Key Fathers Of Evolution Essay

Evolution and natural selection can be summarized by the Oxford definition as the process whereby organisms better adapted to their environment tend to survive and produce more offspring. It hindsight, these definitions may seem somewhat trivial and part of common sense, but the development and understanding of these theories can be significantly more complex and mysterious. These consequences are even important in today’s scientific pursuits as the terms natural selection and evolution are often tossed around without recognizing its implications. For example, many scholars in their own control experiments trivialize and take advantage of the evolutionary theories as justification of their results rather than provide a mechanism of action.

The failure to understand the key of evolution is that it is theory, but it does not provide a specific mechanism for the theory. Species may diverge and select themselves, but what are the driving factors? These are the questions that researchers are still struggling with in the 21st century.

Given this motivation, we hope to understand the development of one of the mechanisms for the development of the evolutionary theory and follow it from its conception in the 1850s.

More specifically, we will examine one of the key fathers of evolution, Alfred Russel Wallace and his conception of the river barrier hypothesis as a mechanism for the speciation that he observes in the Amazon Basin. The idea is the river was a wide enough vector to introduce enough isolation whether through a reproductive or geographic means to produce separate and favorable species on the opposite banks. This is especially prevalent in the Amazon Basin as it encompasses the most diverse collection of species all relying on this large water source.

Our scientific community has barely scratched upon the true basis of how evolutionary mechanisms have produced the biodiversity we see in the world today. Understanding the river barrier hypothesis and its affect on the Amazon biodiversity would be an important step to recognizing specific mechanisms and the goal of this paper is to understand the development of this theory from its conception by Wallace and assess the related research in the last century. In essence, we want to assess the sufficiency of the argument and how much the physical barrier of the river plays a role in developing genetic

branches.

To begin, we have to understand Wallace’s motivation. In 1890, Wallace was the first recipient of the Darwin Medal, awarded to acknowledged distinction for work in evolutionary biology and understanding biological diversity. Although we often do not hear of Wallace’s name as much as we do Darwin’s, his claim of fame and the reason for this distinction was “for his independent origination of the theory of the origin of species by natural selection” (Bulmer). Biology was a very different scientific discipline in the mid 19th century. Much like Darwin, Wallace drew his conclusions from various voyages he took to the Malay Archipelago and conducted his initial and most significant field work in the Amazon River basin.

The first basis of the river barrier hypothesis is outlined in Wallace’s 1852 paper titled “On the Monkey’s of the Amazon” (Wallace). This was at an early point of Wallace’s exploratory career as a naturalist and his accounts in this paper focuses on a few observations about the geographical distribution and habits of the monkeys he saw. Classification of monkeys were determined by their prehensile tails, color, sleeping habits, diet, and noises that they made and certainly Wallace seemed to have no trouble in his accounts distinguishing between the monkeys and taking notes of their characteristics. These accounts were not unique to its time as many naturalists have already determined the scientific name as the binomial nomenclature had already been introduced. In fact, Wallace continually refers to Alexander von Humboldt, an earlier naturalist who had paved the way for these types of studies.

These observational studies were not new to Wallace as he had extensive knowledge in species collection, having produced publications in Britain about beetles in his teenage years. It was these curiosities that drove Wallace to the Amazon Basin. However, it was not unique at the time to describe species especially monkeys in this way; naturalists have been doing so in similar regions of the world for the last century. What was unique about Wallace and the observations he outlines in the next section of the paper can be attributed to his background of geographical surveying and work as a civil engineer (Beccaloni). Wallace is decidedly interested in the locality of the species that he observes: “In going up the Rio Negro the difference in the two sides of the river is very remarkable” He proceeds to criticizes many of the prior mappings of the species to their ambiguity of location and then proceeds to ask questions about the range of the individual species. In short, he found that the Amazon, Rio Negro and Maderia, the largest tributaries of the Amazon formed a barrier for speciation. He stated based on observation even on the banks that species, not just monkeys but also insects and birds, were not found on the other bank. This was not only backed by his short observation but by the natives, who often took advantage of these facts for their own hunting purposes (Wallace).
This particular observation seems quite logical as a simple correlation of species and space. Wallace at this point has not yet developed his own independent theories of evolution and natural selection and he is merely stating a fact about river barrier’s and the location of species. It was these compounding observations throughout his journey’s that Wallace developed the ideas of natural selection and speciation. The logical jump necessary does not seem quite large from these initial observations of riverine barriers to the idea of speciation between them. However, the development of Wallace’s parallel theories outlined in his famous 1858 Ternate paper: “On the tendency of varieties to depart indefinitely from the original type” sent to Darwin, seems much more refined and unwavering as compared to his observational studies from the monkey studies (Bulmer).

Whether we are biased today from the intrusion of the human footprint on the wildlife, it seems that even with an objective observational perspective on animal behavior, Wallace’s conclusions come with a little imagination, creativity and inference, rather than of concrete evidence. Wallace alludes to the Malthusian argument as “the life of wild animals is a struggle for existence” (Wallace) and states the variations in species can provide benefits for individuals without substantiation to observational or real evidence. Much of these conclusions, may very well be the result of his years of experience, but they still lack concrete evidence. In the case of for the argument for the river barrier hypothesis, it is rather more of an observation than a hypothesis. The limit of Wallace’s claims only to asks more questions about this phenomena: “Are very closely allied species ever separate by a wide interval of country?” (Wallace) And for the rest of his academic career, Wallace was consistently dedicated to geographical causation of isolation such as his famous establishment of the Wallace line in the Malays (Beccaloni) and his argument continually remained by comparing the samples on the sides of the divide.

Perhaps it is unfair to criticize Wallace’s scientific methods, but to understand the key issue that it is particular difficult to prove the river barrier hypothesis from any approach, rigorously. This in one sense lies in the time scale necessary to see natural evolution occur. Wallace through any observation was limited to the time scales of a couple months and years and even observations of the last century is minuscule as compared to the millions of years necessary to see or develop any trends in the speciation due to geographical isolation of the rivers. Thus, real proof would need to construct a lineage and time span that would trace back to the “original” divergence.

Adding to this dilemma of the limitations of the time that we can measure, there are also other historical changes that affects the validity of the hypothesis. Given the Amazon Basin’s extreme coverage of the South American land and our understanding of the paleography of the area, there are many dynamic changes that could have happened to the river during this segment of species divergence. From what we understand, the river during the Pangaea region flowed actually to the west rather than to the current river delta in the east. Amazon’s many large and small tributaries had considerably different paths over the years. Haffer who explains the validity of some portions of the river barrier hypothesis focuses on determining the time period of relevance and forcing the more viable time points such as during the Quaternary period (last 2 million years) rather than for the entire Cenozoic era as a warning to the fragility of the river barrier consistency. These issues of time and space are important aspects of the river barrier hypothesis, but they decidedly complicate matters of whether this hypothesis is sufficient in itself to drive changes for some species or is just a large part of the many factors that play into evolution.

This difficult even extends to today over a century later as scholars continue to discuss the validity of the river barrier hypothesis. Validity in this case may not be the particularly apt word for this as correlation is obvious, but it is difficult to demonstrate precisely that the river barrier provides a sufficient agent for speciation. The advent of genomic sequencing has prompted some recent discussion on tracing the species in the last 20 years, but even then these studies are quite contradictory and inconclusive.