The appearance of animal consciousness is evidently the result of biological evolution, but this well-supported empirical fact is not yet an explanation — it does not provide understanding, or enable us to see why the result was to be expected or how it came about. In this case, unlike that of the appearance of the physical adaptations characteristic of life, an explanation by natural selection based on physical fitness to survive is not sufficient. Selection for physical reproductive fitness may have resulted in the appearance of organisms that are in fact conscious, and that have the observable variety of different specific kinds of consciousness, but there is no physical explanation of why this is so — nor any other kind of explanation that we know of.

Mind and Cosmos: Why the Materialist Neo-Darwin
Thomas Nagel