Voodoo zombies

i) One argument for human evolution is encephalization: the development of larger brains over time. That's also used to date the emergence of humans. Skulls with a braincase large enough to accommodate a human-sized brain. 

ii) Now, it may indeed be legitimate to infer brain size from cranial size, although oftentimes we only have skull fragments. Indeed, there's a difference between brain size and internal complexity.

iii) But suppose, for the sake of argument, that we discovered a perfectly preserved hominid corpse in a peat bog. Suppose conventional dating techniques indicate that the specimen is 200K years old. Suppose it had an intact brain the size of a human brain. And it had the same internal complexity of a human brain. And suppose the specimen was bipedal with opposable thumbs. 

A theistic evolutionist or old-earth creationist might conclude that dates to at least 200K BC. But is that a valid inference?

iv) The reservation I have with that inference is the assumed correlation between mind and brain. This raises the perennial issue of the mind/body problem. There's some evidence that's consistent with the proposition that the brain produces the mind. Stock examples include how alcohol, hallucinogens, traumatic head trauma, brain cancer, brain atrophy, and Alzheimer's temporarily or permanently impair cognition. 

v) However, even that's consistent with the receiver/filter model of the mind/body problem propounded by thinkers like William James, Aldous Huxley, and Mario Beauregard.

vi) In addition, there's multiple lines of philosophical and empirical evidence indicating that the mind is essentially independent of the brain (e.g. terminal lucidity, apparitions of the dead, veridical near-death or out-of-body experiences, demonic possession, psi, the hard problem of consciousness). 

vii) If true, this means the correlation between a human brain and human intelligence is contingent rather than necessary. Suppose, for the same of argument, that a human mind requires a brain of sufficient complexity to express itself. (Even that is questionable. John Lorber's hydrocephalic patients seem to present a counterexample.)

Even on that assumption, there's an asymmetry between minds and brains. In principle, you could have a living human body with a functioning human brain without human intelligence. Unless the body has a soul, it will lack human intelligence, regardless of the condition of the brain. Like a voodoo zombie. 

At best, the brain is a necessary but insufficient condition for the presence or expression of human intelligence. And that's an overstatement. There can be mindless brains and brainless minds. 

For a body to possess or express human intelligence requires ensoulment. A body must be paired with a soul. The mind uses the brain. 

Unlike some theistic evolutionists, I'm not suggesting that God produced humans by the ensoulment of preexisting primates. My point, rather, is that even as a matter of principle, you can't date the origin of the human species based on fossil skulls. You couldn't even do that if you had an intact brain, as per my hypothetical peat bog specimen. 

viii) Some people might complain that my objection is special pleading. I'm raising an objection that renders my position unfalsifiable. 

But it's not ad hoc. To begin with, the inference is simply fallacious inasmuch as the evidence for physicalism is equally consistent with substance dualism (v). In addition, we have positive evidence that the mind is not reducible to the brain. Indeed, situations in which the mind functions independent of the brain (vi).