"Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life. Energy processing is also important to life as it allows organisms to move, grow, and reproduce. Finally, all organisms are able to regulate their own internal environments.
Biologists are able to study life at multiple levels of organization. From the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations. Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use. Like other scientists, biologists use the scientific method to make observations, pose questions, generate hypotheses, perform experiments, and form conclusions about the world around them.
Life on Earth, which emerged more than 3.7 billion years ago, is immensely diverse. Biologists have sought to study and classify the various forms of life, from prokaryotic organisms such as archaea and bacteria to eukaryotic organisms such as protists, fungi, plants, and animals. These various organisms contribute to the biodiversity of an ecosystem, where they play specialized roles in the cycling of nutrients and energy through their biophysical environment."
(from Wikipedia)
First three paragraphs of the Introduction of a book "What, If Anything, Are Species?"
"I am amazed how often biologists, who pride themselves on being objective scientists and who criticize the shibboleths of religion, react vehemently when anyone challenges the reality of the rank of species and tries to get rid of binomials. I have heard it so many times:
“We have always had binomials, there would be chaos without them!”
“We must have species in order to do ecology and conservation!”
“How dare you suggest that we get rid of species; they are real entities in the hierarchy of life!”
Species are truly the sacred cow of biology. Most biologists start their consideration of species with an a priori assumption that they exist. For example Kunz (2012), in his book-length treatment entitled “Do Species Exist?”, never provides any good evidence that they do, he just assumes it. He makes tautological statements like: “If species did not exist, it would not even be possible to speak of the boundaries between them.” (p. 12). You could just as easily argue that “if the Tooth Fairy did not exist it would not even be possible to speak of how much she left under a child’s pillow.” Chung (2004) starts out a paper on the educational value of teaching students controversies over species concepts in biology by flatly taking it as “given that species are real,” thus glossing over the most fundamental controversy.
More ink has been spilled on the concept of species than on any other concept in biology. We never seem to eliminate any species concept; rather the field evolves by one concept after another being added to the pile. It is too much to hope that another book on the topic (more ink!) can completely resolve the situation. However, a more modest goal might be achievable, via explaining why there has been such a diversity of views about species and following modern ideas of phylogenetic classification to their logical destination. Perhaps the resolution lies in a different direction than the ever-increasing pile of species concepts. May be we just need to sweep that pile away! May be all the centuries of angst have been due to people striving to define something that does not exist!"
What, If Anything, Are Species?