Pig-human hybrids are just evolutionary story-telling

Human cells integrated into pig and cow embryos


Excerpt: "Those scientists experimented with several different chimeras, including rat cells injected into mouse embryos, rat cells injected into pig embryos, and human cells injected into pig embryos with varying levels of success. The mouse chimeras developed gall bladders made entire of rat cells, even though evolution took rat gall bladders away. The rat-pig chimeras didn’t work at all.

But let’s focus on the pig-human chimeras for now. Last year, we reported that these same scientists were injecting human stem cells, the “blank” cells that can turn into other cell types, into 1500 developing pigs when they were just proto-embryo balls of cells called blastocysts. This new research reports the results of the implantations. Initially, the human cells seemed to attach and grow, but once the pig fetuses had implanted into the uterine walls of the mother pigs and grown for four weeks, the researchers only measured a few traces of human cells."

My comment: Integrating human stem cells into pig embryos has nothing to do with assumed evolutionary relationship between them. Only 0.001% of human stem cells managed to survive in pig embryos during this short petri dish experiment. Why?

1. Stem cells lack epigenetic markers that are needed for cellular differentiation. These pluripotent stem cells are at open state ready for differentiating into any kind of tissue type.
You can read about how removing the epigenetic markers from cells affect their state from here.

2. The experiment was made using petri dishes as platforms for pig embryos. This means they were not affected by the most significant regulatory mechanism, microRNAs. These non coding RNA molecules are crucial elements in the cellular differentiation. You can read about their function from here. 

3. Several mechanisms during pig reproduction will make the embryo to develop into a pig. Too much of foreign stem cells in the embryo will cause the pregnancy to fail. This is ensured by this kind of mechanisms.

Human-pig hybrids are just funny fairy tales. However, I will not read them to my kids. Don't get misled.

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