The first question is, what is the relationship between body size and sexual dimorphism? The answer is complex, and it depends on many factors, including the evolution of head morphology, body size, and fecundity advantage. In this article, we’ll consider some of the more important factors relating to sexual dimorphism and how these factors may have influenced human behavior. We’ll also consider the effects of different physiologies on sexual dimorphism in humans.
Evolution of sexual dimorphism
There are two general approaches to the study of sexual dimorphism: univariate and multivariate. The univariate formulation involves calculating the sex-specific genetic variance and the corresponding covariance between the sexes. The multivariate formulation uses the male and female G matrices and the intersexual genetic covariances. The latter approach is more flexible and takes into account the sex-specific genetic variance.
The former method is based on the idea that a sexual distinction evolved between the sexes. The females are not used to hunting, and the males are largely responsible for rearing the offspring. However, this model fails to explain the observed correlation between sexual dimorphism and polygyny. Additionally, it fails to explain traits like beards and the lack of sexual division of labor in primates. It cannot account for the evolution of the other two methods.
Moreover, the study of fish species shows that social organization has a big role in the evolution of sexual dimorphisms. Female fish with larger sizes than males change sex when they do not have a dominant male. They are generally bigger and prove to be an example of dimorphism. The results from these studies suggest that these organisms have a distinct sexual advantage in their social organization. If sexual selection is weaker than natural selection, they will eventually become extinct.
Effects of body size on sexual dimorphism
The role of body size in regulating sexual dimorphism in humans is controversial. The evolution of sexual dimorphism has influenced theories of early Homo, despite the fact that males are generally larger than females. Most anthropoid primates display some body size dimorphism, including gorillas and strepsirrhines. The most size-dimorphic anthropoid, however, is Mandrillus sphinx.
Several studies have indicated that the relation between male body size and SSD is mediated by the strength of intersexual selection. Using the same methodology, it is apparent that the effect of gender on sexual size dimorphism is not dependent on the strength of intersexual selection. Moreover, it is not clear whether the gender-specific trait bill length reflects the influence of intersexual selection. However, the Rensch’s rule remains significant when the habitat productivity is included in the analysis.
Although there are many genetic factors involved in the development of sexual dimorphism in humans, few data are available to compare the sex differences between adults and children. For example, studies of morphological sex tend to focus on comparisons between adults. On the other hand, comparisons of size dimorphism among adults can reveal the causes of the variation. Nonetheless, studies of size dimorphism in children and adults have yet to reveal conclusive evidence that it may be a result of asymmetrical mating system.
Effects of head morphology on sexual dimorphism
During recent genetic analyses, Olsson and colleagues have found evidence for differences in the size of male and female heads. They hypothesized that sexual selection could have contributed to these differences. Moreover, they found genetic differences between male and female trunk lengths. These findings demonstrate that the body size and head morphology of males and females may be influenced by a pleiotropic effect.
A more systematic study is required to determine whether head shape and size may influence sexual shape dimorphism. Previous studies have shown that allometry may be important in driving evolution in sexual shape dimorphism. However, Berns and Adams did not find significant effects of allometry. This suggests that allometry is a confounding factor. Further, Kaliontzopoulou and colleagues found evidence of sexual shape dimorphism in a group of two species of lizards.
Effects of fecundity advantage on sexual dimorphism
The magnitude of sexual dimorphism depends on a number of factors, including the size of the sex and the species’ body size. As noted by Rensch’s rule, males are larger than females. This trait is an important ecological and evolutionary feature and evolution tends to move towards a favored size in various ecological contexts and for different reproductive strategies.
The struggle to reproduce drives species to develop sexual dimorphism. Some species are highly conspicuous and therefore vulnerable to predation. Others are better camouflaged, such as male game birds. Some woodpecker species have different sized and shaped beaks, allowing them to find insects in multiple layers of bark. Sexual dimorphism is an important evolutionary advantage in enhancing collective survival in many species.
Fecundity advantage is an important evolutionary trait, but its role in determining male and female characteristics is debated. Despite the differences between sexes, human males and females have low levels of sexual dimorphism compared to many other species. Moreover, female and male human sizes are comparable and overlap when size differences are quantified. For this reason, the fecundity advantage is not directly related to a female’s tail size.
