R. Knussmann

Anthropologisches Institut der Universitiit, Von:Mdle.Park 10, D-2000 Hamburg 13, West Germany

Differences Between Mother-Child and Father-Child Correlations in the Human Epidermal Ridge System

Using a sample of 92 families, totalling 518 persons, correlations be- tween the children and their respective parents were computed for 36 quantitative dermatoglyphic characteristics. The correlation coef- ficients- from the mother-child comparisons are, on average, signi- ficantly higher than those resulting from father-child comparisons; whereas no substantial differences exi t between mother-son ancl mother- daughter or between father-son and father-dauglit~r. Sinee~iL is improbable that illegitimate children and influences of th6-1h~a-uterine environment are responsible for the similarity betwe~i] mother and child being higher than that between-fathEr ~ - ~ l - d - ~ - ~ a ~ - - - ~ - O effect of the sex chromosomes can be a s s u m e d T _ o h ~ a u . ~ e _ t l - - i n t o con- sideration that the plasm, which is more abund~t-nt in the female gamefe~ carries genetic information.

1. T e r m s o f Reference

While performing polysymptomatic similarity analyses for opinions of parentage, my attention was repeatedly arrested by high mother-childsimilarities, whereas correspond- ingly high father-child similarities appeared to be a more seldom occurrence. -The question arose, therefore, whether the mother-child sLm.j~ar~y i s r _ ~ n - a v e r a g e , higher than the father-child similarity_. Such an observation would suggest~ or would-at least oblige one to recognise the possibility, that children receive more gennefic-infoUmation from the mother than the father. This, however, gives rise to the interesting problem as to whether there is an extra-chromosomal inheritance in i~an, as is widely accepted especi- ally in botany (Jinks, I967).

2. Material and M e t h o d s

The proof of a quantitative difference between mother-child and father-child similarities cannot be attempted with the same material used for opinions of parentage from which the above-mentioned impressions were gained. This is because the only cases applicable in parent-child comparisons are those in which parentage can be confirmed unequivocally and this would inwolve a biased selection of genetic families with relatively high father- child similarity. Hence, the only alternative remaining was to resort to parent-child combinations of incontestable parentage, which were no~: chosen by aspects of similarity. I had "genuine" family material of this nature at my disposal in the form of a collection of' data compiled by Schwidetzky and Kleftke at the beginning of the fifties (Schwidetzky, 1956). Altogether 92 families comprising 518 individuals could be used from this sample ( Knussmann, 1969).

Not only the kind of sample but also the suitability of the pertinent features are of con- siderable importance. For an examination of the question of differing similarity between children and their respective parents to be promising and genetically relevant, the set of features must meet the following requirements.

Journal of Human Evolution (1977) 6, 123-126

124 r~. KNUgSMANN

1. It must consist of a number of individual features which (a) are clearly definable, (b) are easy to reproduce and (c) can be diagnosed in quantitative gradations.

2. All individual features must emerge under substantial genetic influence. 3. The features must be free of changes brought about by environmental influences

and must not be subject to change through age. Probably the only place where a larger number of features which fulfil all three postula- tions are to be found is in the epidermal ridge system. The question of differing degrees of sinfilarity between children and their respective parents was thus examined by way of the epidermal ridge system.

Investigations of twins and families have provided evidence ot'substantial genetic components in epidermal ridge features (Loeffler, 1969). Furthermore, the epidermal ridge system is determined at a pre-natal, probably even at an early foeial, stage (Wendt, 1969; Schweichel, 1971), and ridge-count and ridge° configuration do not alter during, a human's lifetime. Lastly, the epidermal ridge system contains several features which can be easily defined and determined, viz. as quantitative or at least quantifiable variables. In the present case, the following 36 features were used as such.

(a) Ridge-count of each of the I0 fingers. (b) Type of configuration of each ofthe l0 fingers (quantified in accordance with Wendt (1963)). (e) Ridge-count on the palm, a-b, b-c and c-d of both hands. (d) Palmar main line exit numbers leaving the 4 distal triradii of each hand. (e) Atd-angle of both hands.

The correlation coefficient, i.e. the outcome of the pair correlation*, served as a measure of similarity. The correlation coefficients for all 36 features were computed for the following 4 types of parent-child combination (n = number of correlated pairs) : mother- daughter (n = 141), mother-son (n = 125), father-daughter (n = 134), father-son (n--- 122).

3. Resul t s and Di scuss ion

Although the results do not bear like signs for all the individual features (Knussmann, 1973), definite regularities can be perceived if the 36 correlation coefficients for each type of combination are considered as a statistical set. By calculating the coefficients' means and the appropriate dispersion data for each of the four types of combination and by comparing these means by use of the t-test, the following findings were arrived at (Figure 1). The sets of correlation coefficients from the mother-daughter and mother-son comparison are significantly higher than the corresponding sets of coefficients resulting from the father-daughter and father-sori'comparison. However, no substantial differences could be established between the coefficients from the mother-daughter and mother-son comparison or between the coefficients from the father-daughter and father-son comparison.

A breakdown into the 5 afore-said groups of features reveals that in 3 of them the correlation coefficients of the mother-child comlSarison are, on average, higher than those resulting from the father-child comparison. The same applies to the fourth group of features if the breakdown in sons and daughters is dispensed with. Only the atd-angle manifests a greater inconsistency, since there the father-daughter comparison produced the highest coefficients. However, the atd-angle represents a "bad" epidermal ridge feature. This is became it is influenced bythe proportion of the hand which is subject to growth, an d it is therefore dependent on age (Penrose, 1954/55). It is also conspicuous that the correlation coefficients in r~pect of the atd-angle are fairly low.

* Strictly speaking, the calculation of product-moment correlations pre-supposes the existence of normal distributions, and not all epidermal ridge feature satisfy these requirements. However, the deviations from the normal distribution are relatively small, so that the application of the product-moment formulae produces useful results, and the advan- tages over correlation methods not based on distributions (rank correlation, phl-coefficient) predominate.

HUMAN EPIDERMAL RIDOE SYSTEM 125

Figure 1. Average correlation coefficients for various groups and for the total of the epidermal ridge features examined, broken down by the different parent-child combinations, r = correlation coefficient. The vertical lines denote [.he mean :t: standard error of the correlation coefficients for all 36 features examined and for the different parent- child combinations. A-E = feature groups, cf. list in text.

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There are three possible ways, put to discussion here, of interpreting the observation that the similarity between mother and child is, on average, higher than that between father and child.

1. The findings could be arrived at due to there being illegitimate children in the family material, so that, although the mother-child pairs are, without exception, uncontestable, wrong father-child pairs have, in places, been included. In view of the rather mediocre correlation coefficients, this interpretation of the findings can only explain the considerable difference between mother-child and father-child correlations if one assumes not just isolated but numerous cases of illegitimacy. It can be computed, on model lines, that the proportion ofiUegitimate children would have to be as high as 1/4 in order to explain the difference between mother-child and father-child correlations. Such a large proportion of illegitimate children cannot be seriously assumed especially since the children were born at a time when women were subject to particularly strict taboos.

2. The greater mother-child similarity could be determined by environmental influences which have their origin in the closer contact between mother and child at the time of the emergence of the epidermal ridge system. This explanation of the greater mother-child similarity is plausible, for instance, with respect to size and weight at birth, since the mother's feature-pattern influences the corresponding feature in the child in the same general way due to the fact that a big mother with a large uterus offers the foetus better growth conditions than a small mother (Knussmann, 1968, p. 232). However, intra- uterine influence on the epidermal ridge system which follows a similar pattern to that of the mother's epidermal ridge system is much more improbable, for a precondition of such an influence is the existence of a causal chain reaching back as far as the con- ditions in the grandmother 's uterus.

3. The greater mother-child similarity could be genetically conditioned. An effect

126 R, KNU$$MANN

produced by sex-specific inheritance resp. by a larger information capacity of the X-chromosome can be eliminated here, since both mothers and daughters and mothers ~ ld sons were, on average, more similar to one another than fathers and daughters or fathers and sons, while no substantial differences exist between the mother-daughter and mother-son comparisons. Consequently, there only remains the assumption that more genetic information is transmitted to the child from the mother's side than from the father's.

According to the present state of our cytogenetic knowledge ttle assumption of a closer genetic connection between child and mother implies the hypothesis of extrachromosomal inheritance, i.e. localisation of genetic information in gamete substances outside the cell nucleus, so the more abundant plasm of the female germ cell can exert an influence. Although such a hypothesis, which is by no means new in biology, is unusual in human genetics, it is, given impartiality, worthy of discussion. It is in no way inconsistent with th e proven knowledge of this science. Moreover, there are embryological finds not of humans, but of mammal s which are quite consistent with the assumption of non- chromosomal inheritance. For example, in the ease of mice and rabbits the early development of the germ seems to be contracted by storage products from the mother's cytoplasm which are synthesized during oogenesis, or these products play an important part in the activation of the chromosomal genes (Ohno, 1968; Engel, 1971 ; Wolf & Engel, 1972). Ia view of all this, it seems to me that it would be appropriate to delve further into the problem of the existence of extra-chromosomal inheritance in man.

Adapted fi-orn: Kaussmann, R. (1973). Unterschiede zwischen Mutter-Kind- und Vater-Kind-Kor- relationen ira Haufleistensystem des Men~ehen. Humangenetik 19~ 145-154 (where the bibliography is to be found),