Western science is developed in terms of purely logical, numerical data. We want absolutes. We try so hard to determine infallible truths. A plus B will always equal C. Establishing these base rules or language to describe the world makes communication easier. It allows us to make assumptions which provide a foundation for further science.
However, nature does not like to abide by our laws and definitions. They are strings of concepts we as humans develop to try and make sense or establish some sense of control over the uncontrollable. There is no scientific law that does not have an exception to the rule. Nature is not black and white. There are precious few universal yes or no answers. Those that are probably just haven’t found an exception yet.
How would you define a species? That seems pretty straightforward does it not? Just as a self-assessment see if you can do it. What is the distinguishing characteristic that separates an orangutan from an iguana from a black oak tree?
That is a misleading question because there is no single answer. The definition of the most fundamental unit of life’s classification and scientists cannot agree on it. There are three different definitions of what a species is, each based on its own criteria and none universally true.
There is the biological definition of species – that a species is a group of individuals that can interbreed and produce viable, fertile offspring. This accounts for species in which males and females look drastically different. However, what about hybridizing species? For example, pizzly bears are a reproductively successful cross between polar bears and grizzly bears that occurs naturally in the wild. According to the biological species concept polar bears and grizzly bears are then the same species. Should we start defining them as the same thing even though their evolution, phenotype, and natural history are different?
The second species concept is phylogenetic. This definition is determined by the smallest, distinct group of individuals on an evolutionary tree. It is the “tip” of the phylogenetic tree. The organisms that constitute a phylogenetic species are descended from a common ancestor and possess shared derived characteristics. Essentially, they came down the pipeline of evolution together. This can be problematic because there are a lot of tips on the phylogenetic tree. It indicates that every sub-species should be its own classification. Even slight evolutionary differences can be debated over as a new species. The phylogenetic species concept promotes the over-complication of speciation and extreme division of organisms.
Last but not least, there is the morphological species concept. Morphology is the structure of something. It hypothesizes that individuals who are structurally, anatomically, and visually the same must be their own distinct species. That explains the distinction between the iguana and the oak tree, but it is confounded in situations like dolphins and sharks. These two groups look very similar morphologically, however genetic testing shows that the similarities between the two stop at being top predators and having fins. It promotes inaccurate assumptions about species relatedness.
These are the top three species concepts used in science and they all have significant limitations. And that’s without even touching on the 26 lesser-known species concepts.
Nature, evolution, and life in general cannot be put into a box, not defined by a simple phrase. There is no set ground-rule for how things should work. So much of what governs our world is random and unpredictable. Species adapt to the specific stimuli of their environment. The individual adapts to life experiences. There is a rule of thumb that we might use to predict what comes next, but there is no certainty. That can be intimidating, but isn’t it also exciting?
In my opinion, it is worth talking about the species concepts and the myriad of other similar issues in science. Go ahead and theorize about it, postulate what it means to be a species, to be an ant or a human, what it means to be alive. It is interesting to explore from a scientific and philosophical perspective. But at the end of the day, we must realize that we will not always have the answer. We can, and should try, to put our world into words, but there will never be ‘the answer to everything’ that we want. Nature, life, and evolution are too vast, too miraculous, too wild for us to capture. People have tried for centuries. So sometimes you just have to sit back and watch with gratitude and awe for the unexplainable.