<P> Even certain plants can recognise and respond to kinship ties . Using sea rocket, Susan Dudley at McMaster University, Canada compared the growth patterns of unrelated plants sharing a pot to plants from the same clone . She found that unrelated plants competed for soil nutrients by aggressive root growth . This did not occur with sibling plants . </P> <P> In the wood mouse (Apodemus sylvaticus), aggregates of spermatozoa form mobile trains, some of the spermatozoa undergo premature acrosome reactions that correlate to improved mobility of the mobile trains towards the female egg for fertilisation . This association is thought to proceed as a result of a "green beard effect" in which the spermatozoa perform a kin - selective altruistic act after identifying genetic similarity with the surrounding spermatozoa . </P> <P> Whether or not Hamilton's rule always applies, relatedness is often important for human altruism, in that humans are inclined to behave more altruistically toward kin than toward unrelated individuals . Many people choose to live near relatives, exchange sizeable gifts with relatives, and favour relatives in wills in proportion to their relatedness . </P> <P> Interviews of several hundred women in Los Angeles showed that while non-kin friends were willing to help one another, their assistance was far more likely to be reciprocal . The largest amounts of non-reciprocal help, however, were reportedly provided by kin . Additionally, more closely related kin were considered more likely sources of assistance than distant kin . Similarly, several surveys of American college students found that individuals were more likely to incur the cost of assisting kin when a high probability that relatedness and benefit would be greater than cost existed . Participants' feelings of helpfulness were stronger toward family members than non-kin . Additionally, participants were found to be most willing to help those individuals most closely related to them . Interpersonal relationships between kin in general were more supportive and less Machiavellian than those between non-kin . </P>

The principle of kinship selection is based on the assumption that