Homo sapiens compulsively create and label categories-of things and even of ideas.

We identify and give names, for example, to mountain peaks, rocks, languages,

religions, behaviors, books, subatomic particles, elements, and living creatures. By

placing a semblance of order upon what otherwise might be inchoate complexity,

communication becomes easier. And, in science, categorization and insight into

process have historically advanced in tandem.

In the living world, the widely used hierarchy of categories extends from the

molecular and cellular subunits of individual organisms, through organs and other

body parts, to the individual, the population, the species, and on up the taxonomic

ladder through genus, family, order, class, phylum, kingdom, and then all of life, itself.

Finer divisions arise as well, such as subfamilies, superfamilies, and subspecies, all

with the same intent: to enhance communication and insight.

There, near the midpoint in the categories of life, sits what is arguably the most

widely discussed category of all, at least in biology: species. In the vernacular and

in the scientific literature, it is species that exhibit distinct traits, species that go

extinct, species we must protect, species that provide ecosystem services, species

that need to migrate under global warming if they are to survive, and species that

Darwin unraveled the "origin of". Species, species, species... Why? Does a fixation

on that category truly abet understanding and communication? If not, what is the

alternative? Those and related questions are the focus of this book.

Linnaeus focused attention on species when he invented binomial nomenclature

(a generic and a specific epithet that comprise a species name or binomen), and

Darwin reified the concept in his classic work. Species are collections of twigs on

the evolutionary tree of life that are considered different enough from other collections

to be so designated-basically different "kinds" of organisms. It is generally

agreed that sexually reproducing organisms that are sympatric (live together) without

commonly interbreeding will be considered separate species. But judgments about

allopatric populations (those geographically separated) are mostly matters of taste.

Basically, species are arbitrary stages in a continuous evolutionary process of population

differentiation. Sadly, there is a large silly literature on how to define species

that does not recognize this evolutionary fact.