Scientists at the Salk Institute for Biological Studies developed the first human-animal hybrid, consisting of human cells growing inside a pig embryo.

Labeled a “chimera” after the ancient mythological multi-animal hybrid, the breakthrough is considered a first step toward growing human organs inside animals that could be harvested for organ transplants.

National Geographic reported: “The project proves that human cells can be introduced into a non-human organism, survive, and even grow inside a host animal, in this case, pigs.”

Despite the advancement, scientists share concerns of whether it will ultimately be successful. The magazine continued: “When scientists discovered stem cells, the master cells that can produce any kind of body tissue, they seemed to contain infinite scientific promise. But convincing those cells to grow into the right kinds of tissues and organs is difficult.”

Ke Cheng, a stem cell expert at the University of North Carolina at Chapel Hill and North Carolina State University, believes human organs grown from pig embryos would be rejected if put into human bodies.

Juan Carlos Izpisua Belmonte, a professor at the Salk Institute, “agrees, noting that it could take years to use the process to create functioning human organs,” National Geographic continued.

Other experts are concerned the development could lead to a breach of ethics. According to Tech Times, bioethics professor Insoo Hyun from Case Western Reserve University said that researchers “do not exactly know what effect these experiments will have in terms of animal suffering.” He also expressed concern that “scientists may be ‘flirting’ with a line of human dignity that they do not want to cross, even if the medical or scientific value is quite high.”