Downward Causation: An Example Involving Human Reproductive and Neuroendocrine Systems

Paul Davies (Davies, 2006) provides the following example of downward causation. "Consider a computer that controls a microprocessor connected to a robot arm. The arm is free to move in any direction according to a program in the computer. Now imagine a program that instructs the arm to reach inside the computer's own circuitry and rearrange it, e.g. by throwing a switch...this is software--hardware feedback, where software brings about a change in the very hardware that supports it." Inspired by it, and by Richard Hofstadter's belief (Hofstadter, 1979) that consciousness is an emergent phenomenon in a multi-leveled system in our brain where "the top level reaches back down towards the bottom level and influences it," I've created the following example of downward causation using human reproduction, summarized in tabular form. The communication between system levels (feedback) is not limited to what is presented below--which highlights extracellular signaling molecules known as hormones (Brody 2006).

population	family of humans	Gender		Notes	Feedback
organism	Human	male	female	union in sexual intercourse	<=====>
body systems	reproductive, nervous, endocrine			sexual arousal ===> dopamine released sexual gratification ===> prolactin released neuroendocrine system releases these extracellular signaling molecules (hormones)	<===>
organ	in reproductive system: in neuroendocrine system:	penis	vagina	male genital organ inserted into female organ
organ	in reproductive system: in neuroendocrine system:	pituitary gland		male genital organ inserted into female organ
tissue	connective, muscle, nervous, epithelial			simulation leads to orgasm and ejaculation
cell		sperm	ovum	their union is beginning of new organism	<=====>
molecular	dopamine; prolactin			molecular wt = 153; molecular wt = 24,000	<===>
atomic	dopamine: C₈H₁₁NO₂ prolactin: 199 amino acids

note: <=====> and <===> symbols refer to two feedback loops that operate between different levels in the system representation

One may object to my making this correspondence to Davies' example on grounds that human conscious behavior steers this downward causation--and we consciously do that (and many other things that seemingly violate laws of physics) all the time (and seemingly exercise our free will, violate the second law of thermodynamics in decreasing entropy, select endpoints of our paths in getting from point A to B, etc.). In response I argue that the behavior associated with humans engaging in sexual intercourse is ancient--with evolutionary roots that go back tens of millions of years. And that is behavior that is so programmed that it doesn't require the participation of our conscious mind (although we may have different definitions of consciousness--I'm thinking of it as Julian Jaynes does).

Going even further back in time, a much simpler version of sexual reproduction has evolutionary roots going back several hundred million years. I'd say that at some point natural selection--with global constraints--selected a simple feedback process that involved a higher level communicating with a lower level. Once that feedback loop was selected for (given the downward causation involved, this is a lower probability event, so it may have taken awhile!), it was much easier for it to be selected again and again since it had such obvious reproductive advantage. Evolution then built on it.

References

Brody, S. & Kruger, T. "The post-orgasmic prolactin increase..." Biological Psychology 2006; 71:3 312-15

Davies, Paul "The Physics of Downward Causation" posted at http://www.ctnsstars.org 2006

Hofstadter, Douglas R. Godel, Escher, Bach: an Eternal Golden Braid Random House, New York 1979

Jaynes, Julian The Origin of Consciousness in the Breakdown of the Bicameral Mind

Houghton Mifflin, Boston 1990