Once we were cannibals
5 Sept 2001, Dov to Editors, Scientific American.
Tim D. White concludes his presentation re Once We Were Cannibals: "It remains much more challenging to establish why cannibalism took place than to establish that it did".
If you accept that the basic nature of life is common to individual cells and to poly-cell life forms regardless of overall size and degree of complexity, it follows that what makes an individual cell a LIFE is what makes a poly-cell life form a LIFE (and vice versa) and it follows that cannibalism is an extension of the extensive in-cell protein recycling and so is cell-recycling in polycelled life forms and so is overall Earthly organic matter recycling.
PS: And re the question why cannibalism ceased:
There were two similar revolutionary evolutions in the history of Earth's Life Evolution. The first revolutionary evolution was the "celling", by membrane, of the pre-celled archaic genes-associations plus their retinues in response to environmental developments. The revolutionary aspect of this evolution was being no-longer at the mercy of all environmental circumstances but, instead, gaining control over many of them. The following evolution of poly-celled life has been a continuation and an extension of this revolutionary evolution.
The second, recent, revolutionary evolution has been initiated, in a similar vein, by the primates that adapted from life in semi- or tropical circumstances to life on plains. As their changed living posture led to modified perceptive/adaptive capabilities they replace adaptation to changed circumstances with Culture, control and modification of these circumstances. This is essentially similar to the earlier "celling" revolution, development of capability to control many of the environmental circumstances.Cannibalism is an anti-survival social element and therefore it has ceased.