Chimp human chimeras
Continuing from mouse-humans (below):
Let’s clarify our terminology.
The cow-human “hybrid embryos” are actually chimeras. A chimera contains cell lines that descend from two different zygotes, two different eggs fertilized separately. For instance a person can be born as a chimera combining two sibling embryos. In the cow-human experiments, the two embryos were from a human and a cow.
Alternatively, an embryo can be mosaic. We try to reserve the term mosaic for individuals containing genetically distinct cell lines that originated from a common zygote. For instance (rarely) a mutation occurs early in development; then all subsequent descendents of that cell have a distinct genotype, usually with respect to one gene or trait (or one chromosome). A special case is normal X-inactivation, which causes all human females normally to be mosaic for cell type. I would quibble that females are not really mosaic, at the DNA level (since the inactivated DNA still exists, and could be reactivated) but that is one use of the term.
“Hybrid” should really be reserved for genetic combination of DNA within one zygote derived from two different species or populations; but alas the term is now used more broadly, often including chimeras.
What if someone makes a chimeric embryo containing chimp and human cells?
Suppose it develops longer than the cow-human did?
What about a human 16-cell embryo containing one chimp cell?
Or a chimp embryo with one human cell?
Would either have rights of personhood?
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Ultraphyte 
This suggests that being human can be localized to a specific gene or cell and I don’t believe that this is so. I think that instead we need to look at how human the resulting behavior (outcome) is. Further, trying to establish taxonomy rules for what is a human being would need to encompass other possibilities such as machine/human hybrids as it is conceivable that nanotechnology can come up with an ‘artificial cell’ that performs exactly the same functions as the ‘natural cell’. Computers are a good analogy for this argument. The active components (cells) of a computer have changed/evolved from glass encased electronic tubes -> solid state semiconductors -> etched silicon/gold wafers, yet they are all ‘computers’.
Don’t humans already contain bits of other animals within their genome?
Yes, that’s an interesting point that the human genome already contain lots of genes in common with animals, and many genes transferred from animals by viruses. Genetically, it becomes a semantic question, what is a “human” gene.
The chimera question is rather different in that you would have an entire genome composing cells of tissues, even entire organs of (for example) a human origin within the body of a different kind of animal. So would that portion have a human character? For instance what if you made a chimp with a human voicebox?
Perhaps the chimera morale question has already been addressed: The Vacanti mouse has a human outer ear growing on/out of its back. Despite its clearly human organ, I don’t believe anyone considers that this mouse is less mouse and more human, or a supermouse.
I guess this is one of those questions where my answer is, “is there any answer good enough to justify running the experiment, either in thought or in real life?”
When I think of how little of a person qualifies as a person, I find myself thinking more of the current generation of military vets who are multiple amputees with other massive traumatic injuries, rather than cellular chimeras. This is not to compare the two conditions or to in any way to suggest that a wounded human is any less a human. The point is that asking how little of a human still qualifies as human is one of those questions that provokes misery when it’s asked. It’s better to ask if the question is worth asking, rather than answering it.
Moreover, playing with chimp/human hybrids or chimeras is not a way to get at the rights for chimpanzees or humans.
The reason scientists would think of running such experiments (and do run others related) is to learn something about the human body that could cure genetic diseases. One in twenty babies are born with a birth defect. Some of these defects, adding up to millions of people, cause pain and hardship for millions of people. For example 1 in1000-2000 births has congenital deafness. Others have laryngeal disorders. We could learn more about how the larynx develops by observing it in a monkey. I’m not advocating this personally, but a research foundation funded by people with such disorders, and their families, might ask, why are we not doing this research to come up with treatments and prevention of deafness and mutism?