CHANCE IN DEVELOPMENT 
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stocks this variation dees not occur. Variation appearing under 
uniform conditions of heredity and environment is considered as 
due to slight irregularities of division and distribution of cells 
during embryology and to other more or less intangible factors 
of development. Individual variation resulting from chance in 
development is on the average predictable, just as is hereditary 
variation resulting from chance distribution of Mendelian units 
in gametogenesis and fertilization. It is highly probable that 
many mental and physical differences in man are due to these 
intangible factors of development. A knowledge of these factors 
will be of importance in relation to studies in eugenics such as 
are being conducted at the Iowa Child Welfare Research Station. 
Child Welfare Research Station, 
State University of Iowa 
