W. H. Calvin, The Ascent of Mind, 1990, The University of Washington.

"This is an Alice-in-Wonderland sort of principle: the Red Queen told Alice that you have to keep running just to stay in the same place. The Red Queen is one of the reasons we talk of a naturalist fallacy. "What's natural is good," is, alas, another example of substituting upbeat wishful thinking for familiarizing oneself with the available evidence. Across many species of mammals, the amount of effort devoted to reproduction bears little relationship to niche size. Nature just hasn't developed a way of limiting overproduction of baby bears (or any other species, although humans may yet become an exception), and most animals spend nearly all their life just raising youngsters with which to feed the predators and pathogens."

To discuss the phrase, "What's natural is good." requires that one first define his terms to eliminate unwarranted assumptions and this phrase contains two words difficult to define, natural and good. For the purposes of this discussion we will say that natural means occurring outside the agency of man, that is to say, occurring naturally in the environment, even in the absence of man. Good we will define as accruing to the advantage of mankind in the sense of aiding in the effort to assure the survival of the species. With these definitions in mind it is easy to refute Mr. Calvin's statement. Anything unnatural to the environment must work against the survival potential of any entity made from that environment.
Dr. Calvin spends a great deal of time speculating about the rise of intelligence and his ideas on the subject are compelling. But, from experience I must complain that unless one can grasp the essential difference between conscious and unconscious thought, no success is to be expected. I relate a dream to make my point. At one time in my life, when particularly impressed by unconscious thought in the form of dreams, I had a dream representing me as riding a motorcycle with a college friend riding behind me and steering. So, the point is that since my friend couldn't see, the expectation would be that we would crash. The unconscious thinker, frequently brilliant, suggests that using unconscious understanding in the objective world could be disastrous. An example of this occurs when I get a cup of coffee while thinking hard about something and pour the coffee into the wrong end of the cup. The issue here is: why is consciousness more adept at object manipulation than unconsciousness? Humans tend to think of unconsciousness as coma, but, as with all other states there is a spectrum involved here. We can be more or less unconscious as well as more or less conscious. Consciousness is, no doubt, conferred upon humans because of the unusual size of the brain along with the ratio between it and our body size.
It produces a conscious complex that acquires identity and is distinguished by the owner as distinct from the environment. This is the meaning of objectivity. Objectivity leads to modeling which provides foresight. But, we are still without a clear understanding of the problem with unconscious perception and object manipulation. All other animals are mostly unconscious and do little object manipulation. I guess you have to see objects relative to one's model of oneself to conclude that manipulation is a possibility and that that leads to the development of brain functions, like programming subroutines that are particularly useful for the practice, and that these subroutines aren't available when unconscious.
Dr. Calvin points out, correctly, that language is essential to the development of what we call intelligence, and goes on to suggest that there isn't that much difference between us and chimps that cannot be assigned to language. Probably, but to properly understand language and its manipulation we should probably concentrate on consciousness and object manipulation. Language is made up of symbols that can be viewed as objects and manipulated.
Modeling is probably key, and the development of models no doubt requires the ability to abstract oneself from the model which means objectivity. Model development would confer the ability to string together sounds and concepts.
I hope the problem here is not the consignment of the distinction between conscious and unconscious thought to the unscientific. Dr. Jung has been shamefully neglected by the scientific community and this, I guess, is the result.
As I look further at Dr. Calvin's writings, I see he has a book about consciousness, in which it is clear that he defines consciousness as awareness. This is a grand confusion. Plants are aware, I guess, they turn toward the sun. All animals are aware, and Dr. Calvin does talk about animal consciousness. Animals aren't conscious, they are aware. Consciousness is really shorthand for self consciousness. It is not achieved except by creatures that can energize concepts to the point of distinguishing them from themselves. It is a special sort of awareness in the same sense that steam is a special sort of water.
Unless this confusion is resolved, it is not to be expected that one can grasp the workings of the mind. Perhaps the brain can be understood, in a mechanistic sense, but since consciousness is the essence of humanness, no grasp of people will accrue from this sort of understanding.
Perhaps a concise definition of consciousness is needed: Consciousness has occurred when an event can be recalled after a significant lapse of time.
From this it will be understood that consciousness cannot be discerned by the subject at the moment of occurrence except possibly as a result of understanding and experience. It should also be apparent that, even for the most energetic, only a small part of experience rises to the level of consciousness.
Dr. Calvin has remarkable writing skills, given that he is a scientist.