01 selection and evolution
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This document discusses key concepts of natural selection and evolution, including that organisms overproduce offspring but population sizes remain stable, indicating competition for survival. There is genetic variation within species on which natural selection acts, favoring traits that increase reproductive success. Examples are provided of natural selection in finches and moths. Selection changes allele frequencies over generations, driving evolutionary change.
01 selection and evolution
- 1. SELECTION AND EVOLUTION ALBIO9700/2006JK
- 2. Important terms • Natural selection • Evolution • Variation • Overproduce • Allele frequencies • Isolating mechanisms • Artificial selection ALBIO9700/2006JK
- 4. 1856 Charles Darwin Alfred Wallace ALBIO9700/2006JK
- 5. Evolution • Changes within lines of descent over time • Successive changes in allele frequencies in population as brought about by occurrences such as mutation, genetic drift, gene flow, and selection pressure ALBIO9700/2006JK
- 6. NATURAL SELECTION • The way in which individuals with particular characteristics have a greater chance of survival than individuals without those characteristics, which are therefore more likely to breed and pass on the genes for these characteristics to their offspring • The strongest survive and propagate and therefore increase the strength of the species ALBIO9700/2006JK
- 7. Observation 1 • Organisms produce more offspring than are needed to replace the parents ALBIO9700/2006JK
- 8. "The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when 30 years old and goes on breeding until 90 years old; if this be so, after a period from 740 to 750 years there would be nearly 19 million elephants descended from this first pair." – Charles Darwin ALBIO9700/2006JK
- 9. Observation 2 • Natural populations tend to remain stable in size over long periods ALBIO9700/2006JK
- 10. Observation 1 + Observation 2 Deduction 1 • There is a competition for survival (a ‘struggle for existence’) ALBIO9700/2006JK
- 11. Observation 3 • There is variation among the individuals of a given species ALBIO9700/2006JK
- 12. Deduction 1 + Observation 3 Deduction 2 • The best adapted variants will be selected for by the natural conditions operating at the time. • Natural selection occurs • The ‘best’ variants have a selective advantage; ‘survival of the fittest’ occurs ALBIO9700/2006JK
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- 14. Examples of Natural Selection Darwin identified 13 species of finches in the Galápagos Islands differing in beak size and shape ALBIO9700/2006JK
- 15. Examples of Natural Selection (cont) Natural selection was discovered among "peppered" moths living near English industrial cities ALBIO9700/2006JK
- 16. Overproduction • If left unchecked by environmental factors , numbers in a population may increase exponentially • Environmental factors i) biotic – living organisms (predation, competition for food, pathogenic infection) ii) abiotic – non-living components (water supply, soil nutrient levels) ALBIO9700/2006JK
- 17. • Natural selection keeps things the way they are – stabilising selection • Unless a new environmental factor or new allele is introduced – directional selection • Evolution occurs because natural selection gives some alleles a better chance of survival than others. Therefore, changes in allele frequency in a population are the basis of evolution . ALBIO9700/2006JK
- 18. Processes that affect allele frequencies in populations? • Malaria and sickle cell anaemia • Antibiotic resistance • Industrial melanism ALBIO9700/2006JK