Human ancestors nearly went extinct 900,000 years ago
Human ancestors in Africa were pushed to the brink of extinction around 900,000 years ago, a study shows. The work, published in Science, suggests a drastic reduction in the population of our ancestors well before our species, Homo sapiens, emerged. The population of breeding individuals was reduced to just 1,280 and didn’t expand again for another 117,000 years.
Nick Ashton, an archaeologist at the British Museum in London, who wrote a related perspective, says he was intrigued by the tiny size of the population. “This would imply that it occupied a very localized area with good social cohesion for it to survive,” he says. “Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system.
This period was part of the Early-Middle Pleistocene transition — a time of drastic climate change, when glacial cycles became longer and more intense. In Africa, this led to long periods of drought. Li says that the changing climate might have wiped out human ancestors and forced new human species to emerge. Eventually, these might have evolved into the last common ancestor of modern humans and our extinct relatives, the Denisovans and Neanderthals.
Around 813,000 years ago, the population of pre-humans began to swell again. How our ancestors managed to survive, and what allowed them to flourish once more, remains unclear, says Ziqian Hao, a population geneticist at the Shandong First Medical University and Shandong Academy of Medical Sciences in Jinan, and a co-author of the paper. However, he says that the bottleneck is likely to have had a crucial impact on human genetic diversity, driving many important features of modern humans, such as brain size. He estimates that up to two-thirds of genetic diversity was lost. “It represents a key period of time during the evolution of humans. So there are many important questions to be answered,” he says.
Benefits of bipedalism
What’s so useful about walking on two feet? A lot, actually. A twolegged primate can stand up and reach food (as chimps do) that a fourlegged primate would find challenging. A two-legged primate can move more efficiently between patches, since two-legged walking uses less energy than four-legged walking, and a bipedal ape can stand up to survey for danger (as meerkats do), which comes in handy in a savanna filled with carnivores. In addition, by standing upright, a two-legged primate exposes less of its body’s surface area directly to the hot African sun and thus requires about two-thirds the water of a similarly sized four-legged primate.
Robert L. Kelly, The Fifth Beginning, p. 25
Darwinian dynamics
We argue that the evolution of order in living systems and certain nonliving physical systems obeys a common fundamental principle which we call the Darwinian dynamic. Such ordered systems deviate greatly from the thermodynamic equiprobability rule according to which, for example, all nucleotide sequences of comparable length should be found in roughly equal abundance. We formulate the Darwinian dynamic by first considering how macroscopic order is generated in a simple nonbiological system far from the thermodynamic equilibrium. We then extend our consideration to short, replicating RNA molecules, which we assume to be like the earliest forms of life, and show that the underlying order-generating process is basically similar. The equation we use as an example of the Darwinian dynamic for these simple replicators contains variables that express the basic conditions necessary for the process of natural selection as conceived by Darwin: variation of type, heritability, and competition for limited resources. By starting with such uncomplicated systems, we believe we have clarified the essential elements of natural selection. Specifically, we show that the fitness of an RNA replicator (its per capita rate of increase) is a function of adaptive capacities which are intrinsic (in the sense that they are determined by the nucleotide sequence) and of the availability of resources. The three primary adaptive capacities are, we think, the capacity to replicate, the capacity to avoid decay, and the capacity to acquireand process resource
Bernstein et al (1983). Darwinian dynamics
This is how you pitch evolutionary game theory
All of life is a game and evolution by natural selection is no exception. Games have players, strategies, payoffs, and rules. In the game of life, organisms are the players, their heritable traits provide strategies, their births and deaths are the payoffs, and the environment sets the rules. The evolutionary game theory developed in this book provides the tools necessary for understanding many of Nature’s mysteries.
Vincent & Brown, Evolutionary Game Theory, Natural Selection, and Darwinian Dynamics
Ritual, Religion, and Reciprocity
In mobile forager social life, ritual, and the esoteric narratives associated with ritual, are in part vehicles for the transmission of norms. But they also play an experiential role, and in doing so they increase group cohesion and hence reduce the fragmenting effects of conflict and disagreement (Lewis 2013, Lewis 2016). So while ritual and religion are relevant to the stability of an economy of reciprocation through their role of transmitting norms and giving them authority, ritual is also relevant to the stability of these forager economies through their experiential effects. I have argued that an economy of reciprocation imposes real stresses on cohesion, and so I suggest that proto-religion emerged (or expanded in its social significance) in part as a response to these stresses. The performative aspects of these proto-religions were important for their powerful and bonding experiential effects. On this hypothesis, proto-religion consisted in multimodal performances of music, ritual and dance, often combined with experience-altering technologies. The experiential impacts of song, dance and performance were often supplemented and amplified by experience-altering drugs or by stressing the cognitive system in other ways: sleep deprivation, extremes of heat or cold (for example, Native American sweat lodges), sensory overload, exhaustion or just through the intensity of these emotionally charged events (Baumard and Boyer 2013). While mythic narratives play a central role in ethnographically documented small-world religious traditions, these are often experienced as part of collective, socially bonding, socially marked, mixed modality performance, and often in the grip of altered states of consciousness. Agents encounter these narratives, which are often themselves far from mundane, as part of a package of intense and unusual perceptual experiences, and often while they are themselves taking an active part in the total performance, themselves engaged in coordinated, entrained song, ritual and dance.
Kim Sterelny, The Pleistocene Social Contract, p. 89-90
Cooperation, Stability, and Scale
There is reason to suspect that [the transition from the relatively closed social world of a great ape residential group to the richly connected forager bands of ethnography ] was very gradual. Its initial roots may date back to the Heidelbergensians, at about 800 kya. But it was not complete until the very late Pleistocene (perhaps even later). For it is only then that we find evidence of active cooperation across residential groups, and perhaps of clan structures that transcend an individual forager band. The final transition began in the terminal Pleistocene (about 25 kya–12 kya) and in the early Holocene, with the origins of sedentary society. This led to an increase in social scale and social inequality. In trying to understand why cooperation is stable, scale, complexity and inequality all matter. For mechanisms that suffice to stabilize cooperation in small politically unstructured and relatively homogenous social environments breakdown in larger and more structured ones. Personal knowledge and trust can stabilize cooperation in small, intimate social environments but not larger and more differentiated ones. Continued cooperation is especially puzzling in social worlds that are not just larger but also hierarchically structured. For these seem to be cases where the profits of cooperation are largely hijacked by elites. In such cases, theory predicts the collapse of cooperation. The take-home message of this chapter is that culturally evolved tools—language, myth, ritual, explicit norms—play a central role in the stability of cooperation in the late Pleistocene shift in the economic foundations of cooperation, and an equally central role in the survival of the social contract through the final Pleistocene and early Holocene social revolutions.
Kim Sterelny, The Pleistocene Social Contract, p. 58