Chapter Chapter-by-Chapter Anaylsis of The Selfish Gene (1989 edition) - Study Guide by Richard Dawkins

sisters, nephews, nieces, close cousins etc. What is important in this theory is that even a gene that is rare in the population as a whole is common in a family. Therefore, the chances are good that sisters contain the same particular rare gene.

For this, an index of relatedness can be created that expresses the chance of a gene being shared between two relatives. For example the relatedness between two brothers is ½ since half the genes possessed by one brother will be found in the other. This can then be used to explain apparently altruistic behaviour towards kin. For altruistic behaviour to evolve, the net risk to altruist must be less than net benefit to recipient multiplied by the relatedness – (benefit / cost) x relatedness > 1. For example, a gene for suicidally saving 5 cousins would not become more numerous in the population (because 0.125(5/1) = 0.625) but a gene for saving 5 brothers (0.5*5 = 2.5) or 10 cousins (0.125*10 = 1.25) would. This is because chances of the suicidal altruistic gene in these cases living on in the bodies of the individuals saved are great enough to compensate for the death of the altruist itself. However, having said this, the individual does not actually do the sums before carrying out a particular altruistic act. The individual is just pre- programmed to behave as if it has.

But there is still the problem of how animals know who their kin are? Humans know who their relations are because we are told and because we give them names. Animals, on the other hand, have to be given by their genes a simple rule for action, a rule that does not involve all-wise cognition but that works nevertheless at least in average conditions. One way that has been suggested is to behave altruistically towards individuals who physically resembled you. Another is to behave altruistically to the members who live in the same group as you. This latter method works for species whose members do not move around much, or whose members move in small groups because the chances are good that any random individual you came across is fairly close kin to you.

However, this uncertainty is vulnerable to mistakes and exploitation. Adoption is considered to be misfiring of the built-in rule because the generous female is doing her own genes no good by caring for the orphan. There are also examples of mothers deliberately deceiving naïve young females into adopting their children so that they may get on to reproduce again. One species that uses this deliberate deception is the cuckoos.

Therefore, Dawkins argues that in addition to the index of relatedness, we should also consider something like an index of "certainty" as it seems that it is the best estimate of relatedness that animals use when behaving altruistically. This is probably why parental care is so much more common and more devoted than brother/sister altruism, and also why animals may value themselves more highly even than several brothers. Although the parent/child relationship is no closer genetically than the brother/sister relationship, its certainty is greater.

Family planning

Dawkins believes that animals regulate their birth rates so that any given species tends to have a rather fixed clutch size or litter size: no animal has an infinite number of children. What determines this optimal clutch size is the environmental situation that the mother is in. The selfish individual will choose the clutch size that maximises the number of children she rears. The obvious reason for this is that if she has too many children, the limited resources, such as food, will be stretch so thin that not all of her offspring will survive and she will lose precious genes. Equally, if she devotes all her investment to too few children, her rivals who invested in the optimum number of children will end up with more grandchildren and so again, she will lose precious genes.

Individuals who have too many children are penalised because less of their children survive, and so genes for having too many children are not passed on to the next generation in large numbers. Therefore, evolution will favour those who regulate their clutch size to the optimum. This optimum may depend on factors such as overcrowding, and therefore greatly limited food resources, and the prediction in winter whether the following spring will yield a good crop of the food resources. It is possible that there are some clues that a good prophet could use to adjust her clutch size for year to year to her advantage