In this blog post, we examine Darwin’s theory of survival of the fittest through ‘On the Origin of Species’ and discuss whether evolution remains a valid principle for life’s evolution.
‘On the Origin of Species’ is the book containing Darwin’s theory that all living things evolve according to the principle of survival of the fittest. The publication of this book, which explains the long history of life with a concise theory, was a landmark event in the history of science. However, when ‘On the Origin of Species’ was published, it sparked significant controversy not only among scientists but also among religious figures and humanities scholars. This was because the claim that humans, like other organisms, had evolved gradually conflicted with the prevailing creationism and anthropocentrism of the time. In this respect, Darwin’s theory of evolution is considered one of the theories, alongside Galileo’s heliocentric theory, that had the greatest impact on society.
It is widely known that Darwin gained inspiration for the principles of evolution while sailing the Galapagos Islands aboard the Beagle. Darwin developed the concept of evolution by focusing on the discovery of highly unusual species in places isolated from the outside world, like islands in the sea. Over the next decade, through collecting data and research, Darwin became convinced of evolution by natural selection. In fact, the concept that species had changed existed before Darwin, but opinions were divided on the cause. The survival of the fittest, as argued in ‘On the Origin of Species’, is the concept that individuals best suited to survive in a given environment propagate their offspring. The phenomenon where specific variations are selected from the diverse variations within a species is called natural selection. Since Earth has been constantly changing for over 4 billion years, organisms have had no choice but to continuously adapt. ‘On the Origin of Species’ is significant for providing concrete evidence for this evolution and its causes.
Three main pieces of evidence presented in this book are particularly noteworthy. The first, in Chapter 1, uses the universally relatable example of domestication and cultivation. Humans have domesticated animals like dogs, cows, and horses, creating diverse breeds. This process leverages the phenomenon where repeatedly selecting and breeding animals with desired traits causes those traits to become increasingly pronounced. This is an example of variation accumulating through selection, essentially artificial evolution. Although genetic material had not yet been identified when ‘On the Origin of Species’ was published, Darwin analyzed variation as thoroughly as possible based on the available data at the time.
Second, Chapters 9 and 10 present visible evidence: fossils. Layers of rock formed billions of years ago contain fossils of organisms that lived then, revealing that life during periods like the Precambrian or Paleozoic was vastly different from today. These fossils also show how organisms gradually changed in appearance over time. However, at the time ‘On the Origin of Species’ was published, sufficient fossils to serve as evidence for evolution had not yet been discovered. Darwin attributed the lack of sequential fossils illustrating evolutionary processes to the incompleteness of geological and paleontological knowledge. Due to the nature of fossils, only a tiny fraction of species that once existed are ever found. He also pointed out that due to the repeated uplift and subsidence of strata, many phenomena remained unexplained by the geology of the time.
Thirdly, Chapter 13 explains the process of evolution revealed in embryology and vestigial organs. There are many external differences between the adult forms of vertebrates classified as fish, reptiles, birds, and mammals. However, according to Chapter 13 of ‘On the Origin of Species’, the embryonic forms of all vertebrates are nearly identical, and gills are even observed in mammalian embryos. Furthermore, examining vestigial organs in adults reveals that the number of vertebrae in a giraffe’s neck matches that of other mammals, and the structures of bat wings, human hands, horse leg bones, and dolphin fin bones are all identical. These observations strongly suggest that vertebrates evolved from a common ancestor.
Now, 150 years after the publication of ‘On the Origin of Species’, advances in genetics have uncovered far more evidence for evolution, and there is no disagreement within the scientific community about evolution. However, looking solely at the content of ‘On the Origin of Species’, there is room for some counterarguments. First, the question “Why isn’t evolution happening now?” is valid. This is because all the evidence presented in ‘On the Origin of Species’ demonstrates evolution that occurred in the past. Fossils, vestigial organs, and variations observable in domesticated species or isolated regions are all phenomena that happened in the past. Conversely, no examples are observed today of chimpanzees evolving into humans or lizards evolving into eagles. If we cannot prove that evolution is occurring now, it would imply that the pressures of natural selection that existed in the past have vanished, thereby proving Darwin’s theory of evolution wrong.
However, this objection is invalid because evolution is indeed occurring today. Even as we walk in warm sunlight or eat grilled meat at a dinner party, mutations occur within our cells, and the possibility that these mutations could lead to evolution always exists. In other words, biological species are not fixed in their current forms but are constantly evolving. However, the pace is so slow that it is difficult for humans to perceive it. Experiencing the evolution that has unfolded over 4 billion years within a single human lifetime is practically impossible. It’s difficult to find biological differences between someone born today and someone born yesterday or the day before. Yet, compared to someone from 10,000 years ago, clear differences appear in the skull and spine. Evolution occurs gradually, not abruptly at a specific moment, making it hard to observe from a human perspective.
A second counterargument might claim that the probability of evolving from simple organisms like microorganisms into today’s complex life forms is low, considering Earth’s age. Even acknowledging the accumulation of mutations through natural selection discussed in this book, the likelihood of developing to the level of existing organisms over 4.6 billion years is considered low. Although ‘On the Origin of Species’ presented ample evidence for evolution, it did not calculate the probability of sufficient mutations accumulating mathematically or present it statistically, leaving room for such counterarguments.
During Darwin’s lifetime, even Mendel’s “pea experiments,” which laid the foundation for genetics, were unknown, making it difficult to accurately assess the probability of evolution. Therefore, based solely on the content of this book, one cannot definitively say this objection is either wrong or right. Strictly speaking, this objection also does not calculate probability but is merely a conjecture that it seems impossible. Moreover, based on current molecular biological knowledge, this objection loses its force. This is because the nucleotide sequence is the common genetic material in all living organisms. Bacteria and humans may appear to be completely different life forms, but ultimately, they differ only in the arrangement order and length of the four nucleotides: A, G, C, and T.
Even if the adult forms appear vastly different, the nucleotide sequences containing all the information of the individual are fundamentally identical. Therefore, species variation can occur with just a 1% change in the nucleotide sequence. In fact, even in the field studying the cumulative rate of mutations, evolution is accepted as established fact.
The argument in ‘On the Origin of Species’—evolution through survival of the fittest—was not readily accepted because it shattered the firm belief that humans were the center of the world. The controversy surrounding evolution closely mirrors the situation when the heliocentric theory was first proposed. The more celestial bodies were observed, the more phenomena—like the retrograde motion of planets or the apparent motion of inner planets—could not be explained by the geocentric model. Placing the sun at the center simply resolved these phenomena. Yet, those who had believed since Aristotle that the sun was the center of the world did not readily change their minds, even when presented with evidence for the heliocentric theory. Thus, when phenomena are viewed from a preconceived conclusion, objective judgment becomes difficult. Yet theories grounded in objective evidence and sound interpretation cannot be dismissed. This book presents vast data—domestication, fossils, embryology, vestigial organs—and clearly establishes survival of the fittest as its driving force. Darwin’s theory of evolution, like Galileo’s heliocentric theory, is a concise yet comprehensive explanation for diverse phenomena.
