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Evolution

In 1859, Charles Darwin, an English biologist, published a book which revolutionised the way humans understood life on the planet. His book was 'On the Origin of Species', and it immediately polarised the scientific community.

Although some may claim the debate is still open, without a doubt the ideas of mutation and survival of the fittest have been vindicated by the science of genetics, tying Darwin's evolution, Mendel's inheritance, and the DNA of Crick, Watson, Franklin and Wilson, into a single cohesive theory of species diversification.

The early 1800s was a period of history in which people were able to travel all over the world. Scientists were exploring and bringing back to Europe specimens and samples of living things, and fossils. As the sheer scale of the diversity of nature became more apparent, biologists began to see that species in different places, although very similar, had adapted to local conditions.

When Darwin arrived in the Galapagos Islands in 1835, he saw several species of almost identical finches. He noticed that the beaks of the birds were different slightly, and in a way which matched specific environmental conditions. One bird was adapt at cracking nuts found only on its island, while another had a slender beak suitable for finding insects in the bark of a tree found only on its island. How could these birds be so alike, and yet so perfectly suited to their specific circumstances?

Voyage of the Beagle

Then Darwin has his Eureka moment: if a bird had a more suitable beak, it would have more to eat, so was more likely to live long enough to reproduce. In time, only the birds with that advantageous characteristic would be left. Over time, these would become so different to another population, and a new species would be created. This process of adaptation and speciation (one species dividing into different species) is the process behind natural selection - the survival of the fittest.

Evolution

Phenotype

Phenotype is derived from Greek [phainein = to show, typos = type]. The phenotype of an organism is the total of its observable traits. These include morphological, biochemical and physiological properties, as well as behaviour and life cycle events (phenology). 'Extended phenotypes' refer to products of behaviour, such as nests, beaver dams and larvae cases.

Genotype

A genotype is the collective 'hard-written' instructions contained in the genome of an organism, and which can be passed on to the next generation.

Evolution involves gradual change. More strictly, it is a directional change in the frequency of genes in a population over time. A population is the collective number of individuals of the same species living within a specific area. The individuals of a population are in sufficient contact to allow them to share a common gene pool. Natural selection will cause a change in the composition of this gene pool over time.

For evolution to occur, there must be a variation in the genotype between individuals. This variation is how evolution operates - natural selection does not create genes, only select for those genes which favour the survival of individuals of the species according to the circumstances which exist. Success as an organism is interpreted as reproductive success. Factors which affect success include resistance to disease, hardiness against climatic extremes, effective strategies for protection or flight from predators, and the presence of other species for symbiotic relationships. e.g. flowering plants need bees or other insects to spread their pollen for effective reproduction.

Performance varies according to two types of factors: genetic and environmental.

Evolution Scientists

Martha Chase, Erwin Chargaff, Gregor Mendel, Thomas Huxley.

Around the turn of the 18-19th centuries, the prevailing ideas concerning the diversity of life on Earth did not include changes over time. Species were considered static, or fixed, in their morphology, and had been since their creation. This was based on a literal interpretation of scripture, and claimed that all species were created at the one time. To accommodate the growing fossil record, they allowed for the possibility that some species had gone extinct.

Lamarck and Evolution by Transmutation

Jean-Baptiste de Lamarck, 1744 - 1829
Jean-Baptiste de Lamarck, 1744 - 1829

Jean-Baptiste de Lamarck, 1744 - 1829, was a prominent French botanist and invertebrate zoologist, who developed two theories concerning evolution of species. The Transmutation theory of change in species became the major fore-runner to the Darwinian Theory of Natural Selection. Lamarck also proposed a Theory of Inheritance of Acquired Characteristics, which contained some of the elements which Darwin develops as natural selection.

In his 1802 book, Recherches sur l'Organisation des Corps Vivants, Lamarck set out his theory that life was organized in a vertical hierarchy according to complexity, and that there is a general movement from the simple to more complex through time. The mechanism he favoured was a movement of organisms up a ladder of complexity, with adaptation to local environmental conditions through use and disuse of characteristics.

Although his theory was soon to be superseded by a number of refinements, and then the Theory of Natural Selection, Lamarck's contributions to science were significant. Amongst other things, he invented the term invertebrate, and was an early user of the term biology for the modern science of life.

Darwin

Charles Darwin
Charles Darwin
1809 - 1882

Charles Darwin is not only one of the most famous of all scientists, he is one of the greatest heroes of science. Like Galileo more than 200 years before him, Darwin's scientific discoveries took him into collision with dogma.

His theory explaining the mechanisms of evolution, specifically natural selection, were published in his book On the Origin of Species, in 1859. The impact of Darwin's work was to brush aside the prevailing ideas concerning 'transmutation of species', and fossil genesis. However, it was not until the 1930s, when science had gained an understanding of genes and mutation, could the actual mechanisms behind evolution begin to be understood in detail.

Darwin famously developed his ideas during a long sea voyage aboard the ship Beagle, which spent time in South America, reaching in 1835 the Galapagos Islands, where species diversification was apparent. Darwin's observations of the differences between similar species of birds allowed him to conjecture that adaptation to different environmental conditions was a continuous process.

Voyage of the Beagle

Darwin backed up his theory with decades of painstaking experimentation. He did not possess the modern understanding of genetics, but nevertheless had determined that mutation led to adaptations within species, explaining the change in species over time, and the fossil record.

Publications

On the Origin of Species, 1859.

The Descent of Man and Selection in Relation to Sex, 1871.

The Expression of the Emotions in Man and Animals, 1871.

Many books on plants and earthworms.

Eugenics and Social Darwinism

A shameful phase was experienced in western countries, starting soon after the publication of Darwin's work in 1859, gaining momentum in the early 1900s, culminating in the horrors of Nazi Germany in the 1930s and 40s.

This was eugenics - claimed to be based on the 'science' of biological inheritance, but in reality was more Malthusian (concerned with resource division and economics) than Darwinistic in nature. Eugenics is about 'purifying' the human species by the suppression of those deemed 'inferior' in some way. The USA introduced compulsory sterilization for the 'feeble-minded', in an episode most would prefer to forget.

The initial definitions of 'inferior' were based on what may today be readdressed towards forms of genetic dysfunction. However, seeking only justification for their social principles, and without a knowledge of genetics, it was easy for racists to claim an ethnic distinction in the determination of who should be the masters of the lower orders of humans.

Fortunately, Social Darwinism has been largely eliminated by the advance of science, providing a more accurate picture of the human genome, along with its mutations and inheritable genetic diseases. Today, gene therapy is offered in place of the 'final solution'.

Content © Andrew Bone. All rights reserved. Created : August 21, 2015 Last updated :May 7, 2016

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