230 Pigmentation Survey of School Children in Scotland 
VIII. It is well known that mortality is higher in more densely populated 
regions than others. It has been proved (see VII.) that certain classes are more 
characteristic of crowded areas than others. It is therefore to be expected that 
these classes would be positively correlated with the death rate. It is shown that 
an increase in the proportions of medium hair and dark eyes is associated with an 
increase in the death rate. This does not necessarily mean that persons belonging 
to these classes are less virile but simply that a large proportion of them live 
under conditions which are productive of a higher mortality. A direct investiga- 
tion to determine whether any colour class is associated positively with a high 
death rate is desirable. 
IX. It is shown that neither the Highland, Irish, English nor foreign elements 
ia the population account for the high proportion of medium hair found in all 
densely populated regions. These elements however (excepting the English) where 
present, tend to increase the proportion of dark and jet black hair. 
X. It is proved that the number of births per family is greater on an average 
in densely populated parts, and, as a consequence, that the number of births per 
family is greater where there are large proportions of medium hair and medium 
eyes. The lower classes are found in the denser centres. Thus it is likely that 
the medium haired, medium eyed lower classes are on an average more fertile than 
the remaining population. Here again a direct investigation is desirable. 
XL The main cause of the large excess of medium hair in densely populated 
parts probably arises from the blending of colour in the offspring of fair-haired 
and dark-haired persons : it is pointed out that blended inheritance exists in hair 
colour and what is wanted is a measure of its intensity. In densely populated 
areas, greater opportunities for intermixture of races occur, and it is shown 
(II. and III.) that in the large sparsely populated districts fair hair and dark hair, 
indicative of at least two different types, occur in excess, while in the urban regions 
these excesses mainly disappear and excess of medium hair appears. 
XII. The excess of dark eyes in urban areas does not appear to be explainable 
in the same way. It has been suggested that exclusive inheritance in eye colour 
may be one of the causes of the excess in these areas. In the offspring of dark- 
eyed and blue-eyed parents it is possible that reversions may occur, maintaining 
the dark-eyed type. 
XIII. The extent of the association of the colour classes geographically has 
been determined. One of the main results shows that as a rule medium hair is 
associated geographically with no other hair colour and goes to confirm the theory 
that medium hair is a blend. Thus it is to be expected that the proportion of 
this class will increase, tending to make the hair colour of the Scottish people 
more and more uniform. Excess of red hair is found as a rule only in regions 
where the proportion of dark hair is well below the average ; a slight excess of fair 
is associated with excess of red. There is no positive association geographically of 
