I have tended to include myself in that bunch but this question is driving me to consider vitalism instead. Nagging questions like this are what usually change my mind. Here it is:
“Why are the highest, most rational faculties of a man’s mind the most hereditary?”
The question assumes a number of things which I can try to explain as they come up, but for expediency’s sake I will assume people can fill in at least some of the details on their own. So the only responsibility I’ll take upon myself is to explain why this observation appears to break Cartesian dualism.
We Cartesians assume that humans exist in at least two realms, named the natural world (of material cause and effect) and the supernatural world (of transcendental cause and effect). We identify such aspects as man’s physical body, the inputs from his five senses, and the earthly effects of his actions as his “worldly” part. We identify his reason, soul, intuition, etc. as his “otherworldly” parts which give life to his otherwise inert “worldly” part. Stab a man through the heart and these two parts separate forever, unless they’re Jesus or a personal friend of his like Lazarus was.
Cartesians like to use this faculty of reason in particular to discover truths in the other realms. Hence the term “rationalist”. Our definition presupposes that rational thought is not a material process, obeying cause and effect like a meat computer. But recently we suspect that a great deal of our ability to perform rational thought is due primarily to genetics, and secondarily to other material factors like iodine deficiency. Supernatural factors, if indeed they have any effect at all, seem to be a distant third to nature and nurture, barely causing any noise in the data at all. It may be possible for the son of a carpenter to be a scholar, but it is much more likely for the son of a scholar to be a scholar.
If the supernatural component of a man can be predicted by the natural component, then it must either be true that one of the components causes the other, or they correspond due to a common cause. Examples of each case follow:
1) Material causes supernatural. Example: Astrology. The alignment of the planets determines how much “soul stuff” of various flavors enters the body and brain at conception. Blacks have more soul because they are born closer to the equator, I would guess.
2) Supernatural causes material. Example: Blank slatism. The body and brain are malleable and grow in response to the education, enlightenment, and sheer holier-than-though self-righteousness of the soul inhabiting them.
3) Common cause. Example: Pre-established harmony. You can make rational deductions, but so can your meatbrain, and they just happen to decide the same things at the same time. It’s like if I decided to punch you, and my shadow also punched your shadow.