phylogenetic scalethe scale of animal life, ranging from the simplest organisms to the most complex. This incorporates the idea of evolution (see DARWIN, EVOLUTIONARY THEORY) from simple life forms with rudimentary reactions to environmental stimuli, to the complexity of the higher mammals with their specific and refined sensory systems, their capacity for learning from experience, and, in the case of humans, the ability to reflect on their own experience. The scale therefore not only represents increasing biological differentiation, but increasing brain capacity.
The concept is often used within the context of ETHOLOGY to indicate that the behaviour of animals lower down the scale is controlled by inherited behaviour patterns, often described as INSTINCTS, while animals higher up the scale are more ‘open’ to learning. The increased proportion of cortex in the human brain allows behaviour to be appreciably influenced by previous experience.