Not evaluated

Not evaluated (NE) is a designation in the IUCN Red List Categories and Criteria for taxa that have not yet been systematically assessed for their risk of extinction using the IUCN's quantitative criteria.^[1] This category signifies a lack of sufficient evaluation rather than a judgment on threat level, and such taxa are not included in the published IUCN Red List database.^[2] As of April 2025, the IUCN has assessed approximately 169,420 species, leaving the vast majority of the estimated 1.5 to 2 million described species in the not evaluated status due to resource constraints and prioritization of certain taxonomic groups.^[3] The designation underscores gaps in biodiversity knowledge, emphasizing the need for expanded assessments to inform conservation priorities, particularly for understudied invertebrates and microorganisms.^[4] While not implying safety or peril, the not evaluated status can delay targeted interventions until data collection enables classification into categories such as data deficient, least concern, or threatened.^[5]

Definition and Criteria

Core Definition

The Not Evaluated (NE) category designates taxa that have not yet undergone assessment against the IUCN Red List criteria for evaluating extinction risk.^[6] This status indicates a lack of formal evaluation rather than any inference about the taxon's conservation condition, distinguishing it from categories like Data Deficient (DD), where assessment has occurred but data insufficiency prevents categorization.^[6] NE applies to the vast majority of Earth's described species, estimated at over 99% as of recent assessments, due to limited resources for comprehensive global biodiversity evaluation.^[7] Taxa assigned NE are excluded from the published IUCN Red List, which focuses on assessed species to inform conservation priorities.^[1] The category underscores gaps in taxonomic and ecological knowledge, as only select groups—such as mammals, birds, and certain plants—receive routine scrutiny, leaving insects, fungi, and many invertebrates unevaluated.^[2] Reassessment may elevate a taxon from NE once sufficient data becomes available, potentially revealing previously unrecognized threats.^[8]

Distinction from Other IUCN Categories

The IUCN Not Evaluated (NE) category applies exclusively to taxa that have not undergone any formal assessment against the Red List criteria, distinguishing it from all other categories which require an evaluation process to determine extinction risk.^[8] Unlike the eight published categories—Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), and Data Deficient (DD)—NE taxa are not included on the IUCN Red List itself, as no data compilation or risk analysis has occurred.^[1] This procedural status reflects a lack of systematic review rather than any inference about population status or threats.^[9] A key distinction lies between NE and Data Deficient (DD), where DD denotes taxa that have been evaluated but for which inadequate information prevents a reliable assignment to threatened, Near Threatened, or Least Concern categories, often due to genuine knowledge gaps on distribution, abundance, or threats.^[9] In contrast, NE indicates no evaluation attempt has been made, potentially encompassing undescribed species, newly discovered taxa, or those overlooked in assessment priorities; DD assessments, however, involve documented efforts yielding insufficient quantitative data for criteria application, such as population size reduction thresholds or geographic range metrics.^[8] The threatened categories (CR, EN, VU) and conservation-dependent ones (NT, LC) further diverge from NE by quantifying extinction probability over defined time frames—e.g., CR requires a 50% decline in three generations or a 10% probability of extinction in 10 years—based on empirical evidence like habitat loss or exploitation rates, whereas NE provides no such risk appraisal.^[9] EX and EW, meanwhile, confirm absence in the wild or entirely, verified through exhaustive searches and absence records spanning 50 years post-last sighting.^[8] Thus, NE serves as a placeholder for future scrutiny, not a risk indicator, underscoring the Red List's incomplete coverage of global biodiversity, with millions of species remaining unevaluated as of 2023.^[4]

Historical Development

Origins in IUCN Red List

The Not Evaluated (NE) category was formally introduced in the IUCN Red List Categories and Criteria version 2.3, adopted in 1994, to designate taxa that had not yet been assessed for extinction risk using the established quantitative criteria.^[10] This marked a shift from earlier IUCN Red Data Books, which began publication in 1966 with volumes on mammals and later birds, focusing primarily on listing species considered rare, endangered, or vulnerable without explicit categories for unevaluated taxa.^[5] In pre-1994 assessments, species absent from these lists were implicitly unevaluated, but lacked a standardized designation, reflecting the qualitative and selective nature of initial Red List compilations starting from 1963.^[5] The 1994 framework defined NE alongside other categories such as Extinct, Critically Endangered, Endangered, Vulnerable, Lower Risk (with subcategories), and Data Deficient, emphasizing that NE applied to taxa not subjected to the criteria-based evaluation process.^[10] This introduction addressed the need for a comprehensive system applicable across diverse taxa, acknowledging that only a fraction of described species—estimated at around 1.8 million at the time—could be practically assessed given resource constraints. The category underscored the preliminary stage of global biodiversity evaluation, where NE status highlighted gaps in knowledge rather than implying low risk.^[10] Version 3.1 of the criteria, adopted by the IUCN Council on February 9, 2000, and published in 2001, retained the NE category without substantive changes to its definition, maintaining it as a marker for unevaluated taxa while refining overall assessment methodologies through extensive testing and consultation since 1989.^[11] Unlike assessed categories, NE taxa are not published on the IUCN Red List website, distinguishing them from Data Deficient species, which have undergone evaluation but lack sufficient information for categorization.^[1] This persistence of NE origins in the 1994 system established a foundational principle of transparency about assessment coverage, informing subsequent expansions where, by 2024, over 157,000 species had been evaluated, leaving the majority in NE status.^[1]

Evolution of the NE Category

The Not Evaluated (NE) category emerged as part of the formalized IUCN Red List Categories and Criteria system introduced in 1994, following six years of development to establish quantitative standards for extinction risk assessment.^[8] Prior to 1994, the IUCN Red List, initiated in 1964 through early Red Data Books, focused primarily on compiling lists of threatened species using qualitative judgments without standardized categories for unevaluated taxa.^[5] The 1994 framework (version 2.3) explicitly defined NE as applying to taxa that had not been assessed against the new criteria, thereby highlighting the distinction between unassessed species and those evaluated but data-deficient.^[10] Subsequent revisions, such as version 3.1 adopted in 2001, preserved the NE definition without substantive changes, maintaining its role as a marker for species outside the formal evaluation process.^[9] This stability allowed for consistent tracking of assessment coverage, revealing that NE encompassed the vast majority of described species—estimated at over 2 million eukaryotic taxa—while only 157,000 had been assessed by 2024.^[12] The category's design ensures that the Red List publishes only evaluated species, excluding NE to emphasize empirical evaluations over assumptions of safety.^[1] Over time, the NE category has underscored systemic gaps in biodiversity data, prompting initiatives like specialist group collaborations and data mobilization efforts to transition species from NE to assessed statuses.^[13] Despite these advances, resource constraints and the sheer scale of undescribed or unstudied taxa have sustained NE as a critical indicator of incomplete global conservation knowledge, with no alterations to its criteria reflecting a commitment to unaltered baselines for longitudinal comparisons.^[8] This evolution from an implicit unassessed state to a deliberate category has enhanced transparency in reporting assessment progress without implying lower risk for NE species.^[2]

Assessment Processes and Challenges

IUCN Evaluation Methodology

The IUCN evaluates species extinction risk using a standardized quantitative framework outlined in the Red List Categories and Criteria, version 3.1, adopted in 2001 and retained in the second edition published in 2012.^[9][14] This methodology classifies taxa into one of nine categories—Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD), and Not Evaluated (NE)—based on the probability of extinction in the wild.^[15] A taxon qualifies as threatened (CR, EN, or VU) if it meets quantitative thresholds under any of five criteria (A–E), prioritizing empirical data on population trends, range, and threats over qualitative judgments.^[15][14] The five criteria assess different facets of extinction risk:

• Criterion A: Reduction in population size, measured over specified time frames (e.g., 10 years or three generations), with CR requiring ≥90% decline, EN ≥70%, and VU ≥50%.^[15]
• Criterion B: Restricted geographic range, combining extent of occurrence (EOO) or area of occupancy (AOO) with fragmentation or decline; CR applies to EOO <100 km² or AOO <10 km², EN to EOO <5,000 km² or AOO <500 km², and VU to EOO <20,000 km² or AOO <2,000 km².^[15]
• Criterion C: Small population size with observed or projected decline; CR for <250 mature individuals with ≥25% decline in three years or one generation, EN for <2,500 with ≥20% in five years or two generations, and VU for <10,000 with ≥10% in 10 years or three generations.^[15]
• Criterion D: Very small or restricted population, with CR for <50 mature individuals, EN for <250, and VU for <1,000.^[15]
• Criterion E: Quantitative analysis, such as population viability analysis, estimating extinction probability; CR for ≥50% within 10 years or three generations, EN for ≥20% within 20 years or five generations, and VU for ≥10% within 100 years.^[15]

Assessments are conducted by expert assessors, typically IUCN Species Survival Commission (SSC) members or affiliated specialists, who compile species-specific data on taxonomy, distribution (including GIS-mapped ranges), population estimates, habitat requirements, threats, and conservation actions via the online Species Information Service (SIS).^[16] Assessors apply the criteria objectively, documenting evidence and rationale to ensure reproducibility.^[17] Completed drafts undergo mandatory peer review by at least two independent reviewers designated by Red List Authorities (RLAs)—specialist groups responsible for taxonomic oversight—within three months, focusing on data accuracy, criteria application, and consistency.^[16] The RLA evaluates reviewer feedback and approves the assessment for submission to the IUCN Red List Unit (RLU).^[16] The RLU performs final quality controls, including taxonomic checks, mapping validation, and adherence to guidelines (version 16, updated March 2024), before queuing for publication on the Red List website.^[16][17] This multi-stage process, emphasizing transparency and expert scrutiny, aims to minimize bias and errors, though challenges persist in data-scarce taxa, often resulting in DD rather than definitive threat levels.^[16]

Factors Leading to NE Status

The Not Evaluated (NE) status applies to taxa that have not been formally assessed against the IUCN Red List criteria, encompassing the vast majority of described species worldwide. As of 2024, fewer than 5% of the world's described species—estimated at around 2 million—have undergone evaluation, leaving over 95% in the NE category due to the sheer scale of global biodiversity and the resource-intensive nature of assessments.^[4] This incomplete coverage stems from the IUCN's reliance on a decentralized network of volunteer specialists who compile data on population trends, habitat extent, and threats, a process that demands substantial time and expertise for each taxon.^[8] Primary factors include limited institutional capacity and funding, which constrain the number of assessments annually; for instance, despite assessing over 172,000 species cumulatively, the pace lags behind species descriptions and emerging conservation needs, exacerbating underrepresentation in data-poor taxa.^[1] Prioritization by IUCN and its specialist groups favors vertebrates, plants with economic or ecological significance, and regions with established research infrastructure, sidelining invertebrates, fungi, and microorganisms that constitute the bulk of biodiversity but often lack dedicated experts or baseline data.^[18] Newly described species, numbering thousands annually, routinely enter the NE category as taxonomic publication precedes risk evaluation, with delays arising from the need to verify distributions and threats post-description.^[19] Logistical barriers further contribute, particularly in remote or politically unstable habitats where field data collection is hindered by access issues, safety concerns, or insufficient local expertise; this is evident in lower assessment rates for African taxa despite high endemism.^[20] Additionally, the absence of perceived urgency for widespread or resilient species defers their evaluation, as resources are allocated to taxa showing rapid declines, perpetuating biases toward "charismatic" or threatened groups over those requiring proactive monitoring.^[21] These factors collectively result in NE status not indicating low risk but rather a gap in systematic appraisal, underscoring the Red List's role as a dynamic but incomplete inventory rather than a comprehensive census.^[18]

Global Statistics and Distribution

Quantified Prevalence of NE Species

As of IUCN Red List version 2025-1, released on March 27, 2025, approximately 169,420 species have been evaluated out of an estimated 2,139,242 described species across major taxonomic groups, representing 8% overall coverage and leaving roughly 92% (over 1.97 million species) in the Not Evaluated (NE) category.^[22] This figure underscores the incomplete assessment of global biodiversity, with NE status indicating a lack of systematic evaluation rather than inferred low extinction risk.^[9] The total number of evaluated species has grown from around 150,000 in 2023 to over 172,600 by late 2025, yet the proportion evaluated remains low due to the expansive scale of described species, particularly in understudied phyla.^[1] Taxonomic disparities amplify NE prevalence. Vertebrates demonstrate high evaluation rates, with nearly all mammals (over 6,400 of ~6,500 described species) and birds (~11,000 species) assessed, achieving coverage exceeding 99% in these classes.^[4] Amphibians and reptiles also approach comprehensive evaluation, at around 95-100% for described species. In stark contrast, invertebrates such as arthropods (over 1.2 million described species) have evaluation rates below 1%, resulting in millions of NE insects, crustaceans, and arachnids.^[22] Plants exhibit intermediate coverage, with about 10-15% evaluated (~50,000 of ~400,000 described vascular plants), while fungi and many protists remain largely NE, with less than 5% assessed due to taxonomic and data challenges.^[4] These patterns reflect resource allocation priorities toward charismatic or high-risk taxa, leaving NE dominance in hyperdiverse groups like beetles (over 400,000 described species, fewer than 1,000 evaluated).^[4] IUCN's strategic plan aims to assess 260,000 species by 2030, potentially reducing NE prevalence to under 85%, but current trajectories suggest persistent gaps in microbial and deep invertebrate lineages.^[23] Empirical data from regional assessments corroborate global trends, with NE species comprising 80-95% in tropical insect inventories and marine invertebrates.^[3]

Taxonomic and Geographic Patterns

Among taxonomic groups, the Not Evaluated (NE) status is disproportionately prevalent in invertebrates and fungi, reflecting limited assessment efforts relative to their estimated species richness. Arthropods, particularly insects, exhibit the highest proportions of NE species; for example, less than 0.02% of described insect species had been assessed by 2018, with similar low coverage for arachnids (0.3%) and crustaceans (0.3%).^[24] Fungi show comparable underrepresentation, with fewer than 5% of species assessed as of 2025, despite their critical ecological roles.^[23] In contrast, vertebrates such as birds, mammals, and amphibians have near-complete assessments, with virtually all species evaluated multiple times, leaving minimal NE taxa in these classes.^[25] This disparity arises from resource allocation biases favoring charismatic or economically significant vertebrates over hyperdiverse, less-studied invertebrates and microbes, where basic taxonomic inventories remain incomplete.^[26] Geographically, NE species patterns align with global centers of biodiversity, particularly tropical regions like the Amazon Basin, Southeast Asian rainforests, and Central African forests, where invertebrate and fungal diversity peaks but assessment coverage lags due to logistical challenges, political instability, and prioritization of accessible temperate zones.^[26] In well-studied areas such as Europe and North America, NE proportions are lower even for invertebrates, as national red lists and regional expertise facilitate more evaluations.^[27] Tropical hotspots host the majority of undescribed or unevaluated taxa, exacerbating knowledge gaps; for instance, estimates suggest over 90% of arthropod species in these areas remain unassessed, potentially masking elevated extinction risks from habitat loss and climate change.^[24][26] Overall, these patterns underscore systemic underinvestment in non-vertebrate taxa and remote ecosystems, limiting comprehensive global risk profiling.^[23]

Notable Examples and Case Studies

High-Profile NE Species

Domestic sheep (Ovis aries), one of the most widespread livestock species with a global population exceeding 1.2 billion as of 2020, remains not evaluated by the IUCN due to its domesticated status and lack of extinction risk in wild populations.^[22] The species, descended from wild mouflon (Ovis orientalis) through selective breeding starting around 10,000 years ago, supports major industries in wool, meat, and dairy, yet IUCN assessments exclude domesticated taxa to focus on wild biodiversity.^[28] Similarly, domestic cattle (Bos taurus), numbering over 1 billion individuals worldwide in 2023, are not assessed, as their managed populations obviate natural extinction threats under IUCN criteria.^[29] The domestic dog (Canis lupus familiaris), with an estimated 900 million individuals globally and a history of domestication tracing back 15,000–40,000 years, exemplifies high-profile NE status; while feral populations impact wildlife, the taxon itself is excluded from Red List evaluations.^[28] Domestic pigs (Sus scrofa domesticus), integral to food systems with annual slaughter exceeding 1.5 billion in 2022, share this unevaluated category, reflecting IUCN's policy against including domesticated forms derived from wild ancestors like the Eurasian boar.^[30] These species highlight how NE applies to economically vital but human-dependent taxa, where conservation priorities shift to wild relatives rather than managed breeds. In semi-wild contexts, the dingo (Canis dingo), an iconic Australian canid introduced around 4,000 years ago and culturally significant to Indigenous peoples, is classified as NE, with populations stable at approximately 100,000–500,000 but unmanaged in conservation assessments. Unlike assessed wild canids, its hybridisation with domestic dogs complicates evaluation, yet it remains outside formal IUCN scrutiny due to insufficient dedicated assessment efforts.^[28] Such cases underscore that high-profile NE species often evade evaluation not from data scarcity but from policy exclusions or low perceived wild risk, despite ecological roles.

Transitions from NE to Assessed Status

Transitions from Not Evaluated (NE) to assessed status on the IUCN Red List occur through targeted initiatives by Red List Authorities (RLAs) and specialist groups, which prioritize understudied taxonomic groups or species facing emerging threats. These evaluations follow the IUCN's standardized criteria for extinction risk, involving data compilation on population trends, habitat, and threats via the Species Information Service (SIS) platform, peer review, and final validation before publication.^[16] Such processes are driven by strategic plans like the Barometer of Life, aiming to assess at least 260,000 species by 2030 to fill knowledge gaps.^[23] The 2024 Global Tree Assessment exemplifies large-scale transitions, incorporating first-time evaluations of thousands of tree species previously in NE status as part of a comprehensive review of over 47,000 species. Results indicated that 38% of assessed trees are threatened with extinction (Critically Endangered, Endangered, or Vulnerable), primarily due to agriculture, logging, and habitat conversion, with threatened species documented in 192 countries.^[31] This update, including 4,485 new assessments in the initial 2024 release, revealed disproportionate risks in tropical regions and for endemic species.^[32] Invertebrate groups have seen similar shifts, as in the 2025 European pollinator assessment, where nearly 100 wild bee species transitioned from NE to threatened categories, contributing to 10% of 1,928 evaluated European wild bees now at risk (Vulnerable or higher). Bumblebees and mining bees showed elevated threats from intensive agriculture, urbanization, and pesticide exposure, doubling the proportion of imperiled species over the past decade.^[1][33] Mammalian cases include the Indian wolf (Canis lupus pallipes), first assessed in 2025 as Vulnerable due to a mature population estimated at 2,877–3,310 individuals, fragmented across India and parts of Pakistan and Afghanistan. Key threats encompass habitat loss from agricultural expansion, retaliatory killings by herders, and diseases like canine distemper, with the assessment recognizing its potential as a distinct lineage warranting subspecies-specific protections.^[34][35] These transitions frequently assign higher threat levels than initial expectations, as seen across taxa where data deficiencies previously masked risks, thereby enabling evidence-based interventions like protected area expansions or threat mitigation. Comprehensive group assessments accelerate such moves, but resource constraints limit coverage, with over 96% of described species still NE as of recent estimates.^[36]

Implications for Conservation Policy

Policy and Regulatory Ramifications

The Not Evaluated (NE) status signifies that a species has not undergone formal assessment against IUCN criteria, rendering it ineligible for inclusion on the published Red List and thereby limiting its visibility in regulatory frameworks that depend on categorized threat levels for triggering protections.^[2] This absence of evaluation often results in policy gaps, as international agreements like the Convention on International Trade in Endangered Species (CITES) and national laws such as the U.S. Endangered Species Act prioritize species with documented threat statuses (e.g., Vulnerable or higher) for trade restrictions, habitat safeguards, and recovery funding. Without an assessment, NE species face heightened risks from unregulated exploitation, such as commercial harvesting or habitat conversion, as regulators lack the empirical basis to impose measures like quotas or bans.^[37] In practice, this status delays conservation interventions, allowing potential declines to proceed unchecked; for instance, among North American trees, the vast majority remain NE, complicating forest management policies that rely on risk data for sustainable logging regulations.^[37] Similarly, in marine contexts, numerous shark and ray species classified as NE evade fisheries oversight, contributing to overfishing concerns where IUCN data informs regional management bodies like the International Commission for the Conservation of Atlantic Tunas.^[7] Empirical patterns indicate that NE taxa, particularly in understudied groups like invertebrates and fungi, represent over 80% of described species in some assessments, underscoring systemic under-protection in biodiversity hotspots where local laws mirror IUCN categories.^[13] Regulatory responses have included directives to prioritize NE evaluations in funding mechanisms; the IUCN's strategic goals, aligned with the Convention on Biological Diversity's Aichi Targets (extended via post-2020 frameworks), advocate for assessing high-priority NE species to close these gaps, influencing national budgets for taxonomic surveys and data collection. For example, initiatives like the U.S. Fish and Wildlife Service's coordination with IUCN assessments aim to transition NE species to evaluated statuses, enabling integration into domestic protections under the Endangered Species Act, though resource constraints persist.^[38] Critics note that without precautionary policies for unevaluated taxa—such as interim trade moratoriums—NE status perpetuates a reactive rather than proactive regulatory paradigm, potentially exacerbating undocumented extinctions in data-poor realms.^[39]

Influence on International Agreements

The Not Evaluated (NE) status of numerous species on the IUCN Red List undermines the scope and enforcement of key international agreements by leaving vast numbers of potentially threatened taxa outside formal risk-based protections. Under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which regulates trade for approximately 40,000 species across its three appendices as of 2023, NE species often evade listing criteria that prioritize documented extinction risks, resulting in unregulated commerce for high-volume traded groups like fish and plants. For example, analysis of global trade data revealed 904 species likely threatened by international trade but unprotected by CITES, with hundreds classified as NE or Data Deficient, including 376 unlisted species imported into the United States alone that face documented conservation threats such as overharvesting.^[40][41] This evidentiary gap influences CITES decision-making, as proposals for Appendix II or III listings frequently reference IUCN assessments; without them, species may persist in trade volumes exceeding regulated counterparts by factors of 3.6 in quantity and 11 in species diversity in major markets. To mitigate this, CITES parties and committees have increasingly incorporated supplementary tools, such as trade volume analyses and rapid assessments, to flag NE species for review, as evidenced by mechanisms developed to identify trade-vulnerable NE taxa for prioritization in CoP decisions, including the 2019 proposal processes that integrated Red List data gaps.^[42][41] In the Convention on Biological Diversity (CBD), NE prevalence hampers achievement of monitoring and extinction-risk reduction targets, such as those in the Kunming-Montreal Global Biodiversity Framework adopted in 2022, which calls for halting human-induced extinctions by 2030 and assessing all native species by 2030 under related indicators. With over 80% of described species remaining NE—totaling more than 2 million taxa as of 2024—the Red List Index, a core CBD metric for tracking trends in extinction risk, excludes these from calculations, potentially masking broader biodiversity declines and skewing national biodiversity strategies (NBSAPs) toward already-assessed charismatic vertebrates.^[18] These limitations extend to synergies between CITES and CBD, where joint work programs emphasize data sharing, yet NE gaps contribute to documented shortfalls: for instance, 58% of threatened terrestrial species lack sufficient conservation interventions, partly attributable to unevaluated status impeding threat identification in multilateral environmental agreements. Consequently, agreements like the CMS (Convention on Migratory Species) face similar challenges, with NE migratory taxa underrepresented in action plans, prompting calls for accelerated assessments to align treaty obligations with empirical risk realities.^[43][44]

Criticisms and Alternative Perspectives

Methodological and Bias Critiques

The IUCN Red List's Not Evaluated (NE) category encompasses species that have not undergone formal extinction risk assessment, primarily due to insufficient data or prioritization gaps in the evaluation process. Methodologically, this leads to significant underrepresentation of biodiversity risks, as NE taxa often include inconspicuous or understudied groups like invertebrates and microorganisms, where criteria emphasizing population declines and habitat loss fail to capture subtle threats such as cryptic extinctions. A 2024 analysis found that Red List criteria poorly characterize extinction risk for such species, with few truly extinct taxa recognized, exacerbating data deficiencies that hinder comprehensive global assessments.^[39] Furthermore, the assessment methodology relies on expert judgment for initial triage, introducing inconsistencies; ambiguities in guidelines, such as handling subpopulations under intensive management, allow assessor bias to influence whether species enter NE or proceed to full evaluation.^[45] Taxonomic and geographic biases compound these issues, with NE status disproportionately affecting invertebrates, plants, and tropical species from the Global South, while vertebrates—particularly charismatic mammals and birds—receive earlier assessments due to higher research and funding focus. Over a 25-year period, conservation funding analyses revealed deeper taxonomic biases than previously noted, skewing evaluations away from microbial and fungal diversity, which constitute vast portions of undescribed species.^[46] Geographic imbalances stem from resource allocation favoring well-studied regions, leaving species in data-poor areas perpetually NE despite potential threats; for instance, automated risk modeling predicts many NE reptiles as vulnerable or endangered, yet resource constraints delay formal inclusion.^[47] These patterns reflect systemic priorities in academia and conservation NGOs, where aesthetic appeal and accessibility drive assessments, potentially overlooking ecologically critical but less visible taxa.^[48] Critics argue that the NE category's opacity masks true extinction risks, as predictive models indicate over half of Data Deficient (DD) species—often overlapping with NE in data scarcity—are likely threatened, yet the lack of mandatory thresholds for evaluation perpetuates gaps.^[49] While the IUCN's quantitative criteria mitigate earlier subjectivity, residual expert discretion in scope selection enables unconscious biases, such as overemphasizing observed declines in accessible habitats while ignoring insidious pressures like climate variability in remote ecosystems.^[50] Peer-reviewed evaluations highlight that such methodological shortcomings not only inflate the NE pool—estimated at millions of species—but also undermine policy reliance on the Red List, as unassessed taxa evade protective measures despite evidence of comparable vulnerabilities to assessed ones.^[51] Addressing these requires expanded, unbiased data collection protocols, though institutional inertia in conservation funding limits progress.^[18]

Debates on Risk Prioritization and Over-Alarmism

Critics of conservation strategies contend that the substantial proportion of Not Evaluated (NE) species—estimated at over 80% of described species as of 2023—fuels over-alarmism by implying widespread hidden threats without empirical verification, leading to inefficient resource allocation toward speculative risks rather than documented ones.^[4] This perspective holds that assuming high extinction risk for NE taxa, particularly inconspicuous invertebrates in biodiverse regions, exaggerates the biodiversity crisis, as Red List criteria often fail to detect threats in such groups until post-extinction evidence emerges, yet few verified extinctions occur relative to predictions.^[39] For instance, popularized narratives like "Insectageddon" have been criticized for relying on unsubstantiated extrapolations from localized data declines to global collapse, misusing Red List categories to amplify urgency without rigorous causal links to drivers like habitat loss.^[52] Proponents of heightened prioritization counter that empirical assessments of formerly NE species frequently reveal elevated threats, with studies showing that in taxa like reptiles and mammals, up to 20-30% of newly evaluated species qualify as Vulnerable or worse, underscoring data gaps as a barrier to accurate risk mapping rather than evidence of low risk.^[53] They argue that deferring action on NE species in high-pressure ecosystems, such as tropical forests where over 90% of arthropods remain unevaluated, risks irreversible losses, as spatial modeling predicts disproportionate threats from agriculture and climate change in these areas.^[54] However, skeptics highlight methodological flaws in such predictions, including over-reliance on IUCN categories not designed for prioritization, which can mislead by conflating assessment status with actionable threats and ignoring cost-benefit analyses.^[50] Debates intensify over resource misallocation, where over-emphasis on rare or potentially threatened NE species diverts funding from broader interventions benefiting common taxa that sustain ecosystem functions, such as pollination and soil stability provided by non-threatened insects comprising the majority of biodiversity.^[55] Conservation prioritization frameworks have been faulted for common errors like ill-defined objectives and failure to integrate risk aversion with feasibility, resulting in reactive single-species efforts that prove costly and ineffective compared to habitat-scale protections.^[56] For example, analyses of global funding reveal biases toward charismatic vertebrates, leaving NE invertebrates under-resourced despite their ecological roles, prompting calls for transparent risk-tolerant adaptive management over alarm-driven triage.^{[57] [58]} This tension reflects causal realism in conservation: while NE gaps demand assessment, unsubstantiated alarmism erodes public trust and skews policies toward low-probability, high-visibility interventions at the expense of verifiable, high-impact actions.^[59]

Broader Applications and Analogues

Usage in Non-Biodiversity Contexts

The "Not Evaluated" (NE) designation, primarily established in biodiversity risk assessments by the International Union for Conservation of Nature (IUCN), has seen adaptation in non-biological domains such as cultural heritage evaluation. In frameworks assessing threats to intangible cultural heritage (ICH)—encompassing traditions, practices, and expressions passed across generations—NE is applied to ICH projects lacking assessment against predefined criteria, signaling a need for initial data gathering before assigning threat levels. This mirrors the IUCN's use of NE for taxa or ecosystems not yet scrutinized, preventing premature categorization amid data gaps.^[60] A specific ICH threat assessment model, inspired by IUCN Red List categories, incorporates NE alongside Data Deficient, Vulnerable, Endangered, Critically Endangered, and others like Least Concern. Criteria evaluate two core elements: practitioners (e.g., inheritors' population size under Criterion A, where Critically Endangered thresholds include fewer than 100 individuals or 5–10% project coverage) and habitats (e.g., inheritance mechanisms under Criterion F or conservation funding under Criterion H). Grounded in cultural ecology theory, this approach treats ICH elements as dynamic systems analogous to biological populations, with threats arising from demographic shifts, environmental disruptions, or institutional neglect. The model's rationale emphasizes systematic, quantitative evaluation to inform policy, much like IUCN's role in prioritizing conservation actions.^[60] Testing on 100 ICH projects in Dali Prefecture, Yunnan Province, China, validated the framework's reliability, yielding 92% alignment with expert opinions on threat status. Of these, unevaluated projects were flagged for urgent baseline surveys, highlighting NE's utility in resource allocation for cultural preservation amid rapid urbanization and globalization pressures. This application extends beyond biology by addressing human-mediated cultural erosion, where empirical metrics (e.g., inheritor age demographics under Criterion B) enable causal analysis of decline drivers.^[60] In broader non-biodiversity risk paradigms, NE-like statuses denote pending evaluations in systematic inventories, though explicit adoption of the term remains rare outside IUCN-influenced models. For example, in heritage site assessments or social vulnerability indices, initial triage identifies unassessed assets to avoid underestimating risks from incomplete inventories, prioritizing empirical data collection over assumption. Such parallels underscore NE's foundational principle: deferring judgment until verifiable evidence accumulates, fostering rigorous prioritization in diverse threat landscapes.^[60]

Comparisons to Similar Evaluation Frameworks

The IUCN Red List's Not Evaluated (NE) category, denoting species that have not undergone formal assessment against its criteria, contrasts with the NatureServe conservation status ranking system, which primarily assesses North American taxa using numerical ranks from G1 (critically imperiled) to G5 (secure) based on factors like population size, trends, and threats.^[61] NatureServe does not employ a dedicated NE equivalent; instead, species absent from its database or unranked due to insufficient data are effectively unevaluated, though the system emphasizes subnational and global ranks for included taxa without an explicit "not assessed" designation.^[61] This approach allows for partial assessments, such as unrankable (GU) modifiers in certain contexts, differing from IUCN's binary NE status for unprocessed species.^[62] Comparisons between assessed species reveal moderate correlations between NatureServe ranks and IUCN categories, with G1-G2 often aligning with Critically Endangered or Endangered, but handling of unevaluated cases highlights methodological divergence: IUCN's NE facilitates tracking assessment gaps globally (e.g., only about 2.2 million of 8 million estimated species evaluated as of 2024), while NatureServe's focus on regional data results in fewer global unevaluated entries but prioritizes rarity over extinction risk.^[1][63] NatureServe's criteria overlap with IUCN's in threat evaluation but incorporate broader ecological viability metrics, potentially leading to assessments for species IUCN deems NE due to limited global data.^[64] In regulatory frameworks like the U.S. Endangered Species Act (ESA) of 1973, no direct NE parallel exists; species are either listed as Endangered or Threatened based on petition-driven evaluations or deemed not warranted, leaving most unlisted species—analogous to NE—in a de facto unevaluated state without systematic risk categorization.^[65] ESA assessments emphasize imminent harm and recovery potential under legal mandates, contrasting IUCN's informational NE by tying status to actionable protections rather than comprehensive biodiversity inventories; for instance, as of 2011 analyses, ESA covered fewer IUCN-listed species than expected, underscoring gaps in evaluating NE-equivalent taxa.^[65] Regional red lists adopting IUCN criteria, such as those in Europe or Brazil, replicate the NE category verbatim, minimizing differences but often expanding assessments beyond global efforts.^[66]