Charles Darwin’s theory of evolution confuses the concepts of evolution and progress, but in reality, evolution is not a process of perfection, but rather the selection of variants that are adapted to the environment of their time.
It’s no exaggeration to say that Charles Darwin’s theory of evolution changed the way we look at living things. But unlike the way we think of Charles Darwin when we use the word “evolution” in biology, Darwin didn’t use the word “evolution” when he first wrote On the Origin of Species. He wanted to avoid conveying a sense of “progress” and making his readers think that life was changing toward some goal. But even today, the question of whether evolution is progress continues to be raised. The idea of evolution as progress risks leading to eugenics and speciesism. So, let’s argue why, biologically speaking, evolution is not progress.
The idea of evolution as progress is rooted in the Western view of nature as a “great chain of being” that dates back to Aristotle. The idea is that there are stages of life, with simple, lower animals at the bottom of a giant ladder, and higher animals ascending through the rungs to humans and gods. In addition, because the word “evolution” is widely used in everyday language to mean getting better, we think of biological evolution as moving in a certain direction, and in the extreme, toward perfection. However, the biological definition of evolution refers to a change in the distribution of traits within a population of organisms as environmentally appropriate variation is passed on to the next generation. This definition is based on Darwin’s theory of natural selection, which states that evolution occurs when individuals with variation that is adapted to their environment, i.e. favors their survival, survive. The definition itself doesn’t say anything about the direction of evolution. In fact, to understand that evolution is not progress, we need to look at the whole process of evolution at once. If evolution were progress, then if we compare a squid, an invertebrate, to a human, a vertebrate that has undergone more evolution since diverging from a common ancestor, we would expect the squid to be more perfect than the human.
But if you compare the squid and human eye, you’ll notice that unlike the squid, which has its optic nerve behind a smooth retina, the human eye has its optic nerve and blood vessels in front of the retina, which exit backward through a hole in the retina and connect to the brain. This hole is the “blind spot,” which creates a gap in our vision that we can’t see. This is because the structure of the human eye evolved from one in which the optic nerves were initially stretched out over the retina to one in which they are organized in a circle. Because the entire eye is vibrating slightly to resolve the shadows created by the optic nerves and blood vessels in front of the overlapping retina, the human eye tires easily. The more evolved human eye is not more perfect than the squid’s eye because evolution is not a process of perfection, but rather a selection of variations that are slightly better for the environment in which the organism lives at the time they were selected, meaning that at the time they were selected, they were the best changes and gave the organism a survival advantage over others, but not the best structure. A similar example is that the human airway and digestive tract do not have separate pathways, but overlap. This is a very inefficient arrangement that can lead to death if food passes into the airway, but it was the best option available to life at the time lung breathing arose, not the process that led to what we now consider to be the perfect arrangement: a separate airway from the digestive tract.
Proponents of evolution as progress argue for progress based on the fact that the organisms that exist today have become increasingly structurally complex compared to when life first arose. Of course, if you line up the fossil evidence, you may intuitively feel a sense of progress as you see the long and majestic evolution of life from the simplest prokaryotic cells, through eukaryotic cells, to multicellular life, to invertebrates, to vertebrates, to highly intelligent organisms like humans. However, the argument that increasing structural complexity is progress assumes that organisms with higher structural complexity are better, that is, they have structures that favor survival. According to this premise, nature should have selected for organisms with structures that are better suited to their environment, culling out those that are not. However, the existence of bacteria, single-celled prokaryotes with very simple structures that are still alive and thriving today, refutes this argument. If increasing structural complexity is progress, then bacteria should have been temporarily and gradually wiped out by eukaryotes from the time eukaryotes appeared. But bacteria are still alive and well today, with an enormous diversity of bacterial species infecting and killing higher vertebrates, even those with structures far more complex than their own. Comparing the complexity of structures, it is clear that complex organisms such as extant vertebrates evolved from simpler organisms. However, this is only the result of adaptation and natural selection, and nature does not select with any goal or purpose. The argument that evolution occurs in the direction of increasing structural complexity can also be criticized based on the existence of viruses. Viruses have a simpler structure than bacteria: a protein shell and nucleic acid. This simplicity led scientists who first isolated viruses to think that they might have been the first life forms. However, viruses are not the first life forms because they cannot reproduce on their own and can only multiply through the metabolism of their host cells. This means that viruses may have evolved to have a simpler structure by choosing to be parasitic. Evolution hasn’t always worked in the direction of increasing structural complexity.
Haeckel’s discovery that “speciation repeats phylogeny” also suggests that evolution has increased structural complexity, and some argue that this is evidence of progress. The idea is that the relatively simple structure of embryos in the early stages of vertebrate development, where they have gills (even if they are mammalian) and develop into individuals with increasingly complex organs, resembles the process of phylogenetic evolution from simple organisms to the complex vertebrates of today. However, the repetition of evolutionary processes in the development of individuals does not necessarily support the claim that evolution is progress. The increased structural complexity of life is due to the fact that life is subject to physicochemical laws. There is a minimum simple form that can be called life, and below that point it is not life, so as a result of evolution, either the structure becomes more complex or it remains the same. Stephen J. Gould illustrates this with the drunkard model. A drunken man leaving a bar staggers to the right or left, with a ditch on his right and the wall of the bar on his left. The probability of staggering right or left is equal, but if the drunk hits the bar wall, he can no longer move left, so he ends up moving toward the right ditch and falls into the ditch. To the casual observer, it would appear that the drinker moved in a directional fashion to the right, but this is an accidental result of the presence of the left wall. Haeckel’s embryological argument is similarly refutable. Early embryos are quite unstable, so if a mutation occurs in the early stages of development, the embryo will die, so evolution has inevitably added new stages.
As for why the evolutionary process that seems to be progressing is not progress, it was revealed that the evolutionary process is a process of selecting the best conditions at the time, not a change toward a perfect structure in hindsight. Furthermore, the increase in structural complexity is natural, driven by the passage of time and the laws of physics and chemistry, not by any intended direction. Nature does not make choices. It is only by chance that life appears to progress in some respects, and the structures and functions of the various organisms in existence are the result of natural selection. Hitler and eugenicists, who were believers in the theory of evolution, left indelible scars on many people because they considered evolution to be progress and believed that organisms with certain traits were superior to those without. As you can see, definitions in science can have a profound impact on society, so they need to be approached with care and precision. Such is the case with defining the relationship between evolution and progress.
