Scientists have been growing “minibrains” for a few years now.

Cerebral organoids are not the sentient brains in a jar you might know from cartoons. They’re tiny, “lentil”-size groups of cells that are tricky to make, and so far best resemble very, very young brains, like that of an embryo in the first few months of pregnancy.

They’re being used, with great promise, to study the development and effects of diseases like Zika and Alzheimer’s. More and more researchers are adapting the method to their studies, and a new article from STAT zeroes in on groups that are working on implanting human organoid tissue into the brains of mice and rats. Work like this seems to many people a lightning rod for the ethical questions that the idea of lab-grown brains—however far off—raise.

According to Madeline Lancaster of Cambridge University, who began making cerebral organoids seven years ago and is a pioneer in the field (her Twitter handle is @MiniBrainLab), those questions are far off. The question remains about what happens once scientists are able to grow bigger brains. As SUNY Buffalo neuroscientist Michal Stachowiak explained to Newsweek, if organoids grow closer to the size of full human brains, even the size of an infant’s brain, they’d start to require oxygen and nutrients to keep themselves going. In human brains, all that comes from blood and the network of vessels that delivers it. But once you’ve gone from a tiny “brain in a dish” to a larger organ with more and more of the stuff inside our skulls, it’s hard not to wonder if some lines should be drawn.

“We are a really long way from getting the kind of vascularization to get anywhere close,” Lancaster told Newsweek. “The entire tissue engineering field has been trying to do this for decades, for 30 years.” And, she says, the only tissue that’s been successfully grown and grafted onto a living creature is cartilage, which is not vascularized.

Lancaster, whose work is focused on using organoids for their original purpose—understanding what happens in the brain during the stages of development before birth—speculates that any real progress in that area will probably happen when progress is made in other areas of tissue engineering, and then translated to organoids.

Still, as the STAT article puts it, an ethicist would argue that “not a problem now” doesn’t mean “never a problem.”