Sachs' first level of criteria is whether the human subconscious mind "inhibits" or "indulges" normal muscular activity; the second level of criteria begins with the physiological differences between the sexes of human beings as well as the physiological differences of the races that result from the basic modes of production. Although there are other factors contributing to the physiological differences of the races (e.g., climatic conditions, geography, etc.), and although "purely physiological reality" would not be free from the imprint of man's original social organization, Sachs was undoubtedly very wise in choosing this starting point.