Theosophy, by Rudolf Steiner, , at sacred-texts.com
One learns to know the body of man through the bodily senses. And the way of observing it can differ in no way from that by which one learns to know other objects perceived by the senses. As one observes minerals,
plants, animals, so can one observe man also. He is related to these three forms of existence. Like the minerals he builds his body out of the materials in nature; like the plants he grows and propagates his species; he perceives the objects around him and, like the animals, forms on the basis of the impressions they make his inner experiences. One may therefore ascribe to man a mineral, a plant, and an animal existence.
The difference in the structure of minerals, plants, and animals corresponds with these three forms of existence. And it is this structure, this shape which one perceives through the senses, and which alone one can call body. But the human body is different from that of the animal. This difference everybody must recognize whatever may be his opinion in other respects regarding the relationship of man to animals. Even the most radical materialist who denies all soul will not be able to avoid agreeing with the following sentence which Carus utters in his "Organon der Natur and des Geistes". "The finer, inner construction of the nervous system, and especially of the brain, remains as yet an unsolved problem to the
physiologist and the anatomist; but that this concentration of the structure increases more and more in the animal, and in man reaches a stage unequaled in any other being, is a fully established fact, a fact which is of the deepest significance in regard to the spiritual evolution of man, of which, indeed, we may frankly say it is a sufficient explanation. Where, therefore, the structure of the brain has not developed properly, where its smallness and poverty show themselves, as in the case of microcephali and idiots, it goes without saying that one can as little expect the appearance of original ideas and of knowledge, as one can expect propagation of species in persons with completely stunted organs of generation. On the other hand, a strong and beautiful construction of the whole person, especially of the brain, will certainly not in itself take the place of genius, but it will at any rate supply the first and indispensable requirement for higher knowledge." Just as one ascribes to the human body the three forms of existence, mineral, plant, animal, one must now ascribe to it yet a fourth, the distinctively human form. Through his mineral form of existence man
is related to everything visible, through his plant-like form of existence to all beings that grow and propagate their species, through his animal existence to all those that perceive their surroundings, and by means of external impressions have inner experiences. Through his human form of existence he constitutes, even in regard to his body alone, a kingdom by himself.