Scientists in London investigating human sexuality have found that the brains of gays and lesbians have structural and functional differences from those of straight people. Lesbians appear to have a lower proportion of grey matter in their brains than straight women, giving their brains a more 'male-like' structure, reports the UK's Times newspaper. The brains of gay men appear to have structural similarities to those of heterosexual women. They also exhibit the same powerful response as straight women to the sex hormones released in male sweat. The research comes amid growing interest in how variations in brain structure are linked to human behaviour. It is known, for example, that the greater size of male brains and the higher proportion in females of grey matter – the cells that process signals from the senses – are caused partly by sex hormones released during foetal development. These hormones are also involved in determining sexual orientation. The new research suggests sexual orientation is largely programmed into people early in life; however other studies have shown a person's life experiences can lead to structural brain changes.