Gemara

71a: 'Behemah' includes Tahor Chayos regarding Simanim (split hooves and chewing the cud show that they are Kosher).

92a (Ula): These are the 30 Mitzvos that the Nochrim accepted on themselves. They keep only three - they do not sell human flesh in the market...

(Mishnah): The Gid ha'Nasheh of a bird is permitted.

This is because its Kaf (end of the thigh bone) is not round.

Questions (R. Yirmeyah): If a bird has a round Kaf, what is the law? If an animal's Kaf is not round, what is the law?

Does it depend on each particular case, or on the species in general?

These questions are unresolved.

Kesuvos 60a (Beraisa): The camel... it is Tamei", but milk of humans is permitted.

Suggestion: Perhaps human milk is permitted because milk of some animals is permitted. The blood of every animal is forbidden, so also human blood should be forbidden!

Rejection: "It" is forbidden, but human blood is permitted.

(Rav Sheshes): It is not even a Mitzvah (mid'Rabanan) to refrain.

Krisos 20b (Beraisa) Suggestion: Perhaps "v'Chol Dam Lo Sochlu" includes even blood of people, Beitzim, grasshoppers, and fish!

Rejection: "La'Of vela'Behemah" - birds and Behemos have light Tum'ah (Tum'as Ochlim) and severe Tum'ah (Neveilah), they are (initially) forbidden but can become permitted (through Shechitah), and they are meat. The Isur of Dam applies (only) to everything with all these laws.

We exclude human blood, for people have only severe Tum'ah, and blood of fish and grasshoppers, which are totally permitted (without Shechitah).

Rishonim

Rambam (Hilchos Ma'achalos Asuros 2:3): Even though man is called "Nefesh Chayah", he is not a Chayah with a hoof, therefore, there is no Lav, and one is not lashed for human flesh or milk. However, an Aseh forbids it, for the Torah lists seven Kosher Chayos and says "these you may eat", i.e. but not other Chayos.

Rebuttal (Ra'avad): If so, why did the Gemara say that there is not even a Mitzvah (mid'Rabanan) to refrain?

Ramach: I did not find the Rambam's Drashsah in the Sifra or Sifri. We have no source to distinguish the flesh from the blood and milk.

Gra (YD 79:4): The Rambam relies on Toras Kohanim, which says that human milk is not Tamei, i.e. it is totally Tahor (permitted), but it says that there is no Lav for human flesh. This implies that an Aseh forbids it. Kesuvos 60a mentioned only blood and milk, for they are totally permitted.

Mishneh l'Melech: The Rashba and Ramban say that there is no Isur Ever Min ha'Chai regarding people. The Ritva disagrees.

Rosh (Kesuvos 5:19): We permit human milk only if it separated (from the breast), but not to nurse (except for a nursing baby), lest one come to suckle from a Tamei animal. The same applies to human flesh. One may not cut from a person and eat. Since it is not normal to eat it, people will confuse this with a Tamei animal and come to eat from Tamei animals. If it separated, it is permitted.

Ramban (Vayikra 11:3 DH veha'Rav): The Rambam says that "Osah Sochelu" excludes human flesh. There is an Isur Aseh to eat human flesh or milk. Chazal did not expound this. Perhaps the Rambam learns from Toras Kohanim (4:4), which says that there is no Lav for human flesh or milk. The Rambam inferred that an Aseh forbids it, i.e. "Osah Sochelu". This is wrong. The Gemara explicitly says that there is no Mitzvah to refrain from human milk and blood. If human flesh were forbidden, we would apply 'whatever comes from a Tamei (species) is Tamei (forbidden).' The Gemara says that there is no Isur for blood of a Sheretz or person. This refers to Basar Min ha'Chai (flesh that separated from a living being). A Mes is Asur b'Hana'ah.

Rashba (1:364): The flesh, milk and blood of people have the same law. The Toras Kohanim totally permits them. Some texts of the Gemara say 'perhaps only milk is excluded (from the Heter), but not blood.' Just like the milk and blood are permitted, also the flesh is. Whatever the Torah did not forbid is totally permitted. We needed a verse to permit, for otherwise we would have learned from the verse that forbids camel's milk, or from a Kal va'Chomer from Tamei animals. Once the Torah permitted, it is totally permitted.

Question: Human flesh should require Shechitah! Ever Min ha'Chai, Basar Min ha'Chai, Tereifah and Neveilah should apply!

Rebuttal (Rashba): Not everything permitted requires Shechitah. The Gemara says that grasshoppers are totally permitted, e.g. they do not need Shechitah. Do not say that they require Nechirah (cutting the Simanim lengthwise), but this is not considered anything. If so, they are like fowl according to the opinion that the Torah does not require Shechitah for fowl, only Nechirah, yet birds' blood is forbidden!

Question: Grasshoppers do not require Shechitah or Nechirah because it says about them "Asifah" (gathering), like for fish, like Bahag says (but there is no source to permit human flesh without Shechitah or Nechirah)!

Answer (Rashba): Even fish are permitted (without Shechitah or Nechirah) only because the Torah mentioned gathering them together with Shechitah of animals.

Question: Rav Yitzchak ben Pinchas, who holds that the Torah does not require Shechitah for fowl, needed a source. He did not say that since there is no verse obligating Shechitah, it is permitted without Shechitah!

Answer (Rashba): A verse equates birds to Chayos, so we would have thought that they require Shechitah like Chayos. Likewise, we needed to say that gathering fish is like Shechitah for them, because they are written in a verse that discusses Shechitah of animals. If not, we would not need a source to permit them without Shechitah. According to the opinion that Koy is a species unto itself, we require Shechitah because the Torah made it like a Behemah in every way, e.g. its blood, Chelev and Gid ha'Nasheh are forbidden (Kerisus 25b). If not for this, we would not require Shechitah at all; this was not merely to require two Simanim, unlike a bird.

Question: If so, why did the Gemara (ibid.) need to permit human blood because people lack light Tum'ah? We should say that people are totally permitted, because they do not require Shechitah!

Answer (Rashba): People are not totally permitted. The Gid ha'Nasheh is forbidden, for people have a round Kaf. The Gemara was unsure about a bird with a round Kaf, or an animal with a Kaf that is not round. If the proper species has a round Kaf, it is forbidden. Gid ha'Nasheh is Asur due to an episode with a person, so surely man's Gid ha'Nasheh is forbidden. The Gemara permitted grasshopper blood because they are totally permitted. I.e. not only they do not require Shechitah, rather, also their Gidim and Chelev are permitted, and they do not require even Nechirah. There is no Isur at all.

Rashba: Since people do not require Shechitah, the Isur of Tereifah and Neveilah do not apply. However, presumably there is a Mitzvah to refrain from the flesh, since we forbid an adult (or child who was weaned) to suckle milk that did not separate.

Ran (Kesuvos 24b DH Tanu): The Ramban said that if human flesh were forbidden, we should have said that the Torah excluded blood from the Isur of blood, but not from the Isur of flesh. Dam Sheratzim is not considered blood, but if one was warned for it for (eating) Sheratzim, he is lashed (Kerisus 21b). If human flesh were forbidden, we would say the same about human blood. Our Gemara says that there is no Mitzvah to refrain (if it did not separate). He rejected the Rambam.

Ran: The Beraisos are difficult. The Beraisa brought in the Gemara mentions milk and blood, but not flesh. The Beraisa in Toras Kohanim mentions milk and flesh, but not blood. The latter Beraisa brings two verses to exclude - "Zeh Tamei", but human milk is not Tamei. "Tamei Hu", (but there is no Lav for human flesh or milk). The Beraisa in the Gemara mentioned only "Hu". The Beraisa in Toras Kohanim initially says "Zeh Tamei", but human milk is not Tamei. I.e. it is totally permitted. It concludes ...there is no Lav for human flesh or milk, which connotes that there is an Isur. Also, the Beraisa in our Gemara excludes human blood from "Hu", and in Kerisus (20b) we exclude it for "la'Of vela'Behemah." Therefore, I explain that the Beraisos totally permit human blood and milk. There is no Lav for human flesh, but there is an Isur Aseh. The Beraisa in Toras Kohanim suggested that a Lav forbids human flesh and milk. It did not mention blood, for the Beraisa in Kerisus, which is also in Toras Kohanim, already excludes blood. It answered "Zeh Tamei", but human milk is not Tamei. I.e. there is a Lav only for the species listed. There is another Mi'ut (exclusion), "Tamei Hu", but others are Tahor and totally permitted. The first Mi'ut is for human flesh, which was already forbidden by an Isur Aseh. We exclude it from a Lav. The latter Mi'ut totally permits human milk, for which we have no source to forbid at all. If there were only one Mi'ut, we would exclude only milk, and a Lav would forbid human flesh. Since there are two Mi'utim, we say that the first excludes flesh from a Lav, and an Isur Aseh remains. The latter Mi'ut totally permits human milk. Even though it concludes 'there is no Lav for human flesh and milk', they are not the same. Rather, the latter Mi'ut teaches that there is no Lav also for flesh, and all the more so regarding milk. Alternatively, the first Mi'ut totally permits human milk. The Torah overrides the Kal va'Chomer to forbid (human milk) with a Lav. Therefore, it is totally permitted. The Seifa of the Beraisa discusses also flesh, so it could not say that it is Tahor (and totally permitted). Therefore, it said that there is no Lav. The Beraisa in the Gemara discusses human (milk and) blood. We already know that there is no Lav for blood. It initially suggested that a Kal va'Chomer teaches that human milk is Tamei, and there is a Lav. We answered that "Tamei Hu" totally permits. It is more reasonable to apply this (only) to milk, which is more lenient. Even though we know that there is no Lav for blood, perhaps it is Asur, for it comes from Asur flesh, and whatever comes from Tamei is Tamei. Also, the Mi'ut is only from the Isur of blood, but it is still forbidden like the flesh, like we say about Dam Sheratzim. We conclude "(Tamei) Hu", which totally permits, even though the flesh is forbidden. This supports the Rambam's Perush.

Poskim

Rema (YD 79:1): The Torah forbids eating human flesh.

Taz (3): This is like the Rambam. The Rosh forbids mid'Rabanan. It is astounding that the Tur and Shulchan Aruch did not bring this argument.

Mishbetzos Zahav: All agree that the Torah forbids the Gid ha'Nasheh of people. One cannot (use the Safek of whether the Torah forbids human flesh, to) make a Sefek-Sefeka, for the Rema ruled that it is mid'Oraisa. The Mishneh l'Melech brings that the Ritva holds that Ever Min ha'Chai applies. If so, the Beraisa excludes Basar Min ha'Chai of people, but not Ever Min ha'Chai. All agree that the Torah forbids Hana'ah from flesh of a Mes. There are opinions about Hana'ah from flesh of a dead Nochri.

Bach (DH Kasav): The Ran and Magid Mishneh hold like the Rambam. The Rema derived that the Rosh holds like the Ra'avad, since he said 'it is not normal to eat human flesh', i.e. but there is no Isur. Even so, he rules like the Rambam.