Biocentrism (ethics)

• The scientists genetically altered the embryos to remove their ability to grow a kidney, then injected them with human stem cells.
• The embryos were then implanted into a sow and allowed to develop for up to 28 days.
• The resulting embryos were made up mostly of pig cells (although some human cells were found throughout their bodies, including in the brain).
• Such animals could be used for medical research or to grow organs for transplant, which could save many human lives.

Chimeras are only one challenge among many

• In June, scientists created “synthetic embryos” – lab-grown embryo models that closely resemble normal human embryos.
• Despite the similarities, they fell outside the scope of legal definitions of a human embryo in the United Kingdom (where the study took place).
• Like human–pig chimeras, synthetic embryos straddle two distinct categories: in this case, stem cell model and human embryo.
• In the past decade, we have also seen the development of increasingly sophisticated human cerebral organoids (or “lab-grown mini-brains”).

A new moral framework

• The confusion sparked by chimeras, embryo models, and in vitro brains shows these underlying categories no longer make sense.
• Read more:
  As scientists move closer to making part human, part animal organisms, what are the concerns?
• Should we count the proportion of human cells to determine whether a chimera counts as an animal or a human?

Moral status

• For example, utilitarian philosophers see moral status as a matter of whether a creature has any interests (in which case it has moral status), and how strong those interests are (stronger interests matter more than weaker ones).
• On this view, so long as an embryo model or brain organoid lacks consciousness, it will lack moral status.
• There are other accounts of moral status, and other ways of applying them to the entities stem cell scientists are creating.