Complex sentence: The green-beard effect is a hypothesis used in evolutional biology to explain altruism between individuals and is linked to the gene-centered view of evolution which postulates that natural selection will increase the frequency of those alleles whose phenotypic effects ensure their successful replication.
Split into simpler sentences: The green-beard effect is a hypothesis used in evolutionary biology to explain altruism between individuals. It is linked to the gene-centered view of evolution, which suggests that natural selection will increase the frequency of those alleles whose phenotypic effects ensure their successful replication.