Fossil evidenceFossils are preserved pieces of ancient organisms. We can look at fossils to compare homologues or similar structures to species that are still alive today. In the photo above we follow the evolution of the what from what was once a land mammal. We can see the fist animal has an arm with joints and fingers but as the whale develops into an aquatic mammal it no longer requires an arm for survival. Over millions of generations the arm develops into a fin, though the finger structures from the original organism are still present within the whale's fin. Comparative anatomyComparative anatomy is when we compare homologous structures of spices alive on earth today. This is not just limited to bones, we can compare internal and external organs as well. Most species are descended from a common ancestor we can tell because they have a similar bone structure. The limbs of reptiles, birds and mammals serve very different functions but share a similar bone structure. In some species an organ can become so reduced in size that that it is no longer usable, these structures are called vestigial organs. A good example of a vestigial organ in humans is the appendix, it serves no real purpose in digestion but it douse not impair our survival in any way so it is not eliminated by natural selection. Comparative EmbryologyThe embryo expresses the most basic primitive genes first in its early stages of development. Organisms with back bones appear very similar this is because the same group of cells develops into the same structure in each organism even in different species. Molecular EvidenceLooking at the genes themselves in a lab provides some of the most convincing evidence that evolutionary relationships are possible. Among one species the DNA is virtually identical but when compared to the DNA of other species we can see how similar or how different the two species are. In the example above the DNA of the human and that of the chimp share more in common than that of the human and the chicken we can use this evidence to assume that the human and chimp are descended from a more common ancestor.
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Micro evolution is the change in allele frequencies in a population. Micro evolution can occur because of five different processes; mutation, natural selection, (see above photo) non random mating, gene flow and genetic drift. Mutation is the random change in DNA it is but to a mistake in copying the DNA. Mutations can be good, bad or neutral in the example of the beetles the mutation that caused the beetles shells to turn orange gave them higher fitness. The green beetles will be more likely to die off and the orange beetles will go on to reproduce, this changes the gene pool and the allele frequencies within the population. Natural selection takes place when the fittest members of a population go on to reproduce. Non random mating or sexual selection is when members of one sex compete with members of the same sex for access to members of the opposite sex. A good example of non random mating is when peacocks mate the female looks for the male with the best tail to mate with, this is attractive and shows he is healthy. Non random mating can change the gene pool of a population by favoring desirable traits which will be passed on to the offspring. Gene flow is the transferring of allele frequencies from one population to another this can occur when two population have been geographically isolated and changes over time but are still similar enough to be able to breed with each other. An example of gene flow is if two related species of birds live on separate sides of a mountain but one day a bird from one side of a mountain mates with a bird from the other side of the mountain. This would change the allele frequencies within the population and provide new combinations of genes to the next and future generations. Genetic drift is often caused by random events witch can not be controlled by the population. Events such as natural disasters of part of a population randomly dying off. This changes the gene pool because it limits the genes available to the next generation. Effects of Natural Selection and Micro EvolutionStabilizing Selection Stabilizing selection is a type of natural selection in which the most common trait is made to be even more common. The overall genetic diversity of the population decrees. In the above example the mice in the middle of the graph with tan fur are the most common in the population, because of a process of micro evolution such as a new predator only eating light and dark coloured mice only the tan mice go on to reproduce and pass on their genes. Directional Selection Directional selection occurs when extreme variations at one end of the curve are favored over average variations. In the example of the mice seen above the phenotype that causes the mice to have dark coloured fur is favored over the phenotype that causes them to have light fur. This shift is because of a factor such as a change in their environment. If a once sandy dessert is covered by a lava flow making the mice's habitat darker in colour the mice with the dark fur have a natural advantage over those with a light fur colour because they can no be seen by prey. The light furred mice then die off meaning only the dark furred mice will go on to reproduce. Disruptive Selection Disruptive selection occurs when extreme variations at opposite ends of the curve are favored over intermediate forms. In the example of the mice disruptive selection could occur if the tan mice could no longer survive in the environment. This could be because of a new predator being introduced to the environment that can only see the tan mice. The lighter and darker furred mice at opposite ends of the distribution curve have higher fitness and reproduce.
Decent with evolution is one of the first theories on evolution proposed by Jean-Baptise Lamark. Decent with evolution is the natural process of passing on traits from parent to offspring. It is an important to Darwin's theory of evolution because when the less fit organisms die the fitter ones pass on their genes through reproduction.
Charles Darwin was not the only scientist of his time to contribute to the theory of evolution; Erasmus Darwin, Alfres Russelle Wallice and Jean Baptiste Lamarck where all scientists between 1809 and 1859 who worked influenced Charles Darwin's thinking on the natural world. Erasmus Darwin was Charles Darwin's grandfather he was a doctor and a leading naturalist in the world. He presented one of the first formal theories on evolution in "The Organic Laws of Life". Erasmus Darwin presented his early ideas on evolution in poetic verse in "The temple of Nature". Erasmus Darwin discussed ideas of natural selection with his grandson Charles Darwin. He proposed ideas on how sexual selection could cause changes in species; he proposed that stronger and more attractive individuals went on to reproduce and pass on their traits. He studied domestic animals as well as the behavior of wildlife. Another naturalist who worked with Darwin to form the theory of evolution was Alfred Wallace. Wallace was a welsh naturalist who wrote to Darwin in 1858 on his findings on natural selection. He was one of the first scientists to discover and find evidence that new spices change and develop over time into new species. He traveled to the Amazon river basin to research and collect specimens. When returning to Britain the ship Wallace was traveling on burnt, all of his specimens and research where destroyed resulting in Wallace not receiving credit for his findings. Wallace spent eight years travelling the Malay Archipelago once again collection specimens for sale as well as researching the ways that species appeared to be related to one another. He published his findings in 1855 stating that "Every species has come into existence coincident in both space and time with a pre- existing allied species". He proclaimed that new spices arise by the progression and continued divergence of a parent species. He sent a letter to Darwin explaining his evolutionary findings. Darwin saw a striking coincidence between his own research and the findings of Wallace concluding further evidence that species evolve from pre existing species. Wallace worked with Darwin and made contributions to "The Origin of Species". One of the earlier naturalists who flawed ideas on evolution influenced the thinking of Darwin and Wallace was Jean-Baptiste Lamark. Lamark was a French naturalist who in 1809 published his hypothesis on the inheritance of acquired traits. Lamark was one of the firs people to publish his ideas on evolution. Though now widely discredited his belief was organisms developed from dead matter into progressing complex forms and eventually into "perfect species". Lamarak claimed species did not die out of extinction but changed into other species. He wrongly believed organisms organs changed to adapt to fit their behaviors in their environments, their offspring then would inherit those improved structures. Lamark is credited with creating the "Use Disuse theory" meaning that if an animal did not use a structure or organ the structure would disappear. His idea of evolution was that it was a constant process of striving towards greater complexity and "perfection". Darwin, Wallace and Lamack are all credited as being the men of evolution. Though evolution is still a highly debated and controversial theory it is now back up by a large body of evidence. New ideas such as that of Punctuated Equilibrium are still changing the ideas of evolution.
Biography of Charles Darwin Charles Darwin is credited with hypothesising our modern theory of evolution witch is now supported by a huge body of evidence. He is one of the main original scientists to fist discover organisms change and develop over time and that modern species develop from ancient now extinct species. Darwin was born in England on February 12, 1809 he was the son of a wealthy family who studied at college.
In 1831 Darwin left England aboard the HMS Beagle (Her majesties' ship) while traveling the world he collected plant and animal specimens he was fascinated by the diversity of life on the planet. While abroad he collected fossils of now extinct creatures and compared the fossils to living animals. He wondered why these species went extinct and how they where related to modern species. He found fossils that resembled well know animals such as that of the glyptodon. The glyptodon was an ancient relative of the armadillo native to South America. He was infatuated with the similarities between the two animals. On of Darwin's most significant discoveries in evolution was found on the Galapagos islands. The Galapagos are a small group of islands west of South America each island had a very different climate ranging from hot and dry with sparse vegetation to ones with grater rainfall and a larger assortment of plants and animals. Darwin noticed you could tell witch island a tortoise came from by the shape of its shell along with other physical features such as their legs and necks. The tortoise's shell where an example of adaptive radiation. One species witch had become geographically isolated from one another and had adapted to become better suited to their environments. While on the Galapagos islands Darwin collected several specimens of flinches from each island. He noticed the birds, though all members of the same species had different sized beaks depending on what their food source was. Darwin Then returned to England where he documented his findings on species and the natural world. Darwin published several books in his time, the most important of them being "The Origin of Species". "The Origin of Species" stated Darwin's findings on his travels. It revolutionised the way people thought about species on earth. Before Darwin people beloved that all species had been created separately by a divine being, this thinking of evolution proposes a counter idea. Most of Darwin's ideas on natural are still scientifically valid today. |