The concept of the species

StoryImage( ‘/Images/Story//Auto-img-116845366915591.jpg’, ‘Photo courtesy of’, ‘Carolus Linnaeus (1707-1778), the great Swedish naturalist who founded the modern system of animal and plant classification.‘);

When Charles Darwin published The Origin of Species by Means of Natural Selection in 1859, he had no idea how many different species (the word species is both singular and plural) or types of animals and plants there were on the face of the earth. Charles should not have been ashamed of his lack of knowledge, as biologists today can only make highly speculative guesses on the number. We do know, however, that about a million different insect species have been described, with about a million additional ones waiting to be discovered. In a recent issue of Smithsonian magazine, for example, it was reported that a recent study of 30 caves in Sequoia and Kings Canyon National Parks in California yielded 27 new species of animals.

The science of naming new species is called taxonomy, and any biologist who studies a particular group of organisms becomes a taxonomist when he or she finds what is considered to be a new species. Though there are rules to be followed in naming a new species, the discoverer is free to name it anything he desires.

For hundreds of years, the physical appearance was the primary criterion for stating an animal was previously unknown. If, in the mind of the biologist, it was sufficiently different from previously known forms, he was free to declare it new to science. Taxonomists were thusly divided into two categories, the “lumpers” and the “splitters.” A lumper would declare any two animals with only the faintest of resemblance to be the same species. A splitter would literally split hairs, and if there was even a very slight difference between the two, he would announce they were different species. The splitter did not take into consideration that there are no two living things exactly alike, and variations occur. There was the case of an insect taxonomist in Massachusetts who described more than 10,000 new species of crane flies based on natural variations in the venation of the wings. For many years, two important species of mosquitoes were recognized based entirely on a single hair on the wiggler in one that was branched, while in the other it was straight. After many years, saner heads prevailed, and the two species were accepted as being the same.

Needless to say, the literature concerning a certain group of organisms became polluted with bogus species and in many cases became unreliable for a researcher to use. Confusion reigned.

Some 60 or 70 years ago, a new concept of what constituted a new species was developed and makes sense. It is called the biological concept of a species, which says: If two animals can mate and produce fertile offspring, they are the same species. If they cannot do this, they are different species. A mare and a jackass, for example, can mate and produce a sterile mule, but they are not the same species.

Of course, when a new form is discovered that is so drastically different from its kin, it is permissible to call it a new species. For example, one of the 27 new forms discovered in the caves in California was a blind pseudoscorpion without eyes. All other known peudoscorpions have eyes and excellent vision, so the blind one without eyes can legitimately be called new.

In taxonomic lingo, a category known as the subspecies has been created and frequently causes confusion. A subspecies is in the process of evolving into a new species as a result of geographical isolation. It has recognizable difference from the main population and is going its own way in evolution. However, if subspecies are brought back to contact with the main population after a short period of separation, they can mate and produce fertile offspring. But, after a time, a genetic isolating mechanism will become established, and the subspecies then becomes a new species on its own.

Many times in my career as a medical entomologist who primarily studied medically important mosquitoes in various parts of the world, I was sure I had discovered a new species, only to change my mind after careful study of the situation. I did, however, discover and name as new a species of scabies mite found infesting bat populations while studying the transmission of bat malaria in Texas. So, in a sense, I became immortal when I described and named Sarcoptes myotis Hedeen, 1953. But, who gives a hoot if bats are sometimes infested with scabies?

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the Jan. 10-16, 2007, issue

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