The term "instinct" in psychology was first used in the 1870s by Wilhelm Wundt. By the close of the 19th century, most repeated behavior was considered instinctual. In a survey of the literature at that time, one researcher chronicled 4,000 human "instincts," having applied this label to any behavior that was repetitive. In the early twentieth century, there was recognized a "union of instinct and emotion". William McDougall held that many instincts have their respective associated specific emotions. As research became more rigorous and terms better defined, instinct as an explanation for human behavior became less common. In 1932, McDougall argued that the word 'instinct' is more suitable for describing animal behaviour, while he recommended the word " for goal directed combinations of the many innate human abilities, which are loosely and variably linked, in a way that shows strong plasticity. In a conference in 1960, chaired by Frank Beach, a pioneer in comparative psychology, and attended by luminaries in the field, the term 'instinct' was restricted in its application. During the 1960s and 1970s, textbooks still contained some discussion of instincts in reference to human behavior. By the year 2000, a survey of the 12 best selling textbooks in Introductory Psychology revealed only one reference to instincts, and that was in regard to Sigmund Freud's referral to the "id" instincts. In this sense, the term 'instinct' appeared to have become outmoded for introductory textbooks on human psychology.