CHAPTER XIII 
THE ALLEGED INFLUENCE OF ORDER OF BIRTH 
AND AGE OF PARENTS UPON OFFSPRING. 
Our information on the subjects treated in the present chapter 
is in a most unsatisfactory state. It is with some hesitation that 
I have ventured to discuss them at all, but on account of their 
importance for the general problem of human evolution it was 
thought that it might be useful to treat them briefly, even though 
little more was done than to exhibit the imperfections of our 
knowledge and to point out some of the pitfalls into which the 
unwary have so frequently fallen. 
In regard to the influence of order of birth upon offspring 
there is one conclusion which we may feel warranted in drawing 
with some confidence. The first born children are apt to be 
lighter in weight and shorter in height than those of later births. 
Nothing is involved in the establishment of this conclusion 
beyond the collection and comparison of data on the weight 
and size of newly born infants and there is no reason to doubt the 
generality of the conclusion just expressed. Dr. Matthews Dun- 
can gives the following data on the weights and lengths of infants 
according to the order of their birth: 
Birth Rank I 2 3 | 4 5 | 6 |\7 and over| Average 
Weight in Ibs........... 7.20| 7.31| 7-35] 7-10] 7-45] 7-32] 7-31 7.26 
Length in inches........ 19. 20]19. 24/19. 30/18.96]19.27|18.96] 18.99 | 19.19 
Pearson submits the following table on the weights of 2,000 
babies, excluding twins and illegitimate births, from the records 
of the Lambeth Lying-in Hospital: 
Birth Order 5 co (ae) 3-4 | 5-6 | 7-8 |g-10|11and over|Mecan Weight 
BOYS: dstens smal 7.01 |7.36]7.41]7-.70|7.91|7-590] 7.92 7.40 
GirlSs.5 sae danas 6.76 | 7.08 | 7.33} 7-36] 7-32 17-65] 7.88 EG 
297 
