D^r Sir

I am much interested in the subject of your book on the “Origin of Species”¹ & this must be my apology for addressing you   At the time of its appearance I was a Medical Student in London, & much attached to the study of Geology, general Natural History &c, & more particularly at that time—Animal and Vegetable Morphology.²

It is not surprising therefore that I was obliged to accept your Hypothesis as the only satisfactory explanation of all that is so perplexing & mysterious in these latter subjects. Of course other considerations,—especially the inhabitants of the Galapagos Archipelago & other facts in the Geographical distribution of Animals & Plants contributed to this result.

The remarkable unsymmetrical structure of the Sole, Turbot & other Fishes of the Pleuronectidæ had attracted my attention & appeared a strong argument in its favor.³

The Teats & Lacteal glands of the Mammalia present a difficulty   I cannot imagine how these can have been developed by ‘Natural selection’   I am anxious to know the views of others on the subject.

The degeneration of civilized man appears to be a necessary consequence of your hypothesis—if the following reasoning is correct. Man’s organs of locomotion, hearing smell, taste & sight were modified & maintained by natural selection when the life of the individual & the existence of the species depended upon their efficientcy. After a time his more perfect hand & superior reasoning powers gave him ascendancy over kindred forms in the struggle for life.

Civilization ensues; the strong protect the weak, machinery is used for locomotion, for defence against natural enemies, for preparing food &c &c, & robust health & acute senses are no longer the conditions of the life of the individual & the perpetuation of the species. They must therefore necessarily decay. The consideration of cultivated plants & domesticated animals will prove that variations of scructure are greatest when the plant or animal is placed under unnatural conditions. Civilized Man is thus placed. His various organs &c. will be liable to great variations & since natural selection cannot act in preserving the good & eliminating the bad, They must all ultimately be injurious for those which at first are beneficial, will by exaggeration become so.

This process of degeneration may have a limit for it may be supposed that natural selection will act when variations of structure interfere with a prolific reproduction, yet it is difficult to see how this principle can do so when variations are large & frequent. If these deductions are correct they are of practical importance. The future object of Medical Science will be the prevention rather than the cure of disease; & this will be accomplished by subjecting the body as far as practicable to its former conditions. A more natural diet, thin clothing, a large amount of exercise &c will be some of the conditions of health & physical enjoyment. Extremes will meet for the highest civilization will approximate the savage state.

I am | D^r Sir &c | R F

C. H. Darwin Esq. M.A