In social animal species that choose to live in groups, some members of the group sacrifice their reproductive abilities so that the others which are related are cared for and allowed to reproduce and thus carry on the genetic material of the group. This is referred to as kin selection and over time, species have developed strategies to carry this out. In the following paragraphs I will show why it is advantageous to make this sacrifice by looking at the degree of relatedness of siblings using different genetic systems, and some of the animals that utilise kin selection.

In order to better understand why in some species individuals could make this sacrifice we have to understand what makes a species "successful". An individual is deemed successful if it lives to reproduce offspring. Because in order to live long enough to reach reproductive age one has to have the necessary survival skills to avoid predation and health since they can resist parasites and disease. So that these individuals are favoured by natural selection as they have the best genetic material and what individuals of the species desire to be passed on the future generation.

But why lay down your life for that of your relatives? Well let us look at how much of your genetic material is shared by your relatives. On average the genetic material shared by siblings of the same parents both of whom are produced from fertilised eggs are 50%, while nieces and nephews share 25%, while cousins only share 12.5%. What also has to be taken into consideration is how many relatives are being helped by this sacrifice. Also, by sacrificing one's own ability to reproduce, the individual is ensuring that the relative has more offspring, therefore making up for those that the sacrificial animal would have had during its lifetime.

The best and extreme example of kin selection is that displayed by social insect like termites, and many species of wasps, ants and bees.

In these species there is a single reproductive female (called the queen), while the workers which can consist of both males and females are sterile and perform tasks such as, foraging for food and nest material; construction, maintenance and repair of the nest; rearing the young and defending the colony against predators. Being such small animals some species have adopted the strategy of strength in numbers and would not exist if they did not form colonies. We can also see that building and maintaining the nest to hold such large numbers of individuals is very time consuming and labour intensive. However, insects are not the only animals that exhibit this behaviour. The naked mole rats in South Africa form underground colonies in the dry desert regions. Also what one has to keep in mind is that the parents caring for offspring is not the only type of parental care among animal species, in some species of birds; adult siblings can delay their own mating by a year to care for younger siblings.

However, to better understand why kin selection is more common in species of ants, wasps and bees one has to briefly look at how their genetic material is passed on from parent to offspring.

These insects develop from a genetic system called haplodiploidy. This means that males are produced from unfertilised eggs and are regarded as haploid, so that the 50% of genetic material they get from their parent is shared by all of their male siblings. Therefore the males are perfect genetic copies of each other. However, females are produced from fertilised eggs and are referred to as diploid, so that half of their genetic material is inherited from their mother half of which would be the same, so that ¼ of their genetic material is the same between siblings. So in total with 50% from their father and 25% from their mother, the total relatedness of female siblings is 75%.

One of the mechanisms employed by animal species that utilise kin selection is kin recognition. This is important as one would not want to make this sacrifice for an individual they are not related to. In ground squirrels where females are fertilised by several males the full siblings are less aggressive towards each other.

So as we can see, life in the wild is not as easy as "kill or be killed", there are many complex relationships at work, one of which involves sacrificing their ability of the having offspring of their own, but caring for those of their siblings for the survival of their species.