In April, for the first time, a couple gave birth to a healthy baby conceived using a new technique that mixes the DNA from three people. This mitochondrial replacement technology seems to have eliminated the disease, the group that performed the procedure announced in September. The scientists and clinicians at the New Hope Fertility Center in Mexico were proud that it happened in their country.

That pride soon turned sour. Scientists and ethics societies elsewhere — who have spent years drawing up guidelines for such a procedure — responded to the surprise announcement with criticism. In interviews and at meetings, researchers and experts raised vague doubts about whether the New Hope team had properly informed their patients, or whether it had broken laws. They pointed out the number of back-alley, questionable stem-cell treatment clinics that exist in Mexico. The implication was clear: the group that did the research had not played by the proper rules, by which they meant the rules the experts themselves had agreed.

New Hope’s clinic in Guadalajara is inspected for quality by federal regulators, and the researchers say that an institutional review board (IRB) had approved the mitochondrial replacement project in accordance with federal law. “Why is an IRB in the UK better than ours in Mexico?” medical director Alejandro Chávez-Badiola asked Nature in an interview. “This is scientific chauvinism.”

In fairness, the bad impression was exacerbated by the New Hope clinic’s decision to announce its news through the popular media — complete with a rash comment about the lack of research scrutiny — and at a scientific meeting, rather than publishing in a journal. It is true, for example, that the procedure is impossible under current US stipulations. But insinuations that research is problematic purely because of where it is performed are outdated, damaging and elitist.

Stereotypes are not uncommon when researchers talk about those in a different country. They came into focus last year, for instance, when a group of Chinese scientists edited the DNA of a human embryo for the first time. Most reporters who asked around will have heard the same condescending statements about the supposed lower ethical standards in China. It is hard to believe that the same scientists do not make the same comments to colleagues and others.

History can introduce a similar bias. Countries that were denied access to antibiotics for decades during the cold war, such as Georgia, have years of data on the efficacy of phage therapy — killing bacteria with viruses found in the environment. The idea should work, but some infectious-disease specialists in countries such as the United States and the United Kingdom hesitate to consider the potential of phage therapy, largely because it is something that is done in former Soviet states and not in ‘modern’ medicine. So the cycle becomes self-sustaining, even in the face of rampant antibiotic resistance.

Assumptions writ large about science in a particular country harm relationships.

This is not the sort of criticism that shows up in opinion articles or in letters to journals. It is insidious and therefore hard to confront directly. But neither is it necessarily malicious or even intentional. Like any micro­aggression, it’s more likely to be implied, in meaningful statements along the lines of, “Well, it was in Russia, after all…”. It is dropped into casual conversation with colleagues or mentioned to reporters by way of explanation. It is impossible to challenge precisely because it is vague and implies ‘they don’t do things our way’.

There is, of course, a level of realism that should apply to the capabilities of any single group. Discussions need to be had about whether international accord should be reached in certain areas, such as the inviolable Declaration of Helsinki rules on human experimentation. And researchers should not shy away from demanding that researchers from any country be open about the ethical and scientific underpinnings of their work.

But assumptions writ large about science in a particular country harm relationships and risk creating a backlash. They are also unscientific in evaluating work on some basis other than merit. As a result, they risk hurting the openness that is necessary for international relationships to succeed.

To a large extent, these questions are in the eye of the beholder. Primate research is under legal threat in several European countries. Would critics attack European researchers who travel to the United States to continue their work, in the same way as researchers who travel to a country with fewer regulations on human embryo research?

For better or worse, legal, ethical and even scientific standards are a patchwork and likely to remain so. Many journals try to accommodate this by requiring that an author adheres to his or her own local laws and ethical standards. IRBs set specific protocols for human and animal research, for instance, on a case-by-case basis, in accordance with variables such as state regulations in the United States.

This patchwork demands international dialogue and an openness to achieving understanding and reaching common ground — none of which is helped by assumptions and veiled prejudice. Realizing what prejudices exist — conscious or not — and then considering whether they are valid for the work in question is a necessary step towards the fair evaluation of science.