WEDNESDAY, 4 SEPTEMBER 2024
Evolutionary biologists often talk about the theory of natural selection first proposed by Charles Darwin in 1859, which states that the environment imposes selection pressures on individuals. A selection pressure is defined as ‘an agent of differential mortality’ i.e. a factor that influences which individuals survive and includes predator density, prey availability, and the climate. The most well adapted or ‘fittest’ individuals are more likely to survive. Over generations, random DNA mutations occur and, if beneficial, the individual has a higher chance of survival and is more likely to pass this beneficial genetic information on to its offspring. Less often discussed are the impacts of behaviour, culture, and community on the trajectory of evolution and in no species is this more pronounced than our own. Culture and community coevolve, meaning the development and progression of one relies on the other. Culture holds a community together and a community is necessary for a culture to form - one cannot exist without the other. Culture and community also play an important role in evolution. Cultural practices evolve much faster than genetic factors, transmitting information more reliably and on a shorter timescale. In addition, in a large community more individuals engage in a cultural practice meaning selection has a stronger effect on a gene. In large and long-lasting communities, cumulative culture (an accumulation of beneficial cultural modifications) can develop as seen with increasingly complex languages, tools and artistic traditions.HOW DOES CULTURE AND COMMUNITY IMPACT EVOLUTION?
Gene-culture coevolutionary theory is a complex term describing a simple principle: genes and culture interact and influence one another. Human genetics influence our ability to form connections with and learn from other humans. These connections then feedback and influence our genetics. The social connections within communities have shaped the evolution of humans and our ancestors (collectively termed hominins) for thousands of years by increasing the ease with which information can be shared between individuals (i.e. the ease of cultural transmission). Community changes the selection pressures humans are exposed to, for example, farming communities have a more stable food supply than those who hunt and, more recently, living in heated homes means individuals are less likely to die from the cold. Community can also alter the pattern of gene flow (which genes get passed on to whom), for example, religion and tradition can alter which individuals mate together. The development of group living and agriculture alongside the teaching and learning of tool making and language practices rely on human beings being connected with one another. This article will attempt to demonstrate the impact of human connections on our evolutionary history and suggest how our current level of hyper-interconnectivity might influence the future of human evolution.
VERY EARLY INTRODUCTIONS OF CULTURE AND COMMUNITY
In most animal species, cooperation is either absent or limited whereas in humans it is overwhelmingly prevalent. Although there is debate, many anthropologists agree that 100,000 years ago most people lived in tribal scale societies. How did connections within these communities, and their shared culture, influence evolution? It is thought that modern humans are much less robust than the early hominid due to the widespread use of projectile weapons reducing the need for hand-to-hand combat when hunting. The use of projectile weapons spread within and between communities, altering the selection pressures placed on our ancestors. A large robust build was no longer necessary for combat and would be energetically expensive to maintain; less robust individuals were perhaps more likely to survive. Similarly, the human vocal tract, auditory systems, and the associated neural systems have evolved over time, enhancing our ability to produce and decode spoken language and allowing for more effective communication and deeper connections between humans. Hunting with projectiles or cooperating with language increases an individual’s chances of survival and alters the selection pressures on them. For example, it is beneficial to be able to discriminate sounds in speech or have nimbler fingers with which to make tools. Cultural transmission and learning changes the selection pressure that affects genetics - genetic mutations that make language learning or tool making easier are deemed beneficial and become likely to be passed on. These genetic changes in turn alter culture, for example, they make language learning easier and this cycle continues. Over time this process will direct the course of evolution.
THE MIGRATION OF THE POLYNESIANS
Culture and community affect gene flow between populations which impacts the combinations of genes brought together, altering the evolutionary trajectory. Kayser et al (2006), looked at the genotypes of Polynesian communities and found that the mitochondrial DNA (inherited from the mother) was most similar to those found in Asian populations, whereas Y-chromosome DNA (inherited from the father) was most similar to Melanesian populations. The ‘slow boat’ hypothesis suggests that Polynesian communities originated in East Asia and mixed with Melanesian populations before settling in Pacific islands via long boat journeys. Historical matrilocal tradition in Melanesian populations, in which the husband goes to live with the wife’s community, meant males were incorporated into Polynesian populations but females were not, explaining why the Y chromosome is most similar to Melanesian populations. In addition, the cultural practice of migrating via long ocean voyages created a strong selection pressure for a ‘thrifty metabolism’. The resulting genetic changes in the population over time allowed the Polynesians to survive these long voyages. Interestingly, however, today the descendants of these communities that live in the Western world, where there is an abundance of food, are at an increased risk of type II diabetes. This is partly due to their thrifty metabolism that allows them to efficiently extract nutrients from food. These examples demonstrate how the human connections within societies can play a major role in influencing the direction and strength of gene flow, and the genes that are selected for. This differential genetic inheritance might, in turn, be expected to influence the spread of culture as the different groups will pass on different traditions.
AGRICULTURE
The human connections that grew into communities during our evolution can explain some of the genetic patterns we see today. Farming communities and the domestication of animals like cattle approximately 10,000 years ago reduced our reliance on hunting and gathering. Ancestral humans are known to have been lactose intolerant and raised cattle solely for meat. However, when famines hit and created a new selection pressure, individuals with a mutation for lactose tolerance survived longer and passed that tolerance down to their children. This cultural farming practice changed human genetics. As mathematical modelling by Feldman and Cavalli-Sforza showed, the lactose tolerance allele reaching a high frequency in the population was dependent on milk-drinking parents passing the practice on to their offspring i.e. cultural transmission. As lactose tolerance became more prevalent, dairy farming practices began. The genetic change of lactose tolerance then reflected back into the culture. Descendants of these communities, including most northern European populations and some African and Middle Eastern populations, now have much higher rates of lactose tolerance. Interestingly, lactose tolerance was, for a long time, assumed to be the ancestral condition because Western scientists were biased due to their own experiences. This bias emphasises the importance of cultural diversity and communication between scientists of different perspectives: connections amongst the scientific community are as vital for progress as they were thousands of years ago in transmitting cultural practices like milk drinking.
HOW WILL HUMAN CONNECTIONS CONTINUE TO INFLUENCE OUR EVOLUTION?
The future of human evolution has both inspired and puzzled biologists for generations. The entire debate is too large to discuss in full here but it is important to introduce some of the key questions facing evolutionary biologists. Human cultural behaviours including building houses, wearing clothes, farming, and accessing healthcare have greatly increased interconnectivity and reduced the strength of the selection pressures acting on us. Will this relaxed selection pressure reduce the fitness of the human population? Human mate choice is not well understood and is shrouded in cultural complexity. How will your female friend searching for a six foot tall male partner influence the trajectory of human evolution- should we expect to see males growing taller? Ever increasing levels of interconnectivity might leave us vulnerable to epidemics, but perhaps the same increase in interconnectivity forms part of the solution. Communication between scientific communities, authorities, and the public is known to increase the effectiveness of disease control. Additionally, climate change presents one of the largest selection pressures facing humans and given its rapid nature, cultural evolution will play a key role in allowing humans to both prevent further climate change and adapt to the changing world.
In his seminal text ‘The Evolutionary Manifesto’, John Stewart claims that the evolution of a species that can comprehend evolution is perhaps the most important evolutionary event of all time. He argues knowledge of evolution will allow humans to control and direct the process. Whether humans will consciously alter our evolutionary trajectory is unclear, but what is clear is that human connections will continue to influence the path of evolution.
Article by Rachel Duke
Artwork produced using Dall-E
