Chapter 5-2 The Origin of Species: Evolution Theory
From the late 15th-century Renaissance to the 18th century, it was a period of formation and development for modern natural sciences. During this period, the dominant view in the scientific community was the "Fixity of Species". As Newton stated: the earth, set in motion by the so-called "prime mover", continues to move unchangingly, and biological species were originally like this and would remain so.
The aforementioned French biologist Lamarck was the first scientist to propose "the theory of biological evolution". Lamarck, in his 1809 book "Philosophie Zoologique", detailed his views on biological transformation, providing a theoretical foundation for Charles Darwin's later "Theory of Evolution".
The core concept of Lamarck's theory is "use and disuse". This refers to the idea that: organs and functions of living organisms become more developed with frequent use, while those that are not used often gradually deteriorate.
For example, why do giraffes have such long necks? From the perspective of "use and disuse": the ancestors of giraffes lived in regions that became arid due to changes in natural conditions, leading to scarce pasture. To survive, giraffes had to feed on the leaves of tall trees. To achieve this, giraffes exerted significant effort to stretch their necks. The organs that were frequently used became more developed, while those that were not used gradually degenerated. Organisms have the ability of "acquired inheritance", the superior genes were passed down through generations, and over thousands of years, the necks of giraffes gradually lengthened (Figure 5.4 left).
Figure 5.4: Lamarck's "use and disuse" versus Darwin's "survival of the fittest"
At the time, this viewpoint seemed very advanced, but today's readers would likely disagree. According to this theory, if your father has a high IQ, he would naturally pass on the high IQ genes to you. If your father became a fitness expert with developed muscles through training, you should be born with well-developed muscles.
Nevertheless, Lamarck's "hypothesis" inspired and influenced a young Darwin. As the saying goes, "Reading ten thousand books is not as good as traveling ten thousand miles." In 1831, the 22-year-old Darwin embarked on a 5-year voyage aboard the "HMS Beagle" from England, during which he collected biological specimens. In 1859, Darwin published "On the Origin of Species", after contemplating the subject for a total of 28 years. He observed that many species shared similar or even identical physical structures and bore resemblances to extinct species. He firmly believed that: different species on Earth are connected through gradual evolution to their present forms. Variations, inheritance, and natural selection lead to adaptive changes in organisms. Subsequently, he proposed the famous "theory of evolution", whose core concept differed significantly from "use and disuse": nature selects the fittest, and only the fittest survive.
Let's take the evolution of giraffes as an example again. Darwin believed that: in ancient giraffe populations, individuals had varying neck lengths. Under natural conditions of drought, when grass on the ground dried up and shrubs died, those giraffes with genes for longer necks could reach higher leaves, giving them a broader selection of food. This advantage in the struggle for survival meant that these individuals were more likely to survive and reproduce, while those with genes for shorter necks were gradually eliminated. This is the process of natural selection (Figure 5.4 right).
Darwin's views, supported by extensive evidence from the continuous development of molecular biology, genetics, embryology, archaeology, and other scientific fields, transformed the theory of biological evolution into a rigorous scientific theory that has been included in textbooks worldwide.
Interestingly, biologists have discovered that when comparing the embryonic development of mammals with that of humans, it is almost impossible to distinguish which embryo is human in the early stages of development because human embryos are very similar to those of pigs, cows, sheep, and other mammals (Figure 5.5). It is only in the mid to late stages of embryonic development that one can identify which embryo is human.
Figure 5.5: Embryonic development of animals (fish, salamander, turtle, chicken, pig, cow, rabbit, human)
This fact might suggest that humans and mammals like pigs, cows, and sheep share a common ancestor or appeared almost simultaneously. However, biologists believe that humans are more closely related to chimpanzees. Approximately six million years ago, humans and gorillas diverged, embarking on different evolutionary paths (Figure 5.6). This viewpoint is also reflected in high school biology and history textbooks.
Figure 5.6: Evolutionary process within the hominid family
However, Darwin's description of the "Theory of Evolution" is far more cautious than people imagine. The common belief that humans and great apes share a common ancestor is derived from interpretations of the "Theory of Evolution". Yet, throughout "On the Origin of Species", which spans 120,000 words discussing heredity, variation, and natural selection, Darwin never explicitly states that humans evolved from apes! Perhaps, given the sensitivity of human origins at the time, Darwin's thought was: "I'll dig the 'pit' of evolution, but I definitely won't shoulder the 'blame' for humans."
Returning to the topic, carbon-based life forms on Earth exhibit relatively minor genetic gaps in their evolutionary process. Scientists have discovered that the genetic similarity between humans and chimpanzees is about 96%, indirectly suggesting that the recent ancestors of humans and chimpanzees were the same species. Furthermore, the genetic similarity between cats and humans is as high as 90%. In terms of proteins, the genetic similarity between mice and humans is as high as 85%, which is why mice are often used in biological drug experiments. Surprisingly, the genetic similarity between humans and bananas is as high as 60%! This indicates that: genetic similarity alone does not explain much.
Darwin's "Theory of Evolution" is not without flaws. It posits that: biological evolution progresses from simple to complex, from lower to higher, in a continuous and gradual process. During the Industrial Revolution, other biologists also generally believed that: cells were the simplest structures of life. The typical story began: "Long, long ago, in the sea, there appeared a single-celled organism, which slowly evolved into multicellular organisms, then crawled onto the land..."
It wasn't until 100 years later, with the invention of the electron microscope, that scientists discovered that cells are far from "simple". Each cell contains a nucleus, cytoplasm, DNA, RNA, and more, with each component responsible for different functions such as transport and energy conversion, resembling an automated factory. From this perspective, the evolution of life is not from simple to complex, but rather from extremely complex to an even more incomprehensible complexity.
Flagellates are a typical example of single-celled organisms that can swim using their flagella. In a 2015 scientific paper, a research team noted that the flagella of flagellates function like a biological motor, consisting of switches, gears, drive shafts, propellers, and engines, capable of 100,000 rotations per minute and changing direction in just 1/4 of a second. This biological motor has been simplified to the utmost, with none of the mentioned components dispensable. According to Darwin's theory, this sophisticated biological motor should have evolved piece by piece, from simple to complex. However, flagellates are among the simplest single-celled organisms, so how could they have suddenly mutated to possess such advanced technology?
What happened to the idea of "from lower to higher"?
The cunning and meticulous Darwin also considered this point. He wrote in "On the Origin of Species": "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."
Additionally, according to Darwin, the evolution of life is continuous and gradual, appearing to be uniform (also known as "gradualism"). However, there are two obvious "geological faults" that make the theory of evolution difficult to reconcile: one is the Cambrian period, and the other is the Cretaceous period.
Faced with the fact of the "Cambrian Explosion" 500 million years ago, the biological community was in heated debate, leading to a "century-long turmoil". According to biologists, before the Cambrian period, Earth only harbored a scarce amount of structurally simple organisms, which do not qualify as predecessors to the multitude of life forms that suddenly appeared in the "Cambrian Explosion". Within a mere 40 million years of the Cambrian period, all known categories of marine, terrestrial, and aerial flora and fauna emerged, some even starting as gigantic creatures (such as dinosaurs and mammoths). "Strangely, we still cannot find their developmental traces in early fossils. They seem to have suddenly appeared altogether, fully matured, thoroughly evolved, possessing all functionalities, with sharp teeth and gleaming scales. No one knows what force created them, or why. ("Ancient Traces") This is like knowing about the existence of minerals one second and building an aircraft carrier the next second. The "Theory of Evolution" cannot explain this at all, almost like seeing a ghost...
While the Cambrian period can only be regarded as a "supernatural phenomenon", the Cretaceous period presents a "mass extinction" right before our eyes, where 95% of species, including dinosaurs, suddenly vanished.
What happened to "survival of the fittest" and "gradual evolution"?
Logically, in the millions of years that followed, history could have "repeated itself", witnessing another "biological explosion", generating a broader array of life forms. However, this did not happen. Cambrian animals exhibited greater diversity than modern animals, with far more categories than exist today. Moreover, numerous categories, including dinosaurs, completely vanished.
What happened to so-called "continuous evolution"?
The fact that "transitional species are extremely rare" has long been an uncomfortable "secret" in the fields of Paleontology and Archaeology. Biologists have thus "boldly" speculated: Is it possible that all animal species appeared suddenly, with no process of succession? The idea that one type of animal is the ancestor of another is completely speculative and has no factual basis. This raises the question: Who or what caused these animal species to suddenly appear on Earth?
In fact, the first person to doubt the "Theory of Evolution" was Darwin himself. He devoted an entire chapter in "On the Origin of Species" to discuss "the imperfection of the geological record" and added a hopeful note: "In the future, transitional fossils will undoubtedly be discovered."
Like the life trajectory of many great scientists, Darwin seemed to return to "creationism" in his later years, telling his friends: "I was a young man with uninformed ideas. I threw out queries, suggestions, wondering all the time over everything; and to my astonishment, the ideas took like wildfire. People made a religion of them."
"Ancient Traces" notes that: in a 1978 interview, Prof. Niles Eldredge said: "No 'transitional species' have ever been found, and more and more scientists now believe that these so-called transitional species never existed." Prof. Steve Schindler added: "In fact, in the fossil record, we cannot convincingly find any transitional forms that show the evolution from one species to another — not a single one. For example, no one has ever found a fossil of a giraffe with a moderately long neck. If these fossil records fail to show the expected transitional forms, then what do they show, and what do they prove?"
