How Many Species Are There on Earth?

In biology, the concept of species is used to describe, understand and reduce biodiversity to a specific number. A living species consists of a population whose members can reproduce only among themselves and that share similar structural and functional characteristics. (This concept will be explored further in Chapter 3, "Evolution's Speciation Dilemma.")

How many species are there on Earth? That question has long intrigued a great many people. Wide-ranging research is now being carried out to answer it. To date, scientific studies have revealed that no definite figure can be given, only that it is exceedingly large.

The eminent zoologist Edward O. Wilson, one of the scientists who first came up with the concept of biodiversity, is regarded as an authority in the field.⁴ A professor at Harvard University, he offers the following analysis:

No one knows the number of species of living organisms, but there are probably at least 5 million, and the number could be as high as 100 million. Consider first the question of the amount of biodiversity. The number of species of organisms on Earth is unknown to the nearest order of magnitude. About 1.5 million species have been given names to date, but the actual number is likely to lie somewhere between 10 and 100 million.⁵

Thomas E. Lovejoy is President of the H. John Heinz III Center for Science, Economics and the Environment and an expert on biodiversity:

While the number of species currently described is on the order of 1.4 million, the big question is how many species are there totally? Current estimates of the total number of species run from 10-100 million.⁶

In a paper, Professor Quentin Wheeler of Natural History Museum, London and Professor Joel Cracraft of the American Museum of Natural History submitted their own estimate of biodiversity:

Despite having accumulated significant knowledge about the world's species over the past 2 centuries, we still cannot provide accurate answers to the simplest of all questions about biodiversity. How many species are there? Estimates vary from 3 to 100 million species.⁷

Taylor Ricketts of Stanford University says that: "The Earth is home to over 1.7 million known species, and probably 10 times that number have yet to be discovered."⁸

Alessandro Minelli from the University of Padua states that "Global estimates of existing biodiversity are thus quite uncertain. Figures ranging from 5 to 130 million species have been recently offered for the gross total."⁹

According to The Encarta Encyclopedia, the identified and named species number 1.⁷⁵ million, and some scientists estimate the total number of species on Earth to be around 10 millionand others, more than 100 million.¹⁰ According to the Encyclopedia Britannica, many more species are waiting to be identified and named, and there are currently estimated to be between 10 and 30 million living species.¹¹

Also, these estimates are for species currently living and do not include those that have become extinct.

References

4. Encyclopedia Britannica 2001 Deluxe Edition CD, "The importance of the biosphere." ↩
5. Edward O. Wilson, In Search of Nature, Washington D.C. Island Press/ Shearwater Books, pp. 153-171. ↩
6. Marjorie L. Reaka-Kudla, Don E. Wilson, Edward O. Wilson (editors), Op cit.; Thomas E. Lovejoy, Biodiversity: What Is It?, Washington D.C.: Joseph Henry Press, 1996, p. 7. ↩
7. Marjorie L. Reaka-Kudla, Don E. Wilson, Edward O. Wilson (editors), Op cit.; Q.D. Wheeler, J. Cracraft, Taxonomic Preparedness: Are We Ready to Meet the Biodiversity Challenge, Washington D.C.: Joseph Henry Press, 1996, p. 436. ↩
8. Taylor H. Ricketts, "Conservation Biology and Biodiversity", Encyclopedia of Life Sciences, 2001, ğ.els.net. ↩
9. Alessandro Minelli, "Diversity of Life", Encyclopedia of Life Sciences, 2001, ğ.els.net. ↩
10. M. Encarta Encyclopedia 2001 Deluxe Edition CD, "Biodiversity." ↩
11. Encyclopedia Britannica 2001 Deluxe Edition CD, "Evolution". ↩
75. "Researchers Find Glass-Eating Microbes at the Rock Bottom of the Food Chain," Scripps Institution of Oceanography, 2001, http://www.spaceref.com/news/viewpr.html?pid=6137 ↩