A scientific journal sparked a Twitter firestorm when it rejected two female scientists’ work partly because the paper they submitted did not have male co-authors.

Evolutionary geneticists Fiona Ingleby and Megan Head collaborated on a study of gender bias in academia. They found that women with a PhD in biology published fewer articles than their male peers, which the authors argued showed gender bias,reports Times Higher Education.

When the women submitted the study to peer-reviewed journal PLOS ONE, a male reviewer came back with some pretty shocking suggestions.

“Not only did the review seem unprofessional and inappropriate, but it didn’t have any constructive or specific criticism to work on,” Ingleby told Science Insider.

The women’s reviewer also suggested the publishing gap could exist because middle-aged female scientists preferred spending time with their children to working in a lab.

“Perhaps it is not so surprising that on average male doctoral students co-author one more paper than female doctoral students, just as, on average, male doctoral students can probably run a mile race a bit faster than female doctoral students,” the reviewer added, according to Times Higher Education.

PLOS ONE has since apologized, removed the reviewer from its database, and submitted the paper to be reviewed again, the journal said.