Fitness of the environment

Earlier authors argued that vital phenomena rest on properties found in all matter. Bose, in 1906, held that irritability is not peculiar to organic substances but is a universal property of matter.¹ In 1907 he described the aim of science as finding underlying unity in apparent diversity.² Timiriazeff, in The Life of the Plant (1912), reached a similar view from plant nutrition. He concluded that this process is conditioned by laws common to animate and inanimate nature.³ These authors looked for physical explanations of living behaviour, not for properties set apart for life.

In The Fitness of the Environment (1913), Henderson separated two things that are easily confused. The hand is an instance of adaptation. The anomalous expansion of water on cooling near its freezing point is an instance of environmental fitness.⁴ He argued that while ideas of living things stay vague, the two cannot be told apart in general.⁴ He called the thermal behaviour of water the most familiar instance of fitness, while noting that its importance may have been overestimated.⁵

Bayliss, in Principles of General Physiology (1915), summarised Henderson's case. He noted that ammonia is the only other liquid that approaches water in the thermal properties needed for life as we know it. Even ammonia lacks the anomalous expansion before freezing.⁶ Bayliss also explained why fitness differs from adaptation. The organism can change in response to its environment, but the environment does not change in return.⁷

Water also figured in electrical accounts of life. Crile, in A Bipolar Theory of Living Processes (1926), noted that water forms more than three-fourths of the body content and has the highest known dielectric constant.⁸ He tied this property to the ionization of the many molecules that water holds in suspension or solution.⁸ His aim was to interpret normal and pathological phenomena of man and animals in electrical terms.