212 BIOLOGY, CH 11 Selection Pressures There is variation among individuals within a species Some of these variations may give a slight advantage to an individual over others Selection pressures are factors that influence the survival of individuals, populations or species. Examples include environmental factors (eg. temperature), and competition between individuals for resources and mates. see “The Advantage of Sex” article

312 BIOLOGY, CH 11 Gene Pool The gene pool of a population is the range of genes and their alleles present in the population The allele frequency in a population is not constant because of: Mutations (discussed in CH 8) Gene Pools and Evolution(gene flow) (SRAM 313-4, 2012) Gene Pools and Evolution(gene flow) (SRAM 313-4, 2012) Founder effect (SRAM 328, 2012) Founder effect (SRAM 328, 2012) Population Bottlenecks (SRAM 329, 2012) Population Bottlenecks (SRAM 329, 2012) Genetic Drift (SRAM 330, 2012) Genetic Drift (SRAM 330, 2012)

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512 BIOLOGY, CH 11 Natural Selection

612 BIOLOGY, CH 11 Natural Selection The theory can be summarised by means of four propositions: Individuals differ from one another – they show variation. Offspring generally resemble their parents More offspring are born than can possibly survive to maturity and reproduce. There is a struggle for existence, with some individuals being better suited to their environment than others. Natural Selection (SRAM 316, 2012) Industrial Melanism (SRAM 323-4, 2012)

712 BIOLOGY, CH 11 Natural Selection “I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection.” On the Origin of Species (1859) ch. 3 Charles Darwin English natural historian “[Natural selection] has no vision, no foresight, no sight at all. If it can be said to play the role of watchmaker in nature, it is the blind watchmaker.” The Blind Watchmaker (1986) ch. 1. Cf. Paley 1 Richard Dawkins English biologist

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9 Do the Natural Selection Interactive in the Heineman Biol 3&4 text CD.

1012 BIOLOGY, CH 11 In 1809, Lamarck suggested the idea of inheritance of acquired characteristics – that a lineage of organisms could change over many generations as the offspring inherited characteristics that they had acquired from their parents. Darwin and Wallace concluded that: the differences between individuals determine how well they will survive traits that increase the possibility of an organism’s survival are passed on to their offspring. The Modern Theory of Evolution (SRAM 309, 2012) Evolution theories

1112 BIOLOGY, CH 11 Evolution occurs when the gene pool of a species permanently changes. It refers to the formation of new species from pre- existing species. For evolution of a species to occur by means of natural selection, however, it must take place over time and as a result of isolation. Evolution

1212 BIOLOGY, CH 11 “Two organisms belong to the same species if they can interbreed and produce fertile offspring.” Speciation occurs when a parent species splits into two or more daughter species which over time become different enough so that they can no longer interbreed. Species

1312 BIOLOGY, CH 11 SRAM 347-8, 2012 The Species Concept SRAM 349, 2012 Stages in Species Development SRAM 350, 2012 Isolation and Species Formation Speciation

1412 BIOLOGY, CH 11 Some isolating mechanisms prevent organisms from reproducing, eg: geographic mechanisms: seas, mountains, etc. temporal (time) mechanisms: different breeding seasons behavioural mechanisms: different courtship patterns morphological mechanisms: different reproductive structures. Pre-reproductive isolating mechanisms

1512 BIOLOGY, CH 11 They do not prevent mating from occurring but they do prevent young from being produced. gamete mortality: the gametes do not survive gamete mortality: the gametes do not survive zygote mortality: the zygote forms but does not survive zygote mortality: the zygote forms but does not survive hybrid sterility: adult offspring are formed but are infertile hybrid sterility: adult offspring are formed but are infertile Post-reproductive isolating mechanisms SRAM 351-2, 2012 Reproductive Isolation

1612 BIOLOGY, CH 11 involves the separation of individuals in a population by a geographic barrier that inhibits migration – and therefore reproduction – between the two populations. Allopatric Speciation SRAM 353-4, 2012 Allopatric Speciation

1712 BIOLOGY, CH 11 involves the separation of individuals in a population by niche differentiation or polyploidy. Sympatric Speciation SRAM 355, 2012 Sympatric Speciation

1812 BIOLOGY, CH 11 states that the frequency of alleles will remain constant in a population if: there is a very large population there is a very large population there is no migration of individuals there is no migration of individuals there are no mutations there are no mutations there is random mating there is random mating there is no natural selection there is no natural selection also, for a gene with two alternative alleles of a gene: if p = the frequency of one allele, A if p = the frequency of one allele, A if q = the frequency of the other allele, a if q = the frequency of the other allele, a then p + q = 1 then p + q = 1 Hardy-Weinberg Law

1912 BIOLOGY, CH 11 Set 2

2012 BIOLOGY, CH 11 A phylogenetic tree shows the evolutionary relationships between organisms A cladogram shows derived characteristics. These diagrams show the points at which lineages have diverged and often show time as well as evolutionary relationships. Evolutionary Relationships

2112 BIOLOGY, CH 11 Phylogenetic relationships are based on a wide range of evidence including the use of traditional structural features derived from: fossils genetics biochemical analysis. biogeographical evidence comparative anatomy Groups and species that share recently derived characteristics are more closely related than are those that do not. Evolutionary Relationships

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2612 BIOLOGY, CH 11 Set 3

2712 BIOLOGY, CH 11 Set 3 (Question 18 b) HUMAN 0% CHIMP 1.2% GORILLA 2.3% ORANGUTAN 3.6%

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