extrapolate downward (new)
Basic model of the extrapolate down approach, wherein anthropocentric models of existence, e.g. life, consciousness, free will, etc., are assumed to exist at the atomic or subatomic level, because they are assumed to exist at the human level, and theories are developed to substantiate this view.
In hmol science, the extrapolate downward approach, as contrasted with the extrapolate up approach, is the methodology of applying anthropomorphic logic to explain physics and chemistry behavior, in regard to concepts such as life, death, consciousness, free will, choice, morality, etc. An example of the downward approach is used by American philosopher Christian de Quincey, who in his 2002 book Radical Nature, argues: [1]

“The only way we can coherently explain the existence of choice at our macro level is to assume that it must go ‘all the way down’ to the lowest-level micro entities. Choice—the exercise of free will and self-agency—must exist to some degree at the micro level if it exists at the macro level. Otherwise, the emergence of choice from the utter absence of choice would require a miracle.”

The macro level, for de Quincey, is the human mind and the micro level is the mind of particles such as the photon or electron, which he argues must have consciousness, owing to the perceived 'fact', in de Quincey's view, that humans have consciousness. The extrapolate down approach is exemplified as solution as to where to stop defining entities as conscious, as stated in 1987 by philosopher Thomas Nagel: [2]

“Ordinarily we believe that other human beings are conscious, and almost everyone believes that other mammals and birds are conscious too. But people differ over whether fish are conscious, or insects, worms, and jellyfish. They are still more doubtful about whether one-celled animals like amoebae and paramecia have conscious experiences, even though such creatures react conspicuously to stimuli of various kinds. Most people believe that plants aren’t conscious; and almost no one believes that rocks are conscious, or Kleenex, or automobiles, or mountain lakes, or cigarettes. And to take another biological example, most of us would say if we thought about it, that the individual cells of which our bodies are composed do not have conscious experiences.”

On this passage, de Quincey states the central issue to solve is to find exactly how far down the evolutionary scale consciousness goes? His answer is that it must go all the way down (and supposedly up, i.e. extend to the universe as a whole), if humans are indeed conscious entities.

In sum, one is faced with these two alternative approaches, i.e. up or down, when attempting to reconcile the view that humans evolved, or were synthesized over time through chemical reaction mechanism, from smaller molecules (and before that from hydrogen atom precursors 13.7-billion years ago) when tracing the evolution timeline downward.

Thinkers representative of the extrapolate downward approach include Pierre Teilhard, Arthur Young, and Ted Erikson. The subjects of panpsychism or panexperientialism is a near synonym for this line of thinking.

Difficulties on theory
The central difficulty with this model is that it presupposes certain facts as proven truths that have no proof, such as that "humans are alive" (no one has ever been able to define "life"), that humans have consciousnesses, etc., and extends these models down to the periodic table atomic level as the new governing principle of chemistry, all of which inevitability lead to the final conclusion that the hydrogen atom is alive. This finalized conclusion, however, does not sit well in the stomach. Hence, one is lead to the more cogent "extrapolate up approach", which leads to the new view that "life" is something that does not exist.

Middle grounder
A representative of the middle ground approach might be the circa 1869 discussions of French engineer Francois Massieu, and his effort to explain or understand the perceived dualism issue, in his day, of soul vs body or living vs non-living, by splitting apart the water molecule  H_2 0 \, into oxygen O_2 \, and hydrogen H_2 \, to see if this answers anything.

Alternatives to the up or down approach, used by many, is to use either (a) the emergence approach (b) the unbridgeable gap approach, the latter of which might be representative of the warm pond model.

1. De Quincey, Christian. (2002). Radical Nature: Rediscovering the Soul of Matter (pg. 27-28). Invisible Cities Press.
2. Nagel, Thomas. (1987). What Does it All Mean? A Very Short Introduction to Philosophy (pg. 24). Oxford University Press.

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