learning is a mechanism that not only allows a population to maintain a repertoire of information and behaviours, but also to add new elements to it. But let us turn to the last part of the paper:

How then is information transmitted?

Galef uses an example of food preference and predator avoidance to describe two mechanisms by which information can be transmitted:

§4 Altering the environment – Adult rats heavily mark places with urine or feces to indicate save food sources, which in turn are then preferred by rat pups. The young are also known to prefer feeding in close vicinity to adults. These are two examples that show information transmission due to local or stimulus enhancement. (Galef and Clark, 1971a)

§5 Pairing an innate tendency with a social interaction – In two studies rat pups were shown to start running when adults run (Reiss, 1972, Angermeier, 1959). This unconditioned tendency (run when adult runs) can be used to couple an unconditioned stimulus (fleeing adult) with a conditioned stimulus (sight of predator).

Galef closes his paper by pointing out the evolutionary significance of social learning. He states that if laboratory experiments resemble natural conditions then trial-and-error must be energy consuming and error prone. Therefore, it must impose a fitness benefit on parents if their naïve offspring is capable of rapidly acquiring relevant behaviours (locating and handling food, discovering, avoiding, and escaping predators) to quickly become independent of their parents.

A very nice and insightful read!

EDIT: the title of this post is a play with the title of the book ‘Not by genes alone’ by Richardson and Boyd.

Galef BG (1975) The Social Transmission of Acquired Behavior. Biol Psychatry 10(2):155–160.

Wakano JY, Aoki K (2006) A mixed strategy model for the emergence and intensification of social learning in a periodically changing natural environment. Theor Popul Biol 70(4):486–497.

  1. Sentences like this are the reason why I enjoy communicating science in a, say, simpler language.