Because of a unique method of reproduction
, individual ant
workers (ants and bees are collectively called hymenopteran
s) in a single hive are unusually closely related genetically: they must
in every case be at least 50% genetically identical
Background: Ordinary sexual reproduction
To understand the unique system utilized by the hymenopterans, one must first understand the more usual system used by everyone else. In human beings, for example, as in most sexually reproducing life forms, every individual, male and female, has twice as many chromosomes as he or she needs: one copy of each from the father, one from the mother. It is said that each individual is "diploid" - that is, holding, as it were, a doubled set of genetic material. When forming sex cells (eggs or sperm) the original "duplicated" "normal" (diploid) cells split by a process called meiosis so that each of the two resulting sex cells (either male sperm or female egg) are "haploid:" that is, having only one copy of each chromosome. When a haploid sperm meets a haploid egg, the resultant embryo is back to normal diploid status, having received one copy of each chromosome from each parent.
The sex cells are not made by splitting material from the original father on one side from the material from the mother on the other: the chromosomes are shuffled, as it were, so that eggs and sperm cells produced by a single individual are diverse amongst themselves.
Ants and bees vary this strategy. Females, whether queens (reproductive females) or workers (sterile females) are diploid, just as we are, having developed from fertilized eggs. However, males develop from unfertilized eggs, and are not diploid, but haploid: that is, each male, and each cell of the male, has only one copy of each chromosome, not two. Sperm are not produced by meiosis, but directly, and every sperm cell produced by a particular male is identical to every other sperm cell produced by him, since he has only the one copy of each chromosome; each sperm carries his entire set.
Since he developed from an unfertilized egg, he has no father. Since only the unfertilized eggs of his mate will develop into males, he will never have a son.
When the male ant or bee mates with a queen, she saves his sperm for her reproductive lifetime, since he will die very soon thereafter. All of her female children will result from the union of her (diverse) eggs with the identical sperm of the male. Thus all her daughters will be very unusually closely related, sharing fully half their genetic material (from the father) and probably more.
Evolutionary biologists speculate that this unusual degree of close relationship explains the unusual self-sacrifice exhibited by worker ants and bees. By sacrificing themselves for their sisters, these workers are in reality, to an unusual degree, furthering the success of their own genome.