Scientists have long dreamed of the prospect of being able to grow human organs inside animals for patients needing crucial transplants. Now, they may be one step closer to making this a reality.

Scientists at the Salk Institute for Biological Studies in La Jolla, California, have created a human-pig hybrid, marking the first ever time that embryos of two distantly related species have been produced. Though the goal of creating human organs like hearts, kidneys and livers is a long way off, the project has been named a milestone first step. One in three people die every day in the UK because of a lack of suitable replacement organs being available for them.

The embryo has been named a chimera – specifically an interspecies chimera – after the monstrous hybrid creature in Greek mythology. The mythical name brings up major ethical concerns over the study, including the potential for animals with humanised brains, and for these hybrids to be released into the wild.

Then there is the question of human versus animal identity, which asks whether by raising the biological contribution of human stem cells in an animal means altering them into a human-like animal – with human rights.

For the time being, the US National Institutes of Health have placed a moratorium (temporary prohibition of activity) on funding for these kind of projects while risks are being assessed.

The primary funding for this project came from private Spanish sources.