It is an interesting phenomenon that sometimes does not receive as much attention as it should that people generally aid and support those who are their kin rather than non-kin. Evolutionary psychologists such as W.D. Hamilton have tried to explain this via a gene's point of view. From the point of a view of a particular 'gene', it does not care which particular being propagates the gene, but rather that someone does, giving the gene 'evolutionary success'. Those that are of kin obviously have similar gene make-ups and so, from the gene's perspective, it is advantageous to help out those that are of kin and thereby raising the chances of evolutionary success. Hamilton has mathematically proven this and furthermore, this concept gives grounding to the existence of altruism based on natural selection.
Hamilton's rule can be used to determine whether or not a particular gene will spread throughout a population:
rb > c
Where, c is the reproductive cost; b is the reproductive benefit; and r is the probability of sharing said gene. This gives a mathematical representation as to why it is more likely that people will perform altruistic acts for people of kin than not of kin. People of kin have a higher probability of sharing the same genes and thus a higher number for the left hand side of the equation. This allows them to do more acts with higher costs and still be consistent with this formula.