Unit 5. Human Evolution: Adaptation and Environmental Justice



How are fossil lineages measured?

Phylogenetics is the field of biology that examines the relationships between organisms, and the causes of the evolutionary patterns that are present. Recall that evolution as defined by Charles Darwin is descent through an evolutionary lineage with trait modification. A lineage is a general term that refers to a continuous line of descent, or a series of organisms that is connected by reproduction from parent to offspring. For example, in human evolution, over time we developed bipedal locomotion or an upright posture, and larger brain capacity because there was an evolutionary advantage to having those traits. This means that parents with larger brains and morphology that favored bipedal locomotion had more reproductive success than parents that had smaller brains and whose morphology favored quadruped locomotion. Phylogeneticists use information about organisms to construct phylogenies or maps of the evolutionary relationships between them (Figure 5.1). Phylogenies help us to understand species extinctions, ancestral and modern species origins, and the points at which lineages split, also known as speciation or cladogenesis. Figure 5.1 shows the human phylogeny.


Figure 5.1

Human Phylogeny


One of the most common ways to group organisms into species is by the morphological or anatomical characteristics of the organism (Figure 5.2). For example, in human evolution the shape of the skull is often used to help classify different organisms into species. In human evolution though, scientists also use geochronological dating techniques to help determine species. This means that the age of the soil where the fossil specimen was found is also analyzed and dated to determine how old the surrounding soil is. This helps archeologists better evaluate the age of a given fossil organism.



Figure 5.2

Morphological species differences between human relatives




Radiocarbon dating techniques are also used to age soil and other carbon containing compounds. Other radiation exposure dating methods such as non-destructive electron spin resonance (ESR) allow for the dating of tooth enamel, thermoluminescence (TL) allows for the dating of burnt flint and stone, optically stimulated luminescence (OSL) allows for the dating of sediments and open system U-series dates bones. These techniques measure trapped electronic charges that accumulate in crystalline materials as a result of low-level natural radioactivity at different sites to give an estimate of age.


In the late 1980’s, paleoanthropologists began been using genetic techniques to examine fossil organisms and human evolutionary lineages. This process works by extracting deoxyribonucleic acid (DNA) from fossil specimens and using genetic markers to examine genetic relationships. However, unlike modern genetic analyses, ancient DNA samples are often degraded and have low quality. Therefore, scientists estimate that there is an upper limit on the age of fossil specimens that are useful for paleogenetic analysis.


However, mitochondrial DNA has also been found to be useful in unraveling the puzzle of human evolution because mitochondrial DNA can be examined from living human and fossil populations, and is inherited strictly through the maternal line. This means that you inherited mitochondrial DNA only from your mother, without mixing from your father. Furthermore, your mother’s mitochondrial DNA was inherited only from her mother and so on. Since mutations in mitochondrial DNA are thought to occur at regular time intervals, this straight maternal lineage without paternal mixing gives a mitochondrial clock leading back to the oldest common female ancestor. For example, African people are found to have the oldest mitochondrial DNA, pointing to the oldest common maternal ancestor for modern humans that lived in North Africa between 180,000 and 270,000 years ago.




How did the modern Homo sapiens lineage evolve?


In 1871 Charles Darwin proposed that human and apes might share a common ancestor millions of years in the past. Darwin based his assumption on the morphological, biological and behavioral similarities that humans and apes share. We now know that humans and chimpanzees share more than 98% of the same genes and that we did share a common ancestor about 8 million of years ago. There were many different species of hominids and apes throughout history that went extinct. However, this section will focus on those species that paleoanthropologists believe are our direct ancestors.


Approximately, 8 million years ago lush forests covered most of the African continent. During this time, Miocene ape species flourished because they were very successful in the arboreal environment. However, approximately 6 million years ago, the climate in Africa became dryer and the majority of the Miocene apes went extinct due to the loss of the forests. Yet, some species thrived, and one of those species was the oldest common ancestor of today’s modern humans, Australopithecus afarensis (Figure 5.3).


Figure 5.3

Human evolutionary tree



About 3.5 million years ago in what is now known as Laetoli, Tanzania, there was a massive eruption of the Sadiman volcano, which covered much of land with ash. After the eruption it rained and turned the ash-covered ground into cement. Many animal footprints from that time period were preserved in this cement, as well as three sets of footprints from bipedal hominids. This discovery was important because it highlights the evolution of bipedal locomotion with forward facing toes in our early ancestors. This is unique since chimpanzees and other modern apes have a prehensile toe (toe on the side, like our thumbs) for grasping tree branches. This discovery also shows that our common ancestor with modern apes was before 3.5 million years ago.

Scientists believe that the hominids that made the footprints at Laetoli were of the species Australopithecus afarensis that lived between 4 and 2.7 million years ago (Table 5.1). In 1974, archeologists were exploring Hadar, Ethiopia, which has the right kind of geology for the preservation of fossils when they found the oldest common ancestor for all other hominids that we know of to date. This fossil was a small bipedal female of the species A. afarensis that stood about four feet tall. The skeleton was dated to about 3.2 million years old and was remarkably complete. The fossil was named Lucy due to the Beatles song ‘Lucy in the Sky with Diamonds’ that was playing during her discovery.




Ardipithicus ramidus

5 to 4 million years ago

Australopithecus anamensis

4.2 to 3.9 million years ago

Australopithecus afarensis (Oldest Ancestor)

4 to 2.7 million years ago

Australopithecus africanus

3 to 2 million years ago

Australopithecus robustus

2.2 to 1.6 million years ago

Homo habilis

2.2 to 1.6 million years ago

Homo erectus

2.0 to 0.4 million years ago

Homo sapiens archaic

400 to 200 thousand years ago

Homo sapiens neandertalensis

200 to 30 thousand years ago

Homo sapiens sapiens

200 thousand years ago to present


Table 5.1

Approximate dates in hominid history




About 2.2 million years ago the Homo lineage evolved from A. afarensis with Homo habilis, which is the oldest known Homo species. The next ancestor that evolved was Homo erectus that lived about 1.8 million to 300,000 years ago. Homo erectus had much larger brains than other hominid species and had anatomy that was much more like modern humans. The best evidence we have for H. erectus was found in Lake Turkana in N. Kenya and lived about 1.5 million years ago. This fossil was of a 9 year old male that stood at 5’ 4” inches tall and full grown would have stood about 6’ tall. About the time that this boy lived, H. erectus began to radiate out from Africa and populate other regions of the globe.


Scientists believe that H. erectus populated many regions of the globe including Northern Europe. In 1956, in Feldhoffer Germany, scientists discovered another hominid species that was very similar to modern humans but still showed some anatomical differences. Anthropologists named this species, which lived about 200,000 years ago, Homo neandertalensis. Due to the glaciation that was present in Europe at this time, this species developed in relative isolation, but was far from primative. Neandertals, as they are more commonly known, had complex tools, fire, and culture.


Currently, there is fierce debate over whether Neandertals were a side-branch of human evolution or were part of our direct lineage. Some scientists think they were a different species that went extinct when modern humans arrived on the scene, while others think they are an ancient population that blended with Homo sapiens; therefore, their genes may be with us today. Morphological evidence from Croatia shows that early in Neandertal history, they look like classic Neandertal species. Whereas in later history, the Neandertal fossils show characteristics that more closely resemble modern humans, which suggests that interbreeding occurred and Neandertals were a race of modern humans. Although paleogenetic research is a fairly new tool in paleoanthropology, there have been some DNA analyses on Neandertal skeletons, which have determined that Neandertal DNA is distinct from modern humans, and that these species have been separated for more than 400,000 years.



How did early humans colonize the Earth?


There are two competing schools of thought on how modern humans colonized the Earth: The out of Africa theory and the multi-regionalism model. The debate between the two theories rages because approximately 100,000 years ago the Earth was simultaneously home to Homo erectus, Homo sapiens and Homo neandertalensis, which make interpretation of the historical evidence complicated. By about 30,000 years ago, the only human species still present was H. sapiens or modern humans.


The out of Africa theory is based on the idea that modern H. sapiens lineage evolved fairly recently in Africa; then modern humans radiated out from Africa and spread around the globe (Figure 5.4). This theory suggests that modern humans replaced all other hominid populations that were descendants of H. erectus, without interbreeding with them. This theory also proposes that the populations of H. erectus that had migrated out of Africa more than a million years before, became geographically and reproductively isolated, which caused independent evolution and speciation to occur. The European Neandertals may have been an example of this process.



Figure 5.4

Migration of human populations thousands of years ago




The multi-regionalism theory proposes that pre-modern humans (H. erectus) migrated from Africa to other places on the planet and then slowly evolved into modern humans in many different areas of the world. This suggests that all living modern humans are descendents of H. erectus that left Africa approximately 2 million years ago. This theory also argues that there was gene flow or interbreeding between geographically dispersed populations that prevented speciation between the groups. Furthermore, natural selection caused regional variability between different populations, creating different races of people that are evident in today’s humans.


Currently, most scientific evidence points to the out of Africa theory because ancient fossils of modern H. sapiens have been found in Africa, artifacts and stone tools show African origins, and recent DNA analyses suggest that the founding population for modern humans originated in Africa. Recent DNA studies, especially those of mitochondrial DNA, show that modern humans also have relatively little genetic variation suggesting that all living humans may have originated from a small founding population of H. sapiens in Africa approximately 50,000 to 400,000 years ago. Conversely, some Neandertal fossils and some fossils in China dating back 100,000 years, show evidence of the characteristics of both modern humans and H. erectus, supporting the multiregional model of human evolution.



How did humans evolve from being effected by the environment, to affecting the environment?

Historically, hominid species have been a tribal species, or one that herds together in small groups for survival. Cooperation between individuals gave them a better chance at surviving predator attacks, as well as a better chance of finding sources of food. This social cooperation that developed between individuals in species groups also led to the evolution of greater intelligence and better communication skills. For example, as humans evolved over time, we developed a greater brain capacity. Our oldest known direct ancestor, Australopithecus afarensis, who lived in Africa 3-4 million years ago, had a brain capacity of only 450 cubic centimeters (cc) (Figure 5.5). Our next ancestor in the human lineage, A. africanus, lived between 2-3 million years ago, and had a slightly bigger brain size of approximately 500 cc.



Figure 5.5

Brian size versus height of different hominids




Our oldest known ancestor in the Homo genus, Homo habilis, lived in Africa between 2.4 and 1.5 million years ago, and was a tool user with a brain size of 800 cc. This species also shows evidence of the development of some speech, which would have been useful in a tribal type society. Homo erectus lived between 2 million and 300,000 years ago and had a very large brain capacity of 900–1200 cc. This species was also capable of complex speech. Homo erectus also developed tools, weapons, and clothing, used fire for warmth and cooking, and also showed evidence of primitive culture (Figure 5.6). Modern Homo sapiens evolved around 120,000 years ago with an average brain capacity of 1500 cc, and complex culture and language.


Figure 5.6

Human evolution over time



Since survival was difficult over most of human history due to predators, disease, unpredictable shelter, and lack of stable food supplies, populations never expanded at a fast enough pace to make significant impacts on the Earth system. However, as humans developed larger brains, became more intelligent, and developed culture that was passed down through generations; we acquired skills necessary to modify our environment for better survival, and an enhanced quality of life. At first, hunting and fire were the main tools used to modify the environment. Hunting caused the extinction of most large megafauna species on a number of continents, and the wide spread use and control of fire, especially by aboriginal Australians, altered the landscape so that it was more favorable for hunting. However, arguably the greatest change in human society occurred approximately 10,000 years ago in the Fertile Crescent with the development of agriculture.

Agricultural development allowed humans to begin altering the landscape to fit the needs of growing populations. Agriculture also changed human societies from being predominantly nomadic hunter and gatherer societies to more stationary societies with central villages, towns, and cities. Agricultural development also led to population explosions, which altered the landscape at an even greater rate to provide ever-increasing amounts of food, shelter, and land used for waste disposal. This change to a more stationary society with towns and villages also facilitated the development of cultural activities, specialized professions outside of food production, and the development of arts and entertainment. However, because most societies on the globe have now transitioned into being agriculturally dependent, stationary societies, the human population is now growing at an exponential rate. This unprecedented rate of population growth and the huge numbers of humans on the planet (currently more than 6.2 billion) is altering the surface of the Earth in ways that have never been seen previously in Earth’s history. Human activities are significantly altering the planet surface and atmosphere through large-scale deforestation practices and land-use change patterns, as well as by altering the composition of the atmosphere through the production of greenhouse gases and reactive nitrogen compounds.



How is wealth related to human wellbeing?


In recent decades, human populations have expanded at an exponential rate. In addition, technology and the consumption of vast amounts of natural resources have exploded to keep up with rising demand, predominantly from wealthy societies. But what drives the increased demand on material resources? Studies have shown that in many economically wealthy societies, people often increase the consumption of material goods in attempt to achieve greater happiness, or the so called the good life. Studies in the US have also shown that in recent decades, being financially wealthy has become more important than having a meaningful life philosophy, or in other words having a good sense of wellbeing (Figure 5.7) However, these large-scale increases in the consumption of material good that go along with being very well-off financially have led to declines in the health of Earth’s natural ecosystems, including wide-spread deforestation and land use changes, declines in ocean and coastal reef health, and the loss of countless species around the globe.


Figure 5.7

Financial wealthy compared to wellbeing




Regrettably, this increased consumption of material goods has not led to increased feelings of happiness or wellbeing that many people strive to achieve. Recent studies have shown that happiness and wellbeing only increase with economic wealth for people that are in extreme poverty. This is because extreme poverty causes mental distress about how people will provide even the most basic resources for their families. However, once people’s basic survival needs are taken care of, meaning that they have adequate food supplies, healthcare, shelter, and clean water, increases in income do not necessarily promote greater increases in happiness or feelings of wellbeing (Figure 5.8).



Figure 5.8

Relationship between income and happiness




Several studies have shown that certain things do enhance our feelings of wellbeing; but they are not financially driven. Feelings of happiness and wellbeing increase most dramatically with greater social connections. People that have strong social connections with friends, family, and a spouse generally have a greater sense of wellbeing, and are often much healthier, than more isolated individuals. In addition, people that have a healthy diet, are physically active, get adequate amounts of sound sleep, and engage in leisure and pleasurable activities often have the greatest sense of wellbeing. Individuals also feel the greatest sense of wellbeing when they live in an open and stable society, they do rewarding and engaging work that provides an adequate income, they have personal, value-driven goals, they feel trusted and respected, and have a strong life philosophy that provides meaning to their life.


These studies suggest that societies that are structured, not around economic growth and the accumulation of material goods, but on having healthy societies, with freedom, optimism, security, autonomy, high levels of social interaction, a connection with the natural world, and outlets for creative expression, will be more sustainable, and will have citizens that maintain a greater sense of wellbeing and fulfillment. Additionally, kind societies that are structured so that citizens feel like they are a part of a larger whole foster feelings of happiness and wellbeing. Thus, happiness stems, not from material goods, but from intimacy and connections with other people, from strong personal relationships, and from being engaged in society. Therefore, economic growth and wealth creation as a means to better society is flawed, and governments may be better served by focusing on improving communities and social services, reducing poverty and inequality, and fostering societal connections.




What is the concept of environmental justice trying to examine?


Environmental justice is a movement that developed in the early 1980’s in response to inequality of power structures related to resource availability and consumption of natural resources. The movement grew out of hundreds of localized struggles against corporate and government policies that marginalized socio-economic groups and particular races including native peoples, while exploiting energy and natural resources.


The environmental justice movement strives to protect all peoples from discrimination and bias, and it demands that people are treated equally regardless of race, nationality, or socio-economic status. Furthermore, the environmental justice movement calls for fair and just governmental policies that promote ethical and responsible land use and resource use policies to promote a sustainable planet for all current and future peoples, as well as for the other living organisms with which we share the space. This includes protecting local and native peoples through the implementation and strict enforcement of governmental treaties, agreements, and laws that affirm sovereignty and self-determination for native peoples. This also calls for opposition of military occupations, governmental and military repression, and exploitation of land, natural resources, and particular peoples and cultures by governments, corporations or militias.


Environmental justice groups are also particularly interested in protecting socio-economic groups that are poor and marginalized from governmental or corporate behaviors that threaten the safety of air, water, food and water resources that sustain communities. For example, environmental justice groups often bring about lawsuits and legislation that prevent nuclear testing, unsustainable resource extraction, toxic and hazardous waste disposal, and the implementation of projects that would contaminate, air, water, land, and food supplies in communities dominated by poor people or minority groups that often lack the ability to protect themselves.


Environmental justice groups also demand that corporations that produce hazardous waste, radioactive materials and other toxic substances be held accountable for the clean up and remediation of land that has been contaminated by the production or use of their product. Groups that are committed to environmental justice also strive to make sure that all groups, whether they are rich, poor, minority or majority, are treated as equal partners in every level of decision making when it come to government or corporate projects that have the potential to harm the environment. For example, participants should be involved in the assessment, planning, and implementation phases of projects, as well as the enforcement of environmental protection and the evaluation stage to determine whether projects are meeting the demands of all parties involved.


Environmental justice groups are also important for creating safe working environments for all people and preventing practices such as child labor. Environmental justice groups strive to make sure that poor and marginalized people do not have to choose between hazardous or unsafe working conditions and putting food on their families’ table. One of the main functions of these groups it to make sure that people have the opportunity to work without fear of environmental hazards. In addition, environmental groups also support workers that have been subject to unsafe working conditions to make sure that the victims are sufficiently and fully compensated for any harm that accrued from working in environmentally hazardous or toxic working conditions. This includes providing quality healthcare and monetary compensation and reparations to support families where providers can no longer work.


Lastly, one of the most important things that the environmental justice movement strives to do is to educate present and future generations, emphasizing sustainable social and environmental issues. An environmental justice education strives to appreciate the environment and the diverse cultures that it harbors. Environmental justice also strives to educate individuals to make informed personal choices to protect the Earth for current and future generations by consuming as few resources as possible, in the most sustainable and socially responsible manner possible.



Last updated: 8/14/2006 11:44 AM