Is human flesh a kosher food?
Please provide both modern and classical sources.
The Rambam writes (Hilchos Machalos Asuros 2:3):
האדם--אף על פי שנאמר בו "ויהי האדם, לנפש חיה" (בראשית ב,ז), אינו בכלל מיני חיה בעלת פרסה; לפיכך אינו בלא תעשה. והאוכל מבשר האדם או מחלבו, בין מן החי בין מן המת--אינו לוקה. אבל אסור הוא בעשה, שהרי מנה הכתוב שבעת מיני חיה ואמר בהן "זאת החיה אשר תאכלו" (ויקרא יא,ב)--הא כל שהוא חוץ מהן, לא תאכלו; ולאו הבא מכלל עשה, עשה הוא.
With regard to humans: Although [Genesis 2:7] states: "And the man became a beast with a soul," he is not included in the category of hoofed animals. Therefore, he is not included in the [above] prohibition. Accordingly, one who partakes of meat or fat from a man - whether alive or deceased - is not liable for lashes. It is, however, forbidden [to partake of human meat] because of the positive commandment [mentioned above]. For the Torah [Leviticus 11:2] lists the seven species of kosher wild beasts and says: "These are the beasts of which you may partake." Implied is that any other than they may not be eaten. And a negative commandment that comes as a result of a positive commandment is considered as a positive commandment.
[As a side point - if you stick your hand into a pot of boiling soup do you need shishim? I remember seeing an answer somewhere that taste does not come out of something that is alive..]
Tl;dr According to most Rishonim, humans are not included in the Torah’s prohibitions against eating non-kosher animals, and there is no inherent prohibition against eating human flesh. However, there may be rabbinic issues with doing so. There is no unanimous consensus among later authorities.
Rabbi Dov Linzer writes:
Is human flesh kosher? Halakhah does not classify human beings as animals (if it did, they would be non-kosher, as they do not have split hooves or chew their cud). As humans are not included in the Torah’s prohibitions against eating non-kosher animals, it would follow that there should be no prohibition against eating flesh taken from a living human being. This is the position taken by most Rishonim, including Raavad (on Rambam, Ma’akhalot Asurot 3:4), Tosafot (Ketuvot 60a, s.v. yakhol), Ramban, Rashba and Ran (on Ketuvot 60a), and Rosh (Ketuvot 5:19). Rosh and Rashba qualify this and state that there would be a mitzvat prosh, a rabbinic requirement to separate oneself from this, either because it is repulsive (this seems to be the point of Rashba, Responsa 1:364), or because of concerns of marit ayin, when it would look like one is eating non-kosher meat (Rosh 5:19, quoted in Taz, YD 79:3).
In contrast to these more lenient positions, Rambam rules that while human beings are not “non-kosher,” they are also not “kosher;” one who eats human flesh transgresses the positive Biblical mitzvah “These are the animals that you shall eat,” which is understood to mean “the only meat you may eat is meat which is categorized as kosher” (Rambam, Ma’akhalot Asurot 2:3). Shulkhan Arukh does not rule on this matter but Rema rules like Rambam that, “It is Biblically forbidden to eat human flesh” (YD 79:1). Although many poskim adopt Rema’s strict ruling, other poskim continue to treat the matter as unresolved or even rule like the Rishonim who are lenient (see Taz YD 79:3, Pri Hadash 79:6, and Darkhei Teshuvah 79:15).
 Another related question is whether there is an obligation to bury parts of the human body that have fallen off or been removed during a person’s lifetime. This could include amputated limbs and organs that have been surgically removed, as well as an embryo after a miscarriage or the placenta after a live birth (in these last two cases there is a question of whether we view these as part of the woman’s body or not; in the case of miscarriage, whether the fetus or embryo requires burial for its own sake). In the case of a limb (ever min ha’hai), Rav Moshe Feinstein (Iggrot Moshe YD 3:141) is of the opinion that there is a mitzvah of burial while other poskim (Noda Bi’Yehudah Tinyana, no. 209 and Tzitz Eliezer 10:25, chapter 8) state that there is no mitzvah of burial per se, but that care must be taken to prevent kohanim from coming in contact with it. All poskim agree that in the case of an internal organ or a placenta after live birth, which is not considered a limb and not a source of tumah, there is no mitzvah of burial or a need to dispose of it in any particular way (see Iggrot Moshe, ibid., final paragraph, and Tzitz Eliezer, ibid., par. 9).
 The law would be different regarding flesh taken from a dead body as deriving benefit from a corpse is prohibited. See Avodah Zarah (29b), Ramban Ketuvot (60a, s.v. hakhi garsinan), Rambam, Avel 14:21, Shulkhan Arukh YD 349:1, Shakh YD 79:3).
 Vayikra 11:2
 Ra’ah (Ketuvot 60a, s.v. katav ha’rav) and Ritva (Ketuvot 60a, s.v. uli’inyan basar) also state that it is forbidden to eat flesh taken from a human. They argue that it is Biblically forbidden, derived from the prohibition of eating the meat of non-kosher animals. Ritva adds that it should also be forbidden on the basis of eiver min ha’hai, since other than fish and locusts no meat is permitted without shehitah. Responding to this argument, Rashba states that there is no prohibition of eiver min ha’hai or basar min ha’hai in a case where no shehitah has been mandated (in other words, it is no different than fish and locust). See Teshuvot Ha’rashba (1:364) and Ramban, Commentary on Torah, Vayikra 11:3, and also Arukh Ha’shulkhan YD 79:11-12.
Rabbi Gil Student writes:
There are at least four different opinions on the subject.
The Ramban says that when the Gemara learns that eating blood is permissible, it also learns that eating human flesh is permissible.
The Ra’avad (on Hilchos Ma’achalos Assuros 3:4), the Rashba, and the Rosh (5:19) agree with the Ramban. However, the Rosh adds that the same rabbinical prohibition that applies to human blood (when it is detached) also applies to human flesh.
The Reah and Ritva say that eating human flesh is forbidden because humans are not kosher animals and that the permission learned in the Gemara does not apply to flesh.
The Rambam (Hilchos Ma’achalos Assuros 2:3,3:4) agrees that the permission does not apply to human flesh. However, he feels that the prohibition not to eat non-kosher animals does not apply to humans but the positive commandment to only eat kosher animals effectively excludes the option. The difference being that if you did eat human flesh and it was forbidden by a prohibition (Reah and Ritva) then you would be punished by a beis din (rabbinic court) with lashes. If it was only forbidden from a positive commandment (Rambam) then there would be no such punishment from a beis din.
The Nimukei Yosef agrees with the Ramban that theoretically human flesh is permissible to eat. However, because it forbidden to eat flesh from a live animal (Eiver min hachai) and it is forbidden to derive any benefit from a human corpse, it is impossible in practice to use this permission.
The Tur and Shulchan Aruch do not discuss this issue and the Rema (YD 79:1) says that human flesh is biblically forbidden (not like the Ramban, Rosh, etc.) to eat (not like the Ramban, Rosh, etc.) but does not specify which biblical prohibition.