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There are 8.7 million species on earth

15,000 species are described each year. At this rate, it will take another 480 years to fully catalog

The number of species in classes, orders, and families follows patterns. This enables an assessment

What would aliens want to know about us, should they ever cross the galaxy and meet our planet? One of your questions might be: "How many different forms of life are there on earth?" What would we answer? "We do not know it." There are no exact figures, and estimates show the most varied of values. Depending on the scientist, they range from three million to over 100 million species. Prokaryotes, such as bacteria, are not even included in these numbers.

Now researchers from various disciplines and universities have presented a new method with which the number of species can be estimated more precisely. It should now be 8.7 million, plus minus 1.3 million. 6.5 million of these species live on land, the remaining 2.2 million have made water their habitat.

These figures come about through extrapolation. Every newly discovered species is precisely classified taxonomically by researchers around the world. The classification system developed by Carl von Linné in 1758 is used, which systematically records all living beings according to species, genus, family, order, class, tribe and kingdom. There are also sub-categories. The domestic dog, for example, is a subspecies of the wolf ( lupus ), belonging to the genus canis belongs.

A species is characterized by the fact that its members can reproduce with one another, but not with other species. An example is the barren mule, the descendant of a horse and a donkey, which belong to the same genus but not the same species. The living beings are also named after Carl von Linné's system. The "first name" stands for the genus, the surname for the species.

The scientists working with Camilo Mora from the University of Hawaii have now made use of this system to calculate the total number of all species. Mora explains the system with an example from the computer world: "You have a lot of new files that you put in a folder. That folder is in another folder that contains similar files. And so it goes until you complete your collection We have now discovered that knowing the total number of folders in that archive can predict the exact number of files in the archive. "

The scientists have now made use of two properties of this system: First, the upper categories of the Linnaeus system such as class and realm are described much more completely than the lower levels. Second, the researchers noticed that the number of species associated with each tribe, class, order, family, genus, and species follow constant patterns. Therefore, assuming that these patterns also apply to less explored groups of living things, one can estimate the total number of species within a group based on the information already known about tribe and class. To check the results, the scientists tested the method on smaller, well-researched classification groups such as fish or mammals.

With the help of the new procedure, which has now been published in the online journal "PLoS Biology", Camilo Mora and his team have come up with this large number: 8.7 million species worldwide. That doesn't mean that all of these have already been discovered by humans, on the contrary. Around 86 percent of the species on land and 91 percent of the species living in the water have not yet been discovered, described and cataloged. To some, these 8.7 million species may not seem like a lot when you think of all the different insects, algae and microorganisms that cavort on this planet. However, the research project of Camilo Mora and his colleagues is only about species, not about subspecies or races.

In the 253 years since the publication of Carl von Linné's taxonomic system, around 1.25 million species have been described and entered into a central database. Every year there are about 15,000 more. It is assumed that a further 700,000 species have already been described, but the details have not yet reached the databases. If you continued at this pace, it would take you about 480 years to finish cataloging. A taxonomist describes an average of around 25 species over his entire career. Describing a single species costs 34,000 euros. Researchers are now engaging parataxonomists to support them. These are locals in research areas who are trained in the basic techniques of recognizing and describing new species in order to relieve the scientists of the work on site.

In the future, the "barcode" classification, in which the genetic code of living beings is mapped in the form of a barcode, will probably also be used more and more. In the not too distant future, there may be small portable devices that can be used to perform a quick DNA test to identify species. That would make the work of the systematics a lot easier.

The slow progress made in researching new species also means that some species may already be threatened with extinction or no longer exist before they are even discovered. Even the International Union for Conservation of Nature (IUCN) only observes around 60,000 species. Almost 20,000 of them are on the "Red List" - that is less than one percent of all species if you take Camilo Mora's figures as a starting point. In 2008, the World Wide Fund for Nature (WWF) estimated that the world's biodiversity fell by 27 percent between 1970 and 2005. The European Union had planned for a long time to stop species extinction in Europe by 2010, but this was changed last year so that it now only plans to halve the loss of biodiversity by 2020.

Humans have lived on this planet as Homo sapiens for 200,000 years, and yet he knows little about the diversity of other living beings that share the earth with him. The zoologist Lord Robert May of the University of Oxford writes: "It is a remarkable testimony of our narcissism to know that on February 1, 2011, 11,194,656 books were in the National Library of the US Congress, but I do not tell you how many different plant and animal species we share our world with. "

So why should we know how many species exist on this planet? "Mankind has committed itself to protecting species from extinction, but until now we hardly knew how many there were," explains Boris Worm. Some critics may note that many people do not care about extinction. But according to a survey by the Eurobarometer, 90 percent of Europeans feel obliged to preserve biodiversity - this shows how much species protection is important to the citizens.

New species can have many benefits for humanity, as the past has shown. Many of the ingredients of plants and secretions from animals can have a medicinal effect that we are not even aware of today. The sap of the ginkgo tree, for example, can counteract memory loss. In the 1980s, the gastric breeder frogs were discovered, the young of which mature in the mother's stomach. Scientists were already looking forward to perhaps using this knowledge to develop peptic ulcer remedies. But just a year after its discovery, the frog was considered extinct - a missed opportunity. In order not to lose such opportunities in the future through premature species extinction, it is important to adequately research the living things of the world.

An example from the 1970s shows that taxonomic research also has economic advantages: The Chinese Yuan Longping discovered a new type of rice that, when crossed with conventional rice, brought in 30 percent more yield. Since then, all wild rice varieties have been protected, which of course is only possible if you are already familiar with them. It remains to be seen whether the new scientific findings will result in the coming years becoming an age of discovery - or an age of (actually preventable) extinction of species.