The Selfish Gene: Chapter 8 Summary & Analysis

Dawkins wonders if it is a good strategy for a mother to have a favorite child that she invests in more than others. He borrows a way to measure parental investment (PI) from Trivers, who argues that parental investment is “any investment that increases the offspring’s chances of survival (and hence reproductive success) at the cost of the parent’s ability to invest in another offspring.” Resources a child uses up (such as a pint of milk) are measured in terms of the decrease in life expectancy to his or her (existing or future) siblings. Dawkins supposes that an adult has a fixed amount of parental investment to distribute in her lifetime. This includes food gathered, risks taken, and energy spent caring for her children. What would be a wise investment policy for her to follow?

The reader already knows from Lack that she shouldn’t have too many children and spread her parental investment so thin that her young don’t survive to reproduce. But should she invest in some children more than others? Dawkins says no. Genetically speaking, each child has half of her genes, so the optimal strategy (to maximize the number of her genes in the gene pool) is to invest equally in each.

However, there are other considerations to factor in. A runt has a lower life expectancy than his siblings. It may be wise for the mother to reject the runt and distribute his or her parental investment among her other children. It may even be smart to kill the runt and devour him or her, or to feed the runt to his or her siblings.

Similarly, if a mother can only save one of her two children, it’s wise for her to save the older one, since she’ll need to expend additional parental investment to get the younger one to the older one’s age. On the other hand, if she’s deciding who to give food to, it might be wise to feed the younger one who is weaker and less able to find his own food. It also makes sense that mothers wean their children when they are strong enough to seek their own food. From the mother’s perspective, it’s wiser to save her remaining parental investment for her next child, rather than spend it on a child who is now capable of fending for himself.  

Dawkins wonders why females go through menopause. He thinks the abrupt way menopause comes on seems to imply it’s an adaptation, and concludes that menopause probably happens because women get less efficient at bearing children as they age. If a woman has a child and a grandchild born on the same day, her grandchild has a greater chance of survival than her child. Grandmotherly altruism probably exists because women who were altruistic toward their grandchildren increased the chances of keeping their genes in the gene pool, and passed on the tendency to be caring toward grandchildren. Dawkins believes that focusing on the genetic payoff to one’s genes in one’s relatives’ bodies explains all kinds of kin altruism.

Dawkins then asks what the optimal survival strategy is for a child competing with its siblings for resources. Genetically speaking, one’s sibling (like one’s parents) has half of one’s genes in its body. But on the other hand, one has all of one’s genes in one’s body, so it may be wise to try to “grab” more than one’s fair share of parental investment. Dawkins thinks this is why piglets often race to reach their nursing mother. On the other hand, it might benefit one’s genes if one let one’s younger (and weaker) sibling have more than their fair share of parental investment. An “elder brother may have exactly the same ground for altruism as a parent.” There’s a genetic payoff to caring for replicas of one’s genes in one’s siblings’ bodies.

From a child’s perspective, there’s a point in time when it benefits his or her own genes to wean him- or herself so that his mother can invest in another child which also has some of the same genes. This point in time is usually much later than the optimal time for the mother to wean him or her (which is whenever he or she has had his or her fair share of her lifetime parental investment). This is likely is why children often resist weaning, but eventually accept it.

Dawkins believes that many child behaviors exist because of the genetic payoff across siblings. For example, pretending to be the hungriest sibling (and chirping the loudest) likely survived in the gene pool as a behavioral trait in young birds because it works. On the other hand, some runts give up and stop competing for food. This is because one of the runt’s siblings likely also has the gene for “give up when you’re too weak” and the runt giving up keeps that gene in the gene pool by way of the runt’s sibling, who becomes stronger by taking the runt’s share of parental investment. 

In general, it’s a wise strategy for children to lie and cheat to get as much parental investment as possible. A. Zahavi even speculates that some birds chirp to attract predators to their nest, forcing their mothers to feed them and keep them quiet. Dawkins is skeptical about this strategy surviving in the gene pool, because he thinks it’s too risky.

Dawkins admits, however, that there are some diabolical strategies that pay off in the long run. Cuckoos (who hatch in “foster” nests) tend to hatch earlier than their foster siblings. It’s smart for cuckoos to throw the other eggs out of the nest and hog the parental investment, especially because the cuckoo is not genetically related to the other eggs in the nest. Similarly, there can be a substantive genetic payoff for a swallow who throws out one of the eggs in its nest. Since the swallow is genetically related to its siblings, it doesn’t make sense to throw them all out, but it might make good sense to reduce the nest size and get a bit more parental investment, while also ensuring its genes live on in most of its siblings.

There is often a conflict of interest between parent (who’s optimal clutch size might be five) and child (who’s optimal clutch size might be four). Dawkins wonders who tends to win in conflicts between parents and children. Alexander thinks parents always win this fight, because a selfish chick will grow up to pass on selfishness, meaning their chicks will kill each other, and fewer survive each generation. Eventually this trait would die out, meaning the parent’s optimal clutch size wins out overall.  Dawkins thinks there is more of a situational give and take between mother and child. Mothers are bigger and stronger, but children can manipulate situations by pretending (to be hungry, for example). He thinks a compromise emerges between the optimum situations for the mother and the child.

Dawkins reminds the reader that he is not advocating this kind of behavior, nor saying that anybody does it on purpose. He’s only talking about the types of behavioral traits that tend to survive in the gene pool. He thinks this means that humans need to teach children altruism, because selfishness is favored by nature.