Sir James George Frazer (1854–1941).  The Golden Bough.  1922.

§ 3. Attis, Adonis, and the Pig
PASSING now to Attis and Adonis, we may note a few facts which seem to show that these deities of vegetation had also, like other deities of the same class, their animal embodiments. The worshippers of Attis abstained from eating the flesh of swine. This appears to indicate that the pig was regarded as an embodiment of Attis. And the legend that Attis was killed by a boar points in the same direction. For after the examples of the goat Dionysus and the pig Demeter it may almost be laid down as a rule that an animal which is said to have injured a god was originally the god himself. Perhaps the cry of “Hyes Attes! Hyes Attes!” which was raised by the worshippers of Attis, may be neither more nor less than “Pig Attis! Pig Attis!”—hyes being possibly a Phrygian form of the Greek hy¯s, “a pig.”   1
  In regard to Adonis, his connexion with the boar was not always explained by the story that he had been killed by the animal. According to another story, a boar rent with his tusk the bark of the tree in which the infant Adonis was born. According to yet another story, he perished at the hands of Hephaestus on Mount Lebanon while he was hunting wild boars. These variations in the legend serve to show that, while the connexion of the boar with Adonis was certain, the reason of the connexion was not understood, and that consequently different stories were devised to explain it. Certainly the pig ranked as a sacred animal among the Syrians. At the great religious metropolis of Hierapolis on the Euphrates pigs were neither sacrificed nor eaten, and if a man touched a pig he was unclean for the rest of the day. Some people said this was because the pigs were unclean; others said it was because the pigs were sacred. This difference of opinion points to a hazy state of religious thought in which the ideas of sanctity and uncleanness are not yet sharply distinguished, both being blent in a sort of vaporous solution to which we give the name of taboo. It is quite consistent with this that the pig should have been held to be an embodiment of the divine Adonis, and the analogies of Dionysus and Demeter make it probable that the story of the hostility of the animal to the god was only a late misapprehension of the old view of the god as embodied in a pig. The rule that pigs were not sacrificed or eaten by worshippers of Attis and presumably of Adonis, does not exclude the possibility that in these rituals the pig was slain on solemn occasions as a representative of the god and consumed sacramentally by the worshippers. Indeed, the sacramental killing and eating of an animal implies that the animal is sacred, and that, as a general rule, it is spared.   2
  The attitude of the Jews to the pig was as ambiguous as that of the heathen Syrians towards the same animal. The Greeks could not decide whether the Jews worshipped swine or abominated them. On the one hand they might not eat swine; but on the other hand they might not kill them. And if the former rule speaks for the uncleanness, the latter speaks still more strongly for the sanctity of the animal. For whereas both rules may, and one rule must, be explained on the supposition that the pig was sacred; neither rule must, and one rule cannot, be explained on the supposition that the pig was unclean. If, therefore, we prefer the former supposition, we must conclude that, originally at least, the pig was revered rather than abhorred by the Israelites. We are confirmed in this opinion by observing that down to the time of Isaiah some of the Jews used to meet secretly in gardens to eat the flesh of swine and mice as a religious rite. Doubtless this was a very ancient ceremony, dating from a time when both the pig and the mouse were venerated as divine, and when their flesh was partaken of sacramentally on rare and solemn occasions as the body and blood of gods. And in general it may perhaps be said that all so-called unclean animals were originally sacred; the reason for not eating them was that they were divine.   3