Evolution, Natural selection and Darwinism
Introduction
Evolution refers to the processes that have transformed life on Earth from its earliest forms to the vast diversity that characterizes today. <Ref.1 - p414>
Up until eighteenth century, biology in Europe and America was dominated by natural theology. <Ref.1 - p415> People believed that a supernatural being like God created each and every species as it is now for a particular purpose, at a particular time. However there are differences in people's interpretation of the length of the "day" mentioned in Genesis. Some Christians believe that the day was of 24hours and the world was created in 6 days. In 1650AD, Archbishop Ussher of Armagh calculated that God, created the world in October 4004BC, beginning on October the 1st and finishing with Man at 9:00am, which is not possible as we have no, archaeological evidence that suggest that a civilised life was already established in the Middle East by then. <Ref.2 - p879>
Alternatively, there was the theory of spontaneous generation. A number of Greek philosophers believed in he gradual evolution of life. Amongst those philosophers, Plato (427BC-347BC) and Aristotle (384BC-322BC) influenced the western cultures the most. Plato believed in two worlds: a real world that is ideal and eternal, and illusory world of imperfection that perceive through our senses. He believed that the evolution would be counterproductive in a world where ideal organisms were already perfectly adapted to their environment. Aristotle, who opposed some of Plato's teachings being his student, believed too that the universe never had a beginning and would never end; it was eternal. <Ref.3 - Aristotle> He also believed that all living forms could be arranged on a scale. This is later called scala naturae (scale of nature), where the organisms could be arranged in the order of complexity. However with this view of life also, species are permanent, are perfect and do not evolve. <Ref.1 - p415>
Carolus Linnaeus (1707-1778), the founder of taxonomy, organised organisms in to binomial system, but to him, clustering similar species together implied no evolutionary kinship, but a century later his taxonomic system became a focal point of Darwin's argument of evolution. <Ref.1 - p415> To Darwin, the natural hierarchy of the Linnaean scheme reflected the branching genealogy of the tree of life, with organisms at the different taxonomic levels related through descent from common ancestors. <Ref1 -p420>
Towards the end of eighteenth century, several naturalists suggested that the life has evolved with the evolution of Earth. Also the geologists started looking at the fossil records, palaeontology, which was largely developed by a French anatomist Georges Cuvier (1769-1832). He noted that the deeper (older) the stratum, the more dissimilar the flora (flower life) and fauna (animal life) are from the modern life. However he believed in catastrophism and not evolution, that the natural disasters had driven the organisms living there then, to extinction.
A colleague of Cuvier, Jean Baptiste Lamarck (1744-1829) published his theory in 1809, the year to which Darwin was born. He compared the current species to the fossil forms, and saw what appeared to be several lines of descent, each a chronological series of older to younger fossils leading to a modern species. <Ref.1 - p 417> Lamarck viewed evolution as a process of increasing complexity and "perfection". A change in the environment causes changes in the needs of organisms living in that environment, which in turn causes changes in their behaviour. Lamarck had two laws to his theory of the inheritance of the acquired characteristics:
"First Law" - use or disuse causes structures to enlarge or shrink
"Second Law" - All such changes are heritable
Lamarck did not believe in extinction, but the species that disappeared did so because they evolved into different species. Cuvier and his patron Buffon vilified Lamarck's theory. His work also did not become popular at his time so he died in poverty. However Charles Darwin wrote in 1861;
'Lamarck was the first man whose conclusion on the subject excited much attention. This justly celebrated naturalist first published his views in 1801...he first did the eminent service of arousal attention to probability of all changes in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition.'
<Ref.3 - Lamarck>
A leading geologist of Darwin's era, a Scot named Charles Lyell (1797-1875) introduced a theory known as uniformitarianism, which refers that the profound change is the cumulative product of slow but continuous process that have no changed throughout the Earth's history. <Ref.1 - p416>
In December 1831, Charles Darwin (1809-1882) was selected to travel around the world as the naturalist on HMS Beagle. During his journey, he noticed several things as to difference in species between the continents, - e.g. Species in South America are very distinct in characteristics to those of Europe. Such geographical distribution of species perplexed Darwin, especially of those in Galapagos. Although, they resembled to some species living on the mainland South America, most of the animals lived nowhere else in the world. It seemed that plants and animals that strayed from the South American mainland and then diversified on the different islands have colonized the island of Galapagos. Amongst the birds Darwin collected on the Galapagos were the 13 species of finches that although quite similar, seemed to be different species. Most striking difference was their beaks, which are adopted for specific diets. Some were unique to individual islands, while other species were distributed on two or more islands that were close together. Having read Lyell's Principle of Geology, acknowledging that Earth was very old and constantly changing, Darwin realised that the life on Earth had also evolved. <Ref.1 -418>
After Darwin had returned to Great Britain in 1836, Darwin started to reassess all that he had observed during the voyage of the Beagle, and it occurred to him that a new species could arise from an ancestral form by gradual accumulation of adaptation to a different environment. By the early1840s, Darwin has worked out the theory of natural selection, but as he anticipated the uproar it would cause having published it, he wasn't intending on publishing it until after his death. However, with the advice from Lyell that someone else might come to the same conclusion and publish first, and the prediction having come true, a letter from Wallace asking Darwin to evaluate his work and forward it to Lyell, encouraged Darwin to quickly finish The Origin of Species. Although Wallace's idea was published first, Darwin developed and supported the theory of natural selection so much more extensively than Wallace that he is known as the main author. <Ref.1 - p419>
Introduction
Evolution refers to the processes that have transformed life on Earth from its earliest forms to the vast diversity that characterizes today. <Ref.1 - p414>
Up until eighteenth century, biology in Europe and America was dominated by natural theology. <Ref.1 - p415> People believed that a supernatural being like God created each and every species as it is now for a particular purpose, at a particular time. However there are differences in people's interpretation of the length of the "day" mentioned in Genesis. Some Christians believe that the day was of 24hours and the world was created in 6 days. In 1650AD, Archbishop Ussher of Armagh calculated that God, created the world in October 4004BC, beginning on October the 1st and finishing with Man at 9:00am, which is not possible as we have no, archaeological evidence that suggest that a civilised life was already established in the Middle East by then. <Ref.2 - p879>
Alternatively, there was the theory of spontaneous generation. A number of Greek philosophers believed in he gradual evolution of life. Amongst those philosophers, Plato (427BC-347BC) and Aristotle (384BC-322BC) influenced the western cultures the most. Plato believed in two worlds: a real world that is ideal and eternal, and illusory world of imperfection that perceive through our senses. He believed that the evolution would be counterproductive in a world where ideal organisms were already perfectly adapted to their environment. Aristotle, who opposed some of Plato's teachings being his student, believed too that the universe never had a beginning and would never end; it was eternal. <Ref.3 - Aristotle> He also believed that all living forms could be arranged on a scale. This is later called scala naturae (scale of nature), where the organisms could be arranged in the order of complexity. However with this view of life also, species are permanent, are perfect and do not evolve. <Ref.1 - p415>
Carolus Linnaeus (1707-1778), the founder of taxonomy, organised organisms in to binomial system, but to him, clustering similar species together implied no evolutionary kinship, but a century later his taxonomic system became a focal point of Darwin's argument of evolution. <Ref.1 - p415> To Darwin, the natural hierarchy of the Linnaean scheme reflected the branching genealogy of the tree of life, with organisms at the different taxonomic levels related through descent from common ancestors. <Ref1 -p420>
Towards the end of eighteenth century, several naturalists suggested that the life has evolved with the evolution of Earth. Also the geologists started looking at the fossil records, palaeontology, which was largely developed by a French anatomist Georges Cuvier (1769-1832). He noted that the deeper (older) the stratum, the more dissimilar the flora (flower life) and fauna (animal life) are from the modern life. However he believed in catastrophism and not evolution, that the natural disasters had driven the organisms living there then, to extinction.
A colleague of Cuvier, Jean Baptiste Lamarck (1744-1829) published his theory in 1809, the year to which Darwin was born. He compared the current species to the fossil forms, and saw what appeared to be several lines of descent, each a chronological series of older to younger fossils leading to a modern species. <Ref.1 - p 417> Lamarck viewed evolution as a process of increasing complexity and "perfection". A change in the environment causes changes in the needs of organisms living in that environment, which in turn causes changes in their behaviour. Lamarck had two laws to his theory of the inheritance of the acquired characteristics:
"First Law" - use or disuse causes structures to enlarge or shrink
"Second Law" - All such changes are heritable
Lamarck did not believe in extinction, but the species that disappeared did so because they evolved into different species. Cuvier and his patron Buffon vilified Lamarck's theory. His work also did not become popular at his time so he died in poverty. However Charles Darwin wrote in 1861;
'Lamarck was the first man whose conclusion on the subject excited much attention. This justly celebrated naturalist first published his views in 1801...he first did the eminent service of arousal attention to probability of all changes in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition.'
<Ref.3 - Lamarck>
A leading geologist of Darwin's era, a Scot named Charles Lyell (1797-1875) introduced a theory known as uniformitarianism, which refers that the profound change is the cumulative product of slow but continuous process that have no changed throughout the Earth's history. <Ref.1 - p416>
In December 1831, Charles Darwin (1809-1882) was selected to travel around the world as the naturalist on HMS Beagle. During his journey, he noticed several things as to difference in species between the continents, - e.g. Species in South America are very distinct in characteristics to those of Europe. Such geographical distribution of species perplexed Darwin, especially of those in Galapagos. Although, they resembled to some species living on the mainland South America, most of the animals lived nowhere else in the world. It seemed that plants and animals that strayed from the South American mainland and then diversified on the different islands have colonized the island of Galapagos. Amongst the birds Darwin collected on the Galapagos were the 13 species of finches that although quite similar, seemed to be different species. Most striking difference was their beaks, which are adopted for specific diets. Some were unique to individual islands, while other species were distributed on two or more islands that were close together. Having read Lyell's Principle of Geology, acknowledging that Earth was very old and constantly changing, Darwin realised that the life on Earth had also evolved. <Ref.1 -418>
After Darwin had returned to Great Britain in 1836, Darwin started to reassess all that he had observed during the voyage of the Beagle, and it occurred to him that a new species could arise from an ancestral form by gradual accumulation of adaptation to a different environment. By the early1840s, Darwin has worked out the theory of natural selection, but as he anticipated the uproar it would cause having published it, he wasn't intending on publishing it until after his death. However, with the advice from Lyell that someone else might come to the same conclusion and publish first, and the prediction having come true, a letter from Wallace asking Darwin to evaluate his work and forward it to Lyell, encouraged Darwin to quickly finish The Origin of Species. Although Wallace's idea was published first, Darwin developed and supported the theory of natural selection so much more extensively than Wallace that he is known as the main author. <Ref.1 - p419>
