There are many cases when people commit altruism. One is relationship. I am willing to die for 2 of my children or 8 nieces, say an evolutionary psychologist. Another is reciprocal altruism, which is just a selfish cooperation rather than true altruism.

In the 1930s J.B.S. Haldane had full grasp of the basic quantities and considerations that play a role in kin selection. He famously said that, "I would lay down my life for two brothers or eight cousins".[8] Kin altruism is the term for altruistic behaviour whose evolution is supposed to have been driven by kin selection.

Is it possible that humans may be altruists not for their 2 children or 8 nieces but to say, 1000 people that are similar to them.

If so, how does "Be altruist to 1000 of people similar to you" evolve?

Note: If the answer is negative, then we will have a hard time understanding voting. Why sacrifice your time. However, if the answer is positive that humans do love other humans "a little bit" then voting, or even suicide bombing make sense. Those humans sacrifice their little time to improve reproductive success of those who are similar to them.

Answer DOES NOT have to be about humans. If you can show me why strong/weak chimps tend to help each other or whether alpha males like one another, that'll do. Of course, naturally we would expect that leaders need followers and followers need leaders. But sometimes there are behavior that defy even this complementary nature.

Similarity does not have to be genetic. For example, fellow programmers and fellow engineers tend to be gang up.... Or does it have to be genetic?

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    $\begingroup$ Can you rephrase the question so that the example is not directly political? There's a valid question here, but in my opinion, it's packaged in a way that is not appropriate for this site. $\endgroup$
    – yamad
    Commented Mar 19, 2012 at 15:54
  • $\begingroup$ I see. The problem is voting is always taking from one guy to another. It's not about common goals. I am picking the simplest sample. I suppose I can make that the other way around of middle class diligent people wanting to lower tax. The truly rich don't care about tax though. Google pays like 2% income tax or something. $\endgroup$
    – user4951
    Commented Mar 20, 2012 at 6:19
  • $\begingroup$ Also this "altruism" toward someone not related but similar may explain suicide bombing, rather than just mere voting, for example. It explains why people are loyal to their religion, etc. I think I should have used samples in animals. $\endgroup$
    – user4951
    Commented Mar 20, 2012 at 6:40
  • $\begingroup$ I changed the questions and the packaging. However I can't find a less political samples where I can put some math in it. $\endgroup$
    – user4951
    Commented Mar 20, 2012 at 6:47
  • 3
    $\begingroup$ @JimThio My objection to this question stands. I understand that your questions stems from your political beliefs, but your examples make this question argumentative. $\endgroup$
    – yamad
    Commented Mar 20, 2012 at 13:45

3 Answers 3


This is an important question in evolutionary biology, but you need to distinguish the biological terms 'altruism' vs 'cooperation'.

Altruism in biology means giving up your chance to reproduce so that someone else can more readily. This is not like a gorilla troop, where only one male breeds, and the rest contribute to mutual security. A more typical example is a honeybee or an ant, where the vast majority of the hive have no ability to reproduce at all. This happens in animals, but is relatively rare. Its causes are currently the subject of intense debate but as far as I know, the only cases are where you do this for others who are genetically similar to you. That logic sort of plays out as you say: "My brother has kids, why do I need to have any? I'll just help out a little bit there."

Cooperation includes forming groups for mutual safety and increased competition for food resources are why you might vote or schlep down to the DMV to get a drivers license when simply getting in your car without might be just as good most of the time.

Cooperation is incredibly common in biology. It even happens between species. A dolphin helps a ship navigate submerged rocks, symbiotic bacteria in our gut help us digest food, but also get enough to live and reproduce. The benefit is always win-win in such situations.

To understand how cooperation occurs spontaneously, one of the best experiments to look at is the Prisoners Dilemma experiment. If individuals are in a situation where you are likely to see each other again later (like a society). The most successful ones are the ones who treat each other reasonably well, even if you do look out for less reliable types. Why do people from Northern climates have strong hospitality traditions? "Today you (are in trouble) tomorrow me." As the saying goes.

There are individuals who are not cooperative, but the selection forces are positive enough that those folks will regularly disappear from the group, while more cooperative types will become more numerous.

This is a significant selective pressure that you can train robots with very simple reward mechanisms to cooperate. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=

  • $\begingroup$ +1 for mentioning prisoner dilemma, which is the real issue. In cooperation, every single individuals are better of cooperating. In voting they are better of not voting. Voting are secret anyway. Ah perhaps going to voting booth is a way to hang out with neighbors. Also the cost for voting democrat is the same with the cost for voting republican? Or perhaps humans are not entirely selfish but care about others, say by 1%? But how does care about others' reproductive success, by 1% reproduce? $\endgroup$
    – user4951
    Commented Mar 20, 2012 at 6:22
  • $\begingroup$ thanks - ive had to go over this quite a few times in the past year - glad the question came up. $\endgroup$
    – shigeta
    Commented Mar 22, 2012 at 2:02

The question's a little broad, but I'll answer the question in the title: how does "be altruist[ic] to those who are similar to you" evolve. It turns out one way is discussed by a simple theoretical model called the "green-beard" model. In essence, it says that a gene for altruism can spread if it produces a characteristic that can be perceived by and recognized in others (the 'green beard') and promotes altruistic behaviour towards other greenbeards.

Wikipedia has a round-up of some examples of this in action; my general feeling from reading on this is that though it's a good idea in theory, greenbeards won't be too common in practice because of the difficulties involved in keeping out mimicry (as in many signaling systems) and because of the complexity involved in creating and maintaining all three parts of the greenbeard effect on the part of one gene. For that reason, it's been suggested that it may be more common in smaller organisms like bacteria, where this machinery can all occur in the same cell.

  • $\begingroup$ This answer makes sense. It still doesn't explain why humans vote. $\endgroup$
    – user4951
    Commented May 3, 2012 at 2:20
  • $\begingroup$ That question answers itself if you think about what voting really is. It's the most concise way of stating your opinion - exactly what is needed if a lot of opinions are to be assessed in a short time. It's merely a device, an idea somebody once came up with and which has since proven useful again and again. I wouldn't attach any evolutionary idea to voting (except if we're talking about memes). $\endgroup$
    – Armatus
    Commented May 5, 2012 at 19:42

The above answers are good, but have unfortunately confused some of the concepts in the theory, I will do my best to explain.

What we are assessing is how does one behaviour evolve, links with cooperation and altruism are applications of this. The process of selection in evolution removes the the worst individuals from the gene pool, thus those with comparatively good genes survive to reproduce. With physical traits these mechanisms are well understood, with behaviour there are still multiple theories which have not been concluded but our understanding of them is reasonably complete.

Inclusive fitness is the combination of direct and indirect fitness, direct being your personal fitness, indirect being fitness gained from others. In general this is measured in terms of reproductive success (RS) (the number of offspring you successfully raise to reproductive maturity). Out of this understanding came Hamilton's Rule:

                               r.b > c

Where r is the relatedness, b is the benefit & c is the cost. In this scenario the cost is a reduction in RS, the benefit is a gain in RS. Benefits are multiplied by the relatedness to the offspring. In normal diploid organisms (Gets DNA from both parents) you are related by 0.5 (half from mother, half from father), but only related to your brother/sister's offspring by 0.25. Thus, if you have two children you have a direct fitness of 1, if your brother has two children you gain an indirect fitness of 0.5. Thus, you would prefer under normal circumstances to have your own children rather than raise your brothers.

Altruism is suffering a cost for someone else's benefit, @Winawer mentions the greenbeard theory, which rests on the assumption that if you can tell someone has the same genes as you then you know that you are related to them in someway and this will be on average be greater than to any other individual. Altruism is a behaviour, defined above, and not a specific action like giving up your own reproduction, thus it is a part of cooperation and not separate from it.

It is true that there are different forms of altruism however these are all just perspectives pertaining to the same theory. ALL behaviour is selfish, reciprocal altruism is just an example of this. Reciprocal altruism, is "If you scratch my back, I'll scratch yours" (You need help now, I may need help in the future), it is altruistic because you suffer a cost for another's benefit but it is selfish because it is still in the individual's interest to help. This is where prisoners dilemma comes in, this is basically asking the question "how do I pick the most optimal situation in this scenario?"

For simplicity, it is generally ill advised to study behaviours in humans because of the implicit bias we have in our judgment on ourselves. From political and religious associations that cloud judgment to the fact that we always strive to see ourselves differently. Also, there are all sorts of ethical difficulties in actually testing and manipulating theories on us. Thus we normally study animals to get around this. However your question specifically talks about people so I will try and answer this based on biological theory alone.

Based on the foundations above, why would someone behave altruistically to someone only 'similar' to you? The biggest difficulty is knowing that we understand all the costs and benefits involved, most of the time we only know some of them and its impossible that you can know all of them because you can't know what you don't know. Humans have effectively 'bootstrapped' behaviours which are 'for the good of society' building on from previously developed behaviours. However we are still fundamentally asking a question about Hamilton's Rule. Being seen as a part of society induces altruistic behaviour towards you (because you are seen as worth something), this is good for you and the costs associated with being altruistic are usually low. Thus you would never rationally die for 1000 unrelated individuals unless you had at least had all the children you were going to have and raised them to be independent. But you would vote, by voting you suffer a tiny cost, your time, for a huge benefit. Benefits might include:

  • Being seen as caring for others (altruism given to you)
  • Possible benefits to yourself (less tax, more support, better roads, clean air.. etc)
  • Possible benefits to others related to you
  • General good moral of your community, leading to a better life.

There could be thousands of other benefits that I can't, off the top of my head, think of. The cost is negligible and the benefit is intangible but probably higher than the cost. Relatedness isn't important (so long as it is greater than 0), if the cost is sufficiently low or the benefit is sufficiently high. I hope this has helped clarify your thinking and answer the question.

For further information:

Provides the foundations

Hamilton W.D. (1963) Evolution of altruistic behaviour. The American Naturalist 97 354

Hamilton W.D. (1964) The Genetical Evolution of Social Behaviour I . Journal of Theoretical Biology 7 1

Hamilton W.D. (1964) The Genetical Evolution of Social Behaviour II. Journal of Theoretical Biology 7 17

The current controversy mentioned in another answer is from this paper, it is widely dislike but does have some support. It is slightly off topic from from the question here, but eusociality is fundamental to our understanding of evolutionary behaviour:

Nowak M.A., Tarnita C.E. & Wilson E.O. (2010) The Evolution of Eusociality. Nature 466 1057

  • $\begingroup$ Very good answer. Let me read. By the way, humans related fitness with brothers and sister should be .5 not .25. It's .25 from Mom and .25 from dad. $\endgroup$
    – user4951
    Commented May 21, 2012 at 12:50
  • $\begingroup$ +1 for picking that all actions are actually selfish. The thing is the genes are selfish. So how come gene "be nice to fellow programmers" evolve? $\endgroup$
    – user4951
    Commented May 21, 2012 at 12:56
  • $\begingroup$ Somehow I feel that even suicide bombing (the terrorist die but others can reproduce better when free sex is illegal) is still selfish. Here the cost is actually significant. Moreover, the similarity is religion, instead of genes. I guess I didn't take into account that terrorists do get paid well (by their community standard). But some variables are still missing. $\endgroup$
    – user4951
    Commented May 21, 2012 at 12:59
  • $\begingroup$ For small costs altruism it make sense. I tend to observe that people treat those who have the same religion with them as "family". $\endgroup$
    – user4951
    Commented Jun 11, 2012 at 9:05

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