What separates one species of creatures from another? Naturalist Michael Ellis has the answer.
Taxonomy is the study of the classification of living organisms. A Swedish university professor in the 18th century decided that he was God's chosen instrument to name every living thing on the planet. So, Carl von Linne developed what we still use today - the binomial system. That is each species on Earth is given two names - a genus and a specific epithet or species. Linne used Latin, ancient Greek and occasionally other languages for the designation. Humans are Homo sapiens, Latin for wise man.
So, what is the definition of species? Basically, it is any organism, which is reproductively isolated from another. So, in other words one species cannot mate with another or if they do succeed and produce progeny, that offspring is sterile. The classic examples are donkeys and horses that can produce a mule but the mule can’t reproduce.
Taxonomists use physical characteristics, to determine familiar relationships. If they look alike and share most features they must be the same critter. But too many differences, then they are separate species. It was often arbitrary because with further investigation and especially with DNA tools, many assumptions about species are being overturned.
For example, in the eastern U.S. there is a yellow-shafted flicker and in the western states a red-shafted flicker. They were considered separate species for many years. However, where the two populations meet in the middle of the country they reproduce with no trouble. So now they are considered one species – the northern flicker. On the other hand, there is a bird, the Western grebe, and within its population there were some individuals that had a slightly different plumage pattern. It was very subtle and not thought to be important. Well, that was wrong. While they do look much alike, they are actually two separate species. We now have in addition to the western grebe, the Clark’s grebe or Aechmophorus clarkia – Latin for the spear bearer because of the very sharp pointed beak.