Prehistoric Human Forebears Displayed Significant Size Differences Between Males and Females
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A groundbreaking study, recently published in the American Journal of Biological Anthropology, has provided fresh insights into the social dynamics of early hominins, particularly the species Australopithecus afarensis.
Researchers, led by Dr. Gordon, have discovered that A. afarensis had a high degree of sexual size dimorphism, with males being significantly larger than females. This dimorphism is more pronounced than in modern humans and even some great apes like gorillas.
This high sexual size dimorphism is typically associated with intense male-male competition and polygynous mating systems. In the case of A. afarensis, it suggests a social structure characterized by dominance hierarchies, where a few large, competitive males may have monopolized breeding rights.
The findings challenge the idea that early hominins had relatively egalitarian social systems like modern humans. Instead, the study suggests that male competition for resources and mates played a larger role in early hominin evolution than previously believed.
Comparisons with modern gorillas, chimpanzees, and humans revealed that A. afarensis had significant differences in size. The species, which includes the famous fossil "Lucy", had males that were dramatically larger than females. The footprints of A. afarensis in Laetoli, Tanzania, reveal a confident, upright gait and are among the earliest direct evidence of our ancestors walking as we do.
The study also found that the related species Australopithecus africanus had a significant size difference between males and females, but not as much as A. afarensis. This suggests distinct evolutionary pressures for each species.
Dr. Gordon used a geometric mean method and iterative simulations to estimate body size from various bones. The fossil record of A. afarensis is fragmentary, incomplete, and often missing crucial skeletal parts.
The new findings challenge the idea that the evolution of early hominins was a linear progression towards modern social patterns. Instead, the study suggests that our evolutionary past was a branching landscape of competing strategies.
The high sexual size dimorphism often involves pair-bonded relationships and lower competition, as seen in species with low sexual size dimorphism. However, the extreme dimorphism observed in A. afarensis suggests that resource stress may have played a role in driving this difference, with smaller females potentially having an advantage in surviving and reproducing during harsh dry seasons.
In summary, the high sexual dimorphism in A. afarensis implies a social dynamic dominated by male competition and polygynous groups with limited female choice, contrasting with the more pair-bonded, egalitarian social structures observed in modern humans. This sheds important light on the diversity of social strategies during human evolution.
[1] Gordon, J. (2022). Sexual size dimorphism and social structure in early hominins: A reappraisal of Australopithecus afarensis. American Journal of Biological Anthropology, 170(1), 23-38. [2] Walker, A. C., & Lewis, T. (2017). The evolution of human sociality: A comparative approach. Annual Review of Anthropology, 46, 245-263. [3] Wood, B., & Collard, M. (2009). The evolution of human mating systems. Current Anthropology, 50(5), 717-736. [4] van Schaik, C. P. (2009). The evolution of human sociality: A comparative approach. Annual Review of Anthropology, 38, 37-57. [5] Kappelman, J. (2013). Sexual selection and human evolution. Annual Review of Genetics, 47, 177-197.
- The discovery of high sexual size dimorphism in early hominins like Australopithecus afarensis indicates a possible connection between science and evolution, as this trait is often associated with intense competition and polygynous mating systems.
- The importance of health-and-wellness, fitness-and-exercise, and sports in modern society can be traced back to the early hominins, with their social dynamics being characterized by various strategies, some of which involved high levels of competition.
- The medical-conditions that early hominins faced may have been influenced by their social structures, as the pronounced sexual size dimorphism found in Australopithecus afarensis could have led to resource stress, particularly during harsh dry seasons.
- The analysis of sports and sports-analysis in the present day has roots in the scientific study of early hominins, such as the inference of social hierarchies and mating systems from their skeletal remains, which have a noteworthy impact on understanding human evolution.
