Reflections on Biological Evolution

Evolution is, in the realm of Western thought pertaining to biology, the most profound, important, intellectually stimulating, powerful, and transcendent idea or concept that has been described in all those ways.

Its antecedents can be traced back to Greek philosophy and other cultures, but there is consensus that the starting point of the idea of biological evolution, in its current form, is the publication in 1859 of Darwin's seminal work, "On the Origin of Species." Following its emergence, the idea was quickly accepted in the scientific world, becoming a fundamental element of the body of ideas that shape Western thought. The reason for such success lies, firstly, in that evolution provides meaning to the diversity and complexity of the beings that form and have formed the biosphere over time and to the processes occurring within it, without resorting to unnatural causes; secondly, that beyond its implications in philosophy, it transcends biology to extend throughout the natural sciences and, from there, into the human and social sciences.

The core of the idea is very simple: organisms in a group composed of, for example, a methanogenic archaeon, a streptococcus, a foraminifera, a mushroom, a sequoia, a whale, and the organism from which any fossil derives, share a distant common ancestor from which they diverged along separate evolutionary lines. This applies to any set of species considered, where the common ancestor will be older the more heterogeneous the set is.

The addition of numerous processes and phenomena unknown to Darwin and his contemporaries has complicated and significantly changed the original theory, but its essence remains very simple and intact: a) in any population of organisms considered, evolutionary innovations of different types appear through the introduction of new genetic and epigenetic elements or by altering the existing ones in the genetic and epigenetic pool of the population, innovations that are random concerning the adaptive needs of the organisms that carry them; b) the constant differential renewal of the organisms in the population determines that some innovations persist and/or increase in frequency, while others decrease in frequency and/or are eliminated.

Based on this, the repeated sequences of both phenomena, innovation and renewal, over time determine the transformations of populations and are reflected in the genetic programs of organisms and in the genetic pools of successive generations of the populations. These genetic programs, interacting with the environment, determine the developmental systems that construct the phenotypes of the organisms in each generation, phenotypes to which the action of differential renewal is directed. At the higher level of organization, the sets of populations that make up evolutionary species and lineages give rise, through speciation phenomena, to the multiplication of species or lineages, whereby from one species, a clade is formed that persists until the last descendant species of the initial one goes extinct. Consequently, there is a clade that encompasses all current and past species, within which an infinite number of subclades can be differentiated, as many as the species that have undergone a speciation process over time.

In this book, I aim to present the pillars of the current theory (or set of theories) of biological evolution. Regarding its contents, I refer to what I outline in the section "Presentation," but I advance that I start from the premise that the entities that evolve are biological systems, whose structures determine the hierarchy of their levels of organization upon which evolutionary processes act, and that the text follows two competing threads, chance and purpose, whose meanings are discussed both in general and in the realm of evolution.