Chapter 17: Evolution of the Brain, Intelligence, and Culture
This chapter explores the question of how humans came to possess a brain of such extraordinary powers – one that exceeds necessary functioning of simple day-to-day survival. Scientists have uncovered that our brains have evolved to a threefold increase in the last 3 million years, given fossil evidence of Australopithecus afarensis compared to the average size of the modern human’s brain – an increase in brain size found nowhere else in nature over such a relatively small period.
Encephalization
Although the brain makes up 2% of the total body weight of humans, it uses 18% of the total energy – causing scientists to look at what has caused this brain expansion. Two proposals exist on explaining this problem faced by humans: the first by Martin says that the mother’s metabolic rate is the key to how big a brain species can afford, with the higher the metabolic rate, the bigger the relative brain size; the second from Mark Pagel and Paul Harvey states that gestation time and litter size determine brain size – long gestation and the litter size of one being a component of human development. Coupled with these hypotheses has to be the environmental context – a stable and high-energy food supply with minimal predators.
In comparison to apes, the adult ape brain size is 2.3 times bigger than a neonate, while in humans the difference is 3.5 times. However, although adult apes and humans have similar body sizes and undergo similar gestation periods, human neonates are twice as large both in body size and brain size than ape neonates. Of this, Martin believes that human mothers devote greater energy in the development of neonates. Coupled with this is the secondary altriciality (brain growth) that human neonates undergo that effectively gives them a 21-month gestation period of 9 months inside the womb and 12 months outside, whereas apes are far less dependent and helpless during the length of this period.
The authors describe two types of fossil evidence related to brain size: indications of absolute size and surface features (convolutions and fissures). Figure 17.2 (p. 450) shows average brain size in relation to body weight from different fossil information and its relation to humans and the great apes. By showing through brain anatomy of humanlike vs. apelike traits – parietal and temporal lobes dominate vs. much smaller parietal and temporal lobes – we can start to understand a trajectory of brain size in our ancestral evolution, as shown in figure 17.3 (p. 451).
For measures of intelligence, the archaeological record fills in where much has been lost to time in understanding ancestral economy, symbolism, and technology. Nevertheless, scientists look to find the best measure of intelligence (figure 17.5, p. 453) based on the level of technology apparent in the fossil record showing different levels of encephalization.
Early explanations for brain expansion in hominins were based on the mastering of practical affairs, i.e. the mastering of complex tool-use behavior. Recent ideas point to man as a social animal and point to the study of non-human primates (NHP) in explaining this paradox. Scientists have proved that NHPs are highly intelligent in the lab but live relatively undemanding lives in the realm of subsistence. The answer to their intelligence lies, then, in their social environment and their understanding of complex social behaviors of networking, alliance making, manipulation, etc. The reason for this use of intelligence in social environment is because it opens up more mating opportunities for reproductive success. Figure 17.8 (p. 457) nicely shows the relation of behavior to increased intelligence.
Lastly, since social complexity drives intelligence, it is ecology that drives social complexity, as the authors point out. The ecological preconditions that lead to increased brain size and therefore intelligence is in constant development to afford the high-energy costs that large brains need. There are several possibilities for this, including additional energetics in provisioning, new higher-quality resources (meat and fish) and development of better technologies (cooking and processing). There is thus a triangle of relationships – intelligence, ecology, and sociality – wherein greater social complexity could evolve (figure 17.9, p. 458).
Cultural Evolution
Human evolution is often thought in the sciences as a transition from biological evolution to cultural evolution, a species freed from Darwinian natural selection. There are many other ways of looking at the uniqueness of human culture, with recent research looking at chimpanzee behavior in the attempt to find basic behavioral traits of culture – variation in social traditions, tool use, communication skills, and elementary symbolic understanding.
The authors describe many schools of thought within cultural evolution, all forming their basis around culture representing a system of passing information from individual to individual outside of genetic information. The transmission of information thus must follow different rules for coding within each individual. The several schools of interpreting this include:
- Gene-culture coevolution: Marcus Feldman and Luca Cavalli-Sforza of Stanford and Robert Boyd and Peter Richerson of University of California treat cultural evolution as a dual-inheritance model with cultural inheritance independent from the genetic system and they examine how it may evolve in relation to particular characteristics – with particular interest how ‘cultural units’ may be influenced by the environment.
- Meme: Richard Dawkins defines meme as the minimal unit of an idea of a behavior. Different memes are thus either transmitted or become extinct, much like natural selection, or, cultural selection.
- Primatologist’s views: Andrew Whiten and others mapped many behavioral traditions among many groups of chimpanzees (fig. 17.10, p. 461) to determine environmentally determined patterns of behavior and others seeming to be socially transmitted. Thus, human behavior can be viewed as something rooted in animal basic behavior and therefore hard-wired in our evolutionary behavioral adaptations.
The debate for which school represents the best model in explaining the evolution of culture and behavior is definitely up to interpretation, especially given that the archaeological record is very limited in this regard. However, all schools do believe that language played a major part in the evolution of culture.
-Which model of cultural evolution makes the most sense to you? Or is modern culture too complex to pin down in an evolutionary model, as some (most) cultural anthropologists would argue?
Chapter 18: Language and Symbolism
The Evolution of Language
Because written language has only been dated to emerging in the last 6000 years, scientists easily assume that spoken language preceded this, but when and how is not known but widely interpreted in different ways. Specifically, arguments have centered on the questions: was the evolution of language a slow and gradual process beginning with our hominin ancestors? Or, was it a relatively rapid process, beginning with the origin of Homo?
Fossil evidence is collected from endocasts, or crude maps of the surface features of the brain (of which fig. 18.1 further explains, p. 465). It is also collected from the voice-producing larynx and pharynx of the neck that are unique to humans that would lead scientists to conclude language ability (of which fig. 18.2 further explains, p. 466). Overall, fossil endocasts and laryngeal structure indicate a gradual acquisition of language capabilities through the history of hominins, with the possibility of it beginning with the origin of Homo, but this is still up for debate given the archaeological record.
Other modern interpretations base their beliefs in other anatomical traits – as Richard Kay and Matt Cartmill see with the hypoglossal canal and Ann McLaron with the relation of body size to the spinal canal; and in genetic research as Svante Pääbo studies in modern individuals with language impairment. However, these interpretations lack the evidence needed for validity and therefore remain open for debate.
Further areas of study focus on the archaeological evidence centered on tool use and the use of art. As fig. 18.4 (p. 471), Glynn Isaac shows how the increase in tool specialization must reflect the increase in social complexity and this could relate to the rise of complex forms of language as well. Iain Davidson and William Noble, on the other hand, argue that language is a recent development that is closely tied to imagery and art because of the communicative properties tied to artistic expression.
-Because the evolution of language is obviously so widely open to interpretation, are we still looking for the right fossil that shows the origin of language, or something else? What would this include?
Art in Prehistory
The authors state that the presence of prehistoric art is the most poignant of all aspects of behavior left in the archaeological record. The meaning of their art is still open to interpretation because the individuals living in the societies producing the art lived in a completely different world than our own.
Fig. 18.7 (p. 476) shows the sites of upper Paleolithic art found in Europe, which coincides with the arrival of anatomically modern humans. Much of the art has been found in caves, which coincides with the glacial period bringing extreme temperatures for humans to live in caves where art (paint) could be preserved for us to view today (fig. 18.9, p. 480 nicely shows the climate fluctuations for the period). Thus, the paintings can lead us to infer many aspects of upper Paleolithic behavior based on the paintings themselves as well as the use of caves for collective shelter.
Because many paintings of the Upper Paleolithic were discovered at many different times during the 19th and 20th centuries, interpretations of their meanings changed the more we learned and discovered, as Fig. 18.10 shows (p. 481). Modern interpretations view these paintings as showing the great diversity of the upper Paleolithic in terms of people, cultures, and the art itself, rather than past interpretations based on inductive hypotheses.
- The upper Paleolithic has a great deal of preserved art that can be used to understand the behavior of the people and the cultures living at this time, but this may be due to advantageous preservation conditions resulting from the glacial period that they come from. What does this mean for our interpretations of pre-upper Paleolithic art? What does this mean for our scientific interpretations in general based on the available evidence? What do the authors mean by equifinality in relation to this?
Chapter 19: New Worlds, Old Worlds
This chapter outlines the historical geographical dispersals of modern humans and its relation to ecological, environmental, and social changes.
Completing Colonization
The Americas: Although the route of the colonization of the Americas is undisputed – from Asia across the Bering Strait – the timing of this migration is up for scientific debate. By 11,500 years ago the archaeological evidence shows that America was clearly colonized due to the plethora of Clovis points that characterize their culture. However, scientists argue in the range of 30,000 to 12,000 years ago that the Americas were colonized, with little evidence for consensus as to how many migrations took place. During the period of migration, the Earth was in an Ice Age, making the American landscape much different than it is today. The ice age lasted between 75,000 to 10,000 years ago, with the coldest period between 65,000 and 21,000 years ago.
During a period between 20,000 to 13,000 years ago an ice-free corridor had appeared for populations from Siberia to come across to the Northwest Territories due to the massive drop in sea level captured in the ice caps. However, this is contested for how hospitable the conditions may have been to make such a migration possible. Archaeological evidence (five sites listed on p. 493) does show that humans inhabited South America at a time the predated the Clovis populations by several thousand years, with humans existing in the Americas as early as 30,000 years ago. This has been supported by genetic evidence based on mitochondrial DNA as well, linking early American populations with Asia. The evidence currently supports a multiple-dispersal hypothesis, with the last migration leaving the most archaeological and linguistic evidence and understanding of prior populations still left open for debate.
Australia: Australia has been isolated from other continents for millions of years, developing its own unique and distinctive fauna – making the first human inhabitants of the continent have to travel by water. Archaeological evidence, although debated, points to Australia being inhabited by modern humans as early as 60,000 years ago (see fig. 19.7 for archaeological sites and dates), with many scientists preferring to see colonization around 40,000 years ago as part of a single worldwide event. Many theories exist as to the origin of the Australian Aborigines, with the authors preferring the out of Africa hypothesis of dispersal along the southern coasts of Asia, leading to a long period of isolation from the Asian mainland seen in the narrow variation found in the modern Aborigine population.
The First Villagers
12,000 years ago marked the Neolithic revolution of humans relying on agriculture rather than forms of hunting and gathering and because of this the human population skyrocketed, as shown in fig. 19.9 (p. 501). In such a short period of time, the sedentism offered by agriculturalism led to the Neolithic period of a transition from the simple to the complex in terms of societal structure. Fig. 19.11 (p. 503) shows the modern belief that social complexity, as the result of sedentism, was the result of complexity in hunter and gatherer societies leading towards agricultural technology – a step-by-step introduction to domestication, not an overnight revolution. Several sites support this belief, such as the Russian mammoth-bone dwelling (fig. 19.12, p. 504) of 15,000 years ago showing the complexity of a small hunter-gatherer community.
The cause of this transition has been determined on two factors: population pressure and climate change. Mark Cohen has been a proponent of the first theory, relying on late Paleolithic nutritional stress on skeletal remains to form the causal relationship. Proponents of the second, more convincing factor sees the Neolithic transition coinciding with the end of Pleistocene glaciation. This change would have driven new plant and animal communities into new areas where they did not previously exist, driving humans in turn to take advantage of these new areas.
However, since it had taken modern humans 90,000 years to develop food production techniques, another factor must be understood and for many that is social complexity. Barbara Bender has argued that social complexity was a prerequisite of a sedentary agricultural system, not a product of it. Because much scholarly work has focused on technology and demography in explaining the Neolithic revolution, she contends that not enough attention has been paid to the social structure allowing such a revolution to take place. This is seen biologically in the change that humans underwent between the end of the Pleistocene and the beginning of the Holocene – by reduction in size and the decreased difference in sexual dimorphism – leading scientists to believe this reflects the change in the socioeconomic context.
Scientists agree that the Neolithic revolution played on many factors and a search for a single point of origin is now much less popular. Once agriculturalism developed under the Neolithic revolution, whatever the leading causes, it created an unparalled phenomenon in human history that created an ecological and social momentum all its own.
-Did the Neolithic revolution mark the first time in human history that ideas were spread rather than populations?
-What do you think of the evolutionary psychology argument that human behavior is based on our collective hunter-gatherer past experience?
-As the author’s put forth in Chapter 17 that ecology drives social complexity in creating intelligence, can this also explain the Neolithic revolution?
