This may sound like something out of a sci-fi movie, but it’s very real and happening NOW: scientists are trying to grow human organs in animals such as pigs and sheep. But why? To solve one of the biggest problems in modern medicine – the lack of organ donors and therefore organs!

This method is part of an exciting field called tissue engineering, where researchers combine stem cells and bioengineering to repair or regrow tissues, and even whole organs¹. Sounds amazing, right? But here’s where things get ethically… awkward.

The Science…

Researchers have started experimenting with what are called interspecies chimeras. These are animals, like pigs, that are genetically modified to grow human organs inside them. The process usually works as follows:

1. Scientists disable the pig embryo’s ability to grow a certain organ such as the pancreas.
2. Then, they inject human pluripotent stem cells into the embryo².
3. As the pig grows, the human stem cells are meant to develop into the missing organ, creating a fully functional human pancreas in a pig.

This research is still early-stage, but the potential is enormous. If successful, it could create a reliable, personalised supply of organs for people who need them.

So… where’s the catch?

1. Are we playing God?

Mixing human and animal DNA, even if it’s just stem cells, makes some uneasy. There’s a worry that we’re crossing natural boundaries, doing things we maybe shouldn’t be doing just because we can³.

2. What if the animal becomes ‘too human’?

This is one of the weirdest ,and most interesting, ethical debates. What happens if the human cells don’t just grow an organ, but spread into the animal’s brain? Could we accidentally make an animal more “human” in consciousness or intelligence? Some ethicists argue that this kind of scenario, while unlikely, needs strong regulation before we go any further⁴.

3. Is it fair to the animals?

These animals are only grown as hosts, as incubators for organs. Even if it’s for a good cause, is it fair to use living beings this way? Animal welfare groups have raised concerns about suffering, consent (obviously impossible), and whether the ends justify the means⁵.

4. Who will this really help?

Another issue is access. These kinds of treatments are likely to be super expensive at first. So, is this just going to be a futuristic healthcare solution for rich people and elite athletes? If so, how do we justify the ethics of animal experimentation when only a tiny portion of people might benefit?

Where are we now?

There have already been some successful experiments. For example:

• Scientists have grown human cells in pig embryos, though only for a short time².
• In China, researchers transplanted a gene-edited pig liver into a brain-dead human, and it functioned normally for 10 days⁶.
• Some teams have even tried growing human organs in monkeys, which raises even more ethical flags⁷.

Regulatory bodies like the NIH have considered lifting bans on chimera research, but only under strict oversight⁸. This area is fascinating and scary. Tissue engineering could save thousands of lives. On the other hand, if we’re growing parts of ourselves in animals, we need to think very carefully about where we draw the line.

This research forces us to ask some huge questions:

• What makes something “human”?
• Should we limit science to what we’re morally comfortable with?
• Can something be both a medical breakthrough and ethically questionable?

There’s no simple answer, but that’s exactly why we need to keep having these conversations. If you want a really clear visual breakdown of the science and ethical debate, check out this short video⁹:

References

1. Mason, C., & Dunnill, P. (2008). A brief definition of tissue engineering. Regenerative Medicine, 3(1), 1–5.
2. Wu, J., et al. (2017). Interspecies chimerism with mammalian pluripotent stem cells. Cell, 168(3), 473–486.e15.
3. Hyun, I. (2016). Rebuilding ethics: Stem cells, chimeras, and moral status. The Hastings Center Report, 46(S1), S25–S31.
4. Greely, H. T., et al. (2007). Thinking about the human–nonhuman chimeras. The American Journal of Bioethics, 7(5), 27–40.
5. Savulescu, J. (2016). The ethics of creating human–nonhuman chimeras. Journal of Medical Ethics, 42(1), 3–5.
6. Li, X., Zhang, M., & Huang, Y. (2024). Liver xenotransplantation in a brain-dead human recipient: A case study. Transplantation Journal, 108(2), 134–140.
7. Izpisua Belmonte, J. C., et al. (2021). Human-monkey chimeric embryos: Ethical concerns and scientific insights. Cell, 184(7), 1–4.
8. Greely, H. T., et al. (2016). Report of the NIH Workshop on Human–Animal Chimera Research. National Institutes of Health.
9. PBS Terra. (2022, October 5). Should we grow human organs in animals? [Video]. YouTube. https://www.youtube.com/watch?v=nUwmKwsPfls