In Volume II, Thomson answers two fundamental questions in biology: (1) what are living creatures, statically and dynamically, intact and in all their parts, and (2) how have they come to be? The author concentrates on organisms. Unlike the inorganic, a living unity gives rise to something new. A mutation occurs, there is evolution, a continuous natural process of change in a definite direction ‘whereby distinctively new individualities arise’. Thomson explains the steps for most of the volume.
The author begins his ascent with a brief examination of the origin of the first organisms, what he calls ‘not-living carbonaceous slime activated by ferments’, and the later establishment of many distinct types of cellular organisation. As Adam Smith understood for economics, it was the specialization of function which Thomson explains gave the organism great momentum, such as in storing energy. As Goethe would understand, cellular specialization was also a Faustian bargain, bringing with it natural death.
Another step of far-reaching importance the author investigates is the evolution of male and female multicellular individuals. This too had many organic advantages, helping in differentiation and integration. The invention of haemoglobin and the establishment of internal surfaces was also a primary achievement. Thomson then looks at three evolutionary factors resulting in what for him is ‘the summit of the whole’, man. The first is variation, ‘those variations or mutations that form the raw materials of progress or the reverse’. Some of these mutations happen ‘brusquely, without intergrades’. It is possible that chromosomes, which are living units, may suddenly change like bacteria. Other mutations are much more subtle and difficult to determine.
Thomson reviews the central ideas in Darwinism and chooses selection as critical in the struggle for existence. The author takes pains to ensure that the reader understands that Darwinism today does not advocate a mechanical selective process. Selection is a sifting process, a testing process which does not always work consistently towards an ideal of fitness but does ‘eliminate inconsistent non-viable constitutions’. Thomson gives a number of examples: ‘The community of hive-bees bewilders us with its complexity and subtlety, but there is a long series of gradations.’ The adaptations of all creatures are still in progress and, as Thomson points out, are far from perfect. Adaptation, though, does not conflict with ideas of a transcendent Being.
With variation and selection, a third factor emerges: heredity. It is not a ‘mysterious force but a continuity of germ-plasm, binding one generation to another’. It secures the persistence of resemblance between offspring and their parents, between progeny and their ancestors. ‘Germ-cells carry the whole inheritance without allowing any of it to find expression until appropriate conditions and stimuli are forthcoming.’ Thomson explicates how heredity is a condition of evolution (‘heredity is not so much a factor in, as a condition of evolution’), how nature is always in tension with nurture (‘development is always a result of both’) and how heredity plays a part in what he terms ‘personality” (‘crest and no crest in poultry’). The author feels heredity should not be seen in a fatalistic light—‘the hand of the past has such a heavy grip’—but in a positive way—‘the persistence of the stable, the continual emergence of the new’.
In the last section, Thomson moves to what may have been on the mind of a reader in the middle of the Great War, man and the question of progress. As a naturalist, he agrees there are many ‘masterpieces’ in the realm of organisms. Man, though, is more unique still. He describes man as ‘the outcome of a persistent trend, towards freedom of mind, which has been characteristic of the process of organic evolution for millions of years’. The author draws attention to the evolution of man’s ‘intricate cerebral cortex, a subtle integration of the body, and a masterly resourceful behaviour’. More importantly for Thomson, ‘the moral law is as real and as external to any man or in any single nation. It is the work of the blood and tears of long generations of men.’ Thomson draws on traditions, literature and religions as proofs that still ‘nature is crowned in man’.