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San Marcos Public Library 625 E. Hopkins St. 512-393-8200 Q. How many species are there on planet earth?

Unfortunately, science does not A. have a specific answer for this. While there are many opinions on the answer to this question, all of science agrees that it is an extremely important one to answer.

Taxonomy, the science of naming, arranging, classifying and describing life on earth, is over 200 years old but still cannot tell us for certain how many species there are on earth. To begin with, there is no consensus among biologists on exactly what the term “species” means. The well-known biological species concept states that two organisms belong to the same species if they can interbreed and produce fertile offspring. But since this concept relies on mating, it cannot be used to define species of asexual organisms such as many microorganisms as well as some reptiles, birds and fish. It also ignores the fact that many living things we consider separate species can and do interbreed. For example, dogs, coyotes and wolves readily interbreed, yet are usually considered to be separate species. Other popular species definitions rely on how similar individuals are to one another (if it looks like a duck, it is a duck), their shared evolutionary history, or their shared ecological requirements. Yet none of these definitions are entirely satisfactory, and none work for all life forms. There are at least 50 different definitions of a species to choose from. Whether or not a scientist chooses to designate a newly found life form as a new species or not can come down to their philosophical stance about the nature of a species. (Latty)

While biologists can’t completely agree on how many species, total, there are on planet earth, they can agree on a few things. First, we have not even discovered over 75% of the species on earth. The sheer magnitude of biodiversity on earth prevents this. There are living species that inhabit such inaccessible areas of planet earth that it is doubtful that we will ever know the full extent of life on earth. The second thing we do know is that without knowing how many species there are, we cannot know what we are losing. Species that are instrumental to human life can be lost without our even knowing. Some endangered species that we do know of, like the rosy periwinkle, are important in the fight against cancer. This was on the brink of extinction until scientists discovered its medicinal value.

There is one facet of this topic that lends itself to some consideration, although it is not widely accepted at this time. Because science cannot come to some consensus as to what a species is and how many there are on earth, there is some thought in the scientific community of scrapping the entire way we define species and go to a more holistic approach. Scrapping the idea of a species is an extreme idea: it implies that pretty much all of biology, from Aristotle right up to the modern age, has been thinking about life in completely the wrong way. The upshot of this new approach would be enormous, both for our scientific and philosophical view of life. It suggests that we should give up thinking about life as neatly segmented into discrete groups. Rather, we should think of life as one immense interconnected web. This shift in thinking would fundamentally reorient our approach to a great many questions concerning our relation to the natural world, from the current biodiversity crisis to conservation. (ScienceDaily)

• Davies, N., & Sutton, E. (2017). Many: The diversity of life on Earth. Candlewick Press.

• ScienceDaily. (2011, August 24). How many species on earth? About 8.7 million, new estimate says. ScienceDaily. Retrieved October 22, 2021, fromsciencedaily. com/ releases/ 2011/ 08/110823180459.htm.

• Strauss, R., & Thompson, M. (n.d.). Tree of Life: The Incredible Biodiversity of Life on Earth.

• Tanya Latty Senior Lecturer, & Timothy Lee Associate Lecturer in Life and Environmental Sciences. (2021, June 29). How many species on earth? why that's a simple question but hard to answer. The Conversation. Retrieved October 22, 2021, from theconversation.com/ how-many-species-onearth-why-thats-a-simplequestion-but-hard-toanswer-114909.

Suzanne Sanders is the new columnist for the library. She is the Community Services Manager for the San Marcos Public Library and came from the Austin Public Library in 2015 after having served there as a librarian for over 20 years. She gratefully accepts your questions for this column.