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The honeybee, Apis mellifera, is one of the world’s most amazing animals. Honeybees are highly social, living in complex colonies in which individual bees cooperate and assume responsibility for specialized tasks that benefit the entire hive. In spite of a tiny brain that contains only a million neurons (the human brain contains 100 billion neurons), bees are able to perform intricate behaviors and communicate effectively with thousands of other bees that make up the hive. Each bee recognizes the odor of its own hive, as well as odors that signal alarm, indicate tasks to be performed, and distinguish the caste, age, and sex of other bees. Worker bees possess an extraordinary memory. On finding a clump of flowers that provide a rich supply of nectar, a worker bee returns to the hive and performs the waggle dance, in which it runs a figure eight on the side of the comb. The dance conveys information to other bees about the location of the food source, including the direction in reference to the angle of the sun and the distance from the hive to the source. A bee is able to recall as many as five different flower locations, including the direction and distance of each from the hive, landmarks along the way, and the time of day when the flower produces the most nectar.

Honeybees are not just objects of biological curiosity; they play a critical role in pollinating many important food crops, as well as providing honey and wax. Because of its agricultural and scientific importance, the honeybee was selected for sequencing by the National Genome Research Institute of the U.S. National Institutes of Health. The complete genomic sequence was published in 2006 and has provided a wealth of information about the behavior, neural function, ecology, and evolution of honeybees.

The honeybee genome consists of 10,157 genes that encompass about 236 million base pairs of DNA. On the basis of the genomic information, 36 genes have been identified that encode neuropeptides—brain proteins that affect behavior and memory. More than 3000 genes are active in a bee’s brain, and researchers have located regulatory regions that control the expression of many of these genes, including some that are important in the development of foraging behavior. Compared with other insects, honeybees also have more genes that encode olfactory receptors, which is consistent with their sophisticated chemical communication system.

The honeybee has long been associated with humans, but the precise evolutionary origin of honeybees was unknown until recently. With information from the genomic sequence, honeybee geneticists used single-nucleotide polymorphisms (SNPs, sites that vary in the base present at a single nucleotide) to study the evolutionary relationships between bees from different parts of the world. This study revealed that A. mellifera originated, not in Asia as was formerly thought, but in Africa. African populations subsequently expanded into Europe and Asia in two waves, one wave populating western Europe and another wave expanding into Asia and eastern Europe.

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European honeybees were introduced into North America by early European settlers, but some have been replaced in recent years by descendants of African “killer bees,” known for their aggressive stinging behavior. These bees were introduced into Brazil in 1956 and have subsequently spread northward to the United States. Analysis of SNPs of bees collected in the United States before 1990 showed that they possessed only European genes but, from 1993 to 2001, bees from southern Texas showed a transition to genes of predominately African ancestry.