Environmental impacts of prehistoric humans

Prehistoric cultures significantly transformed their environments by deforestation, fire, construction of structures and irrigation systems, and hunting practices. These behaviors were common in many habitats where humans lived, and culminated in the start of the Anthropocene era – the epoch defined by major human impacts on the Earth. As used here, the term "prehistoric cultures" represents all aboriginal, ancestral, or Indigenous^[a] cultures that were the original inhabitants of a region^[b] prior to the local adoption of a writing system; and also includes Pre-Columbian cultures in the Americas, regardless of writing system usage.

Prehistoric hunter-gatherers used fire to clear dense vegetation, improve mobility, and facilitate hunting.^[c] The development of agriculture accelerated the impact of humans on the surrounding landscapes. Farming often required clearing cropland, preparing soils, diverting or controlling water, and cultivating particular plant species. Forests and grasslands were converted into fields and pastures, while domesticated animals altered grazing patterns. Irrigation systems changed rivers, wetlands, and soil chemistry.

Prehistoric and Indigenous cultures were responsible for contributing to the extinction of scores of animal species during the Late Quaternary extinction events. In that time, the majority of the world’s megafauna – large animals – went extinct. Humans caused some of those extinctions by a combination of over-hunting and destruction of the animal's natural habitat. The extinctions occurred on all continents (except Antarctica) as humans moved into new regions. Because large animals typically had long gestation periods and low reproductive rates, even small hunting pressures could lead to a population collapse. Evidence for humans as a cause of some of the extinctions includes a strong temporal correlation between the arrival of humans and the subsequent rapid disappearance of megafauna, coupled with the lack of evidence of sudden climate changes at the same time.^[d] The elimination of megafauna and the modification of landscapes had cascading effects on prehistoric ecosystems. Large herbivores maintained the environment by grazing, browsing, and trampling open spaces.

By 12,000 years ago, more than 90% of Earth's tropical forests and 95% of its temperate forests were inhabited and shaped by Indigenous peoples. In the modern era, alterations to the ecosystem have increased significantly, particularly after the start of the Industrial Age. Damage to the environment by modern humans – particularly by descendants of Western colonists – is more rapid and intensive than the damage caused by prehistoric and Indigenous peoples. The perception of prehistoric and Indigenous cultures in the Western imagination is sometimes influenced by myths such as the "pristine myth" – the illusion that lands inhabited by prehistoric peoples were a pristine wilderness, essentially unaffected by human impact. Another myth is the "ecological noble savage" – the belief that prehistoric and Indigenous peoples were role models of conservation and never damaged their ecosystems.

Impacts on habitat

Human-caused impacts on the global environment have increased significantly since the start of the Industrial Revolution in the 1700s, but humans have impacted their surroundings since long before that.^[1] The impacts of prehistoric peoples during the Holocene were felt everywhere on Earth except Antarctica.^[2] The impacts were driven by the emergence of complex societies, and the pastoral and agricultural industries that were required to support them.^[2] According to the archaeologist Patrick Kirch:^[2]

Homo sapiens has been an environment transforming species virtually since we gained control over fire and launched our relentless trajectory of technological development, deep in the Pleistocene and early in our own biological history.

Long before humans began modifying their habitat during the First Agricultural Revolution 10,000 years ago, they were modifying their habitats with anthropogenic fires.^[3] Evidence in Africa^[e] shows that about 85,000 to 60,000 years ago, human-created fires were changing the landscape, altering vegetation, increasing soil erosion, and creating alluvial fans.^[3] Thus, the human-driven habitat impacts that came with the agricultural revolution can be viewed, not as a new mode of habitat alterations, but an evolution of fire-driven impacts.^[3]

Over the past 10,000 years, humans have altered the Earth's environment, biodiversity, landscapes, and climate.^[4] These transformations began many thousands of years in the past by traditional, Indigenous, and prehistoric cultures.^[5] These impacts began before the advent of agriculture, and the effects vary widely across regions.^[5] By 1,000 BCE, most of the planet had been transformed by humans.^[6]

Three human activities were the primary drivers for habitat modification: first was hunting-gathering,^{[citation needed]} followed by agriculture, and then pastoralism.^[6]

Major impacts from humans began with the agricultural cultures in the early Holocene. Many of the impacts have resulted in irreversible changes to natural landscapes around the world.^[1] Impacts from prehistoric cultures include landscape erosion, conversion of habitat to cropland, animal extinctions, deforestation, and resource depletion.^[1]

When prehistoric humans began developing large-scale agriculture projects about 7,000 years ago,^[f] they cleared forests, which may have indirectly caused in increase in the amount of greenhouse gases (including CO₂ and methane) in the atmosphere.^[8] This marked the start humankind's contributions to the modern climate change crisis.^[8]

In addition to agriculture, pastoralism also played a major role in modifications to the landscape. Enabled by the domestication of livestock, pastoralism spread across much of the world between the years 10,000 and 3,000 years ago.^[7]^[9]

Some traditional land use practices produced cascading environmental consequences, sometimes leading to extinctions animal species.^[10] Historical land use practices have both improved and degraded the environment: sometimes damaging soil, other times enriching it; sometimes destroying habitat, other time creating new habitats; sometimes causing animal extinctions, other times propagating domesticated species.^[4]

By 12,000 years ago, more than 90% of Earth's tropical forests and 95% of its temperate forests were inhabited and shaped by indigenous peoples.^[11] Scholars have measured the impacts of humans and found (as of 2021) that between 75% and 95% of the world's ice-free land has been transformed by people.^[12]^[g] Humans altered their habitat by polluting, emitting greenhouse gases, fragmenting, altering or destroying habitats, and introducing invasive species.^[12]

Biodiversity losses occurring in the early 21st century are primarily caused by appropriation or intensified use of lands that were already inhabited, rather than by occupation or degradation of uninhabited environments.^[11]

Extinction of animal species

During the Pleistocene epoch, Earth supported an astonishing variety of large animals including saber-toothed tigers, terror birds, wooly mammoths, giant tortoises,^[h] giant ground sloths, and huge armadillos.^[15] Those species, and many other large animals, became extinct, with human activity acting as a driver for many.^{[citation needed]} The loss of large animals such as these may give some modern people a sense of loss.^[15]

The loss of hundreds of species of megafauna fundamentally altered the Earths ecosystem.^[16]

Over the past 129,000 years^[i] many megafauna species around the world became extinct. Although extinctions are common in the geological record going back many millions of years, the speed and magnitude of the extinctions since 129,000 years ago is unusual.^[17] The majority of large land animal species living in the world 100,000 years ago have become extinct since then.^[18] Among these extinctions are over 350 mammal species, which reduced the global count of mammal species (of all sizes) to approximately 5,700 in 2020.^[19] In the Americas, over 66 genera (over two thirds) of large^[j] mammals became extinct.^[20] In North America alone, about 38 genera of large animals became extinct, including 19 genera of mammals.^[21]

The extinctions – though occurring in a brief time span when considered geologically – occurred at different times around the globe.^[18] These extinctions happened during the latter part of the Quaternary geological period – extending from about 129,000 years ago to the present. The extinctions are sometimes divided into two groups: extinctions during the Late Pleistocene (between 129,000 and 11,700 years ago), and extinctions during in the Holocene (from 11,700 years ago to the present).^[22]

Causes of extinctions

Academics have explored the causes of the Late Quaternary extinctions since the early 19th century.^[23] Since the late 20th century, the debate over the cause of the extinctions was vigorous, and often focused on the extent to which humans were responsible for the extinctions.^[24] Causes proposed for the extinctions include:^[25]

Human causes – Over-hunting;^[k] second-order predation (over-hunting an herbivore species upon which the extinct species fed); habitat alterations or reductions; introduction of invasive species; anthropogenic fires (fires set by humans, deliberately or accidentally) resulting in loss of habitat or lack of forage; pollution
Climatic causes – Including gradual climate changes, as well as rapid changes such as Younger Dryas or Clovis age drought
Infectious disease
Natural extinction of herbivores leading to extinction of carnivores
Impact of an extraterrestrial object
Synergistic combination of multiple causes – For example, human activities (fire, hunting, agriculture, deforestation) contributing to climate change^[27]

The two primary causes considered by researchers are climate change and human activity.^[28]^[l] Most of the recent megafauna extinctions occurred after the arrival of humans, but proving cause-and-effect is difficult due to the fact the events happened long in the past. The nature of the extinctions varied between species and locations.^[29]

Extinctions caused by human activity

A large number of Late Quaternary megafauna extinctions were a result of human activity, including hunting and habitat destruction.^[30] Evidence for humans being the primary driver include the timing of extinctions following human arrival, the lack of climate change at the time of extinctions, archaeological evidence of hunting and habitat destruction, geographic correlation of human presence and extinction events, and analysis of large fauna that did not go extinct.^{[citation needed]} Humans were not responsible for all megafauna extinctions. A 2021 study of extinctions on islands found that while extinctions during the Holocene were often caused by humans, earlier Pleistocene extinctions often were not.^[31] Some scholars, as of 2020, argue that the extinctions in North American were primarily caused by climate changes.^[32]

A 2024 review considered the debate over whether humans or climate change were responsible for Late Quaternary large vertebrate extinctions.^[33]^[m] The study reported strong evidence that human activity was the cause of the extinctions, and only weak evidence for climate change.^[33] The study did not find strong support for climate change as a cause in either fine-scale space/time analysis, nor in global analysis.^[33] The earliest extinctions were likely caused by hominims that predated homo sapiens.^[34]

The extinctions of large mammals "elicited profound changes to ecosystem structure and functioning", according to Jens-Christian Svenning.^[35] Thus, the human-driven extinctions are the first major human-driven change to the ecosystem, and can be considered to mark the start of the Anthropocene.^[36]^[n]

Human arrival dates

One of the difficulties in determining causes of extinctions is ascertaining when humans arrived in specific locations on Earth. A technique to estimate arrival time is to measure proxy data which is correlated with human arrival. Proxy data includes pollen counts, traces of small invertebrates (such as rats), increase in charcoal particles, and a decrease in dung-fungus spores.^[38] A 2005 study estimated human arrival dates in several locations and identified a common pattern of faunal collapse after human arrival.^[39] An argument against climate change as a cause is the fact that extinctions around the world happened at various times, whereas a global climate change would tend to produce extinctions at roughly the same time.^[40]

A 2016 study showed that the primary driver of the extinctions was the arrival of humans, but climate change also played a role.^[41] The impact on species of climate change was not rapid: the changes could take several thousand years to affect the species.^[42] The study used a model that performed well (corresponded with known data based on archaeological records) in most of the world, including North and South America, Europe, Australia, Japan, Madagascar, Tasmania, and New Zealand.^[43] The model's predictions did not perform well in Africa and Asia.^[44]

Types of animals

When considering the extinctions of mammals between 50,000 and 10,000 years ago, the majority of species that disappeared were relatively large or were slow-breeding animals.^[45] This preference for large, slow-breeding mammals was not seen in extinctions that happened earlier in the Cenozoic era.^[45] This observation, coupled with the fact that the extinctions happened roughly at the same time that humans spread around the globe, suggests that human activity, particularly hunting, was a contributing factor.^[45] Climate change likely played a role in the extinctions: even if precipitated by human acitivies, climate change may have influenced the timing, location, or magnitude of the defaunation.^[45] Climate change may have combined synergistcally with human activities (hunting, habitat loss, anthropogenic fires) to increase the magnitude of the extinctions.^[45]

Geographic distribution

Late Quaternary megafauna extinctions occurred on all continents except Antarctica. The portion of large species that went extinct was markedly lower in Eurasia and Africa (where many large mammals survived into the 21st century).^[46]

A 2014 study that concentrated on the geographic distribution of extinction events concluded that the extinctions were closely correlated with the geographical locations of human expansion, and weakly correlated with the severity of climate changes. The implication of human causation was especially strong in locations where Homo sapiens were the first hominins to arrive.^[47] The study found significant discrepancies between the locations of climate changes and the locations of extinctions.^[47]^[o]

Extinction rates

Computer models were used in 2020 to analyze how extinction rates evolved since the Late Pleistocene.^[19] The models were used to analyze which factors contributed to the extinctions.^[19] The models showed that climate change was not a likely factor, because random changes to model conditions produced similar results as conditions that varied climate data.^[19] Conversely, the model showed that human impacts were strongly correlated with the extinctions.^[19]

The scientists that ran the models concluded that humans caused many extinctions that followed after human arrival on new landmasses.^[49] The models also predicated that continuing human development in the 21st century will cause a new wave of mammal extinctions to begin around 2100 CE in all regions of the world.^[50]

Analysis of surviving megafauna

To answer the question of whether the megafauna extinctions were caused by human activities or climate change, one approach used by scientists in a 2023 study was to analyze the megafauna species that did not go extinct.^[51] The surviving species faced two possible futures after the extinctions: their populations could grow due to the elimination of competitors for food and habitat; or their populations could shrink due to same reason (whatever it was) that caused the extinctions.^[51]

To determine which of those two explanations was more likely, a 2023 study examined the history of 139 species that survived the extinctions. The study found that 91% of the species suffered a decline in population, with larger-sized species experiencing larger declines.^[52] The population declines were found in all landmasses on Earth, which is consistent with a cause related to human activities (rather than climate change).^[51] Another factor indicating that the declines were caused by humans is that the megafauna abundance and biomass turnover around the world decreased by 92 to 95%.^[51] Human-related causes of the population declines were also implicated by the fact that the declines were most pronounced in particular temporal periods when the presence of humans were expanding into new regions (which would be unlikely if the cause was climate change).^[53]

In the 21st century, megafauna populations have decreased to new lows, and many remaining species are threatened with extinction. Further extinctions would have negative impacts on the ecosystems within which these remaining megafauna species live.^[54]

Impacts by region

Eurasia

Megafauna in Eurasia – such as mammoths, rhinos, and giant deer – lived contemporaneously with humans for 30,000 years.^[55] This in contrast to Australia, North America, and Pacific islands, where megafauna and flightless birds rapidly became extinct after human arrival.^[55]^[p] Many megafauna species in Eurasia were eventually extirpated, due to human hunting in combination with pressures from climate changes.^[56] Between 50 and 10 kya, nine genera (35% of the total) of large mammals became extinct, which is less than in most other continents.^[57]

Eurasia is unique among the world's landmasses, because it is the only one that has a significant correlation between climate change and megafauna extinctions.^[48] That fact, coupled with the paucity of direct archaeological evidence of hunting megafauna in Eurasia, has led some researchers to question if hunting played a role in the extinctions.^[58] The lack of direct evidence is likely due to the fact that the humans did not live in the same regions of Eurasia as the megafauna for most of the 30,000 years: in some cases, the humans lived primarily in the temperate regions, whereas the megafauna lived farther north.^[59] When humans migrated into regions occupied by the megafauna, extinctions followed.^[48]

The Woolly rhinoceros became extinct around 9,800 years ago. A 2024 study of the causes of the extinction concluded that a synergistic combination of climate change (leading to fragmentation and reduction of habitat) and human hunting (low-level, but sustained) caused the extinction, with climate change as the dominant cause.^[60]

Southern Levant

A 2022 study focusing on the Southern Levant examined whether megafauna extinctions were due to climate changes or human hunting.^[61] The size and mass of hunted animals was studied across a time span ranging from 1.5 MYA to 10,500 years ago: during that time span, the mean body mass declined by a factor of about 60 times.^[61] The changes in hunted animal body size over that time declined at a linear rate, and was not correlated with climate changes.^[61] The researchers concluded that humans hunted megafauna until they were extirpated, then shifted to the next-largest prey, and repeated that cycle.^[61] Humans were required to develop new technologies to successfully hunt smaller prey.^[61] The scientists concluded that the extinction of animals in the Southern Levant was due to human hunting, rather than climate change.^[62]

Africa

Around 2 million years ago, hominins in Africa evolved into the carnivore ecological niche.^[63] Since that time, the ecological diversity of other carnivores in Africa has significantly diminished, leading some scientists to speculate that hominins were partially responsible for the loss in diversity.^[64]

The Late Quaternary extinctions were not as acute in Africa as in other continents, possibly because of the very lengthy and gradual co-evolution of large fauna and hominins.^[65] Still, 24 African large mammals species became extinct^[64] including ten genera.^[66] Humans were the most likely driver in these extinctions, based on the timing of the extinctions in relation to climate changes and human behavioral changes.^[64]

Starting in the mid-Holocene, African peoples use of pastoralism (domestic livestock) and agricultural expanded throughout the continent.^[67]

Between 3,000 and 2,000 years ago, large parts of the rainforest in Central Africa became deforested and abruptly changed to savanna.^[68] These changes took place in the modern nations Gabon, Cameroon. Democratic Republic of the Congo, and Republic of the Congo.^[69] Hypotheses to explain this transition include climate change and human activity.^[70] Prior to 2012, the scientific consensus was that regional climate oscillations were responsible for the changes to the landscape.^[71]

The deforestation coincided with the large-scale movement of Bantu-speaking farmers from their original homelands in modern Nigeria and Cameroon, moving south and east through much of Central Africa.^[70] It is difficult to determine if the migration of the Bantu followed opportunistically into areas deforested by climate change, or if the Bantu actively cleared the forests.^[68]

Evidence for human activity causing the deforestation includes the fact that the deforestation happened contemporaneously with the migration of Bantu-speaking people, who required land for crops.^[72] Additionally, the speed of transition from rainforest to savanna was much faster than other climate-based fluctuations during the Holocene, suggesting that climate change alone may not have been responsible, leading some scientists to conclude that human activity was a significant factor in the deforestation.^[72]

Madagascar

In contrast with many Polynesian islands, where Holocene extinctions rapidly followed the arrival of humans, the extinction process on Madagascar was more gradual.^[73] After humans arrived around 2,000 BCE, they lived alongside some large animals for hundreds and even thousands of years: some of extinctions did not happen until about 1,500 CE.^[74] Ultimately, about 45 species of vertebrates (including all large terrestrial animals) became extinct.^[74] The precise causes of the extinctions are not certain, but hunting and anthropogenic fires^[q] appear to have played a significant role.^[74]

North America

Most environmental impacts from prehistoric peoples in North America began 10,000 years ago when the last glacier cover retreated.^[75] The impacts varied widely over time and between locations.^[75] Changes to habitat and biodiversity were in continual flux throughout the continent.^[75] As a result, the anthropologist Peter Stahl cautions that it is erroneous to make sweeping generalizations when assessing the nature and magnitude of changes wrought by the Native Americans.^[75]^[r]

After the arrival of humans in North America in the Late Pleistocene, more than half of the large mammal species became extinct^[76] including 34 genera and two complete orders.^[77] The scientist Paul Schultz Martin proposed in the 1970s that many of the extinctions were due to human hunting.^[78] Whether the extinctions were due to human hunting or other factors (such as climate change) continued to be subject of scientific debate in the early 21st century.^[79]^[k]

Humans arrived in North America from Asia and migrated southward into South America. Measurements of the extinction dates of megafauna in the Americas found that the extinctions chronologically proceeded from north to south, corresponding to the migration of humans, suggesting that human activity played a role in the extinctions.^[80]

A search for direct archaeological evidence of humans hunting Pleistocene mammals found evidence of hunting for only 5 of 37 genera, leading researchers to conclude that human hunting may not be a cause of Pleistocene extinctions of mammals in North America.^[81] Other researchers contend that "absence of evidence for kill sites is not evidence of absence",^[82] arguing that the archaeological record is very sparse, and a paucity of direct evidence is not proof that hunting did not occur.^[81]

Researchers performed computer simulations to assess the hypothesis that human hunting, alone, could account for the North American mammal extinctions.^[76] A simulation was executed in 2001 which assumed random hunting and slow human population increase.^[83] The simulation showed that the most important factor influencing the extinction outcomes was the hunting skill of humans. Factors that were not important included competition for food between prey species, and geographic dispersal of prey.^[84] The simulation suggested that extinctions would occur in three waves: first, within 1,000 yeas of human arrival; second, during the next few hundred years; and third, a few remaining species.^[85] The simulation showed that human hunting alone could readily cause the extinction of many large mammal species.^[83] In fact, the simulation indicated that extinctions were unavoidable.^[86] The decline of prey populations may have been so rapid, that the human hunters did not recognize the ecological consequences while they were happening.^[86]

Some researchers questioned the use of computer models to analyze the causes of extinctions.^[87]

The Clovis culture were peoples living in North America around 12,800 years years ago. Scientists have theorized that the Clovis hunted megafauna.^[88] A 2024 study analyzed the only known Clovis skeletal remains, and compared it to megafauna data. The analysis showed that that mammoth was the largest contributor to Clovis diet, supplemented with bison and elk.^[88] The diet was comparable to the diet of now-extinct saber-toothed cats.^[88]

Megafauna extinctions in Southern California were partially caused by human activity (fires and hunting),^[s] but those actions were exacerbated by an increasingly arid, dry climate.^[90] Indigenous peoples living in the boreal forests of North America used controlled fires to manage their habitat.^[91] The purposes of the fires included controlling undergrowth vegetation, improving hunting success, and clearing campsites.^[91] Practices varied between regions.^[91] In the 21st century, forestry services are working with Indigenous peoples to incorporate traditional knowledge into forest management practices.^[92]^[t]

Native Americans hunted bison in the Northern Great Plains. Before horses were introduced into North America by Europeans (in the early 1700s) Native Americans hunted on foot.^[94] An important technique used for on-foot hunting was buffalo jumps – driving herds of bison over steep bluffs to their death.^[94] Fire was sometimes used during buffalo jumps, used to lure them to the starting location.^[95] After horses were introduced, Native Americans began to use them for hunting, and the use of fire during the hunts diminished.^[94] Archaeological evidences shows strong correlation between climate and anthropogenic fires:^[q] fires were most often used when climate conditions were favorable (wet periods generated more fuel); and the fires influenced the climate.^[96]

Central America

The Maya civilization flourished in Central America from about 2000 BCE to 1000 CE.^[97] The Maya altered their environment with waterworks (dams, reservoirs, and canals), urban infrastructure (temples, buildings, and roads), slash-and-burn fires to clear forest, and establishing terraces, fields, and orchards for agriculture.^[98]^[u] The impacts on the environment affected the Maya negatively in some ways, including soil erosion, sedimentation in bodies of water, and mercury pollution, but these impacts enabled growth and improvements to the Maya civilization, such as roads, gardens, cities, and reservoirs.^[100]^[v]

South America

South America – like most of the world^[w] – experienced Late Pleistocene extinctions, but they were more severe in this continent: over 80% of megafauna species became extinct, spanning 50 genera and extinguishing three complete orders.^[103] As with many Late Pleistocene extinctions, both human activities and climate change were considered as potential causes.^[104] A 2021 study of the distribution of Fishtail projectile points (often used as weapons) in the continent concluded that humans were the primary driver for megafauna extinctions.^[104]^[x] That result was based on a strong correlation – in both time and space – between megafauna remains and the weapons.^[104]

Amazonia

The first humans to settle in Amazonia arrived around 13,000 years ago.^[105] These pre-Columbian cultures extensively modified the environment, and cleared forests to make room for villages and crops.^[106] They did not have iron tools, and used fire to make clearings for structures and agriculture, the remains of which is often visible in the modern era as Amazonian dark earth or terra preta.^[107] They also may have contributed to the extinction of some South American megafauna.^[107]^[y] They introduced crops brought from Mesoamerica, and abandoned fields turned into secondary forests that were different from the original forests.^[107]

Although Amazonia is sometimes viewed in the popular imagination as an untouched wilderness, many parts were heavily impacted by pre-Columbian human settlement.^[108] As late as 2010, some scientists continued to be surprised to find evidence of significant human impacts in certain remote parts of the Amazon basin.^[107] In 2008, some biodiversity scientists studying the Caxiuana National Forest were surprised to discover extensive evidence of environmental alterations caused by ancient human cultures.^[107]

After the arrival of Europeans in Amazonia, the population of Indigenous peoples there diminished, and during the 18th century, many regions were abandoned and agricultural areas were reclaimed by new sorts of biodiversity.^[109] In the early 19th century, European scientists – such as Henry Walter Bates and Alfred Russel Wallace – visited Amazonia and erroneously concluded that the secondary forests were in their original, pre-human condition.^[110]

In the cloud forests of Ecuador, before the arrival of Europeans, prehistoric cultures deforested large amounts of their environment for their own uses.^[111] The intensive management and cultivation of the cleared landscapes continued until arrival of the Europeans caused the Indigenous population to dramatically decrease, leading to a cessation of deforestation around 1588 CE.^[111]^[z] During the next 130 years, a secondary forest grew in the formerly cultivated areas, creating a dense forest that Europeans incorrectly assumed was a pristine wilderness.^[111] The deforestation performed by the Indigenous peoples was more extensive than the post-1950 deforestation performed by descendants of European colonizers.^[112]

Some scholars contend that the impacts of early human inhabitants of Amazonia were sustainable, and even benefited the environment by increasing biodiversity.^[113] Although pre-Columbian humans made extensive alterations to the environment, the magnitude was generally far less than late 20th century large-scale agricultural practices.^[114] The agricultural traditions of the prehistoric peoples may offer examples of less-intensive practices that can be used in the modern era to minimize damage to the Amazonian environment.^[115]

Oceania

The number of bird species that were exterminated on Pacific islands after the arrival of Indigenous peoples is roughly 2,000 – most of them flightless.^[116] This is about 20% of the total number of bird species on Earth. When including species that were extirpated (made locally extinct) on Pacific islands, the total is roughly 8,000 populations.^[117]^[118]

Australia

Australia experienced a tremendous loss of biodiversity in the Late Quaternary: all animals (birds, reptiles, and mammals) weighing more than 100 kg became extinct.^[119] Of animals weighing more than 45 kg, 23 of 24 genera went extinct.^[120] Extinction also claimed all six genera of large reptiles, a giant flightless bird, three marsupial families, and two guilds.^[121]

Proposed drivers of the extinctions are climate change (in particular, gradual aridification) and human activity (hunting and antrhopogenic fire).^[122] Debate about whether the extinctions in Australia were caused by humans or climate change (or both) has been continuing for more than a century.^[120]^[aa] The debate continued into the 21st century partly because of uncertainties about the dates of the arrival of humans, and the dates of the extinctions.^[123]^[ab] An example of data uncertainty is the human arrival date:^[124] one researcher put it at between 60 and 52 thousand years ago (kya),^[120] another at 50 to 43 kya,^[125] another at 65 kya,^[126] and another at 55 and 45 kya.^[127]

Both North America and Australia experienced a large number of extinctions, but it has been far harder to draw conclusions about Australian events because of uncertainty about arrival dates and lack of hard evidence of hunting.^[128]^[129]

Some researchers have asserted that most of the extinctions occurred after or contemporaneously with the arrival of humans^[130] but others have suggested the opposite.^[131]

An example of the confusion surrounding the data for extinctions is a mammoth tibia bone which had scratch marks. Some researchers concluded that they were evidence of butchering by humans, but later analysis concluded that the marks were made long after the animals death, after the bone was fossilized, and hence is not proof of hunting.^[132]

Another example of the uncertain nature of the Australian data is an analysis emu eggshells, ranging back 140,000 years. Researchers analyzed isotopes contained in the eggshells, which provided a history of the diet of the emus.^[133] The isotope history showed that a permanent reduction in the variety of food sources available to the emus happened, beginning at about the time that humans arrived.^[133] Researchers considered various potential causes for the change in vegetation, and discarded climate change because known, large climate changes (at other times) did not produce a comparable isotope change; and because there were no major climate changes between 40 and 60 KYA.^[134] The researchers also considered human-related causes, such as hunting, human-introduced diseases, and fires.^[133] Hunting and disease were discarded as possibilities because they would not produce such dramatic vegetation changes.^[134] The remaining cause, fires set by humans, was consistent with the isotope record, because the record indicated that, soon after human arrival, the available vegetation mixture changed from one adapted to drought to a mixture adapted to fire.^[134] The researchers concluded that fires set by humans was the most plausible cause of the extinctions.^[133] The animals that could adapt to the vegetation change survived; and those that could not became extinct.^[127] Another researcher put the results into doubt, by questioning whether the eggshells were correctly identified.^[135]

Tasmania fossil study

Data from the island of Tasmania is consistent with a chronology where the extinctions followed soon after the arrival of humans.^[136] The arrival of humans on Tasmania occurred between 43 and 40 KYA, ^[136] Analysis of fossils shows that some Tasmanian megafauna survived until 41 KYA, and so there was overlap between the presence of humans and megafauna on Tasmania.^[136] In addition, the historical vegetation data of Tasmania does not show any significant climate changes between 43 and 37 KYA, indicating that humans are a plausible cause of the extinctions.^[136]

New Zealand

New Zealand was home to several species of moa (Dinornithiformes) – large, flightless birds. All moa species became extinct following the arrival of Polynesians in the islands during the 13th century.^[137] The Polynesians caused the extinction through hunting and habitat destruction.^[138]^[ac] The extirpation was one of the final megafauna extinctions of the Late Quaternary extinctions.^[29]

At the time the Polynesians extirpated the moa on the South Island, the total human population of New Zealand was less than 2,000.^[140] The extinction was completed within 150 years of the arrival of the Polynesians.^[140] The population density at the time of the extinction was a very sparse: at most 0.01 humans per km².^[140] Evidence of moa butchery is found in over 100 sites on New Zealand's South Island. Evidence is rarer on the North Island, perhaps because the higher density of Polynesians in the north cause the extinction to proceed rapidly, thus leaving few traces.^[141]

Climate change was eliminated as a possible cause of the extinctions based on scientific analysis of moa fossils and habitats indicate that their populations were stable and large prior to the arrival of humans. There is no evidence of a gradual decline in population, as might be caused by climate change.^[142]^[ad] When Polynesians arrived, the moa population of New Zealand was estimated to be about 9,200 individuals.^[143] Archaeological evidence shows that humans hunted the moa.^[143] The moa were extirpated within 100 to 200 years after humans arrived.^[143] The extinction of the moa was the most rapid recorded (as of 2014) human-facilitated megafauna extinction.^[29] For these reasons, human hunting is most likely the only cause of the moa's extinction.^[143]

A 2025 study investigated whether the extinction of the moa was inevitable. Models showed that the moa would become extinct even under low rates of hunting.^[144] The only scenarios in which moa survived is those where more than 50% of New Zealand's land was protected from hunting.^[144]

Melanesia

Islands of Melanesia experienced dramatic environmental transformations after initial human settlement around 3,000 years ago.^[145] The islands of Fiji were studied to assess the impact of prehistoric humans on the environment, particularly the cause of prehistoric deforestation. Prior to settlement, fires in Fiji caused by lightning would occasionally occur on the islands, typically during periods of drought.^[145]^[ae] After settlement, slash and burn anthropogenic fires^[q] were used by the humans to prepare land for cultivation, and often led to deforestation.^[145] Damage to the environment was not solely caused by human activities: El Niño climate events may have caused droughts which exacerbated deforestation.^[146]

Polynesia

Most islands in the Pacific were settled in the late Holocene, and the arrival of humans caused rapid and significant ecological changes.^[147] In the eastern Polynesian islands particularly, human activity resulted in extensive deforestation, animal extinctions due to hunting, anthropogenic fire,^[q] and the introduction of rats.^[147]^[148] In the eastern Polynesian islands, over 1,000 species of birds became extinct, particularly flightless birds vulnerable to introduced predators and larger birds favored by hunters.^[147]

Tonga

Humans settled in Tonga about 3000 years ago, and soon thereafter the giant iguana and scrubfowl became extinct.^[149] The extinctions were so rapid, the time interval between the arrival of humans and the extinctions was less than the margin of error of the radiocarbon dating used to perform the dating.^[149]

Easter Island

Polynesians arrived on Easter Island between 800 and 1200 CE.^{[citation needed]}^[af] After their arrival, several species of plants and animals became extinct or extinct in the wild, including:^[150]

Easter Island Palm (Paschalococos disperta) - extinct 1650 CE
Sophora toromiro
Two species of rails (including the scientifically designated Easter Island rail and Easter Island crake)
Two species of parrots
One species of owl
One species of heron

Several causes for the extinctions have been suggested, primarily anthropogenic: hunting, deforestation, and introduction of invasive species.^[151]^[152] Climate changes have also been hypothesized as a synergistic, contributory factor.^[153]

Island patterns

The impacts on island environments from early humans began immediately when humans arrived and accelerated as populations grew.^[154] There was no over-arching pattern of human impacts that applied to all islands, but there was some commonality based on whether the cultures were primarily hunter-gatherers or agriculturalists.^[154] The nature and extent of the human impacts depended on many factors, including island geography, population density, and subsistence strategies.^[154]

Some islands in Polynesia, Caribbean, Mediterranean, and North Atlantic shared some common patterns of human impacts, including anthropogenic burning (to clear landscapes) which led to soil erosion.^[154] In some Caribbean islands, humans are implicated in the extinction of sloths.^[155]

Conversely, the California Channel Islands were inhabited by hunter-gatherers; the impacts on these islands were less well-defined, but appear to exhibit less landscape clearing and erosion than agriculturalist islands.^[154] Early humans on the Channel Islands impacted the marine environment, and introduced invasive species such as mice and foxes.^[154]

In the Pacific Ocean, the number of bird species that became extinct was between 559 and 1,696 landbirds. The total rises to between 820 and 1,960 species when including seabirds, Hawaii, and New Zealand.^[156]

Pristine wilderness and the noble savage

Academic discussions of the impacts on the environment by prehistoric or Indigenous cultures are often found as part of a broader discourse that encompasses topics such as the myth of "pristine wilderness", the definitions of "wilderness" and "nature", and the myth of the "ecological noble savage".^[157]

The concept of pristine wilderness – meaning a landscape unchanged by any human activity – is primarily a Western notion, commonly used in that sense in the Scandinavia, USA, and Australia.^[158] In many parts of the world, prehistoric cultures did not (at the time of arrival by Westerners) place value (or, in some cases, even have a word for) the idea of wilderness or "nature untouched by humans".^[159] The phrase pristine myth was coined in a 1992 article by the geographer William Denevan.^[160] The term refers to the illusion that lands inhabited by prehistoric peoples were a pristine wilderness, essentially unaffected by human impact when colonizers or Western peoples first arrived.^[161] Belief in the pristine myth was widespread in the 19th and 20th centuries, and continued into the early 21st century.^[162]^[ag]

In the 1990s, Denevan and several other academics published research that established that the vast majority of lands inhabited by prehistoric cultures were significantly modified by those peoples in virtually all locations on Earth, although the nature and degree of the impact varied widely from location to location.^[164] The consensus of scholars is that there was virtually no pristine wilderness in any of the lands encountered by colonizers or Western peoples, and thus the pristine myth is false.^[165]

If travellers, the moment they set foot in a tropical region and ... imagine that they are within the precincts of a primeval forest, the misconception must be ascribed to their ardent desire of realizing a long-cherished wish. Every tropical forest is not primeval forest. I have scarcely ever used the latter term in the narrative of my travels. – Alexander von Humboldt Views of Nature^[166]

Related to the pristine myth is the myth of the ecological noble savage.^[167]^[ah] The myth of the ecological noble savage is recent variant of the noble savage cultural stereotype, which originated several hundred years ago in the Western imagination.^[168]. During the environmental movement of the 1970s, Indigenous peoples were imagined to be environmental role models: living in perfect harmony with nature, never changing or harming the ecosystem.^[169] The consensus of academics is that the concept of the ecological noble savage was essentially false, and that prehistoric peoples significantly impacted their habitat in virtually all places they inhabited, resulting in significant, permanent changes to the ecosystem, including – in some cases – extinction of species and deforestation.^[170]

When considering the impacts of Indigenous cultures on the environment, some scholars distinguish cultures that are ecologists from cultures that are conservationists.^[171] Historian Shepard Krech, in his work The Ecological Indian, analyzed the Indigenous peoples of North America, and examined extinctions, the Hohokam culture, anthropogenic fires,^[q] and hunting (deer, beaver, and bison). His conclusion was that Native Americans (prior to the 20th century) were ecologists because they were deeply aware of the interrelationships between humans, animals, and nature; but they were not not conservationists because they did not avoid waste and did not preserve resources for future availability.^[172]^[ai]

Applicability of modern conservation ethics to prehistoric and Indigenous peoples

Researchers generally agree that archaeological evidence demonstrates that prehistoric and Indigenous peoples did not practice conservation in the modern sense of maintaining nature in its original state.^[173]^[aj] This research generated new discussions about whether modern values of conservation and sustainability are applicable to prehistoric or Indigenous cultures.^[175] Some scholars contend that it is inappropriate to apply Western concepts of ecology or conservation to Indigenous peoples or subsistence cultures.^[176]^[ak] Many modern Native Americans view the Western concept of nature conservation as inherently flawed, since they view themselves as living within nature.^[75]

The myth of the noble savage has been applied to political ends in two ways: Indigenous peoples have used the myth to support their arguments for equality and self determination. And conservation organizations have used the myth to generate support for their causes.^[178] The anthropologist Mac Chapin criticized several major conservation organizations in 2004, claiming their drives to preserve wilderness in an untouched state was harmful to Indigenous communities that lived in or near those preserves.^[179]

The suggestion that a pristine wilderness, untouched by humans, is an ideal or desirable condition has been criticized as a racist or ethnocentric social construct.^[180] The philosopher J. Baird Callicott wrote that the idea of wilderness is "alleged [by various authors] to be ethnocentric, androcentric, phallogocentric, unscientific, unphilosophic, impolitic, outmoded, even genocidal".^[181] An alternative to the notion of pristine wilderness is a "humanized landscape" or "humanized nature", defined as habitat that has been modified by humans to suit their needs and enable them to survive.^[182] To some prehistoric cultures, the normal, natural state of a landscape incorporates those modifications by humans required for their society to grow and thrive.^{[citation needed]} Many people in the Chinese culture believe that humanized nature is more beautiful than pristine wilderness.^[183]

In the modern era

Defining the start of the Anthropocene

The Anthropocene is a term used by scientists to refer to the period of time when human activity has become the dominant influence on the planet's environment and ecosystems.^[154]^[al] There is uncertainty about when the Anthropocene began, because there is no concrete, geological demarcation of when it started – leading to several proposals for the start date.^[154] Some proposals put the start date fairly recently in the 20th century, but recent research into prehistoric cultures have suggested that a much earlier start may be appropriate.^[154] The archaeologist Bruce D. Smith and others have proposed that the start date should be about 10,000 years ago, roughly at the start of the Holocene.^[154]^[am] The argument to define the Anthropocene start at about 10,000 years ago is that the alteration of the environment has been a continuum, extending back at least that far.^[154] Throughout the Holocene (which started around 12,000 or 11,700 years ago)^{[citation needed]} humans migrated around the globe and commenced extensive modifications of their habitat.^[154] Another proposal puts the start of the Anthropocene even further in the past, when the first human-caused mass extinctions occurred, sometime after 50,000 years ago.^[184]

Informing policy decisions

Studying the human-caused prehistoric impacts on the environment may provide insights that can be used to inform future environmental practices and policies.^[185]

One reason scientists analyze historical human-caused impacts on the environment is to provide insight that may provide guidance into modern environmental challenges.^[186] The manner and speed in which past environmental impacts occurred around the world when humans first migrated into landmasses may yield insights that can mitigate damage to the environment in the future.^[187]^{[citation needed]} The geographer Tim Beach wrote:

Both scientists and the broader public are aware that humans are having profound effects on Earth, but to quantify the scale and rate at which human impacts are altering the planet, we must know about background conditions and the chronology of change. One aspect of the Anthropocene discussion has been its timing, i.e. when did the period of large-scale human impact begin?^[188]

An additional reason why scientists feel compelled to determine if humans caused the extinctions is to inform society's future behavior regarding conservation. If human hunting and habitat alterations caused the ancient extinctions, it may provide motivation to prevent future extinctions, and it may also provide incentive to revive extinct species or to introduce surrogates – such as restoring elephants, cheetahs, or camels to North America.^[189]

A 2022 report on conservation strategies for primates found that the geographic ranges of 71% of primate species are partially within lands occupied by Indigenous cultures, who tend to employ less intensive hunting and land use practices than non-Indigenous communities.^[an] The study concluded that efforts to conserve primate species in the future should include plans to support Indigenous communities in places where primates live.^[191]

Historical examples of environmental damage by prehistoric or Indigenous peoples can also be used in improper ways, for example to demonize modern Indigenous peoples, to justify intensive development of a region because it was already impacted, or to justify new, intensive damage to the environment because prehistoric or Indigenous peoples engaged in similar practices.^[192]

Indigenous peoples and stewardship of the environment

In the past, some traditional land use practices produced cascading environmental consequences, sometimes leading to extinctions.^[10] But in the modern era, some of the most biodiverse regions in the world are those managed by Indigenous peoples.^[10] Lands that apply traditional low-intensity agricultural practices tend to be more biodiverse than lands that use high-intensity methods.^[10] Land use practices in the modern era can be shaped in a way that enhances the fertility of soil, enhances biodiversity, and improves hunting sustainability.^[10]

In the modern era, Indigenous cultures often play an important role in environmental conservation, providing stewardship of habitats, plants, and animals.^[193] Indigenous communities offer unique values, insights, and practices that can help the broader society address-environmental issues.^[194] Indigenous peoples positively engage with the environment in various ways, including:^[194]

Undertaking territorial management practices and customary governance
Participating in environmental conservation efforts
Sharing environmental knowledge
Opposing unsustainable and unjust use of resources
Collaborating in governmental processes related to the environment
Providing alternative approaches for people to relate to the environment

An analysis of Indigenous cultures in South America in the 21st century found that the cultural diversity they provided correlated strongly with biodiversity in the surrounding environment, suggesting that the existence of culturally unique Indigenous communities contribute to conservation efforts.^[195]

History of research

Anthropologists, geographers, and scholars of many other disciplines have studied the impacts of humans on the environment. This field of study is sometimes referred to as historical ecology.^[197] The origins of historical ecology have their roots in 18th century Europe, when serious studies of forestry practices began.^[198] A notable early inquiry was the Ruined Landscape Theory, which hypothesized that much of the Mediterranean landscape's prehistoric forests had been degraded due to deforestation.^[198]

An early work that inquired into the impacts of prehistoric cultures on the environment was the 1867 book Man and Nature: or, Physical Geography as modified by human action by the polymath George Perkins Marsh.^[199]^[ap] Early 20th century works on the subject include two works by the geographer Carl O. Sauer: his 1925 monograph The Morphology of Landscape and his 1952 book Agricultural Origins and Dispersals.^[200]

Academic research into the topic of impacts from prehistoric peoples took a major leap forward in 1955, in a symposium titled Man’s Role in Changing the Face of the Earth funded by the Wenner-Gren Foundation for Anthropological Research.^[2]^[aq] One of the earliest works to explicitly claim that human hunting caused many of the Late Quaternary extinctions was the 1966 article "The Discovery of America: The first Americans may have swept the Western Hemisphere and decimated its fauna within 1000 years" by the geoscientist Paul Schultz Martin.^[201] As late as 1966, some researchers were doubting the possibility that humans caused some of the Late Quaternary extinctions.^[202] The first major article to debunk the Western myth of the pristine wilderness was the 1992 article "The Pristine Myth: The Landscape of the Americas in 1492" by the geographer William Denevan.^[203] An early work to discuss the Western concept of the "ecological noble savage" was the 1999 book The Ecological Indian: Myth and History by the anthropologist Shepard Krech.^[204]

As of 2020, research was focused in four areas:^[205]

Describing the impacts that prehistoric humans had on their environments
Reconstructing specific historical environments
Assessing how climate changes impacted prehistoric societies
Studying how prehistoric humans adapted to their environment