The traditional image of Darwin is the respectable elderly gent with the flowing beard and balding head. But he was once young and full of hormones and, like most young men, preoccupied with vulgar thoughts of booze and sex.
His accounts of the Beagle voyage reveal just a little of this, with Darwin confirming his delight with the ladies of Buenos Aires, agreeing that they are:
the handsomest in the world.., charmingly so [link]
and waxing lyrical about the ladies of Lima:
There are two things in Lima, which all Travellers have discussed; the ladies "tapadas", or concealed in the saya y Manta, & fruit called Chilimoya. To my mind the former is as beautiful as the latter is delicious. The close elastic gown fits the figure closely & obliges the ladies to walk with small steps which they do very elegantly & display very white silk stockings & very pretty feet. — They wear a black silk veil, which is fixed round the waist behind, is brought over the head, & held by the hands before the face, allowing only one eye to remain uncovered. — But then that one eye is so black & brilliant & has such powers of motion & expression, that its effect is very powerful. — Altogether the ladies are so metamorphised; that I at first felt as much surprised, as if I had been introduced amongst a number of nice round mermaids, or any other such beautiful animal. And certainly they are better worth looking at than all the churches & buildings in Lima. [link]
But it was on his return from the Beagle voyage that we find his rudest ruminations. Darwin kept a series of notebooks, which, never intended for publication, reveal his inner thoughts, not just about geology or the transmutation of species but also about matters of a far cruder nature.
In his earlier notebooks, Darwin shamelessly speculates on the evolution of female sexuality:
Female genital organs...In some monkeys clitoris wonderfully produced [C Notebook]
In case of woman instinctive desire may be said more definite than with bitch for some feeling must urge them to these actions These facts may be turned to ridicule, or may be thought disgusting, but to philosophic naturalist pregnant with interest. [D notebook] (NB: a few lines earlier he describes monekys lifting women's petticoats).
However, it is his so-called metaphysical notebooks that the young frisky Darwin most obviously shows an earthy interest in booze and sex:
The student who, when drunk, thought everyone was calling him a bastard:
In drunkedness same disposition recurs, such as . . . of Trinity always thinking people were calling him a bastard when drunk.—having really been so. [link]
The case of a Shrewsbury gentleman who tried to have sex with a turkey:
Case of Shrewsbury gentleman, unnatural union with turkey cock, was restrained by remonstrances on him [link]
The links between slobbering and sex explained by evolution:
Sexual desire makes saliva to flow /yes, certainly/ curious association: I have seen Nina licking her chops.—someone has described slovering teethless-jaws as picture of disgusting lewd old man. ones tendency to kiss, & almost bite, that which one sexually loves is probably connected with flow of saliva, & hence with action of mouth & jaws.—Lascivious women are described as biting: so do stallions always... The association of saliva is probably due to our distant ancestors having been like dogs to bitches—How comes such an association in man.—it is bare fact, on my theory intelligible [link]
And Darwin writes of stallions licking udders:
Stallion licking udders of mare strictly analogous to men's affect for women's breasts [link].
And dogs smelling each other’s bottoms:
Hyaena likes smell of that fatty substance it scrapes off its bottom. it is relic of same thing that makes one dog smell posterior at another. [link]
And grossest of all, Darwin revells in the smell of his own nether regions!!!
We need not feel so much surprise at male animals smelling vagina of females.—when it is recollected that smell of one's own pud[endum] not disagree[able.]—Ourang outang at Zoology Gardens touched pud of young males & smells its fingers. [link]
And perhaps hints at his own history of "self-abuse":
I often have (as a boy) wondered why all abnormal sexual actions or even impulses (where sensations of individual are same as in normal cases) are held in abhorrence. It is because instincts to women is not followed [link]
Darwin also links the profane to the sublime:
A man shivers from fear, sublimity, sexual ardour. – a man cries from grief, joy & sublimity. [link]
One thing is clear, after reading Darwin's notebooks, the young frisky Darwin comes across as lot more interesting than that bearded old man!
As a follow-up to my earlier post on Charles Darwin's smelly rude bits, readers might be interested to see that this week Emma Darwin has been writing about writing about sex—not CD's wife, his great-great-granddaughter, the novelist! 
