Exciting new studies in human evolution are appearing rapidly, transforming scientific understanding of how the human community took form. A 2018 article by archaeologist Eleanor Scerri and colleagues, for example, identifies key debates on this topic. They ask: When and how did Homo sapiens become a species? How important were subgroups and migration in human evolution? And while Scerri cannot yet propose a specific date or place for the origin of Homo sapiens, she reveals certain misunderstandings in earlier thinking about human populations, then points to new directions in interpretation.
Scerri argues that paleontology shows varied physical populations with varied material culture, geographically spread through Africa. She notes genetic evidence suggesting that the lineage for Homo sapiens traces back to 500 ka (“ka,” in this essay, means “thousand years ago”); she also suggests human admixture with other hominin populations in Africa.
Physical remains of humans are now labeled as Homo sapiens from 300 ka. The ecological record suggests shifts in African landscapes over time, and present-day African populations continue to reflect ancient variations. Underlying these patterns, Scerri argues, were “structured” (i.e., subdivided) human populations throughout Africa, rather than an initially small, uniform, and localized population. The key to an improved interpretation of human evolution, she says, is more fully specified models of population structure.
Scerri’s argument on “structured” populations in Africa, while important, is just one issue in the broad debate over human evolution. Many other questions remain. From what ancestors did they come? And more broadly, what types of information do we need to understand such aspects of human evolution? It is remarkable how much has been learned—and how much remains to be learned.
Assessing the Strategy for Evolutionary Analysis
The purpose of this essay is not only to report on recent evolutionary news but to consider the overall strategy of evolutionary analysis. It’s a review of the categories of evolutionary analysis from the beginning of Homo sapiens to recent times, as seen in debates since the time of Darwin.
After identifying categories of information on evolution; I point to dynamics of change within each of those categories, then point to examples of discoveries in evolution. In conclusion, I suggest unification and differentiation of the human population as two broad evolutionary patterns that combine the many specific types of change. A final note focuses on the role of analytical modeling in developing specific arguments within the context of unification and differentiation.
Categories of Information on Evolution
These six major categories show that early humans led complicated lives and that modern evolutionary scientists have had many issues to consider:
- Phenotype (from the 1870s). This is the study of the physical beings of humankind, their historical remains, and their development and behavior over their life course, including the basic biological structures of household and community.
- Genotype (from the 1980s). Genomics is the study of human DNA and its genes, which evolve and produce proteins that generate all human processes and activities.
- Population (from the 1920s). Total numbers of humans and their subgroups are measured in two ways: as “census populations” of all adults and children and as “effective populations” of breeding females, estimated genetically. Population includes the “speciation” or formation of humans into a coherent and distinctive form of life. Population also includes types of human migration.
- Environment (from the 1950s). The environmental factors of physical geography, climatic change, plus flora and fauna—linked into ecological webs—influence human life but are also changed by human activity.
- Culture 1 (from the 1980s). This is culture as understood and studied by biologists and environmentalists, who call it “social learning.” Social learning describes the ways in which individuals observe others, develop new behaviors, expand their cooperation, and influence their genome. Among humans, this process accelerated about 300 ka and is still influential in human networks.
- Culture 2 (from the 2010s). This is how culture is understood and referred to in today’s world. It may also be called “group culture,” and its connections to biological evolution are just now being analyzed. At its most basic level, group culture began when humans formed conscious “we-groups,” whose decisions created syntactic language and institutions to complete tasks—a process that accelerated about 70 ka. This led later to the creation of much larger social groups such as the businesses and states of today.
Major Evolutionary Dynamics
Each category of evolutionary information has subcategories that change and interact with one another. For each category, here are the major dynamics or processes of change:
- Phenotype: changing physical form, steps in life-course development, group behavior, incorporation of new processes into the human order
- Genotype: DNA mutation and selection, RNA and protein creation, epigenetics and regulation of gene activity
- Population: growth and decline in populations (and subpopulations), displacement of migrants, admixture among migrating groups
- Environment: short- and long-term changes in geology, climate, and flora/fauna—and how those changes influence the categories of human evolution
- Culture 1: individual learning in humans and other species (known as “social learning” and “cultural evolution”), the expansion of cooperative behavior
- Culture 2: group decision-making in humans, group activity in representation or modeling of the world, media of expressive culture
Listing these dynamics is instructive, but in viewing them we must keep in mind that the human genome has only 30,000 genes—not much more than in far simpler animals. Thus, it is the interactions among the genetic and other dynamic processes that paint the full picture of human existence.
Some Key Discoveries
For the categories of evolutionary analysis and the dynamics within them, I note some major discoveries and their influence.
- Physical remains: Homo ergaster skeleton of 1.5 million years ago (1984); Jebel Irhoud remains found 1961 and dated in 2017 to an age of 315 ka
- Comparing human and chimpanzee childhood skills (Tomasello, 2018)
- Identification of persistent human community and household groups (2000)
- Mitochondrial DNA analyzed (1987); ancient DNA and human history (2015)
- Human genome initial sequencing (2003), revealing 30,000 genes
- Merge (a genetic category) theorized (1995); Merge in the human brain (2015)
- “Effective population” of breeding females theorized (1931); estimates of early African effective population (1990s)
- Occasional migrations into Arabia from 400 ka, reported in 2017
- Geological observations on long-term African historical climate (after 2000)
- Niche construction theory on interaction among evolutionary categories (1980s)
- Culture 1
- Kin-selection theory and dual-inheritance theory (1980s); cumulative cultural evolution (2009)
- Culture 1 and Middle Stone Age (MSA) technology from 300 ka, with networked communities
- Culture 2
- Hypothesis on adolescent leadership in syntactic language and institutions (2010s)
Understanding Unification and Differentiation
Evolutionary science needs to know more about fluctuations in the variety within human populations. Consider this: Populations with closely similar genomes and phenotypical form and behavior are labeled as “species.” Since the human genome is far more unified than that of other mammalian species, we would seem obviously to be a species. Yet fossils of human populations continue to reveal specific characteristics for every region and local community. Thus, in evolutionary terms, questions remain about when humans have become more similar—or more unified—and when they have differentiated over time.
You can look at the dynamics and discoveries listed above and consider which of them might lead to unification of the human species and which might lead to differentiation. For instance, migration of small and isolated groups leads to differentiation through “genetic drift.” But large-scale migration from one population to another causes the two populations to become more similar. Therefore, processes of both unification and differentiation have taken place throughout human history. Another question to consider: In what situations did either unification or differentiation predominate?
Analytical Modeling of Past Processes
Scerri’s 2018 article makes recommendations for changes in models of genetic change and population structure. To enact such changes, researchers must make explicit and sensible assumptions that define variables and their interactions. This would ensure that the resulting scientific models of unification and diversification can project detailed simulations, which can then be compared to real data.
Fortunately, the science of network analysis has greatly advanced the modeling of large and complex datasets—by including the specific forms of networks and their links to each other. Techniques that are now being applied in medicine, for example, might be modified and applied in the history of evolution. Whatever the application, the modeling will be complex, because it must address the various scales of human existence: those of the genome, cells, human organs, individuals, and the different types of behavior of populations, as well as the environmental influences at each scale. It will be interesting work.
Based on this simplified summary of the strategy of evolutionary analysis, I will return in two later essays to offer narratives of some major steps in human evolution over the past half-million years.
The above categories of evolution of homo sapiens leaves me with a picture of a genome that is clustered in different ways in different places. There must be some percolation between clusters. Culture also percolates, perhaps from certain environments to other similar environments. It makes me see that homo sapiens is not one thing, but a group loosely defined characteristic that has been refined by the effects mentioned above. There is also the effect of “self-selection”; an aspect of culture in which mates tend to be chosen on aesthetic or practical criteria that are cultural in nature. Perhaps the main guidance in the evolution of homo sapiens is governed by culture — the fittest culture, so to speak. Pre-sapiens I imagine that culture may not be the dominant pressure on evolution. But for homo sapiens, culture is the dominant pressure, and if one had to say what made homo sapiens distinct from other primates, it would be culture. Cculture is not only an adaptation to the environment, but the adoption of the understandings that brought about that adaptation to environment (by which I mean, in the discriminatory pattern of the mind). This “pressure” on the members of that culture or neighboring cultures may affect a genotypical or epigenetic selection by the differential adaptability of members of the culture or other neighboring cultures to the, let us say, “dominant” culture. That is, the success of an individual in a culture may affect selection in reproduction towards those most capable of embodying all aspects of that culture.
But what is dominant in one environment may not be in another. So always there will be clusters of relatively successful cultures, so that in a sense, the system as a whole is evolving in the way outlined above. Obviously, cultures have diverged quite a bit in this world, but on one continent, it is likely that the divergence will be limited.
Thanks for the piece; it was stimulating.
This comment emphasizes a clustered genome (and populations) plus the percolation of influences among them, then argues that cultural factors arose and percolated across environments, becoming a dominant influence in the processes of evolution. It suggests that culture is reflected in “self-selection” as in criteria for selection of mates, but also depends on environment and on understandings of the process of adaptation.
I ask, when and how did culture arise? There is a substantial literature applying cultural evolution to songbird behavior. Most evolutionary thinking on culture centers on individual human behavior (what I called Culture 1), analyzed through terms such as social learning, kin-selection, dual inheritance, cultural evolution, and cumulative cultural evolution, surely including basic communication through gestures, vocalization, and perhaps symbols. I acknowledge this work, but don’t think such culture can explain syntactic language, contractual behavior, the functioning of institutions with high knowledge barriers to entry, or the exchange of ideas through explicit representation.
The strength of this comment is in how individual-level culture can play a role in disaggregated human evolution along with environment. But at a certain point, to get to where we are today, humans needed to cross boundaries into group behavior: intensive study, contractual agreements, and exchange of representations. That’s what I called Culture 2, and I see syntactic language as the breakthrough.
I believe I meant culture 1. Culture 2 is how we act like an amoeba. Herd logic. But are they intrinsically different?
Culture 2 seems like the “culture” that comes through mediums of mass electronic connection or communication. But that’s much like a newspaper. There are gray areas everywhere. But as to which culture is most important for the selection that is now active n determining our future, I am not sure that is something we can say. We may have opinions… Right now our future seems to be that culture 2 is wagging the dog. What is relevant to me is which makes us more able to use our wits to survive. But if the future is for us to become hive animals, then culture 2 and mass “culture” may be the thing of the future.
Your point that syntactic language was the starting point of culture 2 can serve as a definition of culture 2. It is hard to dispute this since all of our society is dependent on language, which enables the effective communication of individual thoughts to others within the reach of various technologies that support that means of communication.But are those technologies part of culture 1 or culture 2? At a certain point, such distinctions seem to exhaust their meaning. Are there two aspects of human capability that act together to create the new spaces or regimes in which communication can occur? This suggests a dialectic that is driven by a creative impulse of humanity to expand the domains of their control or understanding. Just what those two aspects are depends on context, of course, and the ideas generated by an individual or individuals of something new — rather like a game.
Where this is headed, who knows?