Evolution: How Population Evolve PreAP Biology

Figure 1.14

Lamarck’s Theory of Acquired Inheritance (early 1800s) Jean Baptiste Lamarck Observed fossil records and the current diversity of life Suggested that organisms evolved by the process of adaptation Traits gained during a lifetime could then be passed on to the next generation

Lamarck’s Theory of Acquired Inheritance Suggested giraffes acquired long necks because ancestors stretched higher and higher into the trees to reach leaves at a time when there was drought in the African prairies Lengthened neck was passed to offspring

Charles Darwin Observed organisms and their distributions on Galápagos Islands Saw similarities b/w Galápagos organisms and those in South America.

Figure 13.5

Darwin’s Theory of Natural Selection Observations: Overproduction of offspring leads to competition of limited resources (food, space, breeding partners) Individuals of a population vary in characteristics, and many such traits are passed on to offspring Conclusions: Individuals with inherited characteristics make them best adapted to survive in their environment and reproduce and leave more offspring than less fit individuals

The theory of natural selection is comprised of several logical steps, based on observation and inference: There is competition among individuals in a population. There is variation among individuals in a population. This variation is, at least in part, heritable. This variation contributes to fitness; fitter individuals will leave a larger contribution of offspring in the next generation. The succeeding generation will have an increased proportion of the traits that confer the higher fitness.

Hundreds to thousands of years of breeding (artificial selection) Natural Selection Prominent force in nature Support in the results of artificial selection—selective breeding of domesticated plants/animals Populations tend to evolve in response to environmental conditions Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Figure 13.2B

Evidence of Evolution Fossil Record Biogeography Comparative anatomy Comparative embryology Molecular Biology

Evidence: Fossil Record Fossils Are preserved remnants or impressions left by organisms that lived in the past. Are often found in sedimentary rocks. http://www.buzzle.com/img/articleImages/191116-18med.jpg

Fossil Formation Dead animal sinks. Tissue begins to decay Carcass covered with sediment. Lower layers turn to rock. Rock is folded. Fossil is exposed at the surface. www.dkimages.com/.../Stage-3/Stage-3-1.html

The fossil record Is the ordered sequence of fossils as they appear in rock layers. Reveals the appearance of organisms in a historical sequence. Fits with other evidence of evolution.

Fossil Record reveals that organisms have evolved in a historical sequence http://cache.eb.com/eb/image?id=398&rendTypeId=4

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Evidence: Biogeography Biogeography, the geographic distribution of species Suggested to Darwin that organisms evolve from common ancestors Darwin noted that Galápagos animals Resembled species of the South American mainland more than animals on similar but distant islands

Evidence: Comparative Anatomy Comparison of body structures between different species Similarities give signs of common descent Homologous structures—features that have similar structure but have different functions

Evidence: Comparative Anatomy Vestigial structures—Small body structures that may have been functional in the ancestors of a species, but has no real function at the present time (appendix, tail bone)

Evidence: Comparative embryology Different organisms go through similar embryonic stages All vertebrates have an embryonic stage in which gill pouches appear in the throat region—evidence of a common ancestor

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Molecular Biology Study of molecular basis of genes and gene expression Universality of genetic code Conservation of amino acid sequences in proteins such as hemoglobin

Figure 13.13

Populations are the Units of Evolution A population Is a group of individuals of the same species living in the same place at the same time A species is a group of populations Whose individuals can interbreed and produce fertile offspring

Populations are the Units of Evolution Population genetics Focuses on populations as the evolutionary units. Tracks the genetic makeup of populations over time. The modern synthesis Connects Darwin’s theory with population genetics

Populations are the Units of Evolution A gene pool Is the total collection of genes in a population at any one time Microevolution Is a change in the relative frequencies of alleles in a gene pool

Genetic Variation in Populations Individual variation abounds in populations. Not all of this variation is heritable. Only the genetic component of variation is relevant to natural selection. A population is said to be polymorphic for a characteristic if two or more morphs, or forms, are present in noticeable numbers.

Sources of Genetic Variation Mutations and sexual recombination Produce genetic variation. Are changes in the DNA of an organism. Sexual recombination Shuffles alleles during meiosis.

Analyzing Gene Pools The gene pool Alleles in a gene pool Consists of all alleles of all individuals making up a population. Alleles in a gene pool Occur in certain frequencies.

Analyzing Gene Pools In a nonevolving population In a nonevolving population The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population Hardy-Weinberg equilibrium States that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool Webbing No webbing Figure 13.7A

Hardy-Weinberg Equilibrium The population is very large The population is isolated Mutations do not alter the gene pool Mating is random All individuals are equal in reproductive success

One or More of these Conditions will lead to Evolution Population is small Population is not isolated; migration in/out Mutations (changes in genes) alter gene pool Mating is non-random Individuals are not equal in reproductive success; natural selection does happen

Causes of Microevolution Genetic drift—change in gene pool of a small population due to chance Loss/gain of individuals

Genetic Drift Bottleneck effect—results from an event/disaster that drastically reduces population size (elephant seals after being hunted in 1890s) Figure 13.9A Figure 13.9B

CONNECTION Endangered species often have reduced variation CONNECTION Endangered species often have reduced variation Low genetic variability May reduce the capacity of endangered species to survive as humans continue to alter the environment Figure 13.10

Causes of Microevolution Genetic drift Founder effect—random change in gene pool that occurs in a small colony A few individuals start a new population

Causes of Microevolution Gene flow—gain/loss of allele from a population Is the movement of individuals or gametes between populations Can alter allele frequencies in a population Tends to reduce genetic differences between populations

Causes of Microevolution Mutation—random change in organism’s nucleotide sequence Can create a new allele Rare events Ultimate source of the genetic variation that initiates evolution

Causes of Microevolution Nonrandom mating males and females with similar phenotypic traits tend to mate In species that stay in one place, individuals tend to mate with neighbors rather than more distant members of the population

Nonrandom Mating Sexual selection may produce sexual dimorphism Sexual selection may produce sexual dimorphism Sexual selection leads to the evolution of secondary sexual characteristics Which may give individuals an advantage in mating Figure 13.17B Figure 13.17A

Natural selection can alter variation in a population in three ways Stabilizing selection Favors intermediate phenotypes Directional selection Acts against individuals at one of the phenotypic extremes Disruptive selection Favors individuals at both extremes of the phenotypic range

Modes of Natural Selection

Insecticide-resistant Populations

Acknowledgements BIOLOGY: CONCEPTS AND CONNECTIONS 5th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2006. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher. Unless otherwise noted, illustrations are credited to Pearson Education which have been borrowed from BIOLOGY: CONCEPTS AND CONNECTIONS 3rd Edition, by Campbell, Reece, Mitchell, and Taylor, ©2000. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.