It was the birthday of a co-worker of Monica’s. It had been four years now them working together. Previously, they just used to greet each other on their respective birthdays. But this year Monica’s friend gave her a gift on her birthday. Monica felt compelled to the same for her friend, even though she’d never done it before.When someone does a favor for us, why do we feel tempted to return it?Why are we likely to help those who’ve helped us before?Why do we tend to buy gifts for those who do the same for us?Reciprocal altruismOne should expect altruistic acts from one’s immediate family- one’s closest genetic relatives. This is because by helping each other survive and reproduce, a family is essentially helping its shared genes to successfully pass on to the next generation.But what explains altruism outside of the family?Why do people form close bonds with those who’re not related to them?It’s all due to a psychological phenomenon known as reciprocal altruism. In simple words, reciprocal altruism is nothing but mutual benefit. We form bonds with people and help them so that we may get helped in return. Friendships simply can’t exist without the prospect of mutual benefit.Origins of reciprocal altruismDuring most of our evolutionary history, hunting was the main activity for procuring food. But success from hunting was unpredictable and erratic. One week a hunter would obtain more meat than required and another week he’d acquire nothing at all. Add to this the fact that meat can’t be stored for long and is easily spoiled. Our hunter ancestors therefore could only survive if they somehow ensured a continual supply of food. This generated selection pressure for reciprocal altruism, meaning that those who had mutual altruistic tendencies were more likely to survive and out-reproduce those who did not have such tendencies. Those who were helped, helped others in the future. Therefore, altruistic tendencies are widespread amongst today’s humans.Reciprocal altruism is found in the animal kingdom too.  Chimpanzees, our closest cousins, form alliances to boost their chances of survival and reproduction. A dominant male-male alliance in chimps is likely to out-reproduce other males.Vampire bats that suck cattle blood at night don’t always succeed. It has been observed that these bats provide regurgitated blood to their ‘friends’ when they’re in dire need. These ‘friends’ are bats who had provided them with blood in the past! They form close associations with each other even though they’re unrelated.Shadow of the futureReciprocal altruism is likely to occur when there’s a large shadow of the future. If the other person thinks that they’ll be interacting with you frequently in the extended future, then they have a strong incentive to be altruistic towards you. They expect you’ll be altruistic towards them in the future too.On the other hand, if the other person thinks that they won’t be interacting with you for long (i.e. a small shadow of the future), then there seems to be no point in being altruistic. This is one reason why most friendships in schools and colleges happen at the beginning of the academic year and not when the course is nearing its end.At the beginning, students seek other students who might benefit them during the course. There’s simply no point in making friends when you’re hardly going to interact in the future. If it looks like a friend is going to be altruistic towards you beyond college, then you’re likely to form a lifelong bond with that friend. If a friend has helped you a lot in the past and so have you, then you’re likely to form a lifelong friendship with them because you’ve both already demonstrated your respective commitment to reciprocal altruism.When there’s no future to look forward to, chances of reciprocal altruism are less. It’s all about mutual benefit.

Scene 1Jenny always felt that her parents favored her younger sister over her. She knew it wasn’t due to the age factor since she was only a few months older than her sister. Also, she was more hardworking, studious, calm-tempered and helping than her younger sister.It seemed to make no sense to her as to why her parents doted more to her younger sister who barely had any good personality traits.Scene 2By the same token, Arun’s parents seemed to prefer his older brother but, on the contrary, it was pretty clear to him why- his elder brother was much more successful than him.Arun would be frequently at the receiving end of his parents’ bashing, pestering him to take his career and life seriously. They compared him to his elder brother, saying things like, “Why can’t you be like him?” “You’re such a disgrace to our family.”Origins of parental favoritismAlthough many would like to believe otherwise, parental favoritism exists. The main reason being that parenting, in and of itself, is a costly affair.Whenever we do something that incurs huge costs on us, we have to make sure that the benefits we gain outweigh them. Take the example of a firm. A firm will only decide to provide specialized costly training to its employees if it knows that it will bring more profits to the organization. Spending a huge amount of money training employees who aren’t delivering is money going down the drain. There has to be a bigger return on investment for the big price paid.Similarly, parents expect a return on their investment from their children. But there’s a catch- they primarily want in the form reproductive success (successful passing of their genes to the next generation). Speaking in terms of biology, offspring are basically the vehicles for parents’ genes. If offspring do what they’re supposed to do (pass on their parents’ genes) without hassles, then parents will benefit from their lifelong investment in their offspring.So it makes sense that parents should favor those offspring who’re likely to contribute to the reproductive success of their genes and press those who’re not to change their ways so that their odds of reproductive success also increase.Jenny’s younger sister (Scene 1) was more beautiful than her. So she was more likely to be reproductively successful than her, at least in the unconscious perception of her parents.Jenny’s mom badgered her to visit salons and parlors to encourage her to improve her looks. Her mother hated the fact that Jenny didn’t maintain herself, and for good evolutionary reasons. (see What do men find attractive in women)On the other hand, resources accrual is the key determinant of reproductive success in men and so, instead of pestering him to change his looks, Arun’s parents wanted him to take his career seriously. They favored their elder son because he was likely to yield a good reproductive return on their parental investment.Why step-parents tend to be jerksIt is well-known that biological parents typically provide more love, care and affection than substitute parents. A child raised by step parents is at a greater risk of physical and emotional abuse. As I mentioned before, parenting is costly. Not only in terms of the resources invested, but also in terms of time and energy devoted into raising children. It makes no evolutionary sense to raise offspring that do not carry your genes. If you invest in such offspring, you’re incurring unnecessary costs on yourself.So to motivate step parents to avoid investing in genetically unrelated children, evolution has programmed them to resent their step-children, and this resentment often rears its ugly head in ugly ways in the form physical and emotional abuse.   Of course, this doesn’t mean that all step parents are abusive, just that the chances of them being jerks are more; unless some other belief or need overrides this evolutionary tendency.The mystery of adoptionSay a couple were unable to have kids on their own and decided to go for adoption. They loved and cared for their adopted child as much as its biological parents would. How does evolutionary theory explain this behavior?It depends on the unique case that one may be considering but the simplest explanation could be that ‘our evolutionary behaviors are not fixed in stone’. A person can, in his lifetime, acquire beliefs that make him act contradictorily to what his evolutionary programming demands.We contain multitudes. We’re a product of both our genetic programming and past life experiences. There are numerous forces battling it out in our psyche to produce a single behavioral output.The important thing to remember, however, is that no matter what the behavior, the economic principle of costs v/s benefits still holds i.e. a person will only do a behavior if its perceived benefit outweighs its perceived cost.It could be that the couple mentioned above, by adopting a child, are trying to save their relationship. Because the news of not being able to have kids can be distressing and a strain on the relationship, the couple can adopt and pretend that they have a child. This not only saves the relationship but keeps alive the hope that if they keep trying, one day they might have kids of their own.Since parenting is costly we’re programmed to enjoy it to offset the costs. Parents get a deep sense of satisfaction and contentment when they care for their young. It could be that parents who adopt are primarily satisfying this pre-programmed need for satisfaction and contentment.Claiming that parents who adopt violate the principles of evolutionary theory is like claiming that having sex with contraceptives goes contradictory to the fact that sex has the biological function of passing on genes.We humans are cognitively advanced enough to make the decision of hacking into that function to just go for the feeling part. In this case, pleasure.