248 



GROWTH 



PRINCIPLES AND THEORY 



growth rates after they have levelled off, appears at puberty. Although this 

 change is heralded in the growth cycles of lower mammals (Fig. 26, p. 221), 

 only in man does it lead to a unique shape of the growth curve. The "abnormal" 

 growth curve of man is of course connected with changes in the hormonal balance; 

 this is shown in pathological conditions such as gigantism and pubertas praecox 

 in pituitary dysfunction, when puberty takes place at an early age, as it does in 

 other mammals and still in apes. The protraction of the juvenile period gives 

 man a long period of somatic and mental maturation and so is a prerequisite 

 of learning, accumulation of experience, and of human culture in general. 



The cycles of human growth are, of course, much more complex than is 

 apparent from the overall curve of weight growth. Successive periods of repletion 

 and elongation are to be distinguished (Stratz, 1928) : Fetal growth is followed by 

 the early infantile period and a first increase of growth in length; growth at 

 puberty is accompanied by a second increase of length growth; after the 40th 

 year, usually weight increase by deposition of fat takes place. 



170 

 150 

 130 



110- 



90 



70 



50 



30 



10 



Concept mastery 



Army alpha (Owens) 



Berkeley growth study 



10 15 20 25 30 35 40 45 50 

 Age in years 



Fig. 47. A proposed age curve of intelligence from birth to 50 years. Based on data from 

 the Berkeley Growth Study, the Terman Gifted Study and Owen's Iowa Study. After 



Bayley, 1955. 



A comparison between somatic atid mental growth in man would be of considerable interest, 

 although little has been done in this respect. Figs. 38 (p. 235) and 47 are presented as 

 being suggestive of possible parallelisms. Brain growth follows a curve resembling a 

 decaying exponential rather than an S-curve. This is probably connected with the strong 

 negative allometry of the brain (p. 238). The "growth curve of intelligence", based upon 

 certain psychological tests, appears to follow a similar pattern. A detailed analysis, taking 

 account of the various periods of somatic growth, the adolescent spurt, critical phases, 

 somatotypes (e.g. types of Kretschmer, Sheldon, autonomic patterns, blood chemistry), 

 and their development in different "channels" (Wetzel, 1947), etc., and comparing 

 characteristics of somatic growth with psychological counterparts (Biihler, 1930), would 

 be rewarding. 



(e) Retardation 



The peculiar curve of growth and prolongation of the growth period in man is 

 a quantitative expression of a more general phenomenon, namely, retardation, 

 stated by Bolk (1926) as being a specific human characteristic. According to 



