In this blog post, we will examine the scientific debate over whether life is following a path of “progress” toward increasing complexity, or whether it has simply diversified into various forms while adapting to its environment.
Bernard Werber’s *The Tree* features a short story about how humans might evolve in the future. It imagines a scenario where, in an effort to reduce the time spent forming relationships, humans become beings possessing both male and female characteristics, only to ultimately evolve into immobile, monstrous trees. Reflections on the direction of human evolution frequently appear in literature, art, and science. But does every living organism have a direction of evolution? Do living beings progress by becoming more complex relative to their capabilities?
In *Darwin’s Table*, Gould and Dawkins debate whether the history of life progresses in a directional manner through evolution. Gould argues that evolution cannot be linked to progress. Gould first states that linking “evolution” to “progress” is rooted in social influences. For example, he argues that the competitive values of the Victorian era influenced the cultural acceptance of Darwin’s theory of evolution at the time it was written.
Dawkins counters this by arguing that science deals only with the reality of the natural world. His position is that natural selection always produces the same results, regardless of social context.
The first life forms discovered by humanity were bacteria, dating back approximately 3.5 billion years. Comparing the early days, when the world was filled only with bacteria, to humanity today, Dawkins observes that life has become more diverse and complex. He argues that this supports the intuitive judgment that life has “progressed.”
Gould, on the other hand, argues that evolution is merely an increase in diversity, not an increase in complexity. Since the vast majority of species are low in complexity, like bacteria, the average level of complexity has not changed significantly; instances of complexity are merely the result of specialized developments in certain lineages.
I would like to first examine the question: “Has the history of life evolved toward greater complexity?” While Dawkins points out that humans are more complex than past bacteria, the crucial question is whether most organisms exhibit a trend toward increasing complexity. Using examples of averages or modes, he points out that a small number of highly complex lineages can skew the overall average upward.
From a taxonomic perspective, the biosphere is divided into bacteria, archaea (prokaryotes), and eukaryotes. Bacteria and archaea remain in a prokaryotic state and account for a vast number of species and individuals. In contrast, humans are merely a single species belonging to a tiny fraction of lineages within the eukaryotes. Therefore, when viewed from the perspective of the majority of organisms, the human-centered increase in complexity does not represent the whole.
If life tends to become more complex, bacteria should have evolved into more advanced forms as well. However, most bacteria have thrived in their own niches without a significant increase in complexity. This is not evidence that the human model is necessarily superior.
Take the example of tapeworms: as they became parasites in the human body, they underwent an evolutionary process in which their legs degenerated. This is an adaptation toward reduced complexity. However, other worms have maintained their legs and increased diversity through speciation. In other words, diversity has expanded through adaptation, regardless of whether complexity has increased or decreased.
The view that less complex organisms are inferior is anthropocentric. Bacteria perform important functions that improve the environment, such as nitrogen fixation, and possess the ability to survive in extreme environments. Human technology cannot surpass many of these capabilities.
Less complex organisms have the advantage of being able to adapt quickly to changing environments. In contrast, organisms with complex internal structures must regulate numerous internal variables, making it difficult for them to respond to environmental changes.
I am not a worshipper of bacteria. I merely wish to emphasize that humans are not absolutely superior beings; differences exist only in the context of species diversity. There is no reason why complexity must increase; species have fostered diversity by adapting and diverging in response to environmental changes.
To argue that evolution has proceeded in a specific direction toward greater complexity, it must be possible to predict the future based on complexity. However, predicting the direction of evolution—including that of the entire ecosystem—is nearly impossible. This is because variables are intertwined, and small changes, like the butterfly effect, can lead to significant outcomes.
I would like to ask both Dawkins and Gould what “biological progress” means, as mentioned in *Darwin’s Table*. Typically, this term refers to the presence of complexity in areas such as civilizational development or communication abilities, but this is a limited, anthropocentric perspective. It is inappropriate to compare which organisms are more “advanced.” These are merely differences between species.
True “progress” cannot be defined by the superiority of a specific species; it must be defined solely from the perspective of the entire ecosystem. On the primordial Earth, where only bacteria existed initially, the ecosystem was vulnerable to external shocks, but as species diversity increased, the ecosystem gained the inertia to mitigate such shocks. Therefore, biological progress can be defined as an increase in the resilience to external shocks.
In conclusion, the history of life was not a process of complexity increasing in a single direction, but rather a process of increasing diversity. Through the accumulation of diversity, the ecosystem’s network became denser, making it less vulnerable to external shocks. If Dawkins and Gould were to move beyond an anthropocentric perspective and consider an ecosystem-centered notion of “progress,” the discussion would become even richer.
