In On Obligations 3.21-2, Cicero says:
If a person deprives his neighbour of something, and furthers his own advantage by another’s loss, such behaviour flies in the face of nature more than death or poverty or pain or anything which can affect our persons or our external possessions; for first and foremost it undermines the fellowship and alliance between members of the human race. Should the spirit move us to plunder or to assault our neighbour for our own profit, that fellowship between the human race which so closely accords with nature must inevitably be dismantled. Take this parallel: if each of our bodily limbs took the notion that it could flourish by appropriating the strength of the adjacent limb, then the whole of our body would inevitably be weakened, and would die. In the same way, if we each laid hold of the possessions of others, and seized from them all we could for our own profit, human fellowship and community would inevitably be overthrown. For though nature does not object to our opting to obtain for ourselves individually rather than for another what is needed for life’s necessities, she does not permit us to increase our own resources, wealth, and possessions by plundering those of other people. (Tr. P.G. Walsh)
P.G. Walsh notes in his translation (183-4) that a similar metaphor is used in a “fable” attributed to Menenius Agrippa, which he used to calm the enraged populace that had withdrawn from Rome during the Struggle of the Orders early in the history of the Roman Republic (494 BC):
The senate decided, therefore, to send as their spokesman Menenius Agrippa, an eloquent man, and acceptable to the plebs as being himself of plebeian origin. He was admitted into the camp, and it is reported that he simply told them the following fable in primitive and uncouth fashion. “In the days when all the parts of the human body were not as now agreeing together, but each member took its own course and spoke its own speech, the other members, indignant at seeing that everything acquired by their care and labour and ministry went to the belly, whilst it, undisturbed in the middle of them all, did nothing but enjoy the pleasures provided for it, entered into a conspiracy; the hands were not to bring food to the mouth, the mouth was not to accept it when offered, the teeth were not to masticate it. Whilst, in their resentment, they were anxious to coerce the belly by starving it, the members themselves wasted away, and the whole body was reduced to the last stage of exhaustion. Then it became evident that the belly rendered no idle service, and the nourishment it received was no greater than that which it bestowed by returning to all parts of the body this blood by which we live and are strong, equally distributed into the veins, after being matured by the digestion of the food.” By using this comparison, and showing how the internal disaffection amongst the parts of the body resembled the animosity of the plebeians against the patricians, he succeeded in winning over his audience. (Livy, History of Rome 2.32)
There is, Walsh says, most likely a Greek source behind the use of the image of the body for this or a similar purpose. Later, it is employed widely. To illustrate, Walsh cites (1) Paul in 1 Corinthians:
For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ.For in one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and all were made to drink of one Spirit.
For the body does not consist of one member but of many. If the foot should say, “Because I am not a hand, I do not belong to the body,” that would not make it any less a part of the body. And if the ear should say, “Because I am not an eye, I do not belong to the body,” that would not make it any less a part of the body. If the whole body were an eye, where would be the sense of hearing? If the whole body were an ear, where would be the sense of smell? But as it is, God arranged the members in the body, each one of them, as he chose. If all were a single member, where would the body be? As it is, there are many parts,5 yet one body.
The eye cannot say to the hand, “I have no need of you,” nor again the head to the feet, “I have no need of you.” On the contrary, the parts of the body that seem to be weaker are indispensable, and on those parts of the body that we think less honorable we bestow the greater honor, and our unpresentable parts are treated with greater modesty, which our more presentable parts do not require. But God has so composed the body, giving greater honor to the part that lacked it, that there may be no division in the body, but that the members may have the same care for one another. If one member suffers, all suffer together; if one member is honored, all rejoice together. (1 Cor. 12.12-26)
…and (2) Seneca, On Anger 2.31.7 (one inevitably recalls here the apocryphal tradition that Seneca and Paul corresponded with one another):
To injure one’s country is a crime; consequently, also, to injure a fellow-citizen – for he is a part of the country, and if we reverence the whole, the parts are sacred -consequently to injure any man is a crime, for he is your fellow-citizen in the greater commonwealth. What if the hands should desire to harm the feet, or the eyes the hands? As all the members of the body are in harmony one with another because it is to the advantage of the whole that the individual members be unharmed, so mankind should spare the individual man, because all are born for a life of fellowship, and society can be kept unharmed only by the mutual protection and love of its parts.