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Darwin's Background

Charles Darwin (1809-1882), like many people of genius, did not at first appear to have extraordinary talents. From a young age Darwin disliked school and preferred observing birds and collecting insects to study. He was sent to medical school in Scotland when he was 16. Young Darwin found medicine "intolerably dull." He was much more interested in attending natural history lectures. Seeing that Darwin lacked enthusiasm for becoming a doctor, his father suggested he study for the clergy. Darwin was agreeable to the idea and enrolled in the university at Cambridge, England, in 1827. Here again, Darwin admitted, "My time was wasted, as far as the academic studies were concerned." However, Darwin found that his friendship with John S. Henslow, professor of botany, made life in Cambridge extremely worthwhile. Through long talks with Henslow, Darwin's knowledge of the natural world increased. Henslow encouraged Darwin in his studies of natural history. In 1831 Henslow recommended that Darwin be chosen for the position of naturalist on the ship the HMS Beagle. 

 

Darwin's Observations

A search for the "mechanism" of evolution did not begin with Darwin, but his evidence for the Origin of Species by Means of Natural Selection, published in 1859, was so comprehensive it swept away all other theories and became a major turning point in the study of biology.

Among the vast body of data supplied by Darwin are five key observations:

 

 

Put in modern terms, Darwin explained that random events create changes in the genotype of the organisms. These changes are then reflected in variations in the phenotype.

Combinations of these variations, distributed among large numbers of offspring and expressed as different phenotypes, are in competition for survival.

Nature and the natural environment "select" the most fit phenotype and discard the least fit phenotypes. Darwin, therefore, viewed evolution as the gradual accumulation of genotypic change in a population of organisms to the point that the population becomes a new species.

 

Here is a simple, easy way to understand Darwin's theories. The video was made in anniversary of his 200th birthday (which was in 2009)

 

 

Darwin's Inferences

 

Inference 1 = There exists a continuous struggle for existence among members of a population.

 

Inference 2 = There are differences in survival and reproduction among the varying organisms in the population.

 

Inference 3 = Over generations, this differential survival and reproduction leads to changes in the appearance of the population & leads to appearance of new adaptations.

 

This is a video explaining the process of evolution using beetles as an example, and it gives a concrete definition of evolution and its processes

 

 

 

To go along with the previous video, this one does a good job of portraying the process of evolution as Darwin himself saw it and observed it.

 

 

 

 

This is a photo of Charles Darwin at age 45 in 1854

 

Charles Darwin's book, "On the Origin of Species" was published in 1859 that explained his theories on evolution, and unusually for a scientist, his theories were accepted to an extent in the scientific community of the time. However, it was not until the 1930s to the 1950s that his natural selection theory was predominantly accepted to be likely. His work and discoveries were also documented in his other books,  The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals.

     Famously, Darwin's theories were in part inspired by his voyage to the Galapagos Islands on the Voyage of the Beagle which landed in September of 1835. He observed the diverse species of the island, including the birds now known as "Darwin's finches," that differed within the species on various islands. This fueled his ideas of adaptation and natural selection because the same species adapted to different environments. 

    During the same stay in the Galapagos, Darwin observed the tortoises on the various islands. Like the finches, the same species of tortoise had differing adaptations depending upon its circumstances because, he theorized, they needed different characteristics to survive better in the particular environment. Based on these observations, Darwin said that they "undermine the stability of Species"

 

·         During his travels, Charles Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

·         Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos.

·         Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development. 

·         In artificial selection, nature provides the variation among different organisms, and humans select those variations that they find useful.

·         Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

·         natural variation- differences among individuals of a species

·         artificial selection- selection by humans for breeding of useful traits from the natural variation among different organisms

·         struggle for existence- competition among members of a species for food, living space, and the other necessities of life

·         fitness- ability of an organism to survive and reproduce in its environment

·         adaptation- inherited characteristic that increases an organism’s chance of survival

·         survival of the fittest- process by which individuals that are better suited to their environment survive and reproduce most successfully; also called natural selection

 

·         natural selection- process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest

·         descent with modification- principle that each living species has descended, with changes, from other species over time

·         common descent- principle that all living things have a common ancestor

·         homologous structures- structures that have different mature forms in different organisms but develop from the same embryonic tissues

·         vestigial organ-organ that serves no useful function in an organism

 

 

Darwin's Observations

A search for the "mechanism" of evolution did not begin with Darwin, but his evidence for the Origin of Species by Means of Natural Selection, published in 1859, was so comprehensive it swept away all other theories and became a major turning point in the study of biology. Among the vast body of data supplied by Darwin are five key observations:   More offspring are born than ever survive to become adults (an idea he found in a 1789 essay on economics by Reverend Thomas Malthus). Female fish can lay thousands of eggs, but usually only one or two survive to become adults.   Among these offspring, there is a range of values for any trait; in other words there is variation. Some goldfish have golden scales, some have orange scales, some have brownish scales, and some have a mixture.   This variation extends to all traits, even those vital for the survival of the individual. An eagle, which depends on superior eyesight to locate its prey, can still be born shortsighted. All variations are, therefore, random and not specifically directed toward any preferential adaptation.   All offspring compete within their natural environments for food, resources, mates, and safety from harm. Those with the weakest combinations of traits die, whereas those with the best combinations of traits survive to reproductive maturity more often. There is a natural selection for those individuals that are the fittest.   The survivors pass on their traits to the next generation and the process is repeated. Over millions of years, such gradual changes lead to changes in the whole population and hence to the origin of an entirely new species.   Put in modern terms, Darwin explained that random events create changes in the genotype of the organisms. These changes are then reflected in variations in the phenotype. Combinations of these variations, distributed among large numbers of offspring and expressed as different phenotypes, are in competition for survival. Nature and the natural environment "select" the most fit phenotype and discard the least fit phenotypes. Darwin, therefore, viewed evolution as the gradual accumulation of genotypic change in a population of organisms to the point that the population becomes a new species.

 

Inference 2: Differential survival and reproduction = NATURAL SELECTION

 

Inference 3: Continued over many generations = DESCENT WITH MODIFICATION  

 

 

 

 

 

 

 

 

This is a video on natural selection 

 

Natural Selection is a theory about evolution that was originally proposed by Darwin. There are five basic rules in this theory:

1. Organisms increase at a higher rate than their food supply. But overpopulation doesn't occur because many of the young organisms don't ever reach adult hood.

2. Because there is a limited food supply, only the organisms with superior qualities will be able to survive, and the others will die off.

3. Every individual is different. Every organism has some quality that makes them different than any other.

4. Some of these individuals have traits that better suit them to their environment, enabling them to adapt with it.

5. Children will inherit the favored characteristics of their parents, and pass them on to subsequent generations. Each generation will have these adaptations, which will change the species so that eventually, the new generations would not be able to breed with the older ones. This is the creation of a new species

 

How it works

 

When answering a question on explaining the evolution of a species, such as the giraffe, it is best to approach the question with the following format:

Variation

Inheritable

Selection

Time (a very, very, very long time)

Adaptation

 

Variation exists in nearly every population/speies on the planet.  In any given school, there will be a great range in height, with most people somewhere in the middle.  In the giraffe species, long ago, there was a range of heights as well.  In both species, this characteristic is inheritable, and while not all offpsring have a height equal to that of their parents, it is most certainly connected.  However, unlike in the human species, in the giraffe species it was reproductively advantageous to be tall (have a long neck).  Those giraffes had a much easier time acquiring leaves in tall trees, which kept them alive long enough to serve their purpose of reproduction, and therefore made them more reproductively fit than smaller giraffes.  While this long-necked trait may have been just a mutation at first, natural selection made this trait more common over a very, very, very long time.  More tall giraffes were breeding than small ones, because more tall giraffes were surviving.  So eventually, this long neck trait became an adaptation to the surrounding environment of tall trees.  The species/population of giraffes evolved over a considerable time.  One giraffe does not just evolve in its lifetime.  It takes thousands, or millions of years for natural selection to gradually 'choose' those with the most reproductively advantageous inherited genes. 

 

Natural Selection works because animal that have genetic traits that incease their ability to compete for resouces, avoid predation, and attract mates are likey to have more offspring, who may inherit those traits.

 

Natural Selection--> Evolution- Natural selection, acting on existing inheritable genetic variation in the population and accidental results of genetic mutation, led to increasing survival and reproductive fitness of individuals better adapted to the existing or changing environment conditions; this selection, over long periods of time, led to characteristics which may be called evolutionary adaptations to a niche.

 

 

Darwin's key observations were: •  Two strange armadillo-like animals, one extinct species and one living species, were found in the same geographic area. •  Same or similar species seemed to vary somewhat in populations in different localities. •  There was geographic variation in species on islands. Different but related species lived on different islands, and island species were most closely related to species on the nearest mainland.

http://www.pbs.org/wgbh/evolution/educators/course/session3/explain_b_pop1.html