Aggression, Digit Ratio, and Variation in the Androgen Receptor, Serotonin Transporter, and Dopamine D4 Receptor Genes in African Foragers: The Hadza

Abstract

The role of genes in the expression of aggression and masculinity traits in humans has been a focus of recent behavioral genetic studies. This is the first study on the variation in aggression, the digit ratio (the ratio between the second and the fourth digits, 2D:4D), the directional asymmetry in 2D:4D (D(R-L)) and polymorphisms of the AR, DRD4, and 5-HTTL genes in simple hunter-gatherers, namely the Hadza of Tanzania (142 adult men). The distribution of AR, DRD4E3, and 5-HTTLPR genotypes and allele frequencies in Hadza was compared to other African populations on which the data were available. Hadza and Ariaal differed significantly in the distributions of frequencies of AR alleles with different numbers of CAG repeats. Hadza population was similar to other African populations in the distribution of allelic frequencies of the DRD4E3 locus, and to Afro-Americans in the distribution of allelic types of the 5-HTTLPR locus. We found no influence of AR gene on the right hand 2D:4D ratio, D(R-L), and any of aggression subscales of the Buss-Perry Aggression Questionnaire (AQ). Although, a weak positive correlation between CAG repeats and the left hand 2D:4D was found. The multiple regression analysis with digit ratios, D(R-L) and aggression subscales of AQ as dependent variables and the three gene candidates (AR, DRD4E3, and 5-HTTLPR) as independent variables revealed the following: men with lower number of CAG repeats had significantly lower left hand 2D:4D ratio; men with higher numbers of 48-bp unit copies in exon 3 of a VNTR polymorphism in the DRD4 gene had significantly lower digit ratios on both hands; no effect of the 5-HTTLPR gene on either the digit ratio or aggressive behavior. These findings demonstrate the complexity of gene effects on digit ratios and aggression and call for simultaneous analysis of more candidate genes. It is noteworthy that these results were obtained for a human population that is still practicing foraging and has been subjected to a high selective pressure due to harsh environments and practically has no access to modern medical care. Hadza are highly egalitarian, and their culture does not favor persons with a dominant or aggressive behavior. It is still to be found to what extent the relationships observed in this study are similar to those in other human populations.

Molecular-Genetic Polymorphisms of Dopamine, Serotonin and Androgenic Systems as Molecular Markers of Success in Judo Wrestling Sportsmen

“…The association between the lower number of CAG-repeats in AR gene and masculinity, particular with the lower digit ratio (2D:4D) in men from the population of the Hadza (traditional East African huntergatherers) had been recently found [9]. Also, the data from China have indicated that AR CAG repeat polymorphism was associated with the exercise performance after simulated normobaric hypoxic training in North China Han men, and that the shorter genotypes (21 repeats and lower) had a better individual response to hypoxic training, compared to the carries of longer variants (22 repeats and longer) [21].…”

“…Obviously, environmental factors such as training, parental support play an important role in successful sportive career, but as mentioned above genetic factors do matter. Ten polymorphisms selected for analysis in this study are connected to the functioning of serotonergic, dopaminergic and androgenic systems according to other studies presumably may be associated with resistance to psychological stress, emotional control, competitiveness and aggression [6][7][8][9]13,19,37]. Although the sample size in this study was quite low it is still possible to suggest that functionally important polymorphisms of genes in serotonergic system provide some evidence of strong selective pressure in direction of genotypes associated with low level of free serotonin in successful judo athletes.…”

“…DNA extraction and DRD4Pr, DRD4E3, AR и 5HTTLPr loci polymorphism study was performed as mentioned before [9,13]. In table 1 there are the primers sequences and the annealing temperatures.…”

“…The results were photographed and analyzed using BioDocAnalyze device (Biometra, Goettingen, Germany). The amplification products of loci AR and DRD4E3 were analyzed according to protocol published before [9].…”

“…It was demonstrated that the lower number of CAG repeats the receptor is more sensitive to androgens. The CAG repeat polymorphisms of the AR gene play an important role in aggressive behavior [9].…”