Expert: Jonathan Wright - 10/3/2007

Question
I read with interest your response to a question on incidences of animals killing their young and in some cases the offspring of other animals.
i am in the process of writing a book on steparenting and in one chapter would like to go into some detail on comparing humans with animals within this area. Are there any cases of steparenting amongst animal species and whether or not this is a natural process for them?
I also vaguely remember reading or watching a documentary claiming that we are not by nature or gentically designed to care for others offspring and would rather be "rid" of them to keep the bloodlines and dna pure.Is this something common amongst certain animals that they would kill off offspring to keep genes and dna pure?
If you could suggest some reading material on the subject as well, I would appreciate it.

Answer
Dear Azure

Thanks for your question. I also wish to thank the authors of the websites I used.

There are various examples of animals showing behaviour similar to step-parenting. Some animals, such as koalas, will provide milk for animals other than their own for a short time. Some animals will unwittingly look after eggs and young of other species. Cuckoos and various other birds lay their eggs in the nests of other birds and the young cuckoo will often eject the other eggs and chicks from the nest, so it doesn’t have to share food with them. If a baby rabbit is put into a nest early in the morning, its scent may be masked by the other babies, so their mother may nurse it when she returns in the evening. Bantams can be used to brood eggs of various species and look after the chicks. Some animals have also “given birth” to young of another species – this has been useful in breeding endangered species. So animals will look after young that are not their own.


The following websites give details of source material: http://www.ingentaconnect.com/content/els/10905138/1999/00000020/00000006/art000... (this sounds ideal for you and you may be able to get information via http://linkinghub.elsevier.com/retrieve/pii/S1090513899000276), http://members.iinet.net.au/~sejones/PoE/pe15socl.html#sclscblgystprnts and http://www.news.cornell.edu/releases/Feb97/AAAS.emlen.hrs.html (biological concepts of human step-parenting)

I couldn’t find any examples of non-human species where a stepfather takes over the role of father to his partner’s young, although there are several cases where he will kill the young of other males. When lions take over a territory, they will kill the cubs, so that the females will come into oestrus and the males can mate with them. I should imagine that the information you saw in the documentary has some truth to it. Stepfathers may generally be less attentive to their partner’s babies than they would to their own. Monogamy is very rare among mammals, where the male often leaves the female soon after mating, leaving her to look after the young by herself.

I accept this is a very controversial area, but I don’t feel that humans are naturally monogamous and I wonder if our ancestors either had a system like chimpanzees or bonobos (where the father of a baby is often in doubt, so several group members help out) or gorillas, where one male has a harem of several females). I doubt if a male and female early human stayed together to look after the babies and I would be surprised if a stepfather would spend time looking after the young of another father and I suspect that he may have killed the young, given a chance. While the "husband, wife and children man" is common in many human societies, there are alterntives to this. These include polygyny and polyandry, as well as childless adults, bisexuals, asexuals, homosexual men and lesbians. There are also various religious groups who do not accept partnerships from people outside their group. This may lead to "honour killings" if people go against family norms. This may be an example of keeping DNA pure, although the animal examples you mention are more linked to the 'selfish gene', where animals are more inclined to defend close relatives, as they share some of their genes. This also leads to killing off young that are not their own, so a female can breed earlier.

I hope this wasn't too confusing, but it is an interesting, contentious subject.

All the best

Jonathan