Objection 1. It would seem that anger is not more natural than desire. Because it is proper to man to be by nature a gentle animal. But "gentleness is contrary to anger," as the Philosopher states (Rhet. ii, 3). Therefore anger is no more natural than desire, in fact it seems to be altogether unnatural to man.
Objection 2. Further, reason is contrasted with nature: since those things that act according to reason, are not said to act according to nature. Now "anger requires an act of reason, but desire does not," as stated in Ethic. vii, 6. Therefore desire is more natural than anger.
Objection 3. Further, anger is a craving for vengeance: while desire is a craving for those things especially which are pleasant to the touch, viz. for pleasures of the table and for sexual pleasures. But these things are more natural to man than vengeance. Therefore desire is more natural than anger.
On the contrary, The Philosopher says (Ethic. vii, 6) that "anger is more natural than desire."
I answer that, By "natural" we mean that which is caused by nature, as stated in Phys. ii, 1. Consequently the question as to whether a particular passion is more or less natural cannot be decided without reference to the cause of that passion. Now the cause of a passion, as stated above (Question 36, Article 2), may be considered in two ways: first, on the part of the object; secondly, on the part of the subject. If then we consider the cause of anger and of desire, on the part of the object, thus desire, especially of pleasures of the table, and of sexual pleasures, is more natural than anger; in so far as these pleasures are more natural to man than vengeance.
If, however, we consider the cause of anger on the part of the subject, thus anger, in a manner, is more natural; and, in a manner, desire is more natural. Because the nature of an individual man may be considered either as to the generic, or as to the specific nature, or again as to the particular temperament of the individual. If then we consider the generic nature, i.e. the nature of this man considered as an animal; thus desire is more natural than anger; because it is from this very generic nature that man is inclined to desire those things which tend to preserve in him the life both of the species and of the individual. If, however, we consider the specific nature, i.e. the nature of this man as a rational being; then anger is more natural to man than desire, in so far as anger follows reason more than desire does. Wherefore the Philosopher says (Ethic. iv, 5) that "revenge" which pertains to anger "is more natural to man than meekness": for it is natural to everything to rise up against things contrary and hurtful. And if we consider the nature of the individual, in respect of his particular temperament, thus anger is more natural than desire; for the reason that anger is prone to ensue from the natural tendency to anger, more than desire, or any other passion, is to ensue from a natural tendency to desire, which tendencies result from a man's individual temperament. Because disposition to anger is due to a bilious temperament; and of all the humors, the bile moves quickest; for it is like fire. Consequently he that is temperamentally disposed to anger is sooner incensed with anger, than he that is temperamentally disposed to desire, is inflamed with desire: and for this reason the Philosopher says (Ethic. vii, 6) that a disposition to anger is more liable to be transmitted from parent to child, than a disposition to desire.
Reply to Objection 1. We may consider in man both the natural temperament on the part of the body, and the reason. On the part of the bodily temperament, a man, considered specifically, does not naturally excel others either in anger or in any other passion, on account of the moderation of his temperament. But other animals, for as much as their temperament recedes from this moderation and approaches to an extreme disposition, are naturally disposed to some excess of passion, such as the lion in daring, the hound in anger, the hare in fear, and so forth. On the part of reason, however, it is natural to man, both to be angry and to be gentle: in so far as reason somewhat causes anger, by denouncing the injury which causes anger; and somewhat appeases anger, in so far as the angry man "does not listen perfectly to the command of reason," as stated above (4, ad 3).
Reply to Objection 2. Reason itself belongs to the nature of man: wherefore from the very fact that anger requires an act of reason, it follows that it is, in a manner, natural to man.
Reply to Objection 3. This argument regards anger and desire on the part of the object.
Source: Summa Theologica (New Advent)