Why do selfish genes not always make us selfish individuals?
Because this question is categorized under science, I am going to answer it based on the genetic basics that were originally laid out by Gregor Mendel rather than discussing Richard Dawkins's book The Selfish Gene, which is somewhat controversial and has been described as a mixture of philosophy and science.
Genes come in pairs, and often they are not identical. There are two versions to a gene called alleles. One allele says blue eyes, and the other allele says non-blue eyes, but the gene is still the eye color gene. In that particular example, the blue eyes gene is the recessive allele, and the non-blue-eyes gene is dominant. If the dominant allele is present in the gene pair, then a person will phenotypically show the dominant trait. The only way to phenotypically express the recessive trait is to have both recessive alleles.
It is the same with the hypothetical "altruism" gene. If you have the dominant version of the trait, then you are not selfish. Let's use the letter "A" for the dominant, non-selfish allele and the letter "a" for the recessive, selfish allele.
A person that is genotypically AA will not be selfish. A person that is genotypically aa will be selfish. They have both recessive alleles. A person that is genotypically Aa will not be selfish. They have the gene for selfishness, but they are not a selfish person because the dominant, non-selfish gene is present.
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