The idea of creating hybrid creatures has tantalized humankind for a long time - imagine CatDog, but in real life. In the first step towards bringing a hybrid animal to life, scientists in China successfully injected monkey stem cells into two pig embryos, which were born through surrogate sows. The two piglets that were born are officially part pig, and (a very small) part monkey.

However, the ultimate goal of creating chimeras is not to make pigs that can swing from trees (or any other weird combinations); it is to grow human organs inside animals, which can be used for transplant procedures. Although access to healthy organs will no doubt save many lives, the idea of a human-animal chimera comes with many ethical issues.

We don't need to ponder these dilemmas just yet, because we're only at the beginning of this interesting journey. The scientists injected monkey cells into 4,000 pig embryos, but while 10 piglets were born from these embryos, only two of the piglets had monkey cells. The monkey cells were able to be tracked in the embryos and piglets by altering the monkey cells to become a fluorescent green color. The scientists could then scan the cells and organs for fluorescent cells.

But the two chimera piglets are nowhere near being half monkey half pig: at this stage, they are 99% pigs, with one in 1,000 to one in 10,000 cells being a fluorescent monkey cell.

While the amount of monkey cells inside the pigs is very small, it is larger than the amount of human cells that have ever been inside an animal embryo. In 2017, scientists created human-pig chimeras that had one human cell to every 100,000 pig cells. The embryos were only allowed to develop for a month due to ethical reasons (mainly the concern that the embryo could develop human-like consciousness).

For now, the focus is on animal chimeras and scientists hope to increase the number of monkey cells inside pig embryos. This could be the start of some very strange new animals, but it'll take a lot of time before we see half-half animals. Until then you'll have to be satisfied with your one-species pet.