Number of Estimated Species Reaches 8.7 Million

by Dr. Elizabeth Mitchell on September 3, 2011

BBC: “Species count put at 8.7 millionClassification scheme is key to species count.

No one really knows how many species of organisms share the earth. About 1.2 million have been described, but we really have no idea how many there are. “Globally, our best approximation to the total number of species is based on the opinion of taxonomic experts, whose estimates range between 3 and 100 million species.”1

An international team publishing in PlosBiology has come up with another way of tallying species unaccounted for. They estimate there are about 8.7 million species on earth. Of these 2.2 million are marine. They write, “In spite of 250 years of taxonomic classification and over 1.2 million species already catalogued in a central database, our results suggest that some 86% of existing species on Earth and 91% of species in the ocean still await description.”2

“When you go to a tropical rainforest, it's easy to find new insects, and when you go to the deep sea and pull up a trawl, 90% of what you get can be undiscovered species.”

So what’s missing? “The rest are primarily going to be smaller organisms, and a large proportion of them will be dwelling in places that are hard to reach or hard to sample, like the deep oceans,” said team member Dr. Derek Tittensor. “When we think of species we tend to think of mammals or birds, which are pretty well known. But when you go to a tropical rainforest, it's easy to find new insects, and when you go to the deep sea and pull up a trawl, 90% of what you get can be undiscovered species.”

The method used to count the missing is an extrapolation based on the classification system itself. "We've been thinking about this for several years now - we've had a look at a number of different approaches, and didn't have any success," Tittensor added. "So this was basically our last chance, the last thing we tried, and it seems to work."

The team looked at the various levels of classification—kingdom, phylum, class, order, family, genus, and species. For each broad group, they catalogued the number of known members in each subcategory. Since the numbers seemed be come out in consistent ratios for the more well-known groups, they assumed the method worked. Then they added up the categories that were short and came up with 8.7 million.

They actually left out bacteria because those numbers didn’t come out consistently.3 The reason, they suspect, has to do with the horizontal transfer of genes between bacteria and the effect that has on species distinctions.

The team did note that the definition of species varies greatly. “Different taxonomic communities (e.g., zoologists, botanists, and bacteriologists) use different levels of differentiation to define a species.” Therefore, they add, “although estimates of the number of species are internally consistent for kingdoms classified under the same conventions, our aggregated predictions . . . should be interpreted with that caution in mind.”4

Commenting on the calculations, Professor Jonathan Baillie, director of conservation at London’s Zoological Society, said “I think it's definitely a creative and innovative approach, but like every other method there are potential biases.”

One of those biases is of course the subjective nature of the classification systems, but since the method was predictive for some categories, the team thinks the method at least gives a reasonable estimate of the world’s biodiversity.

Today, species and created kind are not synonymous.

Back when Linnaeus developed his classification system, species was used to denote a created kind. The definition changed in subsequent years. Today, species and created kind are not synonymous.

Created kinds are organisms representing or descended from those originally created by God about 6,000 years ago. Organisms within a created kind generally interbreed and produce only more organisms of their own kind “within the limits of preprogrammed information, but with great variation.”5 Organisms that can interbreed are of the same created kind, since God designed organisms to reproduce “after their kind.” Due to loss of information and other factors, however, some organisms lose the ability to interbreed. Created kinds correspond roughly to the family level of the current classification taxons but may vary from order to genus level.

Although evolutionists imbue taxonomic classification with evolutionary implications—believing that the taxonomic groupings roughly depict common ancestry— taxonomy is really nothing more than a useful bookkeeping system to sort and group organisms according to their shared characteristics.

As creationists, we must frequently remind detractors that we do not deny that species vary, change, and even appear over time. The biodiversity represented in the 8.7 million or so species in the world is a testament, not to random chance processes, but to the genetic variability and potential for diversification within the created kinds that God built into the genomes of the originals 6,000 years ago.


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Footnotes

  1. www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001127
  2. www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001127
  3. www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001127
  4. www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001127
  5. Classifying Life

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Answers in Genesis is an apologetics ministry, dedicated to helping Christians defend their faith and proclaim the gospel of Jesus Christ effectively. We focus on providing answers to questions about the Bible—particularly the book of Genesis—regarding key issues such as creation, evolution, science, and the age of the earth.