A Deep Dive into the Unified Theory of Evolution
We have a tendency to think of science as all-knowing and definitive in its claims, for how can the sum of centuries of precise investigation be anything but the truth? Yet, as we dive deeper into the comprehension of scientific concepts, even those fundamental to how we understand the world around us such as “natural selection” or “survival of the fittest,” the reality unearthed is far more intricate. The merging of scientific knowledge, past and present, creates a fascinatingly layered comprehension of our universe, allowing new scientific discoveries to be made by, in the words of Isaac Newton, “standing on the shoulders of giants.”
General knowledge of evolution is neatly summarised by the familiar anecdote of Darwin and his finches, birds studied during his journey to the Galapagos. Upon observing that otherwise similar finches on varying islands of the Galapagos differed in the form and function of their beaks, naturalist Charles Darwin purported that the differing species had come from a single common ancestor, then separated into distinct species as groups of finches adapted to the unique selection pressures. This meant that finches with short, thick beaks were present on islands with a primary food source of seeds, and where insects proliferated, finches had long, slender bills to catch them. While this suffices for a superficial understanding of evolution and variation, it might be a surprise to learn that, in contradiction with this simplified example, the question of evolution doesn’t necessarily have a single right answer.
Although Darwin is frequently heralded as the father of evolutionary theory, scientists and thinkers had been pondering the delineation of species for centuries. Jean Baptiste Lamarck was the first to propose a concrete theory of evolution, which stated that an individual evolved and adapted to its surroundings during its lifetime, then passed on these changed characteristics to offspring. Although discredited by most by the 1930s, Lamarckism presents an important landmark in the study of evolution, as the first comprehensive theory of evolution. Darwin himself was a proponent of Lamarckism, viewing it as a means to create variation that natural selection could act upon. When many predictions of Lamarckism could not be supported by empirical observations, new theories came to light. This was largely due to the contributions of Alfred Russel Wallace, who, after collecting thousands of specimens in Brazil, the Malay Archipelago, and Southeast Asia, began to draw conclusions regarding the distribution and evolution of species, before Charles Darwin had published his theory of natural selection. The eight years that Wallace spent in Southeast Asia studying mammal, bird, fish, and insect species and how they differed across geographic regions led him to propose that species evolved by adapting to their environment, a theory first published in a paper with Darwin.
While this is the extent of common understanding of evolutionary theories, new theories continued to develop in order to map the change of organisms over time. In 1901, Hugo de Vries also proposed the Mutation Theory of Evolution, which suggested that evolution was the result of random change in each subsequent generation that was then selected for by environmental conditions. This theory serves as a sort of “null hypothesis” for evolutionary change, should no other conception prevail. Yet, as various theories of evolution were developed and debated, a mechanism for mutation and inheritance was still lacking at this time.
Although Darwin and his associates could clearly observe that certain behaviours were heritable, they were not aware of the genetic code of DNA, which was responsible for significant variation within populations. Random mutations in DNA, as it is passed from parent to offspring, usually have no effect, but in some cases they can be harmful or beneficial. The cumulative effect of mutations leads to some organisms being more suited to their surroundings, and therefore they are selected for through the process dubbed “survival of the fittest.”
Even through the process of random genetic mutation, the rapidity of trait variation could not be clarified solely through classic genetics. As evolutionary biologists puzzled over potential explanations for this discrepancy for decades, a humble experiment on the embryonic development of fruit flies by Conrad Waddington would mark the beginning of a deeper understanding of evolutionary change and - surprisingly - a return to Lamarckism. When he observed that the chemical stimuli and temperature that a fruit fly embryo was exposed to determined wing development later in life, Waddington coined a new term: epigenetics. Now, the prominent study of epigenetics refers to the influence of environmental stimuli on the expression of genes, leading to variety not caused by mutation. As Lamarck had originally proposed, the environment could directly impact an organism’s characteristics and, therefore, chances of survival.
On reflection of the tangled and intriguing scientific history of evolutionary biology and its theories, it is easy to remain limited to a single perspective - to decide that it was really Lamarck, or Darwin, or Wallace, or Waddington who was right all along. Instead, the Unified Theory of Evolution consolidates centuries of evolutionary study to conclude that both environmental epigenetics and genetic mutation provide mechanisms of variation for natural selection to act upon. This theory is the amalgamation of the early work of Darwin and Lamarck, refined through the more modern discoveries of genetics. The reality of a discipline as vast as evolutionary biology is that often, an integrated approach such as the Unified Theory of Evolution, is essential to comprehensive understanding. As we navigate and study our interactions with other species, it is crucial to keep in mind that the study of life is not limited by absolutes.
For further reading:
Unified Theory of Evolution by Michael Skinner
Evolution - Modern Conceptions on Britannica
Darwinian Evolution Includes Lamarckian Inheritance of Acquired Characteristics by Yongsheng Liu
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