Year 10 Biology Natural Selection and evolution Chapter 4 This Photo by Unknown Author is licensed under CC BY-SA-NC 4.1 Diversity of life • Species- smallest unit of biological classification • can be hard to determine on physical characteristics alone so also use DNA evidence • different species usually genetically incompatible • Hybridisation • • • • two very similar species can interbreed offspring called hybirds. hybirds often have health problems or infertile horse + donkey= mule lion+tiger = liger • some plants species however hybirdise naturally • agriculture- breed hybirds to enhance qualities This Photo by Unknown Author is licensed under CC BY-NC-ND 4.1 Diversity of life (contd) • Classifying organisms • science of classifying called taxonomy • classifying since ancient times • 1700s Carl Linneaus devised system we still use today • used to classify on morphology ( physical features only) , now + DNA • today we use 4.1 Diversity of life (contd) Evolution • term first used Lyell- to refer to difference in complexity of animals in fossil record, not individual species had changed. • 1800s analysing rock layers believed that species had developed from simple to complex organisms. • 1841 geological time scale developed- three eras • science of geology and palaeontology rapidly progressed. • Began using word “evolution”• species can change over many generations to form a new species. • generation- time when individual born and then produces offspring. • Many scientist saw evolutions and an improvement of species • doesn’t always lead to more complex species • depends on characteristics species needs to survive in its environment 4.1 Diversity of life (contd) Evolution • Charles Darwin- (1809- 1882) English biologist • sailed ship Beagle as a scientist 1831 -1836 • reported on the amazing variety of life he had seen. • his observation of finches started his thinking- whether species can change to suit environment live in. • didn’t try and explain differences at this stage. • Alfred Wallace (1823 -1913) • evolution and biogeography (distribution of species across the world) • Between 1854 and 1862 collected 126 000 specimens. • During this came up with theory of natural selection. • Sent a paper to Darwin about theory that change in species can occur. • Darwin called this process – natural selection Darwin + Wallace credit codiscoverers of theory 4.1 Diversity of life (contd) Artificial Selection • process by which we choose to breed particular organisms with desirable features. • only happens over generations • breeders cross (mate) selected parents, and then choose between mature offspring to decide which will be bred. Selective breeding cross breeding • cross one individual with desirable features with another individual with different desirable features inbreeding • related individuals allowed to mate but.. • offspring deformities, sterility and genetic disorders 4.2 Natural selection Natural Selection • Natural selection is the process by which an environmental factor acts on a population and results in some organisms having a greater chance of survival and producing more offspring than others. Selective agent An environmental factor that acts on the population: factor that “selects” which organisms • could be biotic- another living thing eg bacteria infections, predator • could be abiotic (physical factor) eg temperature, water, fire • most agents act by killing individuals “less suited” or “poorly adapted • not always female birds choosing brighter coloured males for breeding (sexual selection) Selective pressure - effect of selective agent on population Natural selection can have the outcome that the species becomes better adapted to its environment 4.2 Natural selection Variation • Darwin said natural selection only act where there is variation. • Didn’t know about genetics so didn’t know how or why variation • Now know variation caused by differences in genes hence different characteristics. • Because genes are inherited, the characteristics carry inherited too. • Variation is inherited. Genetics and natural selection Particular phenotype in a species changes because individual with a particular genotype within it are being favoured to breed. 4.2 Natural selection Natural selection and evolution • Evolution is change in species over many generations, resulting in the formation of a new species. • Speciation- process where one species splits into two or more separate species. - responsible for formation of any new species in fossil record. - resulted in high level of biodiversity on Earth • Speciation occurs three basic steps step 1- Variation step 2- isolation step 3- selection 4.2 Natural selection Natural selection and evolution • Step 1- Variation o must be variation in population for speciation to occur. o Natural selection can only act on variations already present in population. Step 2- Isolation o isolation required. o different groups of the population are in some way prevented from interbreeding. o can occur in several waysclimatic barrier (rainfall, temperatures, salinity, sunlight) or geographical barrier( oceans, mountains, rivers ) Natural selection and evolution 4.2 Natural selection Natural selection and evolution • Step 3- Selection o once population isolated natural selection affects genotype of each group o can lead to changes that may prevent groups breeding with each other if reunited. 4.2 Review questions • Pearson Science 10 Page 151 • Remembering and Understanding
