Then and Now: Ecological Links in Human Evolution

The leading theory of human origins suggests that our species evolved in, and subsequently dispersed from, Africa. In this respect, to better understand human origins and evolution we can use living societies of Africa to enlighten our perspective of this origin. Specifically, the sociocultural behaviors of hunter-gatherer groups could offer insight into our distant past and pre-history. The human evolutionary trajectory following the Pan-Homo split from a common ancestor is not only necessarily complex, but entails challenges that must be confronted through the empirical domains of paleoecology, archaeology, evolutionary anthropology and ethnography. Through a more holistic approach it may be possible to determine the similarities and differences between modern, ancient, and evolutionarily distal hunter-gatherer groups, and thus form a coherent history of our species. To accomplish this accurately means investigating the evolutionary factors associated with early hominins, as well as interpreting ethnoarchaeological findings in light of contemporary ethnographic observations of African bands.

To begin, we must understand the evolutionary path of the anthropoid line toward hominin species. Kaplan and Hill (2000) have developed a very complex and useful model which can be incorporated with Foley’s (1995) model of a human environment of evolutionary adaptiveness (EEA). It can be supposed that human qualities have developed over a long period of evolutionary time in reaction to specific environmental pressures. A specific order of evolutionary processes took place to lead anthropoids to humanity. Noting the obviously unique traits of humans (such as a long developmental period, high degree of sociality, and high cognition), evolutionary logic could be applied to speculate a potential list of events. The availability of high-quality foods would be one critical component. Behavioral adaptations could evolve from a shift to visual sensory emphasis for selecting foods that are of the best condition. Along with the need for forward facing, biocular eyes for depth perception necessary to arboreal angulation. With bipedalism, a species could become better able to abstract and transport these essential aliments on the open plains; when leaving the forest for the plains as climate change reduced the longitude of the rainforest. This likewise meant these eyes no longer were useful for traversing the trees, but re-purposed for hunting with well aimed projectiles..
All this means a richer diet. An increase in recognition and obtainment of higher-quality foods would likely fuel encephalization; which surely happened for a good survival reason as it’s so resource heavy and dangerous to birth. Notably, encephalization would have to co-evolve with an increase in the length of juvenile development, in order to distribute the increased energy costs intrinsic to such a process. With increased encephalization comes greater cognition; with greater cognition comes increased sociality; with increased sociality comes a decreased mortality, through social support against prey and compensation of energy costs through reciprocal food distribution.

Importantly, the disadvantage of the energy deficit inherent in this process would be overcome by the increased food production that comes with the maturity of a highly social, highly cognitive bipedal animal. Once energy-expensive offspring reach sexual maturity, they begin to grow in both competence and physical ability to locate, procure, and return high-quality food sources, as socialization is peaking and mate-acquisition/family-building becomes critical. As this evolutionary process begins in its basic form, it increases in complexity and efficiency over evolutionary time; in a sense self-perpetuating itself. This evolutionary function may have begun around 35 Mya(million years ago) with early primates in an arboreal habitat (+/- a few million years with variance due to fossil and dating analysis, let alone Creationist chronology).

As this speculative process continues, more and more dietary elements can be added as increased cognitive abilities to locate and manipulate high-quality food sources evolve and as food sources evolve and change as well. Importantly, generation-to-generation behaviors are taught such that strategies perpetuate and evolve, rather than die with individuals or subpopulations. Additionally, social support systems can evolve in tandem to enhance the protection and energy receipt of vulnerable members (i.e. the young, old, pregnant, or injured/disabled) through the efforts of relatives and non-family-related members alike. This extends to social organization, as an ecologically determined home range will result in subunits dispersing, and then returning, to an established social center with valuable sustenance.

Bio-Logically, all these factors would evolve as pre-adaptations, co-adaptations, in an interactive and cyclic dynamo to eventually evolve a social animal that has qualities similar to those seen in a hunter-gather individual.

Modern examples of these arguments can be found in the !Kung and Hadza, historically persistent African indigenous peoples. Shostak (1981) describes the role of a !Kung hunter as beginning after puberty and reaching his maximum efficiency by the age of 30 to 40 years. Also, the role of a gatherer begins incompetently and grows over years until one is able to extract high-quality foods, such as mongongo nuts or honey. Furthermore, the Hadza break up into small groups of hunters and gatherers, subsequently returning with food for all members to utilize, balancing energy costs evenly over the group. These two examples support the trade-off hypothesis of costly development in exchange for highly productive adulthood years

Paleontologically, evidence of early hominins (such as Australopithecus africanus and Paranthropus robustus) shows their environment was rich and abundant in the Pleistocene (2.5Mya to 12,000 ya) in comparison to how it exists today. Specifically, in South Africa, there was a greater magnitude of biomass. Paranthropus and other early potential Homo ancestors moved into this open woodland environment as late as 2.5Mya, where they inevitably competed for superiority. This context can be viewed as an EEA in which hominins would continue to evolve toward a hunter-gather lifestyle. This concept holds importance in that subsistence strategies are greatly determined by ecology; a species’ diet has critical influence on its evolutionary course. In the Pleistocene environment of South Africa, hominins would find a variety of foods available from both plant and animal sources, which would lead one species to out-compete and dominate the others through optimizing their behavior and physiology. This could be accomplished through evolutionary adaptations that allowed meat to supplement a flora-based (and oft insectivorous) diet.

The foods available to hominins in the open woodlands of the Pleistocene included underground storage organs (USO), grasses and their grains, and perhaps some animals, insects, eggs, and even carion. Sponheimer (1999) argues that the diet of two hominins, P. robustus and A. africanus, contained high C4-type plants (C4/C3 are specific photosynthetic carbon-fixing processes in plants) based on analysis of tooth enamel specimens. This suggests that these species ignored C3-type plants, perhaps to avoid competition from other grazers, in favor of C4-type plant sources. However, the wear patterns on these species’ teeth were inconsistent with a high fiber diet, leading Sponheimer to infer that they may have been feeding on animals that consumed these plants (i.e. eating the grazers rather than what the grazers ate). Most underground storage organs of modern and Pleistocene Africa are C4-type. Through determining the toughness of these USOs and comparing USO selectivity in chimpanzees and the Hadza band of Tanzania, Dominy concluded that A. Africanus and P. robustus could have utilized tuber, corm, and bulb species (all USOs). The availability, lack of competition, and ease of mastication makes these sources ideal for hominins. However, – as is consistent with Sponheimer’s findings – both USOs and grasses cannot be total staples of their diets (as previously mentioned, hominins need rich diets to feed their large brains). The critical point with all this, is that it leads both researchers to infer that these two hominin species may have been incorporating animal meat into their USO-rich diet. O’Connell’s (1988) ethnographic study of Hadza scavenging strategies may reveal the solution to this conundrum.

The Hadza obtain a significant portion of their meat from scavenging large game across the savanna. All members of the band are vigilant for signs of a recent kill or death and will converge on a carcass with haste. They cooperatively scare away predators, and other scavengers, to procure the meat. This practice is opportunistic, rather than consistent, but still offers significant meat sources to an otherwise foraged diet. Using the Hadza as a model and speculations of hunting as a source for C3-plant traces in enamel, it’s reasonable to conclude that A. africanus and P. robustus had evolved scavenging strategies. So, combining these two scholars’ hypotheses, it may not be that these hominins hunted to obtain more meat, but rather consumed C4-rich USOs supplemented with scavenged meat, thus creating a better developed omnivorous diet.

Conclusionary Caveat:

With the preceding methodology of inferring human evolution through these various evolutionary processes and modern biocultural comparisons, comes the struggle of determining the validity of this process and it’s prominent conclusions. Many of these arguments are substantiated through comparative models of band groups, such as the Hadza and !Kung, however, without a fully encompassing comparison of all hunter-gatherer groups there is the risk of an alarmingly parochial scope to this approach. Primarily, modern African hunter-gatherers may not serve as appropriate models for an EEA. The adaptive and diverse nature of hunter-gatherers may have initially evolved in a specific environment but that environment cannot be easily inferred; over millions of years hunting-and-gathering was likely continuously adapting and changing. In fact, at present the !Kung and Hadza occupy a much more marginal ecology and geography due to historical events. Modern African bands have had thousands of years of interaction and conflict with agriculturalists and pastoralists, including contention over desirable land. Furthermore, the subsistence strategies and social behaviors of modern hunter-gatherers may not be equivalent to past groups, due to cultural and environmental changes that have occurred during the timespans separating past and present populations. Even in the same chronological period, hunter-gatherer groups exhibit a large degree of diversity. In the “Bushmen” bands alone, there are cultural differences that result in the variance of language, social organization, food selection, and subsistence strategies. Moreover, some evolutionary paradigms may be weakened with an ethnographic investigation. For instance, the typical theory that males are the sole providers of meat is not consistent with the involvement of women in Hadza-scavenging, nor is it supported by the fact that !Kung women provide a portion of meat production through trapping small game. Shostak’s (1981) ethnography also describes male meat distribution behaviors as inconsistent, and dependent on social relationships and previous reciprocal interactions, which opposes a strictly egalitarian system of equal resource distribution among the group. Generalization and speculation of the past is confounded by the specifics of its present comparison.

In the archaeological record, there is even more confounding factors that limit the utility of these comparisons. Technologies of Stone Age peoples show inconsistent transition patterns from past to present; population fluxes are found that could cause marginalization and competition between groups, influencing resource strategies; cultural change can cause variance in meaning and purpose of apparently similar rock art, ornamentation, and tools, thus bemusing interpretations; variance in cattle remains could mean replacement by, or acculturation to, pastoralists, or even a hybridization that conserves band culture and merely utilizes cattle as a food source. Even if there are similarities between Pleistocene, Stone Age, and modern hunter-gatherer patterns and material culture, the difference in ethos and the problem of migration will always reduce the accuracy of comparisons. Ethnoarchaeology risks misinterpretation through its use of modern groups as models, because of the multifarious qualities of hunter-gatherer lifestyles around the world. This challenge requires a pragmatic accompaniment, shifting the paradigm towoards a social and ideological perspective rather than a purely (paleo-)ecological one. In other words, a biocultural approach.

We could certainly assume the usefulness of the cultural traits of bands that are very consistent across the globe, such as practices of egalitarianism, reciprocity, and animism. However, we must always account for changes in culture, diversity between groups, changes in environment and context over time, and our human weakness to be hasty in attributions and interpretations. Nonetheless, there is still much to learn from modern hunter-gatherers about our biocultural evolution. We must not view them as pristine, living relics or artifacts, but rather as our best source of advice when interpreting evolutionary and archaeological findings. In a way, we must come to terms with the uncertainty that is essentially affiliated with such a field of study and feel fortunate that there are still band-level societies in existence to even try to use as models for the past.