The Evolutionary Psychology FAQ

Edward H. Hagen, Institute for Theoretical Biology, Berlin

What is a psychological adaptation?

A psychological adaptation is a functional component of the nervous system that solves a particular reproductive problem. Information processing is the highly abstract domain upon which psychological adaptations are thought to operate. That is, the reproductive problems solved by the nervous system are thought to be best characterized as information processing problems. Computer algorithms, broadly construed, are usually thought to provide the best model currently available for the information processing abilities of psychological adaptations. This model of animal psychology derives, in part, from the following observations:

The information content of a physical system is the number of distinct and detectable states that that system can assume. Thus, a light switch can be either off or on--two distinct states that can be abstractly represented by 0 and 1. Since two is the minimum number of discrete states possible for any system, the minimum unit of information--the bit--represents two states (e.g., 0 or 1). Notice that flipping a light switch on or off is a physical transformation of the switch that requires *energy.* This is true of any change in the information state of any system. All 'information processing' involves energy dissipating transformations of physical systems. Because all adaptations (e.g., hearts, lungs, etc.) effect transformations of physical systems that involve a change in the informational state of that system, all adaptations can be thought of as 'processing information'. THERE IS NO FUNDAMENTAL OR QUALITATIVE DIFFERENCE BETWEEN INFORMATION PROCESSING ADAPTATIONS (i.e. psychological adaptations) AND ANY OTHER TYPE OF ADAPTATION!

All adaptations effect physical transformations of target systems (e.g., the lens focuses light, muscles move bones) that can be construed as changing the informational state of the target system. So, in principle, the information processing model could be applied to all adaptations. However, there are quantitative differences that usefully distinguish information processing adaptations from other adaptations:

1. High information content--the system can assume a large number of distinct and detectable states. For example, hearts can assume only a limited number of different states (e.g., beating fast, beating slow), whereas the retina can assume an astronomically large number of different states (e.g., all the possible combinations of activation levels of the 125 million rods and 6.5 million cones in each eye)

2. State transformations only require small amounts of energy. Again, heart muscle requires a significant amount of energy to contract compared to the amount of energy necessary to activate a cone on the retina.

3. State transformations can occur very rapidly. The frequency of contractions of heart muscle is slow compared to the potential frequency of state changes in the cones of the retina.

The structure of animal senses suggest that the information processing model is apt. Animals devote a considerable fraction of tissue to sensors. Skin contains an extremely high density of tactile receptor cells that can individually change state in response to touch, temperature, and tissue damage. For example, the human hand has 17,000 such cells per square inch. Further, the energy required to register a sensation is relatively low. Finally, in addition to their high spatial density, receptor cells also possess the ability to represent changes with a high degree of temporal resolution. These cells are connected to the brain by nerve fibers that can communicate state changes in about 1/50 of a second. Thus, the properties of tactile sensors matches our definition of information processing adaptations quite well. If we then consider that animals also possess other high bandwidth sensors like eyes, ears, taste, and smell, and that each of these can assume a *vast* number of possible states in response to environmental conditions, we are forced to conclude that animals are organized to collect astronomical quantities of information, information which must then undergo further processing in order result in reproduction facilitating actions on the part of the animal. These, then, are the functions of psychological adaptations: collect information on the environment (including the organism itself), process this information to extract reproductively salient conclusions about the environment (e.g., there is a predator staring at me), and initiate reproduction facilitating transformations of appropriate target systems (e.g., turn around and run).

Copyright 1999-2002 Edward H. Hagen