Do Species Really Exist?

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"Nor shall I here discuss the various definitions which have been given of the term species. No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species." 
- Charles Darwin, On the Origin of Species, Chapter 2.

"I have just been comparing the definitions of species [...] It is really laughable to see what different ideas are prominent in various naturalists' minds, when they speak of 'species'; in some, resemblance is everything and descent of little weight – in some, resemblance seems to go for nothing, and Creation the reigning idea – in some, descent is the key — in some, sterility an unfailing test, with others it is not worth a farthing. It all comes, I believe, from trying to define the undefinable."
- Charles Darwin, in a letter to Joseph Hooker, 1856.


Faced with the rich diversity of living beings around us, humans have proven unable to resist the temptation to try to organize and categorize them. We have a natural tendency to classify things, a habit that's deeply rooted in our cognition and use of language. Our brain excels at recognizing patterns (and thus finding meaning where it doesn't exist), an ability that allows us to interact with the world using names — like "chair" — that we might be hard-pressed to properly explain. In fact, it's surprisingly difficult to define even a seemingly straightforward word like "chair" in a way that would let us recognize everything that should be included (from office chairs and recliners to stools and wheelchairs) but nothing that shouldn't (like tables, tree stumps, or other things we might decide to sit on).

Despite these difficulties, we've been classifying organisms throughout the history of human thought, from Aristotle's division between plants and animals to modern scientific nomenclature. The modern classification system is based on grouping organisms into units called 'species'; species, in turn, group together into a larger units called genus, family, order, and so on through the nested hierarchy of life. What make a species, though? Why should a particular group of organisms be thought of as a unit and given a distinct name? How do we decide which organisms make up a species?

Biologists have struggled with these questions (the "species problem") since before Darwin's time. Over the years, they've come up with a cornucopia of different answers, or species concepts. It's important for students of the natural world to appreciate and consider the different ways that "species" is used, since its meaning can change in different contexts. To me, it often seems that no single definition will ever suffice to capture the variety of ways that wildly different sorts of creatures (like plants and animals) manage to maintain their identity as a species or to form a new one.

Written By: Sedeer el-Showk
continue to source article at nature.com

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  1. I find the different species concepts useful in different situations. In the macroscopic animal world it helps to think of a species as being a group of organisms that can interbreed and make fertile offspring. This loses it’s utility when dealing with bacteria or asexual fungi…etc….

    The thing is, most creationists, while spouting their deliberate nonsense, crap all over the idea os species and show their ignorance of even the most basic definitions. In particular, when confronted with an example of …..say…. the subway mosquito, Culex molestus. It is clear that speciation has occurred and clear that a new environment has caused the speciation. The creationist then answers “yes, but they are STILL mosquitos”…

    Yes, but they are no longer the same species!!!

  2. Species are fuzzy, but so are physical objects, as they continually gain and lose atoms. Technically, the chair I’m sitting in is gradually changing, and searching for an exact to-the-atom statement of how much it could change while still being a chair is a mug’s game. The only reason physical objects can be discerned is because quantum effects, such as indeterminacy of particles’ positions, die down for large particle numbers. According to quantum field theory, even the particles themselves aren’t absolute. But no-one would say objects don’t exist. Species are not-too-big, not-too-small neighbourhoods in the space of living things, including things as long as they’re similar enough, or something like that. It’s not a perfectly precise concept, but it’s going a little far to say it’s all make-believe. It might even be true in some sense, but it’s not a useful approach to scientific semantics, is it?

  3. @OP – The modern classification system is based on grouping organisms into units called ‘species’; species, in turn, group together into a larger units called genus, family, order, and so on through the nested hierarchy of life. What make a species, though?

    In looking at classification, we must also look in both directions from “species”!

    Going up into wider groupings we have;-

    • species, genus, family, order, and so on,

    but in the opposite direction, working down to specific details, we have:-

    • sub-species, hybrids, varieties, cultivars, forms, clones, and the genomes of individuals.

    @OP – Why should a particular group of organisms be thought of as a unit and given a distinct name? How do we decide which organisms make up a species?

    Since Dawin’s time, scientific bodies have addressed this issue.
    The term “species” has different defined meanings in relation to specific groups of organisms. The structure of the usable classification is decided in the agreed codes of the specialist bodies covering those fields of study.

    crookedshoes – 1

    I find the different species concepts useful in different situations. In the macroscopic animal world it helps to think of a species as being a group of organisms that can interbreed and make fertile offspring. This loses it’s utility when dealing with bacteria or asexual fungi…etc….

    Each specialist area has its own rules of nomenclature, so that meaningful discussions can take place with agreed understanding of general terms and definitions. These are up-dated from time to time.

    International Code of Nomenclature for algae, fungi, and plants

    International Commission on Zoological Nomenclature-http://iczn.org/

  4. a better title for Darwins book would be “On the Assumption of Species”

    ‘Species’ has biblical baggage, Adam named them all apparently in the garded of eden where all the kangaroos, snow leopards and cuttlefish used to live

    since the discovery of the structure of DNA we should have been trying to either come up with a universal definition (hard to do) or just accept it’s a word people use that has no scientific definition

    • In reply to #4 by SaganTheCat:

      since the discovery of the structure of DNA we should have been trying to either come up with a universal definition (hard to do) or just accept it’s a word people use that has no scientific definition

      Species are just patches of related organisms within a continuum. In some places there are natural gaps in the continuum which separate them , in other places there are not, so one species merges into others – as in ring species!

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