The advances in biotechnology have given rise to a discussion concerning the strong emotional reaction expressed by the public towards biotechnological innovations. This reaction has been named the ‘Yuck-factor’ by several theorists of bioethics. Leon Kass, the former chairman of the President's council on bioethics, has appraised this public reaction as ‘an emotional expression of deep wisdom, beyond reason's power fully to articulate it’.1 Similar arguments have been forwarded by the Catholic Church, several Protestant denominations and the Pro-Life movement. Several (...) bioethicists have, however, opposed the idea of a disgust-based morality.2Recent findings in cognitive science support the view that the strong negative emotions people often experience when faced with biotechnological ideas are not expressions of inner wisdom. The negative emotions may rather be the result of a cognitive violation the biotechnological innovations easily cause.Due to their evolutionary background, people have certain automatic and quick cognitive tendencies routinely used for categorizing and reasoning about nature, usually termed ‘folk biology’. Biotechnological processes like hybridisation and cloning clearly violate several of the cognitive rules people naturally apply for the explanation and categorization of their natural environment.As the cognitive tendencies routinely applied to the explanation of biological world are violated, an emotional response of fear, disgust and of something unnatural being underway is easily provoked. It is suggested in this paper that the reason behind the Yuck-factor is not a deep inner wisdom, but a violation of natural human cognitive tendencies concerning the biological world. (shrink)