Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Species Definition
Name: Christopher
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A

What are the primary facts that one must consider when examining organisms that are obviously closely related in determining whether or not they should be in a single or separate species? For example, the blue heron of North America (Ardea herodias) and the grey heron of Europe and Asia (Ardea cinerea) are treated as separate species even though there is considerable argument that they should be treated as a single species. How should one weight the merits of cases similar to this? Even though in this example it is obvious that the two species have been separated by geography (allopatric speciation) but it does not seem as though that alone should render them into two distinct species.

Well, the species concept is one of the most hotly debated in science. After all, it is a man made concept. The organisms don't know what species they are supposed to be in. The wolf and dog are another good example. Modern genetic analysis nests them together in some cladograms, which some think means they really are not separate species. And the most commonly accepted definition is that if they can breed and produce fertile offspring, they are considered the same species. Wolves and dogs can still interbreed. It's possible we are watching a speciation event in progress. Speciation doesn't happen overnight. There has to be something that prevents interbreeding, such as the fusion of chimp chromosomes to become one, which some use as evidence of speciation between humans and chimps. The herons of which you speak may be assumed to be separate species because it is unlikely they will be able to interbreed because of the distance between them. One could bring two together and see...


Click here to return to the Zoology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory