The Tree of Life Sketch from Charles Darwin's Notebook B, 1837
Darwin returned from his five-year long voyaging on HMS Beagle in 1836.
During the years away on the high seas and in distant lands the skeptical attidudes of many of his ship-mates and the various geological and biological
phenomena he had witnessed had caused his mind to entertain critical doubts of the biblical explanations of Creation he had formerly fully accepted.
He continued to keep notebooks as he had on his voyages and, as early as
1837, in a Notebook B that the editors of Darwin's papers regard as being the notebook Darwin had specifically
dedicated to his thought, during 1837 and into 1838, on the subject of the
Transmutation of Species his theorising about the origin of species included his famous Tree
of Life sketch.
Charles Darwin's Tree of Life sketch shows his early theoretical
insight of how a genus of related species might
originate by divergence from a starting point (1).
Charles Darwin's - I Think - moment
The text annotations read:-
Case must be that one generation then should be as many living as now. To do this & to have many
species in same genus (as is) requires extinction.
Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater
distinction. Thus genera would be formed. - bearing relation (page 36 ends - page 37 begins)
to ancient types with several extinct forms...
From Darwin's Notebook B now stored in Cambridge University library
N. B. Darwin elaborated significantly on this "Tree of Life" insight in his seminal work 'On the Origin of Species' as first published in 1859.
The above "Tree of Life sketch" appears on page 36 of the notebook - the first 35 pages being effectively taken up by Darwin's consideration
of his grandfather Erasmus Darwin's earlier evolutionary as published in Zoonomia; or the Laws of Organic Life (1794) a two-volume medical work
dealing with pathology, anatomy, psychology, and the functioning of the body.
Erasmus Darwin's work includes the following passage:-
Would it be too bold to imagine that, in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind
would it be too bold to imagine that all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality, with the power of acquiring new parts,
attended with new propensities, directed by irritations, sensations, volitions and associations, and thus possessing the faculty of continuing to improve by its own inherent activity, and
of delivering down these improvements by generation to its posterity, world without end!
Darwin's I Think diagram on page 36 may then represent his own claim to distinct theorising.
It seems that at this early time Darwin felt himself to be actually on the
cusp of developing a theory.
If we peruse another Notebook page dating from 1837 it can be appreciated how much of the foundation for his eventual
Origin of Species theory was already being "mentally" laid out:-
The text reads:-
… led to comprehend true affinities. My theory would give zest to recent & Fossil Comparative Anatomy: it would lead to study of instincts,
heredity, & mind heredity, whole metaphysics, it would lead to closest examination of hybridity & generation, causes of change in order
to know what we have come from & to what we tend, to what circumstances favour crossing & what prevents it, this and direct examination
of direct passages of structure in species, might lead to laws of change, which would then be main object of study, to guide our speculations...
Page 228 ends page 229 begins:-
...with respect to past & future. The Grand Question, which every naturalist ought to have before him,
when dissecting a whale, or classifying a mite, a fungus, or an infusorian, is "What are the laws of life".-
Is Human Being more truly Metaphysical than Physical?