What is a chimera? You can be a chimera and not know it. A chimera is the product of two embryos in one individual. A person with this "complaint" is absolutely normal and can live most of their lives without knowing they are "afflicted". They are usually diagnosed in a medical examination.
A case in point was a woman who was found not to be the mother of one of her sons. Tests indicated that genetically the child was not hers. Further test, however, showed that she a chimera and the child was hers.
Human chimeras are not common. In some species they are more the norm. In dahlia anemones, for example, it was noticed that their larvae were fused together like conjoined twins. Out of a batch of 27,169 young, 120 were visibly chimeric. Most of these died. The true chimeras live don undetected. It is believed that 90 per cent of young can be affected There may an evolutionary benefit from this. It appears that chimeras grow faster and are more aggressive than normal larvae. Dahlia anemone are certainly at the halfway point between colonial organisms and individuals.