The Selfish Gene – Part 3

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Sperm Meet Egg

Continuing to blog my way through Richard Dawkins’ book, The Selfish Gene, I’ll summarize the 3 chapters that lead up to the stunning conclusion.

Chapter 7 – Family Planning

We might think that animals would have as many offspring as possible in order to maximize the propagation of their genes, but evolution is smarter than that. If an animal has more children than it can care for, it may end up with fewer surviving progeny than if it had had a more manageable number. So, it may make sense for it to limit its offspring, and that is exactly what we find in many species — particularly species that must time and energy caring for their young.

Chapter 8 – Battle of the Generations

Every parent wants all of her children to have what they need to thrive; every child wants more than his fair share. This chapter explores the strategies various species have evolved to resolve that conflict. Through it all, as usual, the real master of ceremonies is the gene, which apparently programs both parent and child to create as many copies of itself as possible.

I’ll quote an example. “Consider the question of when weaning should take place. A mother wants to stop suckling her present child so she can prepare for the next one. The present child, on the other hand, does not want to be weaned yet, because milk is a convenient, trouble-free source of food, and he does not want to have to go out and work for his living.”

That is a familiar example, but Nature has contrived a seemingly infinite number of arenas in which this type of battle takes place. Cuckoo birds outsource the conflict: the mother cuckoo lays her egg in the nest of another species. “As soon as it hatches, blindly and mechanically, but with devastating effectiveness, it throws the other eggs out of the nest” so that it has its foster parents’ attention all to himself. Cute!

Dawkins explains how all this behavior is in the service of the gene’s desire to maximally replicate.

Chapter 9 – Battle of the Sexes

I’ve always wondered how sexual reproduction could have gotten started. What good is a sperm if there is no egg?

The first step toward an answer is to observe some primitive species that are isogamous: each parent contributes half the chromosomes to the offspring, but those genes come packaged in cells that are alike. Now to quote Dawkins, who is quoting Parker:

“In the days when all sex cells were interchangeable and of roughly the same size, there would have been some which happened to be just slightly bigger than others. …[The large sex cell] would get its embryo off to a good start by giving it a large initial food supply. There might therefore have been an evolutionary trend toward larger gametes. But there was a catch. The evolution of isogametes which were larger than strictly necessary would have opened the door to selfish exploitation. Individuals who produced smaller than average gametes could cash in, provided that they could ensure that their gametes fused with extra-big ones. This could be achieved by making the small ones more mobile, and able to seek out large ones actively. The advantage to an individual of producing small, rapidly moving gametes would be that he could afford to make a larger number of gametes, and therefore could potentially have more children.”

Men and women have been negotiating the behavioral implications of this ever since. A woman can only bear one child every year or so, but a man can father hundreds of children in that time. A woman is motivated to ensure that all of her relatively rare children survive and for this she needs the help of her mate. The man, on the other hand, can afford a quantity-over-quality strategy. If the men were to have their way, there would be many babies, but they would be malnourished at best. In the most successful human societies, the women have managed to tame the men, refusing sex unless they are sure their men will be around for the long haul.

Other species that must care for their young have evolved similar solutions. For example, the female might require a long courtship ritual or a fresh-built nest as proof of her suitor’s devotion.

It’s fascinating to think that the devotion of the male is the long-term result of the sperm’s selfish exploitation of the extra resources in the egg.

>> Next in this series: The Selfish Gene – Part 4 (Chapter 10)