Most advanced lab-grown human embryos prompt a pressing question: Are they getting too real?
The stem cells were no more than a week old when scientists moved them from their slick-walled plastic wells into ones lined with a thin layer of human endometrial tissue. But in that time, the cells had multiplied and transformed, organizing themselves into semi-hollow spheres. Per the instructions of the chemical cocktail in which they’d been steeping, they were trying to turn into embryos.
Video cameras captured what happened next: The balls of cells rotated until they were cavity-side-up, before finally touching down and grabbing onto the endometrial layer, a cellular proxy for a human uterus. Days later, when the scientists dipped paper test strips into the wells, pink lines appeared. Their Petri dishes were pregnant.
