No individual gene alone makes a person gay, lesbian or bisexual; instead, thousands of genes likely influence sexual orientation, a massive new study of the genomes of nearly half a million people suggests.

Across human societies and in both sexes, between 2% and 10% of people report engaging in sex with a member of the same sex, either exclusively or in addition to sex with a member of the opposite sex, the researchers said. The biological factors that contribute to sexual orientation are largely unknown, but many scientists suspect that genetics plays a role, given that same-sex sexual behavior appears to run in families and is seen more often in identical twins than in fraternal twins.

But a precise genetic basis for sexual orientation has been elusive, largely  because scientists previously had relatively small groups of volunteers to investigate.

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