The History of Evolutionary ThoughtThe Oxford English Dictionary defines evolution has “the process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth”[1]. Throughout the years there have been many thoughts and ideas that have been brought forward to explain the aspects that define the meaning of evolution. For centuries researchers and thinkers have given various ideas about evolution. Some of these individuals include Jean-Baptiste Lamarck, Charles Darwin, Gregor Mendel and Theodosius Dobzhansky. This paper looks at the history of evolutionary thought from the 18th century to the mid-20th century.Jean-Baptiste Lamarck was a French naturalist who lived from 1744 – 1829[2]. Lamarck is viewed as one of the pioneers who proposed a transformative idea about evolution that was dependent on physical evidence; his theory would later become known as Lamarckism. When Lamarck proposed his theory of evolution, it conflicted with the widely accepted view of evolution at the time. The accepted view during Lamarck time was that all species originate from a common ancestor whereas Lamarckism theory emphasises the idea of soft inheritance, a concept based on the idea that evolution occurs because of the inheritance of acquired traits that are passed down from parents to their children, over time. Lamarckism theory has two fundamental principles to it; the first principle is the idea of use and disuse. The idea of use and disuse is that individuals strengthen the traits that are the most useful to them and the traits that are useless or hardly used deteriorate or are lost completely. The second principle is the idea of inheritance of acquired traits; an individual’s children will inherit the traits that are acquired by them during their lifetime. To explain the principles of his theory, Lamarck used the example of giraffes. Regarding giraffes Lamarck proposed that since giraffes constantly had to stretch their necks in order to reach the leaves that are on the higher branches of a tree, it caused the muscles in the necks of giraffes to strengthen and gradually lengthen over time, Lamarck gave two reasons as to why he thought that this occurred. The first reason is known as a complexifying force which states that the frequent and continual use of an organ causes the movement of vital fluids to corrode out the organs from the tissues and aids in the creation of complex structures from simple structures[3]. The second reason is known as an adaptive force which states that the changing environment that an individual finds itself in would lead to the use or disuse of specific traits, which would then lead it to develop suitable adaptations for its environment[4]. These new adaptations would then increase the complexity of the individual’s structure, causing the individual to become practically well fit to thrive in that particular environment. Lamarckism theory would be disproved many times in the 20th century.Charles Darwin was an English naturalist who lived from 1809 to 1882[5]; he is credited with being the father of modern evolutionary thought. Many people believe Darwin was the first person ever to suggest that living things evolved from other living things, other scientists lived before him and who lived during the same time as him who claimed that living things evolved from other living things. However, none of these scientists had any physical evidence to support the idea. It was Darwin however in his 1859 book The Origins of Species who put forth this idea which he called the theory of Natural Selection. Unlike his counterparts who also had this idea Darwin was able to support his theory with actual scientific evidence. Darwin conducted substantial research on plants and animals in order to study how living things evolve. While studying birds in the Galápagos Islands, he realised how things evolve. He noticed that birds inhabiting different islands had a slight variation in their features. Darwin identified different species of Finches that had differences in the size and shape of their beaks. These differences in the beaks were related to the foods that were available in the area where the Finches lived. Contrary to this, Darwin observed only one species of Finches in South America. He then concluded that Finches that inhabited the Galápagos Islands might have evolved from the Finches in South America[6]. According to Darwin, after the original species of Finches arrived on the islands they were dispersed in different environments and because of this over a period of time, the anatomy of the birds changed naturally. The new anatomy of the Finches was an adaptation to the help them survive in their environment. Another way to put it is the Finches evolved so they would better access to food, thus increasing their survival rate for reproduction. Since the birds were anatomically different from one another, they were unable to reproduce with one another; this gave rise to separate species. A new species of Finches evolved from the original one. Since observing the differences in the Finches of the Galápagos Darwin then applied the concept of evolution to every living being, he stated that individuals belonging to the same species showed some difference between them. The individuals who possess traits that are favourable for survival will pass these traits down to future generations. And, after many generations, the favourable traits will become more common in the species. Thus, the population evolves with the traits that give them the best chance of survival.One of the societal influences on Darwin that aided him in coming up with his theory of natural selection was the field of economics. In 1797 Thomas Malthus an English parson named Thomas Malthus published a book called Essay on the Principle of Population[7]. In his book, he argued against policies in England that were designed to help the poor. He stated that these policies were doomed and only encouraged people to reproduce. Malthus believed because of the continuous population growth of Great Britain during this period that within a few decades there would be a widespread famine because there would not be enough food for the population because of the rapid growth leading to a miserable existence for the entire population. When Darwin read Malthus book, it occurred to him that animals and plants would also be experiencing the same pressure of population growth. Darwin thought that because of this pressure that beetles should overrun the world because of the abundance of food for them, but the world is not overrun with them, or any other species for that matter. The reason why certain species did not overrun the world was that they could not reproduce to their full potential. Many members of species die before they become adults. They are vulnerable to environmental conditions such as droughts and storms, and their food supply, like that of Great Britain, is not infinite. Individuals must compete for what little food there is in order to survive.Gregor Mendel was an Austrian monk who lived from 1822 to1884; he ran monastery in what is now known today as the Czech Republic[8]. During the 1850s and 1860s, Mendel conducted a series of experiments using a garden of peas to understand why some species were distinct from one another and what made it possible for hybrid species to form. During his experiments, he bred thousands of pea plants and recorded how the traits were passed on from one generation to another. While conducting his experiments, he selected 22 different varieties of peas and interbred them[9]. He kept track of several different traits of the interbred peas. For example, he kept track of the texture of the peas. Mendel found that when he crossbred smooth and wrinkled peas, the peas that were produced were all smooth. Mendel then produced a new generation of pews from the crossbred peas and discovered that 25% of the new generation of peas were wrinkled[10]. Mendel came up with the idea that the peas were not combing their wrinkled and smooth traits together. He stated that each crossbred pea inherited both the wrinkled and smooth trait, but only the smooth trait became visible. In the next generation of peas though, the traits were handed down again, and around 25% of the new peas inherited the wrinkled trait[11]. From his experiments, Mendel came up three laws that are known today as Mendel’s Laws of Heredity. The first law is the Law of Segregation, the second law is the Law of Independent Assortment and the final law is the Law of Dominance. Mendel published his findings in 1865, but the scientific community overlooked them at the time, it would not be until the 20th century that his work would receive recognition and would be used alongside Darwin’s theory of natural selection to further the understanding of evolution[12].During the early 20th century Darwin’s theory of evolution was causing much debate in the scientific community as it had done in Darwin’s time. During the early 20th century scientists were confused and divided over what the main thing was that drove evolution. Darwin’s theory of natural selection had only a few supporters in the scientific community this was because many people found the theory to be off-putting because it was seen to be ruthless and a complete waste of life and had no positive effect or goals for humans. Some critics of Darwin’s theory argued that Jean Baptiste Lamarck view of evolution was correct. Others scientists proposed that random mutations, or changes, in species accounted for the variety of species. In this view Natural selection was not needed in for the explanation of evolution. It was not until the 1930s that many scientists in different areas of studies began to piece together that there were connections between genetics and inheritance of traits with Darwin’s theory of evolution. The new theory that came out of this was called the Modern Synthetic Theory of Evolution, and one of the key contributors to this new theory was Theodosius Dobzhansky a Ukrainian-American geneticist and evolutionary biologist who lived from 1900 – 1975[13]. During the 1920s Dobzhansky worked at Thomas Morgan’s Fly Room, at this place the mutations of species were being studied. Dobzhansky also followed the work of population geneticist Sewall Wright very closely. In his work, Wright was showing that the size of a population affects the speed at which mutations in the species spread. Faced with what he was studying and the work of Wright, Dobzhansky become interested to find the answer to what genetics determine the variation between populations of species. When Dobzhansky was conducting his research, it was the common belief among people in the scientific community that all members of any species would most likely have identical genes. Dobzhansky travelled to Mexico to obtain a species of wild fruit fly named Drosophila pseudoobscura after returning he began analyzing the genes of wild fruit flies[14]. He discovered that different populations of Drosophila pseudoobscura did not have identical sets of genes. Each population of fruit flies he studied had distinctive markers in its chromosomes that set it apart from other populations of Drosophila pseudoobscura. Dobzhansky concluded that if no specific set of genes distinguished the species from one another, the answer to why species are different from one another must be because of sex. He realized that it was highly unlikely that animal that belonged to a particular species would even attempt to breed with another animal from a different species, and even if for some reason they did mate their offspring would most likely not survive because they would not possess the necessary traits for survival. For Dobzhansky, a species was just a group of animals or plants that reproduce almost exclusively among themselves. Dobzhansky conducted experiments on fruit flies to prove his theory; his experiments showed that the incompatibility for the offsprings of two different animals or plants that mate with one another is caused by specific genes carried by one species that are not compatible with the genes from the other species. In 1937, Dobzhansky published his findings from his experiments in a book titled, Genetics and the Origin of Species. In the book, he explains how species came into existence. For Dobzhansky, mutations occur naturally all the time. Some mutations in species are harmful in specific circumstances, but for the most part, most mutations do not even leave an impact on the species. Since most mutations do not affect a species, changes that appear in different populations and linger for a long time in a species will create a variability that is much greater than anyone had previously thought of, this variability to a species serves as the primary material for making new species. If the members of a specific population of flies breed among themselves more than breeding with other members of the species, new mutations will occur in their population, but since they are isolated and were only breeding within themselves, the mutations will not spread to the rest of the species. The isolated population of flies would become more genetically distinct from the other members of their species, and because of this some of their new genes would be incompatible with the genes of the flies from outside their population. Dobzhansky believed if the isolation lasted long enough the flies would no longer be able to mate with other flies from outside of their population. They would solely be able to mate with one another, and because of this, a new species would be created. It was the research that was conducted by Dobzhansky that showed how genetics and natural selection could cause sizeable evolutionary change. Dobzhansky contribution to the Modern Synthesis theory would be a foundation for further research about evolution for the rest of the 20th century and today as well.Although ideas about evolution have been around since ancient times, it was not until the 18th century where the modern idea of evolution started to take shape with Jean-Baptiste Lamarck. Then in the 19th century, Charles Darwin and Gregor Mendel made further advancements in the study of evolution. Then in the 20th century, Theodosius Dobzhansky furthered the study of evolution more by showing that natural selection and genetics were both contributing factors to the evolution of living beings. As like in the past the study of evolution continues today and will for the future.SourcesAbzhanov, Arhat. “Introduction: Darwin’s Galápagos Finches in Modern Biology.” Philosophical Transactions: Biological Sciences365, no. 1543 (2010): 1001-007. http://www.jstor.org.ezproxy.cbu.ca/stable/20721438.Ayala, Francisco J. 1976. “Theodsius Dobzhansky: The Man and the Scientist.” Annual Review of Genetics 10 (December): 1–6. doi:10.1146/annurev.ge.10.120176.000245Francisco J. Ayala & Timothy Prout (1999) Theodosius dobzhansky, Social Biology, 46:3-4, 184-189,DOI: 10.1080/19485565.1999.9988998Barahona, Ana, & Ayala, Francisco J. (2005). The emergence and development of genetics in Mexico. Nature Reviews Genetics, 6(11), 860-6.Beutel, R., Friedrich, G., & Leschen, F. (2009). 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