Natural Selection. Charles Darwin & Alfred Russell Wallace

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1 Natural Selection Charles Darwin & Alfred Russell Wallace

2 Darwin s Influences Darwin observed such variations in species on his voyage as a naturalist on the HMS Beagle

3 Darwin s Influences Kept vast diaries of the many organisms seen and their tremendous variations Ex. Galapagos Islands finches, tortoises Ex. Snakes with legs Ex. Penguins use wings to swim Ex. Fossils of extinct animals as well as those that closely resemble modern animals

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5 Darwin s Influences J. B. de Lamarck - Claimed that all organisms had a desire to change - The more an organism used a structure, the larger it became - These acquired traits could be inherited by their offspring

6 Darwin s Influences Charles Lyell Principles of Geology Geological processes on Earth resulted from continuous cycling over a long period of time. This allowed Darwin to consider that the Earth was much older than originally believed and thus organisms could change over a very long period of time

7 Darwin s Influences Artificial Selection The process in which breeders choose the variations to be used to produce the following generations Darwin noted that breeders and farmers create better (stronger/faster) livestock and crops through selective breeding Would make sense that this could occur in nature too.

8 Artificial Selection All these veggies from wild mustard plants?!

9 Darwin s Influences Thomas Malthus theory Natural populations do not grow out of control in nature, even though some reproduce by the 1000 s Populations are kept in check by predators, diseases, limitations in food, water, and other resources that are essential for survival, hence.there is a struggle for existence (Darwin)

10 Change is slow but it does happen! The following circumstances are needed for natural selection to occur..

11 Population Size Natural populations do not grow out of control in nature, even though some reproduce by the 1000 s Populations are kept in check by predators, diseases, limitations in food, water, and other resources that are essential for survival, hence.there is a struggle for existence (Darwin)

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13 Variation Variation in genotype and phenotype exists in populations (from sexual reproduction) Some variations are more suitable for environmental conditions

14 Variation in Cuban tree snails

15 VARIATION in flowers In lady bugs

16 Fitness of Individuals Some individuals have genetic variations that create more favourable traits in a particular environment or habitat. These favourable traits may allow an individual to live longer and produce more offspring. This individual is more fit

17 Natural Selection The organisms best suited for the environment will survive The best suited individual will live longer and leave more offspring These offspring will inherit the advantageous genotypes and phenotypes of their parents and will also be fit for their environment.

18 At the same time. Organisms with less favourable traits are less likely to survive and reproduce Thus, they are less likely to pass on these unfavourable genes to the next generation Over time, these genes may be wiped out of a population.

19 Struggle for Survival The fact that there is a constant struggle for survival among individuals in an overcrowded. population means that some of the individuals will die before reproducing. The most fit individuals in a population are the ones that are least likely to die of starvation etc.

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21 NOTE: Natural selection will usually only cause changes in a population if the environment the population is in is changing. If the environment stays the same, it will always be the same traits that are favourable (fit).

22 A summary of natural selection 1. No two members of a species are identical (there is variation) 2. Variation is inheritable (alleles of genes are passed from parents to offspring) 3. More organisms are born than reach adulthood 4. Organisms compete for resources (struggle to survive) 5. Survival of the fittest

23 New Species Over time, this process can result in adaptations that specialize populations for particular ecological niches and may eventually result in the emergence of new species.

24 Pepper Moths & Natural Selection In the beginning Trees covered in offwhite lichens moths rest on trees Industrial Revolution Soot starts to cover trees, darkening them Light coloured moths have a survival advantage (camouflaged) Dark coloured moths have a survival advantage (camouflaged)

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26 Discuss with your partner how you think the peppered moth example demonstrates all the conditions needed for natural selection to occurs

27 Summary Both colour variations exist in the moth population BEFORE the industrial revol. Environmental changes select one colour over the other as a survival advantage More of one colour moth survives longer, reproduces more thus, the population of each colour increases or decreases

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