The Selfish Gene: Chapter 9 Summary & Analysis

Trivers argues that sexual relationships are shaped by mutual mistrust and mutual exploitation. Dawkins agrees, because from a genetic perspective, mates are not genetically related. Mates share an investment in their child (which has half of each parents’ genes), which demands a certain amount of cooperation, but overall it would be a smart strategy to trick the other parent into “caring” for existing children, and focus on more mating, to get more genes into the gene pool.

In order to address selfishness and altruism between mates, Dawkins first needs a way of characterizing the sexes. The problem is that many species don’t have the same markers of sex as humans do. For example, male frogs don’t have penises. The only consistent difference across species is that the egg is larger than the sperm. Dawkins decides to call organisms with small sex cells “male” and organisms with large sex cells “female.” 

The first thing that’s obvious from the get-go is that larger sex cells provide more nourishment for the embryo. Even at this stage, the female contributes more. Dawkins says that “female exploitation begins here.” It’s likely that natural selection favored large female sex cells, since more nourishment gives the embryo a good start. If so, it would have made good sense for the male sex cells to evolve to be as small as possible (effectively making more small sex cells than few big ones). In this sense, eggs are playing an “honest” behavior strategy and sperm are “exploiters.”

Dawkins believes that group selection theorists run into problems when sex ratios come up, since it’s obvious that only need one or two males are needed to get a whole population going. In many animal populations, only some of the males actually mate. For example, only 4 percent of male elephant seals mate. So, why don’t the other males kill themselves to save resources for the good of the species? 

Dawkins believes that selfish genes provide a better explanation for why there are roughly equal numbers of males and females in a species. R. A. Fisher’s research explains sex ratios from the gene’s eye view. Suppose that among elephant seals, there’s a trait for having more daughters than sons. This would work for a while, as the group would survive even with only a few sons doing all the mating. Daughters would become very common. But then sons would have an advantage, since they’d be doing most of the mating. So, the gene for having sons would spread through the group and become numerous. Ultimately, an equal ratio of males to females ends up being the evolutionarily stable state.  

Dawkins recalls that he is thinking of individuals as survival machines for their genes. Each individual wants to mate and pass on as many genes as possible.  It makes good sense to trick one parent into caring for existing children while the other keeps mating. Dawkins thinks it’s harder for females to trick males because their sex cells are larger, meaning they have already invested more in the embryo than males. Females have more to lose if the offspring doesn’t survive, especially if the female has incubated an embryo in her body. This means that males face more evolutionary pressure to desert their mates. 

What about a deserted female, however? Trivers thinks it would make sense for her to trick another male into thinking the baby is his. He thinks this is why male mice evolved to secrete chemicals that trigger a miscarriage when inhaled by a female carrying another mouse’s embryo. Similar counter-strategies include male lions murdering existing cubs when joining a pride, and males who prefer long courtships before mating, just in case the female is already pregnant.

Trivers also believes that female birds require extensive courting because it makes males less likely to desert them after mating. The male has to secure territory and build a nest. With an increased investment in the courtship, he has more to lose by walking away. Dawkins disagrees, because he doesn’t think prior investment makes males more likely to invest more in the future, especially if there are other females in the group who demand less of their mates.  

Dawkins draws on Maynard Smith to work out the likelihood of females being “coy” (require a lot of courting) versus “fast” (easy to court), and males being “philanderers” (likely to desert his partner) versus “faithful” (likely to stay and care for future offspring). If one does the math, looking at the genetic costs and benefits of each strategy over a few generations, it turns out that the evolutionarily stable state is reached when most females act “coy,” and just over half the males act “faithful,” or when females act coy most of the time, and males act faithful more often than not.

Dawkins speculates that it pays off for females to be coy in ways that enhance egg cultivation. He thinks this is why “courtship feeding” happens. In many bird species, the male has to feed the female for a length of time before mating, which gives her (and her sex cells) energy for future embryos. Courtship feeding happens among insects and spiders too. For example, it’s smart for a praying mantis to feed his mate before copulating, because it reduces the chance of her being hungry and eating him after mating.

Dawkins wonders why there are some species in which males look after embryos or children. This happens a lot in fish.  He concludes that since fish spray their sex cells into the water (where they combine), and embryos aren’t grown in the female’s body, it pays for the female to spray her cells near a male and then desert him.

Many people think females are drawn to mates for reasons like having long legs to escape predators, or strong arms to carry food. Darwin thought this was incorrect, and Dawkins thinks so, too. He thinks females want sons who are likely to breed and pass on their genes. This means older mates are better (because it’s clear they live long and can breed more), and attractive mates are best (since inherited attractiveness will help their own sons mate later on).  

Zahavi has another explanation. He thinks that some males have “handicaps” (like large antlers, or long flowing tails) to show females they are strong and powerful despite these handicaps, meaning they’re more attractive overall. Dawkins finds Zahavi’s explanation a bit ridiculous. Dawkins thinks it’s clear that strong males mate with females because they win fights with challengers who try to move in on their “harems.” Dawkins believes he’s shown that selfish genetic motivations underlie a host of mating behaviors, including monogamy, promiscuity, and harems. He wants to show that this is true for other aspects of mating too.

Birds with brightly colored feathers attract mates, but birds with “drab” feathers blend in and hide from predators. Dawkins thinks that both kinds of genes compete, and what actually happens is a compromise. Females have “drab” feathers and males have colored feathers. Eggs are a scarcer resource, so females don’t need bright colors to nab a mate, but muted feathers help disguise them from predators. Males, however, only need to live long enough to mate to keep their colored feathers in the gene pool, even if they are eaten by predators shortly after. Females who are “fussier” about choosing a mate have a smaller chance of accidentally breeding with the wrong species (for example, with a donkey instead of a horse) and birthing sterile offspring, which stops their genes from living on in the gene pool.

However, the oddest mating habits in a species actually arise in humans. Human women tend to beautify themselves and act as if they are competing for male mates. This is the opposite of what normally happens in nature.