The Natural History Museum in London boasts that it holds “the world’s most important natural history collection”. But, while excited families queue this half-term to explore its exhibits on volcanoes, dinosaurs and creepy-crawlies, one of its scientists has revealed a fatal flaw among the 29m animal specimens it holds for research purposes.

A study led by NHM researcher Dr Natalie Cooper has uncovered discrepancies in gender representation, with significantly more male specimens than female.

Cooper found the same male skew in four other leading natural history museums around the world and the NHM reports that her work reflects “a growing awareness across all areas of science of underlying sex biases in data and their repercussions in the wider world”. And repercussions there will be.

At a time of unprecedented importance for scientists to understand ecosystems and work to protect endangered animals, any research that has used these kinds of collections is likely to be inaccurate. For instance, chemicals found in specimens are analysed to learn about their migration patterns, but some species have gender-specific diets.

“It’s very clear from a scientific perspective that we would want to study males and females,” says writer and feminist campaigner Caroline Criado-Perez, who won the Royal Society Science Book prize this year for Invisible Women: Exposing Data Bias in a World Designed for Men.

While it may not be surprising that Charles Darwin and other male, mutton-chopped 19th-century specimen collectors were a bit sexist, the study has discovered that the bias remains unchanged among more recent collections. Criado-Perez doesn’t find this surprising “when you look at everything else in the world and see this is what we do when we collect data on anything”.

The study, which focused on birds and mammals, found that the worst discrepancy lay in the individual specimens on which a species description is based – known as type specimens, with 25% of female birds represented, and 39% of female mammals. It would be easy to fix this, notes Cooper, but “people don’t seem to have bothered to take that option”.

The scientific world and wider society sees male as the default setting, says Criado-Perez. So it’s not about evil, misogynistic specimen collectors deliberately ignoring female examples. “We all have this bias of seeing male as the neutral, the default, the baseline – those are the words that get applied to men. Even in clinical data sets you’ll find male represented as the baseline and female represented as an effect.”

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But the result is bad science. “You would think that if you care about the procreation of certain species, you would need to know what both sexes are like,” she adds. “And if you care about accurately studying and representing the world, which of course is the whole point of science.”

Criado-Perez hopes this is the start of a new movement. “This is a revolution that needs to happen in science. Women are dying because we don’t know how female bodies respond to all sorts of medication, because the diagnostic tests were developed in male bodies.”

The NHM’s website advertises the fact that its collections are used by the scientific community to “answer key questions about the past, present and future of … life on Earth”. Do we want the same to happen in the natural world?