EVOLUTION

Definition Change in the structure, function and behaviour of organisms between generations over time.

It has only been in the last 200 years that the idea that species might change has come about Fossils of organisms that once existed soon became discovered which made scientists wonder why some species disappear= some of the first evidence for the theory of evolution Do species change over time? Have we evolved from a common ancestor? There are 9 million different species on Earth- 1.2 have been described, classified and named What accounts for this biodiversity?

History of the theory of evolution Carl Linnaeus James Hutton Georges Cuvier Thomas Malthus Jean B. Lamarck Charles Lyell Charles Darwin Alfred Wallace Gregor Mendel Alfred Wegener

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Alfred Russell Wallace in the Malay Archipelago from began to wonder about how species evolved from the distribution of species. He wrote a paper and his ideas were similar to Darwin who had been reluctant to publish his findings of the last 20 years. In 1859 Darwin wrote his book ‘ The origin of species by means of natural selection’. It became one of the most influential books of all time. It outlined his theory of evolution by natural selection.

Darwin’s four main observations Offspring generally appear similar to their parents. No two individuals are identical Organisms have the ability to produce large numbers of offspring Populations in nature tend to remain fairly stable in size.

Natural Selection Process by which organisms most suited to their environment are most likely to survive and pass their genes on to their offspring ( those less well adapted produce fewer offspring or do not breed at all) Survival of the fittest

Variation in organisms characteristics are caused by the organisms having different DNA (genes). These genes are produced as a result of mutations and / or during meiosis. Some differences enable the organism to survive better (compete more successfully) The ones with beneficial DNA survive, breed and pass on their DNA to the next generation = SURVIVAL OF THE FITTEST Those without beneficial DNA die before they reproduce, so their DNA is less likely to be passed on. The beneficial DNA increases in frequency in the population and over time may eventually produce a new species.

New species For new species to arise there needs to be: -variation -isolation and competition -selection and speciation

In meiosis several factors assist to mix up the maternal and paternal DNA within the cell: -interphase: mutations can occur when DNA is replicating -prophase I: crossing over of homologous chromosomes to produce 4 unique chromatids -anaphase I: separation of homologous chromosomes occurs randomly Results in 4 haploid gametes each with a unique set of DNA which produce further variation through sexual reproduction and fertilisation

Isolation and competition Because individuals over produce, yet populations remain stable COMPETITION must take place. Ie. Thomas Malthus- a much larger number of individuals are produced than can possible survive In COMPETITION there are “winners” and “losers”. Winners are better adapted with more useful characteristics, they are more able to survive and breed, so pass on their beneficial DNA. Over time when this happens continually, accumulated changes can give rise to a new species- speciation

Two populations of the same species may become isolated from one another due to continental drift, earthquake etc. This could lead to speciation

Selection and speciation Competition for food, water Predation Disease Physical and chemical factors Competition for mates Competition for space, nesting sites, territory etc A section of DNA that helps an organism compete better is “selected for”, so it increases in frequency A section of DNA that fails to help an organism survive is usually “selected against”, so it decreases in frequency SELECTION PRESSURES

A few South American finches arrived to the islands (with slight genetic variations. Eg colour Drier islands had seeds with thick coats Natural selection would have favoured birds with larger, stronger beaks They were better able to survive, breed and pass on the genes of larger, stronger beaks Over time the whole population had larger stronger beaks When no longer able to breed with those with shorter beaks they are different species They are different species but are closely related

Darwin proposed that Natural Selection could lead to new species being produced over time. This was his explanation for the large number of different species of finch found in the Galapagos Islands. Each species has adaptations to its body, beak and feet that allow it to feed on specific types of food in specific areas.

What is a species? Definition

Evolution of a new species Speciation occurs when there is a “Reproductive Barrier”, some thing that stops members of an original population passing their DNA freely among all members, ie PREVENTS FREE GENE FLOW The barrier may be a geographical barrier = ALLOPATRIC speciation The barrier may be behavioural, biochemical, or anatomical =SYMPATRIC speciation

Allopatric speciation

Sympatric speciation When there is NO geographical barrier Initially individuals in the original species may have variations that can be divisive of the population. Eg in birds some might have slightly: -different shaped beaks -shorter wings, -better nocturnal vision, -different colour plumage or courting behaviour, etc

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Peppered moth simulation Go to: Read through the information and follow the instructions Answer questions 7-12 and 21-24