It is really laughable to see what different ideas are prominent in various naturalists’ minds, when they speak of ‘species’… It all comes, I believe, from trying to define the indefinable.
—Charles Darwin, letter to Johnathan Hooker (December 24th, 1856)
One of the ideas that still prevails in much of the world is Creationism: That life and all of its diversity came into being through a supernatural act of God, rather than through natural forces that are gradually developing over time.
Despite an ever-growing body of evidence, creationists, under the guise of Intelligent Design, still try to oppose the natural origins of life with twisted argumentation.
Although nearly every culture had creation myths, the Judaeo-Christian story that God created the Universe from nothing in seven days has thrived for almost three thousand years, and is undoubtably the most prevalent creation myth today.
The concept of distinct groups of living things is tacitly baked into Judaeo-Christian belief. God created plants, animals, then humans on different days; The entire sub-order of snakes (Serpentes) was cursed by God to crawl on its belly for deceiving Eve; Humans are considered to be distinctly different from animals, and were granted dominion over them; and didn’t God instruct Noah to take two of every kind on his Ark to preserve them (species is Latin for kind)?
Western philosophy has also played a key role in shaping how we perceive and organise various categories of living things, with Plato and Aristotle being the most notable contributors. Plato’s introduction of Universal Forms claimed that there are ideal forms of each thing, and that all of the real things we see on Earth are merely copies of them. In other words, somewhere outside of space and time, there exists a perfect blueprint for a dog, and your pet dog is an imperfect attempt to copy this perfect dog. This claim presupposes the existence of a particular thing called “dog” that has always existed and will always exist, cementing the species dog for eternity.
Aristotle was, in many ways, a more sensible philosopher than his predecessor Plato. He laid many of the foundations for modern science, including the idea that the Universe is made up of continual and causally connected series of events—everything is part of a single continuous process. However, in an effort to better understand the world, Aristotle named and categorised every living thing around him—which again, enforced the notion of separate and distinct categories of living things.
But one doesn’t have to be an ancient philosopher to conclude that there are separate and distinct groups of living creatures. When we look around, we see that butterflies are different from bees, and dogs are different from dandelions. And for most of our history, people would only come into contact with a handful of the different forms of life that we now know of.
It should be fairly uncontroversial then to claim that our personal experience, our shared belief systems, and the roots of our cultural philosophies have all trained us to perceive the natural world as being separated into different and distinct groups of living things.
On the Origin of Species
Until about two hundred years ago, this way of thinking remained essentially unchallenged, but started to shift when a group of scientific thinkers known as “naturalists” began to recognise and speculate over the dynamics of evolution. Most notably, Charles Darwin’s On the Origin of Species presented an alternative view of life in which the diversity we see gradually emerged over an immense amount of time, and that all species probably shared a single common ancestor.
I believe that animals have descended from at most only four or five progenitors, and plants from an equal or lesser number. Analogy would lead me one step further, namely to the belief that all animals and plants have descended from some one prototype… Therefore I should infer from analogy that probably all organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.
—Charles Darwin, On the Origin of Species
Around the same time, fossils of extinct species were beginning to be discovered and studied, and the science of palaeontology emerged. Our increasing understanding of the historical fossil record, and advancements in genetics and microbiology have all tested and validated the essence of Darwin’s ideas.
Still, recent Gallup Polls show that over 40% of people in the USA believe that God created all life on Earth in its present form.
“Intelligent Design”
Religious opposition to the view that life’s origins are natural tends to centre around deliberately misleading claims. Proponents of Intelligent Design (creationism disguised as science) can often be caught misrepresenting scientific ideas in the hope that their audience is not able to recognise the flaws in their arguments.
One of the most common arguments against a natural origin of life, which intelligent designists like to make, is to claim that:
Evolution can only occur within a species, and cannot create new species.
In other words, dogs can be domesticated from wolves, but breeding dogs could never create something that is not a dog. New species, it is presumed, can only be created in the mind of the Creator.
The problem with this argument is that it’s based on a somewhat false premise, and one that was created by biologists.
The problem with species
Many biologists have struggled with providing clear rules for defining what makes a species distinct from another. When scrutinised, the rules for separating the different types of living things all seem to have problems with them. There isn’t even an agreement on the number of different definitions of species, let alone an agreement on a definition (some consider there to be seven main definitions, some twenty-six, some thirty, and so on). This is known as The Species Problem.
This is not a new problem. In On the Origin of Species, Darwin wrote:
Nor shall I here discuss the various definitions which have been given of the term species. No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.
To provide just a few examples of species definitions: The Phenetic Species Concept defines a species as a group of organisms that look significantly similar to each other. The Recognition Species Concept defines a species as a group of organisms that will recognise each other as mates. And the Genealogical Species Concept defines a species by how genetically similar organisms are to each other in comparison to other groups
But the definition that has become the most popular, is what is known as the Biological Species Concept, which describes a species as the largest group that can potentially breed with each other, and share in a gene pool.
No term is more difficult to define than “species,” and on no point are zoologists more divided than as to what should be understood by this word.
—H. A. Nicholson
Proponents of Intelligent Design use this Biological Species Concept to argue that natural selection can not explain the diversity of life, since a species can, by definition, only interbreed within its own gene pool, and will only produce offspring that are also of their same species. And so, organisms are perpetually trapped to share genetic information only within the confines of their species. In technical terms, they allow for microevolution (which is irrefutable), but not macroevolution (which may challenge deeply held religious beliefs).
But the slow and gradual process of small changes producing new species (which they deny) can be seen in action in a phenomenon known as ring species—populations that can share a gene pool with a more distant population through an intermediary population.
For example, suppose population A and population B are similar enough to interbreed. And population B and population C are similar enough to interbreed. But A and C are geographically separated, and A is too genetically distant from C to interbreed. In such cases, A and B could be considered the same species, and B and C the same species, but A and C are, by our definition, distinct species.
There are numerous examples of ring species in nature, sometimes with many compatible intermediary populations, but two or more that are incompatible at the extremes. This can be thought of as a geographical example of what has probably taken place over time, for hundreds of millions of years—just replace the geographical barrier separating the different populations for a time barrier instead.
It should be apparent then, that even our best working definition of species cannot accurately model the reality of the diversity found in nature.
The glaring problem with the creationist argument about species is that species don’t really exist—at least not in the way that they would like them to. Rather, they are a construct created by humans to help us make sense of the world.
The concept of a species is a concession to our linguistic habits and neurological mechanisms.
—John B. S. Haldane
Often in nature, things change gradually, slowly, and by degree. It’s only when enough changes in degree have taken place that we perceive them to be a difference in kind. In reality, the natural world is a near-infinite collection of individual entities that are more or less related to each other by degree.
To help us organise and make sense of the insurmountable diversity found in nature, we have to create some system that allows us to identify and describe the differences and similarities that exist at every level of life, and biologists have done well with this Herculean task. But these groupings will always be arbitrary, or suitable for certain purposes but not for others.
The claim that evolution can only occur within a species, and can never lead to new species, can be demonstrated false by recognising that there isn’t such a thing as species to begin with. The bold lines and distinct categories between different groups of species that creationists would like there to be, simply do not exist.