From Hugh Browne   17 April [1871]¹

Dear Sir

As to aquatic birds having acquired white plumage (2 vol p 229 of Descent of Man) may I suggest two things²   First that as birds sail over the sea the least conspicuous of all colors is white or sky blue (or something lighter than sky blue because objects seen from blue all seem darker). This is on account of the white clouds or blue sky being the background but when birds perch much on rocks & perhaps also when ⁠⟨⁠they d⁠⟩⁠ive deep for prey, dark colors are least seen—e.g. cormorants, penguins.— For similar reasons the rule as to whiteness does not apply to freshwater birds or those living mostly in rivers & swamps & small lakes.—

Second.— There is a remarkable prevalence of white on the under surfaces of both birds & beasts & I suggest that this may be because white is the least radiator & therefor keeps warm the parts most exposed to damp & other causes of cold, e.g. at p 289 of 2 vol you notice of the Wapiti Deer “during the winter the darker tints gradually fade away”— Also p 298 “Many quadrupeds inhabiting moderately cold regions … become paler during winter⁠⟨⁠.⁠⟩⁠

I have never seen ⁠⟨⁠    ⁠⟩⁠ what I doubt not is an importa⁠⟨⁠nt⁠⟩⁠ agent in modification viz the eff⁠⟨⁠ect⁠⟩⁠ of the will which may be even unconsciously exerted by the brain & which is also exerted I believe by every nervous centre or ganglion having reflex action—perhaps by every nerve—for instance when the stomach pours out gastric juice & the liver pours out bile & bone is formed to repair fracture. People may say the will has nothing to do with these things but if all mental effort be paralysed by grief or anxiety we know how the stomach & liver are incapacitated

When a lad at school I once involuntarily moved my ear— another lad noticed it, & having done it once I directed my attention to it during some hours & I doubt not, from what I then felt, that I might in a few days or weeks or months ⁠⟨⁠have⁠⟩⁠ pricked my ears like a ⁠⟨⁠po⁠⟩⁠inter simply by directing my will to them & obtaining the power by modifying the growth of skin or integument into muscle or development of germs (or gemmules as you term them) of muscles.— If I had a butting match with a negro every day do you think my skull would not thicken? I’ll write more on this if you care to have it.—³

I am observing what you prophesied as to color blindness of my sons & daurs nephews & nieces.—⁴ I have not yet had much opportunity but I think your views will be realized—my daur & two nieces having I think escaped.— As to the goodness of my sight in other respects, I have twice won the first prize in the annual competⁿ of the Robin Hoods & I can count 10, 11, & now & then 12 Pleiads.—⁵

Yours faithfully | Hugh Browne

Cha^s Darwin Esq