94 
PROFESSOR K. PEARSON AND DR. A. LEE ON 
Now the colours of all the horses are returned wheu they are foals, so that there is 
no question of any variation of colour with age, yet we notice that— 
(i.) The horse is lighter in colour than the mare. 
(ii.) If we go back two generations (grandsire) the horse is lighter than if we only 
go back one generation (sire), and the sires are again lighter than their colts. 
In other words, there seems a progressive change towards a darker coat. 
(iii.) On the other hand, the mares one generation back appear to be darker than 
their daughters. 
(iv.) The average sire of colts is lighter than the average sire of fillies ; the average 
dam of colts is darker than the average dam of fillies. 
Now these conclusions seem to indicate that the older horse was lighter in coat, and 
the older mare darker in coat than either the colt or filly of to-day, and that there is a 
tendency in the thoroughbred racehorse of to-day to approach to an equality of colour 
in the two sexes, an equality which is a blend of the sensibly divergent sex-colour of 
the older generation. 
Whether this secular change is due to the “ breeding out ” of the influence of light 
Arabian sires, or to a tendency in the past to select light-coloured sires and dark- 
coloured mares for. breeding, or to the fact that such coloured sires and mares are the 
most fertile, i. e ., to an indirect effect of reproductive selection, is not so easy to 
determine. But what does appear certain is that the average thoroughbred is 
approaching to a blend between its male and female ancestry, which were sensibly 
divergent.* 
(8.) On the Relative Variability of Sex and Class in Horses — The following table 
gives the length of the bay range in terms of the standard deviation for each class. 
If e represent this range, then in terms of the previous notation e — u X cr — v! X cr', 
and from these values of u and u’ the ratio, £ = cr cr' of Table II. was calculated. 
* Mean of dams and sires of colts = - 5735, i.e., ^(’6111 + '5359). 
Mean of dams and sires of fillies = ‘5813, i.e., ^-(’6061 + - 5565). 
These are curiously enough almost exactly equal to the mean values - 5753 and -5S16 obtained for fillies 
and colts. This inverse relationship is too close to the probable errors of the quantities under investiga¬ 
tion for real stress to be laid on it, but it- may still turn out to be suggestive. 
