Twin Data on the Genetics of Ageing 133 



subnormalcy and emotional instability, including schizoid 

 personality traits, compulsive drinking patterns and the like. 



Exact genetic information about the manner in which 

 presenescent maladjustment affects adaptability to ageing 

 has yet to be obtained. Longitudinal studies are needed to 

 demonstrate how specific traits tend to complicate, or are 

 complicated by, the ordinary phenomena of old age such as 

 those described by McFarland (1956) and various Russian 

 investigators (Bogomolets, 1938; Gakkel and Zinina, 1953). 

 Since the few studies made in this field have been related 

 largely to chronological rather than biological age, present 

 appraisal of changes due to ageing can be no more than a gross 

 approximation. 



It would be difficult, for instance, to determine whether 

 complications in the later stages of chronic pathological 

 conditions, such as hypertension or hypothyroidism, arise in 

 the period of senescence by coincidence or as the result of a 

 causal constitutional relationship. In the case of a gene- 

 specific underproduction of the thyroid, the connecting link 

 may be a disturbance in cholesterol metabolism which affects 

 both physical and emotional equilibrium. 



On the whole, the impact of the senium may be expected to 

 intensify pre-existing maladjustment. Old schizophrenics and 

 mental defectives tend to deteriorate, and alcoholics almost 

 always show a marked decline in tolerance and general resist- 

 ance. 



Regarding emotional maladjustment which phenomeno- 

 logically falls into the involutional period, the relationship 

 between the effect of advancing biological age and declining 

 adaptability is demonstrated by persons distinguished by a 

 schizoid type of behaviour pattern. There is substantial 

 evidence in support of the theory that the schizoid personality 

 structure is that of a heterozygous carrier of the schizophrenic 

 genotype with an inadequate degree of general constitutional 

 resistance (Kallmann, 1952). The presenescent traits most 

 commonly associated with this type are rigidity, compulsive- 

 ness and oversensitivity. Along with the cumulative emotional 



