Why people in warm places have a smaller stature and less strength and boldness than those in cold places.
One inquires further why people in warm places have a smaller stature and less strength and boldness than those in cold places, when, however, the opposite thing occurs in other animals and in plants.
And it seems that naturally this ought not to be the case. Because heat, together with moisture, is the principle of growth. Therefore, there will be more growth in what is generated in warm and moist places than in cold ones.
Moreover, strength and audacity arise from heat. Thus choleric people are bold due to the heat. Therefore, for the same reason, people in warm places will have more strength and boldness.
Moreover, this is the case in other animals, like the lion. Therefore, it will also be the case in the human.
The opposite is evident, thanks to Avicenna. For he says that in Germany and Flanders and Poland, which are cold places, the people have a larger stature and are bolder. It is even commonly said that people of warm regions are naturally timid and incapable of war.
One must reply that things are different for the human, plants, and other animals. For human seed is naturally warm and moist, and this is why it liquefies and is consumed by the heat in a warm region, and as a result people of smaller stature are generated there. But the plant's seed is cold and hard, and [its life] cannot be extended except by an abundant heat, and this is why plants grow more, are nourished more, and age more in warm places than in cold, and they also have a larger size. And it is the same for the seed of brute animals in comparison to the human.
Moreover, strength and properly ordered audacity arise from a natural and tempered heat. But such heat abounds more in people in a cold region, because the heat is strengthened and focused by the region's cold and this is why they are stronger and better ordered for audacity and attack with discretion and deliberation, because the cold remits the force of the heat to some extent. But in people in a warm region the heat is dispersed and, if it is intensified, this occurs per accidens, by means of an accidental and disordered heat. Thus, if they are bold, this is inordinate, and they withdraw in a rush and quickly. Such are the French, who want to do wondrous things at the beginning and in the end accomplish nothing, and people like this are called hardi [bold] in French.
Through this a solution to the arguments is apparent.
Whether youth can be restored.
One inquires further into the renewal of age, and first, whether youth can be restored.
And it seems not. Age follows upon complexion. Thus, to the extent that the natural heat consumes more of the radical moisture, age approaches more quickly. But when the natural moisture is consumed, it cannot be restored. Therefore, neither can youth be renewed.
Moreover, if age could be renewed, then it would either be returned to a prior state, and if this occurs, then life could be preserved in perpetuitywhich is false, and therefore so is its premise. Or, it could turn into a better state, and then the same will follow as before, or into a worse one, and then the renewal of age would not follow but more deterioration.
Moreover, age follows upon the complexion, because in the first age the complexion is warm and moist, as it is in children, and in the second age it is warm and dry, as it is in youths, and in the third it is cold and moist, and in the fourth age cold and dry. Therefore, the same situation exists among members generated from the warm and moist, or the cold and dry, as exists for age following on the complexion and, as a result, for life. But members generated from spermatic moisture cannot be regenerated. Therefore, neither can the age following such a complexion be renewed.
The Philosopher says the opposite. For he says that some animals alter their old age [senectus], as when serpents change their skins and birds change their feathers, etc.
One must reply that age is of two kinds: one is natural and one is accidental. Natural age arises from the consumption of the natural or radical heat and moisture, and this age cannot be renewed just as the natural heat and moisture cannot be regenerated or restored. The other age is accidental, and it arises from accidental causes and from the consumption of the nutrimental heat and moisture, and this is an apparent age. And in this age two things come to be considered. For either the consumption of the radical moisture accompanies the consumption of the nutrimental moisture, and in this respect age [ aetas] cannot be renewed. Or it does not accompany it clearly and manifestly, but only in an unseen manner, almost imperceptibly, and in this respect it can be renewed. And this very often occurs in serpents and birds. For serpents are cold. Thus many superfluous, viscous humors are generated in them. And this is why when they lie hidden, in winter, nature falls back upon these humors, digesting them, and as a result a certain empty spot, as it were, is left between the flesh and the skin where the humors had been. Thus nature was previously dulled and blunted by humors like this, and this is why, once they have been digested, it is strengthened and then they come out of their entire old skin and put on a new one, which nature generates in them.
And it is the same for the birds. For birds are hot and dry. Thus in old age there abounds in them a great deal of melancholy matter generated by the burning from which their feathers are generated. And this is why their feathers grow longer in them and, due to their old age, are less solidly attached to the skin. And this is why the feathers fall out in old birds, as is clear in cranes, which are sometimes captured plucked, almost nude. But because matter still remains in them, this is why new feathers are regenerated and birds like these appear to grow younger. Nevertheless, because a continual voiding of natural heat and the consumption of the radical moisture occur in them, this is why they are in reality growing older even though they appear to be growing younger.
Thus one must reply to the question that in reality youth cannot be renewed, and the arguments reveal this. Nevertheless it can be renewed in an apparent way, and the Philosopher understands this.
-  In what follows, senectus is, for the sake of clearer English, sometimes translated simply as "age," but see the one instance in which A. does indeed use aetas.