From Causation to Mechanisms Review Experiments provide the best evidence of a causal relation but sometimes they are not possible Since it is impossible physically or morally to manipulate the independent variable Two strategies Prospective studies Divide groups according to the independent variable and investigate correlation with the dependent variable Retrospective studies Divide group according to the dependent variable and investigate correlation with the independent variable Two limitations of causes for science Individual causal relations do not accomplish much It requires a coordinated system of causes to get something done What relates causes to their effects Typically there are processes intervening between causes and their effects Between and within causal relations scientists look for mechanisms Parts entities and operations activities organized to produce an phenomenon 1 The Ubiquity of Mechanisms in Science Mechanisms in physical sciences Solar system mechanics Mechanisms of chemical reactions Mechanisms in biological sciences Mechanisms of photosynthesis Mechanisms of reproduction Mechanisms in behavioral sciences Mechanisms of memory encoding Mechanisms of decision making Mechanisms in social sciences Mechanisms of consensus formation Mechanisms as Coordinated Causation Mechanisms are made of parts causing changes in other parts enabling mechanisms to cause changes in yet other things Muscles in heart contract while valves open and shut enabling The heart to move blood through arteries and veins Understanding a mechanism requires experimental procedures designed to figure out the parts their causal operation and how these operations are coordinated so that the mechanism can produce its effect Designing Mechanisms vs Discovering Mechanisms The challenge in engineering is to design new mechanisms that produce the phenomena we are interested in Typically engineers begin with an objective and recruit parts already known to perform operations Their challenge is to discover new modes of organization that enable the parts to together do somehting new Scientists do not have access to the design manuals of the mechanisms operative in the natural world They must reverse engineer them them discover the parts the operations and the organization 2 Early machines Variations on a theme Ramp Screw Wedge Early simple machines used human energy but extended its capacity In these cases shape and spatial layout explain the causal efficacy Early machines Variations on another theme Wheel Lever Pulley In these cases shape and layout together with coordination of parts explains the effect Simple mechanisms as tools to make tasks easier Permit the performance of activities that otherwise would not be possible 3 Combining simple mechanisms Engineering organizing components to produce effects Common force for creating new machines warfare The Gastrophetes or belly bow introduced around 400 BCE designed to launch arrows further and more accurately than the traditional bow The Oxybeles introduced around 375 BCE provided ever greater power and accuracy Common force for creating new machines warfare Ballista introduced around 50 BCE used more for throwing stones than arrows Onager developed around 350 CE was a low cost way of launching projectiles such as clay balls with Greek fire inside 4 Common force for creating new machines warfare Trebuchet a counterweighted catapult designed to throw heavy projectiles Such as pianos Chris throwing Maggie s piano in Northern Exposure From Simple to Complex Common theme in both engineering and science Begin with simple designs but increasingly engineer or discover more and more complex mechanisms Large numbers of parts Performing many different operations Coordinated in ever more complex ways Nature as a machine Rene Descartes I have described this earth and indeed the whole universe as if it were a machine I have considered only the various shapes and movements of its parts Principia IV 188 All action in the physical universe due to shape and motion of physical matter No vacuum No action at a distance Magnetism Screw shaped particles formed in vortices fit into threads in iron 5 Robert Boyle Restorer of the Mechanical Philosophy Introduced the name mechanical philosophy Air pump adapted design of Otto von Guericke Air molecules as springs Boyle s law the hypothesis that supposes the pressures and expansions to be in reciprocal proportion Descartes Animals as machines Impressed by the statuary in the Royal Gardens that moved by hydraulic principles Animal bodies are purely mechanical devices Circulation of blood due to heating in the heart causing the expansion of droplets of blood which then forced their way through the arteries Nerve transmission and brain activity purely mechanical albeit influenced by the mind in humans Humans as machines Descartes could not conceive of a mechanism that could think or use language Accordingly held that the human capacity for thought was not due to a mechanism Rather thought due to a nonmaterial mind Julien Offray de La Mettrie objected that Descartes did not go far enough all human activities including thinking explained in mechanical terms Man the Machine in 1748 6 Newton Expanding the mechanical philosophy Endorsed the mechanical philosophy Light and heat nothing but particles in motion I wish we could derive the rest of the phenomena of Nature by the same kind reasoning from mechanical principles for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies by some causes hitherto unknown are each mutually impelled towards one another and cohere in regular figures or are repelled and recede from one another These forces being unknown philosophers have hitherto attempted the search of Nature in vain but I hope the principles here laid down will afford some light either to this or some truer method of philosophy Preface to Principia Jacques de Vaucanson 1709 1709 1782 Moving Anatomy Mechanical duck could move in the typical wagging way of a duck eat and digest fish excrete the remains in a natural way Mechanism was driven by a weight Consisted of more than a thousand moving parts concealed inside the duck and the base on which the bird stood Besides the duck a flute and tambourine player Applying mechanical ideas to living organisms Living things seem to behave in complex ways that defy simple mechanical explanation Vitalists maintained that the