In the 1930s, with his wife Lyle, he made a worldwide survey of the distribution of blood types.

Boyd's signal contribution was to discover that human blood groups are inherited and not influenced by environment.

By genetic analysis of blood groups he hypothesized that human races are populations that differ by alleles.

On that basis, he divided the world population into 13 geographically distinct races with different blood group gene profiles.

In 1955, Boyd co-published the book Races and People with Isaac Asimov; they were both then professors at Boston University School of Medicine.