I recently got hooked on to the Behavioural Biology lecture series of Prof. Robert Sapolsky. It is absolutely addictive to watch, and highly recommended to anyone who is interested in evolutionary biology. In the third lecture of the series, he talks about a very interesting phenomenon called infanticide. The word is a combination of the words infant and homicide, and means intentional killing of infants by unrelated males. Simply put : males killing other males' new borns. But why would the males of any species kill other males' infants in a population, intentionally? The answer is pretty obvious when the concept of individual selection is applied. What happens is the following : You are a male in a group of males, and you guys just invaded a new population. You probably have a few more years left to reproduce, but the females in the population are either already pregnant or nurturing the infants of other males that were there before you. Following the concept of individual selection, you have only one purpose in mind : to pass the copy of your own genes onto the next generation as much as possible. But how can you do that if all the females are pregnant or dealing with their new borns, and therefore not avaliable?
Maybe a quick pause and some background information can be useful at this point. It's obvious that females can't get pregnant when they are already pregnant, but there is also a phase called lactation after birth, which is colloquially known as breastfeeding. During this phase, the female cannot start ovulating, and therefore cannot get pregnant again (called Lactational Amenorrhea). So dealing with a new born is not an obstacle only in terms of energy and time, but also an obstacle in terms of physiology.
Now it becomes easy to connect the dots : "the female that can potentially give birth to my kids, and pass on the copies of my genes, is dealing with some other guy's new born, and therefore I cannot get her pregnant", says the inner voice of the male. The solution becomes obvious : kill the new born, make the female available again for mating. Basically, it is a male "trick" to obtain sexual access to females who are otherwise preoccupied with maternal duties [1].
Maybe a quick pause and some background information can be useful at this point. It's obvious that females can't get pregnant when they are already pregnant, but there is also a phase called lactation after birth, which is colloquially known as breastfeeding. During this phase, the female cannot start ovulating, and therefore cannot get pregnant again (called Lactational Amenorrhea). So dealing with a new born is not an obstacle only in terms of energy and time, but also an obstacle in terms of physiology.
Now it becomes easy to connect the dots : "the female that can potentially give birth to my kids, and pass on the copies of my genes, is dealing with some other guy's new born, and therefore I cannot get her pregnant", says the inner voice of the male. The solution becomes obvious : kill the new born, make the female available again for mating. Basically, it is a male "trick" to obtain sexual access to females who are otherwise preoccupied with maternal duties [1].