wikimedia commonsIn 2009, we will celebrate the 150th anniversary of the publication of The Origin of the Species and the 200th birthday of its author, Charles Darwin. Everyone has already heard the name Darwin, one of the scientists with the highest number of biographies in history. Even children are able to identity the image of the bearded, old man with the sad eyes. His ideas, however, are still less familiar to the public than the person himself. This is an undesirable situation, because biological evolution is a subject that is not of interest to specialists only. On the contrary – it is perhaps the scientific subject with the utmost importance to people in general. By understanding evolution, we can begin to understand the meaning of life, our role and our position in the world.
Darwin believed that life on our planet was united by a network of genealogical relationships, created by a modified descending process. Thus, all live beings are related to each other at different levels of kinship because of a common ancestor. The diversity of life is a function of time: live beings are different because they have become different throughout time and not because they were created different. Darwin´s undeniable merit was to gather evidence beyond any doubt that demonstrated the truth of the evolution of life. This distinguishes him from various other prominent predecessors who had flirted with the idea of evolution before he came around. But Darwin went beyond. He also created the notion of natural selection, a mechanism through which evolution operates. The idea that complexity and design could happen through purely natural processes, without planning, is the gist of natural selection. This idea goes against our trivial perceptions of how the world operates. For no other reason, his idea took longer to be acknowledged than the entire development of classical physics. But this strength, subtle in the world of ideas, is powerful in the real world and built up the diversity of life as we know it. It acts constantly, on all species, without the need of an external driving force or conscious implementation, in bacteria that produce three generations per hour as well as in sequoias that can take up more than one thousand years to evolve from one generation to the next. Only such a general, tireless and omnipresent force can explain the extraordinary refinement of live beings at all levels, no matter where they exist. This is how it works on our planet and this is how these things will work on all planets that have some form of life.
The idea of the tree of life has always attracted the attention of thinkers. Long before the advent of evolution, people already acknowledged that the diversity of live beings could be organized hierarchically, like a vast system of groups within groups. This is what allows for biological classification. But more important is the fact that the recognition of these groups is not something arbitrary. The characteristics of the organisms themselves evidence this organization, because the characteristics of live beings are not distributed randomly, but rather in a clearly hierarchical design. The classification system devised by Linnaeus, which is quite sophisticated and synthetic, precedes the publication of Darwin´s masterpiece by nearly one hundred years. Therefore, when Darwin developed his ideas, several major organic classification patterns had already been acknowledged. The sign evidencing such patterns was already so clear that it was recognized as a pattern of nature and not as a human artifice. Groups of organisms are not invented – they are discovered. Darwin, who had firsthand experience with taxonomy (the study of classifications), understood that such organization could not be devoid of meaning in his theory. In his opinion, that hierarchy meant something, not related to divine creation, but related to the diversification and branching out process of life – a result of the evolutionary process. Darwin immediately identified a strong relatedness among the classification patterns of live beings and evolution: the patterns were the result of evolutionary history. Indeed, the importance of phylogenetic patterns for his theory was so strong that a phylogenetic diagram is the only illustration in the Origin of the Species.
Nowadays, the study of kinship relationships between live beings is a biological sub discipline called phylogenetic reconstruction, currently a particularly dynamic area of evolutionary biology. The ideas of lineage connections are expressed as a branching process, referred to as phylogenetic trees. The phylogenetic structure is the cornerstone for the understanding of evolution. It allows us to understand the ubiquity of evolution in the structure of life on Earth. There are no more or less evolved organisms. The current lineage has exactly the same time of evolution as the one that generated the bacteria in our intestines. The fact is that some lineages differed more, others less. Some became more complex or bigger, while others went down different paths. But all are products that have been equally refined by the same billions of years of evolution.
This view is more valid than ever nowadays, when it is widely known that the same hierarchical order detected centuries ago in the morphology of organisms also occurs on other levels, such as on the level of DNA, structure, physiology, behavior, and anywhere else where scientific investigation has been conducted. This order is the result of evolutionary history. Whether it is in the form of a tree or of a web, the methods of phylogenetic analysis already have the necessary tools to unveil this story.
Equally important in Darwin´s contribution was the proposal of an operating mechanism that is supposedly behind some of the great patterns of the history of live beings. Natural selection is a simple idea, of an algorithm kind. But simplicity does not imply superficiality. Natural selection is a deeply powerful force, which shaped life as we know it. The understanding that Darwin had of this matter is surprisingly profound, considering that almost nothing was known of genetics in his time. Darwin understood that natural selection should not be understood as an absolute or unvarying process. The adaptation and reproduction differential are context-dependent, in such a way that environmental circumstances determine which variants are favorable (and therefore positively selected) and which ones are unfavorable (and therefore negatively selected). In view of the fact that the environment changes, so can the direction of selection. Characteristics that are favorable to individuals in one situation can be unfavorable in another situation and vice versa. Nowadays, many biological factors that apparently contradict the logic of selection are perfectly understood, such as unselfish behavior, sociability, etc. Classifying the multi-sided paths of natural selection under the unfortunate category of “ survival of the fittest” is a gross mistake. In the real selective world, the privileged ones are often among the “ weakest.” Darwin´s subsequent concept of sexual selection was truly subtle, and able to explain several phenomena of the live world that mere natural selection is unable to explain. It took the scientific community a long time to accept this other evolutionary force. One can speculate how much time it would have taken before the idea of sexual selection had been conceived by someone else, if Darwin had not conceived it.
Even when they are not evident, the forces that shape the biological systems are tireless, although they do not provoke any apparent change. Highly complex systems invariably tend towards disorganization, unless there are forces that continuously repair the defects and correct the deviations. This occurs especially when these systems produce copies of themselves or reproduce, such as the biological systems. Active mechanisms are necessary to maintain the level of organization of the organic systems. These mechanisms are the same classic forces of evolution. Natural selection acts constantly on the maintenance of the organization of live beings throughout the times, and not only during their changes. Unlike the common belief, the continued existence itself of live beings is evidence of the evolutionary forces in action. The action of selection is necessary not only to build up biological complexity but also to maintain it.
Evolution governs all the aspects of the live universe. It is impossible to understand any phenomenon of life without the evolutionary perspective. We, as part of the great web of evolution, are no exception – we never were an exception in the past, nor are we an exception in the present. Understanding our own species, of human nature, necessarily includes an understanding of our biological evolution. We owe this to Darwin. Our efforts to build constructive morals and ethics both for us and for our planet must follow the same path.
Mário de Pinna is an evolutionary biologist, with a specialty in zoology. He is currently a full professor and deputy director of the University of São Paulo´s Zoology Museum. He is also an associate researcher of the American Museum of Natural History and of the Smithsonian Institution.Republish