36 The Descent of Man. Past 1 



projection over the eye-brows, is largely developed, and the jaws 

 are prognathous to an " ejfrayant" degree * so that these idiots 

 somewhat resemble " the lower types of mankind. Their in- 

 telligence, and most of their mental faculties, are extremely 

 feeble. They cannot acquire the power of speech, and are 

 wholly incapable of prolonged attention, but are much given to 

 imitation. They are strong and remarkably active, continually 

 gamboling and jumping about, and making grimaces. They 

 often ascend stairs on all-fours; and are curiously fond of 

 climbing up furniture or trees. We are thus reminded of the 

 delight shewn by almost all boys in climbing trees; and this 

 again reminds us how lambs and kids, originally alpine animals, 

 delight to frisk on any hillock, however small. Idiots also 

 resemble the lower animals in some other respects ; thus several 

 cases are recorded of their carefully smelling every mouthful of 

 food before eating it. One idiot is described as often using his 

 mouth in aid of his hands, whilst hunting for lice. They are 

 often filthy in their habits, and have no sense of decency ; and 

 several cases have been published of their bodies being re- 

 markably hairy. 37 



Reversion. — Many of the cases to be here given, might have 

 been introduced under the last heading. When a structure 

 is, arrested in its development, but still continues growing, 

 until it closely resembles a corresponding structure in some 

 lower and adult member of the same group, it may in one sense 

 be considered as a case of reversion. The lower members in a 

 group give us some idea how the common progenitor was 

 probably constructed ; and it is hardly credible that a complex 

 part, arrested at an early phase of embryonic development, should 

 go on growing so as ultimately to perform its proper function, 

 unless it had acquired such power during some earlier state of 

 existence, when the present exceptional or arrested structure 

 was normal. The simple brain of a microcephalous idiot, in as 

 far as it resembles that of an ape, may in this sense be said to 

 offer a case of reversion. 38 There are other cases which com e 



37 Prof. Laycock sums up the pp. 46-51. Pinel has also given a 



character of brute-like idiots bv striking case of hairiness in an 



calling 1 them thsroid ; 'Journal of idiot. 



Menta. Science/ July 1863. Dr. 38 In my 'Variation of Animals 



Scott ('Thf Deaf and Dumb,' 2nd under Domestication ' (vol. ii. p. 57), 



edit., 1870, p 10) has often ob- I attributed the not very rare cases 



served the imbecilt smelling their of supernumerary mammae in women 



food. See, on tnis same subject, to reversion. I was led to this as a 



and on the hairiness of idiots, Dr. probable conclusion, by the additional 



Maudsley, 'Body and Mind,' 1870, mammas being generallv placorf 



