It is important to understand the fundamental difference between humans and nonhuman animals. Nonhuman animals such as apes have material mental powers. By material I mean powers that are instantiated in the brain and wholly depend upon matter for their operation. These powers include sensation, perception, imagination (the ability to form mental images), memory (of perceptions and images), and appetite....To put it differently, both animals and humans are sentient, but only humans are sapient. The difference is enormous. As Egnor says, "We are more different from apes than apes are from viruses. Our difference is a metaphysical chasm."
Nonhuman animals are purely material beings. They have no concepts. They experience hunger and pain. They don't contemplate the injustice of suffering.
A human being is material and immaterial -- a composite being. We have material bodies, and our perceptions and imaginations and appetites are material powers, instantiated in our brains. But our intellect -- our ability to think abstractly -- is a wholly immaterial power, and our will that acts in accordance with our intellect is an immaterial power. Our intellect and our will depend on matter for their ordinary function, in the sense that they depend upon perception and imagination and memory, but they are not themselves made of matter. It is in our ability to think abstractly that we differ from apes.
It is a radical difference -- an immeasurable qualitative difference, not a quantitative difference.
If this is so we might wonder how such a chasm came to exist. How did a purely physical, material process like evolution ever give rise to the abilities Egnor mentions. Indeed, how does the material brain of any animal convert physical stimuli, the firing of synapses and the flux of molecules in neurons, into immaterial sensations like pain or pleasure, and experiences of sound, color, fragrance or flavor? We take it all for granted, but it really is an astonishing mystery how a material brain could produce not only these sensations but also conceptualize abstractions and give meaning to words on paper.
indeed, Egnor believes that these phenomena are beyond the capabilities of matter alone which is why he believes that we also possess an immaterial mind.