Source Guide: The Sixth Mass Extinction and Human Impact on Biodiversity

Frame the question

The Sixth Mass Extinction represents a critical juncture in Earth's history, with debates over whether current biodiversity loss constitutes a true mass extinction event. This guide examines the evidence from multiple disciplinary perspectives, including paleontology, ecology, and conservation science. The anchor source [1] argues for a human-driven extinction crisis, while [2] contextualizes this within a 12,000-year history of human ecological impact. Sources [3] and [4] provide methodological frameworks for understanding extinction dynamics and conservation education, though their direct relevance requires careful contextualization.

What the evidence shows

The evidence matrix below synthesizes key claims from all sources:

Claim	Source [1]	Source [2]	Source [3]	Source [4]
Human-driven extinction rates	7.5-13% invertebrate extinctions since 1500	Human land use shaped 95% of temperate woodlands 12,000 years ago	No direct relevance	No direct relevance
Red List bias	0.04% species loss recorded	Natural landscapes exhibit long histories of human use	No direct relevance	No direct relevance
Conservation priorities	Focus on charismatic vertebrates	Biodiversity patterns correlate with historical land use	No direct relevance	No direct relevance
Scientific urgency	Need for preventive archaeology	Ecological transformation is ancient and pervasive	No direct relevance	No direct relevance

The timeline table below contextualizes key events:

Timeline	Event	Source	Notes
1500 CE	Estimated start of accelerated invertebrate extinctions	[1]	Based on extrapolated data
10,000 BCE	Beginnings of human ecological transformation	[2]	Land use practices shaped ecosystems
2007-2019	Peak of prejudice reduction research	[3]	Methodological frameworks for social change
2019	Emergence of immersive VR educational tools	[4]	Potential for conservation awareness

Callout quotes:

"We take issue with these stances. Humans are the only species able to manipulate the Earth on a grand scale..." [1] "Nearly three quarters of Earth's land was inhabited and therefore shaped by human societies..." [2]

Follow the source trail

The sources form a complex web of evidence and interpretation. Source [1] presents a direct argument for the Sixth Mass Extinction, emphasizing invertebrate loss and Red List biases. Source [2] contextualizes this within a 12,000-year history of human ecological impact, challenging the notion of 'natural' landscapes. While [1] and [2] both highlight human agency, they differ in temporal scope: [1] focuses on modern acceleration while [2] frames human influence as ancient. Sources [3] and [4] offer indirect relevance through methodological frameworks, with [3] providing insights into social change mechanisms and [4] suggesting educational tools for conservation awareness. These sources collectively suggest that understanding extinction requires both paleontological data and socio-ecological analysis.

Use these sources well

Students can structure an essay by first establishing the scientific consensus on the Sixth Mass Extinction using [1], then contextualizing this within the long history of human ecological impact as described in [2]. The Red List bias discussion from [1] can be paired with [2]'s analysis of historical land use to show how conservation frameworks may overlook critical data. While [3] and [4] are less directly relevant, they can be used to explore how societal attitudes (from [3]) and educational innovations (from [4]) might address extinction challenges. Avoid overstating correlations: while [2] shows humans shaped ecosystems for millennia, [1] emphasizes the unprecedented scale of current extinction rates. Use the evidence matrix to compare claims and the timeline table to show historical context.

What to search next

Further research could explore: 1) Regional variations in extinction rates, particularly the island species focus from [1] 2) The role of colonial-era land use in modern biodiversity loss, connecting [1] and [2] 3) How prejudice reduction frameworks from [3] might inform conservation policy 4) The effectiveness of VR-based education tools from [4] in raising extinction awareness. Students might also investigate the methodology behind invertebrate extinction estimates in [1] or the spatial reconstruction techniques in [2]. These questions highlight the need for interdisciplinary approaches to understanding and addressing the Sixth Mass Extinction.

Verbatim source abstracts

[1] The Sixth Mass Extinction: fact, fiction or speculation? — Biological Reviews, 2022-01-10, doi:10.1111/brv.12816

There have been five Mass Extinction events in the history of Earth's biodiversity, all caused by dramatic but natural phenomena. It has been claimed that the Sixth Mass Extinction may be underway, this time caused entirely by humans. Although considerable evidence indicates that there is a biodiversity crisis of increasing extinctions and plummeting abundances, some do not accept that this amounts to a Sixth Mass Extinction. Often, they use the IUCN Red List to support their stance, arguing that the rate of species loss does not differ from the background rate. However, the Red List is heavily biased: almost all birds and mammals but only a minute fraction of invertebrates have been evaluated against conservation criteria. Incorporating estimates of the true number of invertebrate extinctions leads to the conclusion that the rate vastly exceeds the background rate and that we may indeed be witnessing the start of the Sixth Mass Extinction. As an example, we focus on molluscs, the second largest phylum in numbers of known species, and, extrapolating boldly, estimate that, since around AD 1500, possibly as many as 7.5-13% (150,000-260,000) of all ~2 million known species have already gone extinct, orders of magnitude greater than the 882 (0.04%) on the Red List. We review differences in extinction rates according to realms: marine species face significant threats but, although previous mass extinctions were largely defined by marine invertebrates, there is no evidence that the marine biota has reached the same crisis as the non-marine biota. Island species have suffered far greater rates than continental ones. Plants face similar conservation biases as do invertebrates, although there are hints they may have suffered lower extinction rates. There are also those who do not deny an extinction crisis but accept it as a new trajectory of evolution, because humans are part of the natural world; some even embrace it, with a desire to manipulate it for human benefit. We take issue with these stances. Humans are the only species able to manipulate the Earth on a grand scale, and they have allowed the current crisis to happen. Despite multiple conservation initiatives at various levels, most are not species oriented (certain charismatic vertebrates excepted) and specific actions to protect every living species individually are simply unfeasible because of the tyranny of numbers. As systematic biologists, we encourage the nurturing of the innate human appreciation of biodiversity, but we reaffirm the message that the biodiversity that makes our world so fascinating, beautiful and functional is vanishing unnoticed at an unprecedented rate. In the face of a mounting crisis, scientists must adopt the practices of preventive archaeology, and collect and document as many species as possible before they disappear. All this depends on reviving the venerable study of natural history and taxonomy. Denying the crisis, simply accepting it and doing nothing, or even embracing it for the ostensible benefit of humanity, are not appropriate options and pave the way for the Earth to continue on its sad trajectory towards a Sixth Mass Extinction. [1]

[2] People have shaped most of terrestrial nature for at least 12,000 years — Proceedings of the National Academy of Sciences, 2021-04-19, doi:10.1073/pnas.2023483118

Archaeological and paleoecological evidence shows that by 10,000 BCE, all human societies employed varying degrees of ecologically transformative land use practices, including burning, hunting, species propagation, domestication, cultivation, and others that have left long-term legacies across the terrestrial biosphere. Yet, a lingering paradigm among natural scientists, conservationists, and policymakers is that human transformation of terrestrial nature is mostly recent and inherently destructive. Here, we use the most up-to-date, spatially explicit global reconstruction of historical human populations and land use to show that this paradigm is likely wrong. Even 12,000 y ago, nearly three quarters of Earth's land was inhabited and therefore shaped by human societies, including more than 95% of temperate and 90% of tropical woodlands. Lands now characterized as "natural," "intact," and "wild" generally exhibit long histories of use, as do protected areas and Indigenous lands, and current global patterns of vertebrate species richness and key biodiversity areas are more strongly associated with past patterns of land use than with present ones in regional landscapes now characterized as natural. The current biodiversity crisis can seldom be explained by the loss of uninhabited wildlands, resulting instead from the appropriation, colonization, and intensifying use of the biodiverse cultural landscapes long shaped and sustained by prior societies. Recognizing this deep cultural connection with biodiversity will therefore be essential to resolve the crisis. [2]

[3] Prejudice Reduction: Progress and Challenges — Annual Review of Psychology, 2020-09-14, doi:10.1146/annurev-psych-071620-030619

The past decade has seen rapid growth in research that evaluates methods for reducing prejudice. This essay reviews 418 experiments reported in 309 manuscripts from 2007 to 2019 to assess which approaches work best and why. Our quantitative assessment uses meta-analysis to estimate average effects. Our qualitative assessment calls attention to landmark studies that are noteworthy for sustained interventions, imaginative measurement, and transparency. However, 76% of all studies evaluate light touch interventions, the long-term impact of which remains unclear. The modal intervention uses mentalizing as a salve for prejudice. Although these studies report optimistic conclusions, we identify troubling indications of publication bias that may exaggerate effects. Furthermore, landmark studies often find limited effects, which suggests the need for further theoretical innovation or synergies with other kinds of psychological or structural interventions. We conclude that much research effort is theoretically and empirically ill-suited to provide actionable, evidence-based recommendations for reducing prejudice. [3]

[4] A review of immersive virtual reality serious games to enhance learning and training — Multimedia Tools and Applications, 2019-12-05, doi:10.1007/s11042-019-08348-9

Abstract The merger of game-based approaches and Virtual Reality (VR) environments that can enhance learning and training methodologies have a very promising future, reinforced by the widespread market-availability of affordable software and hardware tools for VR-environments. Rather than passive observers, users engage in those learning environments as active participants, permitting the development of exploration-based learning paradigms. There are separate reviews of VR technologies and serious games for educational and training purposes with a focus on only one knowledge area. However, this review covers 135 proposals for serious games in immersive VR-environments that are combinations of both VR and serious games and that offer end-user validation. First, an analysis of the forum, nationality, and date of publication of the articles is conducted. Then, the application domains, the target audience, the design of the game and its technological implementation, the performance evaluation procedure, and the results are analyzed. The aim here is to identify the factual standards of the proposed solutions and the differences between training and learning applications. Finally, the study lays the basis for future research lines that will develop serious games in immersive VR-environments, providing recommendations for the improvement of these tools and their successful application for the enhancement of both learning and training tasks. [4]