CHAPTER 13: THE THEORY OF EVOLUTION COACH FULTS

Darwin Proposed a Mechanism for Evolution The idea that life evolves may have been 1 st proposed by Lucretius, a Roman philosopher who lived nearly 2,000 years ago b4 the modern theory of evolution was proposed 1859, Charles Darwin published convincing evidence that species evolve, and he proposed reasonable mechanism explaining how evolution occurs

Darwin Proposed a Mechanism for Evolution Like all theories, this has been developed through decades of scientific observation and experimentation Today almost all scientists accept that evolution is the basis for the diversity of life on earth As a youth Darwin struggled in school; his father was a wealthy doctor

Darwin Proposed a Mechanism for Evolution He enjoyed being outdoors, so his dad sent him to Edinburgh, Scotland, to study medicine at the age of 16 The site of blood made him sick, so medicine was out of the question 1827, he went to Cambridge University to become a minister Although, he completed a degree in theology, he spent much of his time with naturalists

Darwin Proposed a Mechanism for Evolution 1931, the professors at Cambridge University recommended him to be the naturalist on a voyage HMS Beagle The ship already had a naturalist but the captain wanted someone of his same social class on the ship At the age of 22 he changed his life

Science b4 Darwin’s Voyage Most ppl viewed that each species is a divine creation that exists, unchanging, as it was originally created But scientists had begun to explain fossils 1809, Jean Baptiste Lamarck proposed the hypothesis for how organisms change over time Lamarck believed that over a lifetime of an individual, physical featured increase in size b/c of use and those features that are not used will decrease in size

Science b4 Darwin’s Voyage Lamarck said that those “used” features would be passed on to offspring He was proven wrong, but he was correct when he pointed out that a change in species is linked to the physical conditions of life He was referring to an organism’s environmental condition

Darwin’s Observations During the voyage, Darwin read Charles Lyell’s book Principles of Geology Lyell proposed that the earth’s surfaced changed slowly over many years As Darwin visited places, he saw things that he thought could be explained only by a process of gradual change He found armadillo fossils in S. America that resembled current armadillos, but not identical

Darwin’s Observations He visited the Galapagos Islands; he notice how the plants and animals resembled the ones off the coast of S. America He concluded that the animals descendants came from the mainland and had changed “descent with modification”- evolution He returned when he was 27, and he continued his lifelong study of plants, animals, and geology He didn’t report his finding until much later, in that time he studied his data (which increased his confidence) but he didn’t know how it worked

Growth of Populations The key that unlocked Darwin’s thinking about how evolution takes place was an essay written in 1798 by the English economist Thomas Malthus Malthus wrote that the population are able to increase faster than the food supply can He said that human growth is kept in check by death, disease, war, and famine Population- all the individuals of a species that live in a specific geographical area and that can interbreed

Evolution by Natural Selection Darwin realized that Malthus hypotheses about human population apply to all species Every organism has the potential to produce many offspring In most cases, only some survive that are able to reproduce So Darwin thought about what Malthus said and what he observed in breeding domestic animals

Evolution by Natural Selection Then Darwin made a key association: “Individuals that have physical or behavioral traits that better suite their environment are more likely to survive & reproduce more successfully than those that do not have such traits”

Evolution by Natural Selection Darwin called this differential rate of reproduction natural selection In time, the # of individuals that carry these favorable conditions will increase in a population. And thus the nature of the population will change– a process called evolution Darwin further suggested that organisms differ from place to place b/c their habitats present different challenges to, and opportunities for, survival and reproduction

Evolution by Natural Selection Each species has evolved and accumulated adaptations in response to their environment Adaptation- is a feature that has become common in a population b/c the feature provides a selective advantage

Publication of Darwin’s Work In 1844, Darwin finally wrote down his ideas in an outline and showed his friends that he trusted At about this same time, Lamarck’s hypotheses and also another book that favored evolution were being highly criticized, so Darwin stopped writing 1858, Darwin received a letter and essay from the young English naturalist Alfred Russel Wallace stating that evolution occurs by natural selection So Darwin’s manuscript was paired with the essay for a public scientific meeting

Darwin’s Theory On the Origin of Species by Means of natural Selection appeared in Nov Ppl were disturbed that he suggested that humans were related to apes But he had very convincing evidence His theory was supported by 4 main points

Darwin’s Theory 1. Variation exists within the genes of every population or species (the result of random mutation and translation errors) 2. In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation) and have more offspring (natural selection) 3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population

Darwin’s Theory 4. There is overwhelming evidence that fossils and many other sources that living species evolved from organisms that are extinct

Darwin’s Ideas Updated In the area of genetics, new insight of how natural selection occurs

Change Within Population Scientists now know that genes are responsible for inherited traits. Therefore, certain forms of a trait become more common in a population b/c more individuals in the population carry the alleles for those forms Natural selection causes the frequency of certain alleles in a population to increase or decrease over time Mutations & recombination of alleles that occurs during sexual reproduction provide endless sources of new variations for natural selection to act upon

Species Formation Reproductive isolation- is the condition in which 2 populations of the same species do not breed with one another b/c of their geographical separation As 2 isolated populations of the same species become more different over time, they may eventually become unable to breed with one another Ex: Kaibab and Abert squirrel

The Tempo of Evolution Gradualism- a gradual change over a long period of time leads to species formation Punctuated Equilibrium- periods of rapid change in species are separated by periods of little or no change

Evidence of Evolution: Fossil Record Think of how a city changes over time, streets are made and destroyed This resembles how evolution works Scientists look at fossil and see how the earth once was Darwin predicted that intermediate forms of species would be found in these fossils

Evidence of Evolution: Fossil Record Most scientists agree on the 3 major points: 1. Earth is about 4.6 billion years old 2. Organisms have inhabited earth for most of its history 3. All organisms living today share common ancestry with earlier, simpler life-forms

Formation of Fossils The fossil record has holes in it Many species live in areas where fossils do not form Most fossils are formed when they are rapidly buried in fine sediment by wind, water, or volcanic eruptions Wet low-lands, shallow seas, slow moving streams, and near volcanoes Some animals preserve better, like a crab vs. a soft- bodied organism

Formation of Fossils Paleontologist- study fossils They can use radiometric dating to date the rock that the fossil is in So putting these animals in a pattern, shows us hoe evolution occurs

Anatomy & Development Comparisons of the anatomy of different types of organisms often reveal basic similarities in body structures even though the structure’s function may differ between organisms Vestigial structures- evidence of an organisms evolutionary past Ex: hind limbs of a whale Many vertebrates have the same bones, but arranged differently

Anatomy & Development Homologous structures- are structures that share a common ancestry This can be seen in the embryo stage All vertebrate embryos have a tail, buds that become limbs, and pharyngeal pouches (gills) In humans, the tail disappears during fetal development and the pharyngeal pouches develop into structures in the throat

Biological Molecules If a species have changed over time as the fossil record indicates, then the genes that determine the species’ traits should have also changed by mutation or selection Therefore, more and more changes in a gene’s nucleotide sequence should build up over time

Proteins Recall that the amino acid sequence of proteins is genetically determined If evolution takes place, then species descended from a recent common ancestor should have fewer amino acid differences between their proteins than do species that share a common ancestor in the distant past Comparing 1 human hemoglobin protein with the same hemoglobin protein of other species reveals the predicted pattern.

Proteins Species that share a common ancestor more recently (human & gorillas) have few amino acid sequence differences. However, those species that share a common ancestor in the more distant past (gorillas & frogs) have many amino acid sequence differences

Nucleic Acids Scientists evaluate the number of nucleotide changes that have taken place in a gene since 2 species diverge from a common ancestor by comparing the nucleotide sequence of genes Data from proteins and nucleotides, lets scientists generated hypotheses about how organisms are related thru evolution The data from molecular data reflects what the fossil record indicates

Examples of Evolution The key lesson scientists have learned about evolution by natural selection is that the environment dictates the direction and amount of change If the environment changes, then the traits that cause an organisms to be successful may change as well

Factors in Natural Selection 1. All populations have genetic variation. That means that in any population there is an array of individuals that differ slightly from each other in genetic makeup; this includes bacteria 2. The environment presents challenges to successful reproduction. Do not survive to reproduce then genes don’t get passed on

Factors in Natural Selection 3. Individuals tend to produce more offspring than the environment can support. Thus individuals of a population often compete with one another to survive 4. Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those less suited for the environment

Evolution of Antibiotic Resistance Bacteria can become immune to our medicine we use, which results in a sharp increase in infections after previously thought to be eradicated

Evolution of Darwin’s Finches He collected 31 specimens of finches from 3 islands from the Galapagos Islands He collected 9 distinct species; that were similar except for their beaks Studies have shown that birds with the larger beaks over a 25 year study showed that those birds reproduce better than those with slender beaks b/c of very dry seasons

Formation of New Species Species formation occurs in stages Divergence- the accumulation of differences between groups Speciation- process by which new species form

Forming Subspecies Separate populations of a single species often live in several different kinds of environment Over time, populations of the same species that differ genetically b/c of adaptations to different living conditions become called a subspecies These have taken the 1 st step towards speciation

Maintaining New Species Species can be separated by geographical structures, physical differences As change continues to build up over time, living species may become very different from their ancestors and from other species that evolved from the same recent common ancestor, leading to the appearance of new species