5.4 Evolution

1. 5.4 Evolution We will be studying this topic at the Higher Level (Option D)

3. 5.4.1 Define evolution. • Syllabus definition: Evolution is the cumulative change in the heritable characteristics of a population. • It is the changes in allelic frequencies in the gene pool of a population over time, as a result of natural selection, genetic drift, gene flow, and mutation pressure.

4. 5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures Fossil Record: • A fossil is the ancient preserved remains of an organism • The fossil can be dated from the age of the rock formation it is found in • Sequences of fossil can show the gradual change of an organism over geological time • Continuous fossil records are rare with most containing large time gaps until subsequent discoveries are made.

5. Fossil Record-Radiometric Dating Half Life: the time it takes for half of the parent isotope to become the daughter isotope • There are some radioactive elements in rock that decay by giving off energy and turning into different, more stable elements. This radioactive decay is predictable for each radioactive element. • Eg. potassium-argon dating. The half-life of potassium-40 is 1,310 million years, after which half of its substance will have changed into stable argon-40. • For shorter time periods, Carbon-14 has a half-life of 5730 years

16. Selective breeding Man has selectively breed animals and plants for 1000’s of years. If an animal posses a characteristic that is desirable, then the animal is selected for breeding. This characteristic will be present in the next generation and at a higher frequency than before.

17. Selective breeding Example: - In a population of cows (generation 1 = G1) it is noticed that some produce more milk during lactation than others. - These cows are selected for breeding and the other low milk yield cows are rejected for breeding. - The calves of these high milk yields cows (G2) are then produced and once mature they themselves will have calves. • These now mature cows (G2)will be producing on average, a higher yield of milk than G1 cows. • The G2 population of cows will show variation in milk yield. • The breeder will select higher yielding G2 cows for the next breeding population. • The cycle is repeated until the cow population is producing very large yields of milk way beyond level seen in the G1 population.

18. Selective breeding • Selective breeding can work in another manner in which breeders selectively cull the weaker members of the population. • There could be two modes of selection. • Selection for • Selection against

19. Homologous structures • Closely connected organisms could share common or homologous structures. • Groups of organisms closely related share a common form or derived trait which has been inherited from the common ancestor. • This classic example of homologous structures is the pentadactyl limb of the vertebrate. • In each example the humerus(a) radius(b) and ulna(c) bones are modified and adapted to the locomotion of the animal.

20. Homologous structures • certain homologous structures exist in some species with no apparent function. They are vestigial structures. • ie. human appendix • ie. Whale pelvis • ie. Phalanges in many mammals

21. 5.4.3State that populations tend to produce more offspring than the environment can support.5.4.4Explain that the consequence of the potential overproduction of offspring is a struggle for survival. • Darwin’s views on “overreproduction” were heavily influenced by an essay on human population by an economist: Thomas Malthus in 1798. • Malthus contended that much human suffering - disease, famine, homelessness, war - was the inescapable consequence of the potential for human populations to increase faster than food supplies and other resources.

22. 5.4.3 State that populations tend to produce more offspring than the environment can support • The population produces more offspring than the carrying capacity of the environment can support • Offspring/population compete for limited resources • Some individuals have characteristics giving them a competitive advantage. • These individuals are consequently 'fitter' in terms of freedom from disease, food availability and most importantly, ability to reproduce. • Through inheritance of the genes for these advantageous characteristics the frequency of these characteristics become greater in the next generation. • The alleles for the advantageous characteristic becomes more frequent in the population

23. 5.4.5State that the members of a species show variation. • All members of the same species are not genotypically identical. • These genotypic differences lead to phenotypic differences

25. 5.4.6Explain how sexual reproduction promotes variation in a species. Meiosis: • Crossing over of homologous chromosomes during prophase I results in a recombination of maternal and paternal alleles within chromosomes • Independent assortment as homologous chromosomes randomly orient at metaphase I causing a randomized inheritance of maternal and paternal chromosomes within gametes

26. 5.4.6Explain how sexual reproduction promotes variation in a species. Fertilization: • New combinations of alleles appear during fertilization • As the unique set of haploid alleles in the egg • Combine with the unique set of haploid alleles in the sperm

27. 5.4.7 Explain how natural selection leads to evolution. The theory of Natural Selection was put forward Charles Darwin and Alfred Russell Wallace It is based on four observations: • Individuals within a species vary in many ways • Some of this variability can be inherited • All species tend to show an overproduction of offspring • Populations of species tend to remain stable

28. 5.4.7 Explain how natural selection leads to evolution. These observations led to three inferences: • Members of the same species compete with each other for survival. • Individuals with more favourable variations are more likely to survive to reproduce and pass on these variations. • As these individuals contribute proportionately more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)

29. 5.4.7 Explain how natural selection leads to evolution. • Biologist Richard Dawkins: • "the non-random survival of random variants."

30. 5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria. Antibiotic resistant bacteria: • Variation exists in the species (some are resistant to antibiotics, others are not) • Humans use antibiotics to kill bacteria (i.e treat bacterial infections) • This kills all the bacteria that are susceptible to antibiotics • Therefore, antibiotic resistant bacteria are more likely to survive and reproduce • Their genes can be passed to other bacteria via plasmids • This is an example of natural selection • Antibiotic resistant alleles become more common in the population, which is termed evolution

31. Example 2Industrial Melanism and the Peppered Moth Peppered moths are native to England. Prior to the 1800s, they looked like this: Afterwards, 1800s, they looked like this:

32. 5.4.8 Explain two examples of evolution Peppered moths: • They live on birch trees and prior to the industrial revolution, the birch trees were white, so white coloured moths were less visible to predators and were more likely to avoid predators and therefore were more common • After the industrial revolution, the trees turned black with soot so the black moths were less visible to predators and were more likely to survive and reproduce • This is an example of natural selection • This resulted in is alleles for darker colouring becoming more common in the population, which is termed evolution