A natural chimera is the opposite of a ramet, i.e. this is an individual whose body is formed by cells and tissues, derived from two or more genetically different organisms. Chimeras are regularly encountered in some plants. For example, the body of strangling fig tree, which, from an external viewpoint, looks like a single plant, is frequently formed by the combining and intergrowth of tissues belonging to several plants sprouting from a group of seeds that were transported to the host tree by bird droppings. The formation of chimeras is again a result of ecological causes. Under certain conditions, it is advantageous, i.e. increases the chance of survival of the organism, when genetically unrelated individuals, finding themselves in close proximity, do not compete together, but rather cooperate and together rapidly form the body of an organism that is capable of producing progeny. Amongst fig trees, the reason could be that the host tree is only a temporary resource and, if the ficus is not capable of rapidly utilizing it, i.e. climbing up its trunk to the sun, sooner or later it will die and, together with it, its parasite. Thus, in a certain sense, the fig tree is racing against time. If it does not form a sufficiently strong body fast enough, its host will die, either through natural causes or could even be killed by some other fig tree. The parasite would thus lose the opportunity of climbing up to the light, forming a massive crown with reproductive organs and producing enough seeds. Chimerism is encountered to a certain degree in other organisms, including humans. It has been observed that 8% of fraternal twins have chimeric blood, i.e. that part of the blood elements in the body of the individual are derived from the other twin. The professional literature contains cases where one the body of individual contained islands of tissue consisting entirely of maternal cells. Chimerism in humans is sometimes suspected of leading to serious defects, which could be true, e.g., in the development of autism (Pearson 2002).