Why do animals choose to reproduce and why do they choose to control birth rates? What are the different theories of reproduction and birth control that explain these behaviors?
Theories of reproduction consider altruistic and selfish reasons for foregoing reproduction and using birth control. The Wynne-Edwards theory argues that there are natural rules for keeping animal populations in check.
Read on to understand theories of reproduction and how they apply the Wynne-Edwards theory of population control.
Theories of Reproduction: Altruism or Selfishness?
Animals reproduce to fulfill the mission of passing on their genes. That’s the argument Richard Dawkins puts forth in The Selfish Gene. But, theories of reproduction also have to consider the idea that animal populations also have natural methods for population control. This natural birth control can be explained with altruism or selfishness.
Altruistic Theories of Reproduction
The Wynne-Edwards theory says that animals have natural rules and guidelines that keep their populations in check. He takes observed territorial and hierarchical behaviors as evidence that animals follow certain rules for the good of the whole species.
He notes that males of many species will not even try to reproduce if they don’t have territories of their own. Since there is a limited amount of territory, that naturally limits the number of new births there can be. Similarly, among many species, males with low social status will not be able to reproduce—either females will not mate with them, or higher-ranking males will prevent lower-ranking ones from accessing the females. As with territoriality, in many species the low-ranking males will not even try to breed. These contests over territory and social status take the place of direct contests over females, which could result in wasted energy or injuries.
The most remarkable part of this theory may be epideictic behavior, which is a term that Wynne-Edwards himself created. Many animals tend to gather in large groups, and there are clear evolutionary advantages to doing so, such as protection from predators. However, epideictic behavior suggests another explanation: Animals gather in this way to conduct a sort of informal census of the population.
By seeing how large and dense the herd or flock is, animals can then determine whether they need to restrain their reproduction. Overcrowding is a clear sign that famine may be imminent, and the animals will need to adjust accordingly. This decision isn’t made consciously, but seeing a dense enough population will trigger natural responses in the animals that lead to lower birth rates, according to this theory.
The Selfish Theory of Birth Control
There are costs as well as benefits to reproducing: remember bearing vs. caring. Therefore, even from a purely selfish standpoint, having as many children as possible isn’t usually the best strategy. That is important for understanding the selfish theories of reproduction and avoiding it. For example, swifts have a standard clutch size of three eggs. That suggests that three is the ideal number of offspring for a swift to raise at one time. Having more than three at a time may mean the offspring wouldn’t get enough of their parents’ time and resources, and could die. Fewer than three, naturally, would mean that there are fewer offspring to pass those genes on to the next generation.
A selfish gene would want the animal to produce as many successful offspring as possible, given the resources available. Therefore, it’s selfishness, not altruism, that leads animals to limit their reproduction; having too many children would make it less likely for each to survive. Similarly selfish explanations can be made for the other aspects of Wynne-Edwards’s theory as well.
Animals who stop competing for territory or social dominance may have determined that their best bet is to hope that one of the others dies, rather than waste energy and risk injury with repeated contests that it has little chance of winning. The fact that these gambles often don’t pay off doesn’t necessarily mean that they were bad gambles. The chances of it working are slim, but perhaps the chances of winning such a contest and successfully defending a new position are even slimmer.
Even so-called epideictic behavior can be explained in selfish terms. Animals may lower their breeding rates during times of overcrowding because it gives them, personally, the greatest chance of raising the most surviving offspring. If resources become more limited, such as during a famine, a selfish gene should encourage the animal to have fewer children to split those resources among.
In practice, the altruistic vs. selfish reproduction theories are nearly identical. The only difference is whether animals practice population control for the good of the species as a whole, or purely for selfish reasons. Right now there’s no definitive way to tell which is correct, but—as previously shown—pure altruism is not a stable strategy since it’s bound to be taken over by selfish individuals. Therefore, it currently appears that the selfish reproduction theory is the stronger of the two.
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- Why organisms don't matter, only genes do
- How all life forms begin with a replicating molecule
- How species need to balance aggression and pacifism to survive