One of the most important facts which stand out in a comparison of the physical traits of men and women is that man is a more specialized instrument for motion, quicker on his feet, with a longer reach, and fitted for bursts of energy; while woman has a greater fund of stored energy and is consequently more fitted for endurance. The development of intelligence and motion have gone along side by side in all animal forms. Through motion chances and experiences are multiplied, the whole equilibrium characterizing the stationary form is upset, and the organs of sense and the intelligence are developed to take note of and manipulate the outside world. Amid the recurrent dangers incident to a world peopled with moving and predacious forms, two attitudes may be assumed--that of fighting, and that of fleeing or hiding. As between the two, concealment and evasion became more characteristic of the female, especially among mammals, where the young are particularly helpless and need protection for a long period. She remained, therefore, more stationary, and at the same time acquired more cunning, than the male. In mankind especially, the fact that woman had to rely on cunning and the protection of man rather than on swift motion, while man had a freer range of motion and adopted a fighting technique, was the starting-point of a differentiation in the habits and interests, which had a profound effect on the consciousness of each. Man's most immediate, most fascinating, and most remunerative occupation was the pursuit of animal life. The pursuit of this stimulated him to the invention of devices for killing and capture; and this aptitude for invention was later extended to the invention of tools and of mechanical devices in general, and finally developed into a settled habit of scientific interest. The scientific imagination which characterizes man in contrast with women is not a distinctive male trait, but represents a constructive habit of attention associated with freer movement and the pursuit of evasive animal forms. The problem of control was more difficult, and the means of securing it became more indirect, mediated, reflective, and inventive; that is, more intelligent.