I might approach one human group treating another human group “like animals” in a number of ways. However, hypothesis one in no way applies to human groups. This is for three reasons: 1) despite different ancestries, there is no agreed upon modern human lineage and thus, no phyletic distance; 2) genetically, humans vary so little between groups that phyletic distance becomes arbitrary; and 3) cultural evolution provides better explanations.
This is the fundamental difference between anthrocentric and ethnocentric. One way to think about either is as a discriminatory cognitive process. Between species, this clearly applies to determining prey from predator, an old and acute mental faculty closely linked to animal survivability. This kind of inter-specific relationship ultimately leads to an inter-generational arms race.
A disposition such as this might have proved useful in human prehistory for distinguishing between friend or foe, axis or ally and if linked to survival (or reproduction indirectly) may be subject to directional selection. My view is that among humans this is better explained by cultural evolution. For example, the transmission of things like ethnic markers may have played a significant role. Given the proper ecological pressures, an ethnic arms race could even occur.
Another way to think about this is game theoretically. In many ways this is similar to indirect reciprocity where an ethnic marker is essentially a cue of reputation. The cultural evolution perspective is also more biologically parsimonious because all that is necessary is social learning in general. It is for this reason that ethnic biases are learned and not ingrained. This is why if an ethnic arms race were to occur, it would require particular ecological circumstances that favor the same cultural traditions through many generations. Such circumstances might involved immense competition over resources, may favor boom-or-bust population dynamics, or multiple ESSs (can also be thought of as stable inequalities).
It should be noted that by ethnic marker, I do not refer to any known biological marker. That said, cultural evolution and biological evolution are inextricably linked, even if they operate on dramatically different temporal scales.