Downward Causation: An Example Involving Human Reproductive and Neuroendocrine Systems

copyright 2008, Stephen P. Cook            Home

 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).


family of humans








union in sexual intercourse


body systems


nervous, endocrine



sexual arousal ===> dopamine released  

sexual gratification ===> prolactin released

neuroendocrine system releases these

extracellular signaling molecules (hormones)




in reproductive system:

in neuroendocrine system:



male genital organ inserted into female organ


pituitary gland


connective, muscle,

nervous, epithelial



simulation leads to orgasm and ejaculation






their union is beginning of new organism



dopamine; prolactin




molecular wt = 153; molecular wt = 24,000




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.


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 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