Birds do it, bees do it - well, perhaps bees don't do it quite like birds and people do and scientists have found one piece of the puzzle.
The international team of researchers has discovered the gene that allows male bees to have no father.
"We found the section of honeybee genome responsible for the differentiation between female and male," Mr Kim Fondrk of the University of California Davis said, who worked on the study.
The discovery helps explain a lot of things that are strange about bees and may help experts preserve endangered bee populations so they can keep the busy insects pollinating crops and wild flora.
Writing in the latest issue of the journal Cell, Mr Fondrk and colleagues in Germany and Norway said the responsible gene is called complementary sex determiner, or csd.
Csd has in 19 alternative versions, called alleles.
Female bees have two copies of csd which are always different alleles - males have only one copy.
About one-fifth of animal species including all ants, bees and wasps use a similar system of sex determination, but the actual genes and mechanisms involved are not well understood.
Mr Fondrk said it helps explain their complex social systems.
"There are three castes - the queen, who is the egg layer and mother of all the bees in the hive," he said.
In the wild she mates only once with a male to get the two sets of genes that go to all of her female offspring.
"Then the workers are females and they do all the work.
"They are the ones that sting, they are the ones that bring the honey in too."
Then there are the males - the drones.
"Drones just have a sexual function," Mr Fondrk said.
They also do not inherit a second set of genes from a father bee.
They are half-clones of the queen.
Understanding why this happens genetically can help bee breeders, Mr Fondrk said.
When bees are inbred to select desired traits, eggs can accidentally be fertilized with two copies of the same version of csd.
These eggs develop into sterile males.
Worker bees find and kill these sterile male larvae and inbred honeybee colonies can die out.
"This problem has haunted bee breeding since the 1940s," Mr Fondrk's colleague at UC Davis, Robert Page, said in a statement.
"As we understand more, there will be ways to get around this problem."