A prevalent error that is due to an incomplete knowledge of the facts of evolution is the belief that organs readily change or adapt themselves to the habits or environment of the individual. This is not true to the extent that it is ordinarily believed. Each individual has a certain limited power of adaptation. He may develop his lungs to a greater breathing capacity, or train his hand for certain skilled work, but these particular acquired habits of the individual are not inherited.
Evolution of the race proceeds by the law of natural selection. Thus, if those who are born with great vigor and strong lungs are enabled to live where their weak-lunged neighbors will die, the result will be that their offspring, having greater lung capacity, will form a race with increased lung capacity. But the individual training of the lungs, or of the hand, or of any other organ of the body, will not of itself change the inherited tendency, or, to use a common term of the scientist, the germ-plasm of the race.
Organs and functions will change or become evolved by natural selections; that is, where it is a matter of life and death. But where the selective agencies depend upon other things, an organ may be used or abused for thousands of successive generations, and yet the natural inherited organ of the new-born child will be identical in development and function to that of the remote ancestor.
Acquired characteristics are not inherited
There are abundant proofs that so called "acquired characteristics" are not inherited. Were acquired characteristics inherited, Chinese women would be born with small feet and the babies of the Flathead Indians would inherit the flat head which has for generations been produced by binding a flat stone on the soft skull of the new-born infant.
In the light of this fact we may understand how it has been possible for man to live through the varying dietetic habits and customs that the constantly changing ideas and tastes of civilization have thrust upon his physical organism. Each individual has transmitted to his offspring the same type of digestive organs and functions that he himself inherited from his remote anthropoid ancestors.
Meaning of expression "natural" diet
Thus, such terms as "back to nature," "natural diet," etc., only mean to the food scientist the habits of life or the dietary which is most suited to the unperverted physical organism of man. They do not imply the meaning that is popularly given to the term, of casting aside all the habits and customs of civilized man, but only the adapting of these customs to the inherited physiological organism of man.
Indeed, science may actually improve upon primitive conditions, and still not be inconsistent with the requirements of the inherited physiological machine. No intelligent man will dispute the advantage of a house in a snowstorm. Yet the house is artificial. It is not "natural" in the sense that the term is commonly used.