Philo

And God says, he “who slays Cain shall suffer sevenfold” (Gen. 4:15). But I do not know what analogy this real meaning of this expression bears to the literal interpretation of it, “He shall suffer sevenfold.” For he has not said what is to be sevenfold, nor has he described the sort of penalty, nor by what means such penalty is excused or paid. Therefore, one must suppose all these things are said figuratively and allegorically; and perhaps what God means to set before us here is something of this sort. The irrational part of the soul is divided into seven parts, the senses of seeing, of smelling, of hearing, of tasting, and of touch, the organs of speech, and the organs of generation. If, therefore, any one were to slay the eighth, that is to say, Cain, the ruler of them all, he would also paralyze all the seven. (Det. 166b-168b).

Philo in Bruce Corley, Biblical Hermeneutics (Nashville: Broadman and Holman, 2002), 62.