This month, scientists gathered at the National Academy of Sciences in Washington to talk about Crispr, a new method for editing genes. In the past couple of years, the technique has become so powerful and accessible that many experts are calling for limits on its potential uses — especially altering human embryos with changes that could be inherited by future generations.

Among the scientists describing recent advances was one of Crispr’s pioneers, George Church of Harvard Medical School. In the midst of his presentation, packed with the fine details of biochemistry and genetics, Dr. Church dropped a bombshell.

In a typical experiment, scientists use Crispr to alter a single gene. But in recent work with pig cells, Dr. Church and his colleagues used Crispr to alter 62 genes at once. The researchers hope that this achievement may someday make it possible to use pig organs for transplantation into humans.

But the experiment also raises a deeper question: Could scientists someday alter complicated human traits by manipulating many genes at once?