The argument presented in the rest of this paper has two main goals. In Part I, I will argue that Singer's theory is not capable of providing precise enough guidance with regard to what ethical choices we should make in the less obvious and more complex cases. This is, first, because Singer's theory doesn't distinguish between different kinds of interests and their relative moral weight and does not specify which creatures have which interests. And, second, even if we try to make Singer’s theory more precise, under his framework, moral consideration is skewed in favor of creatures with lesser mental capacities because of his low threshold of sentience as the criterion for moral consideration. This can be problematic because a focus on sentience alone can lead to creatures with greater mental capacities receiving the same or even a lesser treatment than the creatures with lesser mental capacities (that result in a diminished ability to hold a particular interest). From the perspective of common sense, the creatures with greater mental capacities thus end up being treated ‘unfairly’. Next, in Part II, I will propose an alternative to Singer's view that uses neurophysiology as the foundation for establishing a clearer differentiation between creatures' mental capacities, and then uses these new distinctions as a basis for determining how different creatures ought to be treated. My alternative neurophysiological theory of animal ethics offers more precise prescriptions for which capacities matter most for ethical consideration and identifies which particular animals possess these capacities. In doing so, my theory possesses a level of precision that a theory of ethics needs in order to be useful in practical cases. However, this precision comes at a cost: the neurophysiological theory is based on cutting-edge science which is controversial in many places and downright contradictory in others. Because the science is not firmly established, I take the presentation of the neurophysiological account to be an approximation that is open to change in light of further developments in neuroscientific research. However, I still think it is very important to offer something constructive to the discussion of animal ethics rather than mere criticism of other views. With that said, I will present the scientific evidence that I take to be the most plausible given our current state of affairs, with the caveat that, at any time in the future, this evidence could be modified or even refuted. My ultimate goal, then, is not to provide a definitive account of animal capacities as they relate to ethics, but rather a view that can function as a model for a principled method for determining the kinds of capacities and interests that should be considered important for animal ethics.