Bogaert argues that understanding asexuality is of key importance to understanding sexuality in general. For his work, Bogaert defines asexuality as "a lack of lustful inclinations/feelings directed toward others," a definition that he argues is relatively new in light of recent theory and empirical work on sexual orientation. This definition of "asexuality" also makes clear this distinction between behavior and desire, for both asexuality and celibacy, although Bogaert also notes that there is some evidence of reduced sexual activity for those who fit this definition. He further distinguishes between desire for others and desire for sexual stimulation, the latter of which is not always absent for those who identify as asexual, although he acknowledges that other theorists define asexuality differently and that further research needs to be done on the "complex relationship between attraction and desire". Another distinction is made between romantic and sexual attraction, and he draws on work from developmental psychology, which suggests that romantic systems derive from attachment theory while sexual systems "primarily reside in different brain structures".