God’s Lego set

In this layer the cells are polygonal, triangular, or fusiform in shape. Each polygonal cell gives off some four or five dendrites, while its axon may arise directly from the cell or one of its dendrites. The axons and dendrites of these cells ramify in the molecular layer.

Henry Gray, FRS, Anatomy, Descriptive and Surgical

Just as a thermostat keeps the temperature of a room constant in the face of external perturbations, so life uses feedback to maintain itself, to adapt to change, to grow and to reproduce its pattern indefinitely across generations. But although some living creatures may seem barely more sophisticated than thermostats, the task facing them is in reality nowhere near as straightforward.

Take Domesticus suburbii, for example. Commonly known as the couch potato, this primitive species maintains a homeostatic (self-regulating) balance by the simplest possible means. When it finds itself getting bored, it just reaches out and changes the TV channel. When it is hungry, it simply increases its intake of popcorn to compensate. Yet even these straightforward reflexes are far more sophisticated than they might appear at first glance. The function of a thermostat is to send out a correction signal based on the difference between the current state and the desired state. If the room is colder than it should be, then the thermostat switches on the heater; if it is too hot, the heater is switched off. Although the couch potato achieves a similar effect by minimizing the difference between its current and desired states of hunger or boredom, it cannot do so by sending out a simple error correction signal. Knowing how far it is from the ideal level of hunger does not in itself tell D. suburbii how to eat. An extreme variety of couch potato might connect itself up to a drip feed, and so be able to regulate its beer intake in proportion to its degree of thirst merely by opening or closing a valve. But even turning a valve requires rather complex muscle movements. More sophisticated homeostatic behaviours, such as phoning out for pizza, require incredibly long sequences of carefully scheduled muscle contractions, many of which themselves involve feedback control. And yet the couch potato is one of the lowliest kinds of life form. More advanced species, such as frogs or spiders, may have to carry out far more elaborate foraging, mating or defensive activities in order to survive.

Copyright © 2004 Cyberlife Research Ltd.
Last modified: 06/04/04