The categorisation of male and female laboratory animals in terms of "gender".

In reports of scientific investigations the terms “sex” and “gender” are frequently used interchangeably in spite of longstanding acceptance that each refers to different qualities of an individual’s sexuality [20]. While sex is generally acknowledged as determined by biological characteristics that, in most cases, reasonably clearly define an individual as “female” or “male” in terms of their chromosomes, hormones, genitals and secondary sexual characteristics, gender is a human social construction pertaining to qualities of “masculinity” or “femininity”. Gender accordingly refers to the way in which an individual is defined and seen in terms of the psychological, social and cultural factors that determine it [10] i.e. gender attribution. It also reflects the extent to which individuals define themselves as masculine or feminine i.e. gender identity. Although there is almost complete consistency between sex and gender in how most individual humans are classified, notable exceptions do occur. For example, because of genital ambiguities, mismatches between biological sex and gender development may occasionally occur as a result of inappropriate gender assignment at birth [11]. Likewise, transsexualism can be viewed as a conflict between gender identity and gender assignment independent of biological sexual characteristics [10]. Therefore, in biomedical/behavioural research where the biological substrates of genetically determined sex are important, reference to the gender of participants has little meaning. This applies particularly to research involving laboratory animals. Given that the concept of gender is a construction relating to the social attribution of and personal identification with human qualities of femininity and masculinity, it is absurdly anthropomorphic to classify animals in this way. And yet in recent years there has been a significant increase in the number of research reports which refer to the gender (rather than sex) of experimental animals.