“There have been claims that the species are ‘just too close, and the results too disturbing to contemplate’”“Theoretically the human cells could have the potential to end up contributing to any part of the animal, and to any degree”Human-animal hybrids are no longer the stuff of science fiction. Aisling Brennan investigates.[br]THE idea of human-animal hybrids is something that has fascinated humanity for millennia. In fact, you’d be hard pressed to find any culture or mythology (or fantasy novel) which doesn’t explore this intrigue with creatures like the minotaur, merfolk, winged-men, or werewolves. And while figures like the Minotaur, Bastet, Chu Pa-chieh or Pan are cool to imagine, how does the part animal/part human idea translate into modern science?To gain insights into biology and disease, scientists have created and used animal models containing human cells for decades. A common example is growing a human tumour inside of a mouse. Organisms resulting from this sort of genetic manipulation are often referred to as ‘hybrids’ or ‘chimeras’. Specifically, the terms refer to an organism that ‘contains cells or tissues from more than one species’.More modern research takes a slightly different approach, with the idea being to inject ‘potent’ human stem cells into an early-stage animal embryo when it itself is only a few dozen cells in size. Theoretically the human cells could have the potential to end up contributing to any part of the animal, and to any degree.What even is the point of this research? The answers are widespread and staggering. Imagine being able to grow a human liver or heart in the body of a pig for example. Organ waiting lists could be cut in half, transplant rejection rates could similarly shrink, and a whole new way to farm human transplant organs would be opened up.While there is definitely interest within the scientific community to pursue these fields of study, various government and ethics bodies make sure that there are limits and rules imposed as to how that research occurs and how far it can go.As science has progressed, and fields like stem-cell research and gene-editing techniques have become more and more refined, we’ve come closer than ever before to the edge of some of these ethical concerns.The result is groups and panels trying to find a careful balance between advancing knowledge and science and an ethical (and political) disaster that could result in a lot of public backlash.In August 2016, it was reported that the U.S. National Institute of Health (NIH) plans to lift the funding ban on research creating human-animal hybrids, which had been placed in September 2015.This moratorium prevented funding for experiments involving injecting human stem cells into animal embryos. While such experiments were already underway in the U.S., none of the animals had been brought to term out of ‘scientific caution’. Furthermore, the scientists working on the project (at the Salk Institute and at Stanford University) said that the foetal animals would have only contained at most a small proportion of human cells.Going forward, the NIH said it would form a special committee to oversee funding of human-animal projects, a move which in and of itself could raise questions of political interference in science. It also tried to firm up its restrictions on some of the ‘scariest’ of possibilities resulting from this research.The NIH expressed wishes to expand an existing regulation that forbids funding for any research combining human cells and early ape or monkey embryos. There have been claims that the species are ‘just too close, and the results too disturbing to contemplate’.Another restriction is planned to explicitly bar any of these hybrids from being allowed to reproduce. The main risk named in such an occurrence is the, extremely remote, possibility that two chimeras could mate and produce a human foetus, which could be theoretically possible if their sperm/eggs were human.While this situation unfolds, it’s interesting to think about all of the breakthroughs that are possible, and the progressions that are feared.