Altruism is the act of putting yourself at a disadvantage so that other members of your group can prosper. Many species exhibit altruism, as it is a key to survival (there’s actually this monkey that was born with no hands and no feet, but the members of its troop bring him food and water so that he can survive, even though that means that the other monkeys get less food). The main reason that this applies to evolution is to think in terms of the “selfish gene” theory of evolution.
This theory suggests that our bodies (our brains, our concept of self, hearts, organs, skin, bones, cells, etc. Everything that we are) only exist to support the duplication and passing of genes and that our bodies are only vessels for our genes. We have such complex bodies because it takes all of these to support and protect our genes. This theory holds that it is our genes that drive evolution because it is our genes that want to survive, not us. As long as our genes are passed on to our posterity, then we are useless vessels.
Animals of the same species fight because they want THEIR genes to be passed on, not their competitor’s. Animals have defense mechanisms like quills on a porcupine or human ability to run long distances and all of the other genetic variations in the global gene pool for the express purpose of protecting their genes.
Now that I have explained that, I’ll now relate it to altruism. I’ll just explain family-first altruism because it’s less complicated than group-oriented altruism. So, recall the definition of altruism (the act of putting oneself at a disadvantage for the betterment of the group).
Let’s say that you are a monkey in central Africa and you are standing watch in case of danger (monkeys, specifically chimps, are known to form watch patterns with monkeys standing guard to alert the troop of danger). Suddenly, you see a lion (theoretically) but it cannot see you yet. It is inching closer to your troop and crouching down to get ready to pounce. You can do one of two things. You can either a) keep quiet and hide so that the lion doesn’t eat you but would eat other members in your troop, or b) you could alert the troop to the danger and expose yourself and your position to the lion.
If you keep quiet, yes, you would keep yourself safe and, therefore, your genes safe, but the members of your troop would be killed and eaten. In which case, you and your genes would actually be at a disadvantage because you, a lone monkey, would not be able to defend yourself from danger later in life. In which case, your genes and the genes of yours that are present in the troop genome would all be lost and extinct, so this would not be beneficial to your genes.
If you alerted the troop of the danger, you would most likely be killed by the lion, but your troop would have time to mobilize and defend itself from the threat. You might wonder how this benefits your genes if your genes just want to survive. But if you think of it, the members of your troop have similar genes to yours. They are members of what we consider to be family so you actually share the same genes. Because of this, your genes are actually present in the troop genome. Because they are present in the genome, your genes do not need you to protect them because they have already been passed on to others. It is for this reason that alerting the troop would be more beneficial. You would die, but your genes would live on in the members of your troop because your troop was saved from a threat. You’re being altruistic by doing this because you are sacrificing yourself for the protection of your troop.
This is how altruism relates to evolution. Altruism is actually the act of your genes being selfish, which sounds like the opposite of what the definition of altruism is. Altruism helped to drive evolution because it relied on genes taking steps of self-preservation. (This last paragraph was kind of wishy-washy and weird, so feel free to just scratch it if it confuses you)
