Definition
In legal usage, species carries two distinct meanings depending on context: a classical Roman law concept concerning form and particularity, and a modern regulatory classification drawn from biology.
1. Civil law / Roman law. Species denotes the particular form or shape impressed upon a material, as distinguished from the raw material itself (materia). In this sense, it is the counterpart to genus — species identifies a specific, individual thing, while genus identifies the broader class to which it belongs. The concept is most significant in the Roman law doctrine of specificatio, which asked who holds ownership when one person fashions a new object (nova species) from materials belonging to another. Species also describes a particular thing singled out for attention among others — a discrete object or item, as opposed to a general category.
2. Modern regulatory law. Species means a category of living organisms recognized under biological taxonomy, ranking below genus. This meaning drives the entire body of federal law under the Endangered Species Act (ESA), which defines "species" to include any subspecies of fish, wildlife, or plants, and any distinct population segment of any vertebrate species. The regulatory definition is deliberately broader than the strict biological definition, allowing listing decisions to protect geographically isolated populations without requiring action against a species globally.
Common Language
Modern common usage (Wiktionary): A group of sexually reproducing organisms that can interbreed and produce fertile offspring; a category in biological taxonomy ranking below genus.
Historical common usage (Webster's 1913): Visible or sensible presentation; appearance; a sensible percept received by the imagination. Also a group of individuals agreeing in common attributes.
The gap here is threefold. In everyday English, species is almost exclusively a biological term. In classical civil law, it was a philosophical and property concept concerning form, individuality, and ownership — with no biological content whatsoever. In modern regulatory law, the term is biological in origin but has been deliberately stretched beyond strict scientific taxonomy to serve conservation policy. A researcher encountering "species" in Roman law sources and ESA materials is encountering three substantially different concepts wearing the same label.
Common Confusion
Species and genus are frequently contrasted in Roman law materials in ways that can confuse researchers unfamiliar with the underlying philosophy. Genus in this context does not mean biological genus; it means the general class or category of a thing. Species is the particular instance. This philosophical pairing maps loosely onto the modern distinction between general and specific obligations in contract — an obligation to deliver a thing of a type (genus) versus an obligation to deliver a particular identified thing (species or res certa). Conflating the Roman law usage with the modern biological one produces serious interpretive errors in historical property and contract sources.
Recognized Forms
/SUBTYPES
Species facti (Scots law): The particular criminal act charged against a person — the specific factual species of the offense as alleged. This usage combines the civil law sense of species as a particular identified thing with the procedural context of criminal pleading. Historical Scottish sources treat this as a term of art requiring the indictment to identify the exact nature of the alleged conduct, not merely the genus of offense.
Why It Matters in Research
Researchers face a hard disambiguation problem with this term because the corpus contains sources spanning Roman private law, Scots criminal procedure, and modern federal environmental regulation — all using "species" in materially different ways.
In Roman law and civil law sources, species always concerns the philosophical and property dimensions of form versus substance. The specificatio problem — who owns a new thing made from another's materials — was a major debate among classical jurists and appears throughout the Institutes and Digest. Burrill's entry gestures at this with the Justinian passage. Do not read these sources through a biological lens.
In modern regulatory research, the ESA definition of species is a deliberate statutory expansion. The inclusion of "distinct population segments" (DPS) for vertebrates is a major litigation battleground; courts have grappled repeatedly with what makes a population segment sufficiently distinct and significant to qualify. Researchers using the encyclopedias linked here will find the listing and critical habitat framework, but should track agency guidance on DPS policy separately, as it has evolved through administrative practice.
The jurisdictional overlay matters too. Several states have their own endangered species statutes with definitions of "species" that differ from the federal ESA definition, sometimes offering broader or narrower protection. State-law sources must be checked independently when research concerns a particular geographic region.
Historical dictionaries are useful for the civil law meaning but largely silent on the modern regulatory meaning — unsurprisingly, since the ESA dates to 1973. Anderson's cross-references to IN SPECIE and SPECIE are worth following; those terms concern specific performance and coinage respectively, and the shared Latin root creates genuine research hazards.
Historical Dictionary Support
The four source dictionaries agree closely on the civil law meaning: species is form or shape given to materials, and a particular thing as distinguished from genus. Burrill is the most useful on specificatio, including the Institutes passage that captures the ownership problem directly. Black's first and second editions track the same definition with minor variation; the second edition's entry on species facti adds the Scots criminal procedure usage, which is otherwise easy to miss.
Anderson's is distinctive in emphasizing the etymological note (specere — to look, see) not for its own sake but because it illuminates why species carries connotations of visible particularity: it is the thing you can point to, identify, perceive. This nuance is genuinely useful when reading Roman law arguments about whether a nova species is sufficiently distinct from its materials to constitute a new thing in law.
None of the historical dictionaries address the regulatory meaning. Researchers working in environmental law should not expect these sources to be helpful beyond confirming that species denotes particularity and distinctness — a conceptual thread that does, faintly, connect to why the ESA uses the term to isolate specific populations for protection.
Jurisdictional Note
The federal ESA definition of "species" — expressly including subspecies and distinct population segments — controls in federal regulatory proceedings. Several states, including California under the California Endangered Species Act, define species differently, with California's definition extending DPS protection to invertebrates as well as vertebrates. Researchers advising on compliance or listing petitions must verify which statute governs.
Encyclopedia Cross-Reference
Endangered Species Act — Listing, Critical Habitat, and Section 7 Consultation (The Law Mind Environmental & Energy Law Encyclopedia)
Endangered Species Act (ESA) — Listing, Critical Habitat, and Section 7 Consultation (The Law Mind Administrative Law & Government Encyclopedia)
Environmental Restrictions on Property — Endangered Species, Wetlands, Superfund Liens (The Law Mind Property Law Encyclopedia)