Representation in Animal Research

Despite widespread assumptions of scientific objectivity, biomedical research continues to suffer from critical representation gaps. A striking example is the routine exclusion of female animals—especially rodents—from preclinical studies. Historically justified by concerns over hormonal variability, this practice has contributed to a crisis in translation: treatments that appear effective in homogeneous animal studies often fail in human trials.

Monika Piotrowska’s 2023 essay in the Journal of Medical Ethics argues that this lack of diversity in animal models is not just a scientific flaw but an ethical failing. Homogenised test populations, often made up entirely of inbred male mice (particularly the C57BL/6 strain), produce findings with limited generalisability. This not only undermines scientific outcomes, but also results in animal suffering without corresponding human benefit. Piotrowska calls for animal ethics committees to treat representativeness as a core ethical concern and to challenge the design of overly standardised studies.

Other research supports this call. Studies by Beery (2018) and Smarr & Kriegsfeld (2022) show that female rodents do not introduce greater variability than males—challenging the primary rationale for their exclusion. Further, a 2023 study from Harvard demonstrated that female mice often exhibit more consistent behaviour than their male counterparts. These findings invalidate outdated assumptions and reinforce the need to incorporate sex-based biological variation into study designs.

Improving the diversity of animal subjects—by including variation in sex, age, genetic background, and environment—is crucial for generating representative source data. It is also an ethical imperative: without it, we risk perpetuating ineffective science and inequitable healthcare outcomes.

Diversity and inclusion for rodents: how animal ethics committees can help improve translation by Monika Piotrowska. You can also read a related blog post by the same author Diversity and inclusion initiatives for laboratory animals.

Inclusion of females does not increase variability in rodent research studies by Annaliese Beery.

Female mice exhibit less overall variance, with a higher proportion of structured variance, than males at multiple timescales of continuous body temperature and locomotive activity records by Smarr and Kriegsfield

Mouse spontaneous behavior reflects individual variation rather than estrous state by Levy et al. You can also read a press release here: Findings reveal that despite hormonal fluctuations, female mice exhibit more stable exploratory behavior than their male peers by Catherine Caruso.