While hybrids in general can sometimes create a disagreeable mixture of fear and disgust, this is not always the case. Take for instance the boysenberry (a cross between the raspberry, blackberry, dewberry and loganberry) or the clementine (a cross between a mandarin and an orange). We have little trouble consuming such hybrids for our lunch.

Our apparent comfort with some hybrids does not stop at plants. Mules have never been a source of alarm, yet they are the offspring of a male donkey and a female horse. And what about the Liger, Tigon, Zonkey, Geep, or Beefalo?

Still, while hybrids in general can create a sense of foreboding, not all hybrids do, and it may be that mixing biology is most psychologically problematic when it comes to our own human DNA – and perhaps especially when it comes to mixing it with that of other animals.

We are not animals

One reason that human-pig hybrids are a source of anxiety is that they can conjure up a fear of our own death. The possibility that a pig could grow your next pancreas is a cogent reminder that humans are also animals, and this very biological reminder can create existential angst.

The notion that humans have souls, but animals do not, was (and still is for some) a popular belief. It gives us a sense of being superior, above or outside the biological order. Harvesting human hearts from goats can shatter this protective belief, leaving us feeling disgusted and dismayed.

Human-animal hybrids turn one’s mind to the inevitable fact that we will all be pushing up the daisies one day. By keeping thoughts of our animal nature at bay, we conveniently forget that we are nothing more than mortal biological organisms waiting to fertilise the fields.