Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 20

Empedocles is then in error when he says that those animals whichhave the most warmth and fire live in the water to counterbalancethe excess of heat in their constitution, in order that, since theyare deficient in cold and fluid, they may be kept in life by thecontrary character of the region they occupy; for water has lessheat than air. But it is wholly absurd that the water-animals shouldin every case originate on dry land, and afterwards change their placeof abode to the water; for they are almost all footless. He,however, when describing their original structure says that, thoughoriginating on dry land, they have abandoned it and migrated to thewater. But again it is evident that they are not warmer thanland-animals, for in some cases they have no blood at all, in otherslittle.The question, however, as to what sorts of animals should becalled warm and what cold, has in each special case receivedconsideration. Though in one respect there is reason in theexplanation which Empedocles aims at establishing, yet his accountis not correct. Excess in a bodily state is cured by a situation orseason of opposite character, but the constitution is bestmaintained by an environment akin to it. There is a difference betweenthe material of which any animal is constituted and the states anddispositions of that material. For example, if nature were toconstitute a thing of wax or of ice, she would not preserve it byputting it in a hot place, for the opposing quality would quicklydestroy it, seeing that heat dissolves that which cold congeals.Again, a thing composed of salt or nitre would not be taken and placedin water, for fluid dissolves that of which the consistency is dueto the hot and the dry.Hence if the fluid and the dry supply the material for all bodies,it is reasonable that things the composition of which is due to thefluid and the cold should have liquid for their medium [and, if theyare cold, they will exist in the cold], while that which is due to thedry will be found in the dry. Thus trees grow not in water but ondry land. But the same theory would relegate them to the water, onaccount of their excess of dryness, just as it does the things thatare excessively fiery. They would migrate thither not on account ofits cold but owing to its fluidity.Thus the natural character of the material of objects is of the samenature as the region in which they exist; the liquid is found inliquid, the dry on land, the warm in air. With regard, however, tostates of body, a cold situation has, on the other hand, abeneficial effect on excess of heat, and a warm environment onexcess of cold, for the region reduces to a mean the excess in thebodily condition. The regions appropriate to each material and therevolutions of the seasons which all experience supply the means whichmust be sought in order to correct such excesses; but, while states ofthe body can be opposed in character to the environment, thematerial of which it is composed can never be so. This, then, is asufficient explanation of why it is not owing to the heat in theirconstitution that some animals are aquatic, others terrestrial, asEmpedocles maintains, and of why some possess lungs and others do not.