Evolution The Nature of Change and Variation

What is Evolution? Simply… a change in living organisms over time Simply… a change in living organisms over time

Why study evolution? Evolutionary concepts provide a solid foundation to much of modern biology Evolutionary concepts provide a solid foundation to much of modern biology - you can’t fully understand current trends in biology or you will have difficulty understanding evolution - you can’t fully understand current trends in biology or you will have difficulty understanding evolution

Evolution Evolution involves inheritable changes in organisms through time involves inheritable changes in organisms through time is fundamental to biology and paleontology is fundamental to biology and paleontology Paleontology is the study of life history as revealed by fossils Paleontology is the study of life history as revealed by fossils Evolution is a unifying theory Evolution is a unifying theory like plate tectonic theory like plate tectonic theory that explains an otherwise encyclopedic collection of facts that explains an otherwise encyclopedic collection of facts Evolution provides a framework Evolution provides a framework for discussion of life history for discussion of life history Why Study Evolution?

Many people have a poor understanding Many people have a poor understanding of the theory of evolution of the theory of evolution they hold a number of misconceptions, they hold a number of misconceptions, which include: which include: evolution proceeds or advances strictly by chance evolution proceeds or advances strictly by chance nothing less than fully developed structures nothing less than fully developed structures –such as eyes are of any use there are no transitional fossils there are no transitional fossils –so-called missing links –connecting ancestors and descendants humans evolved from monkeys humans evolved from monkeys –so monkeys should no longer exist Misconceptions about Evolution

Evolutionary theory is the framework tying together all of biology. It explains similarities and differences between organisms, fossils, biogeography, drug resistance, relative virulence of parasites, and much more. What is a scientific “theory”? Theories are structures of ideas that explain and interpret facts.

In the early days... Prior to people believed organisms were fixed- that is they didn’t change Prior to people believed organisms were fixed- that is they didn’t change – Jean Baptiste Lamarck – Jean Baptiste Lamarck Evolution through the inheritance of acquired characteristics Evolution through the inheritance of acquired characteristics Traits acquired during an organism’s life could be passed on to their offspring Traits acquired during an organism’s life could be passed on to their offspring Giraffes long necks explained by repeated stretching Giraffes long necks explained by repeated stretching hypothesis rejected hypothesis rejected

According to Lamarck’s theory of inheritance of acquired characteristics According to Lamarck’s theory of inheritance of acquired characteristics Lamarck’s Giraffes –ancestral short-necked giraffes –stretched their necks –to reach leaves high on trees. –Their offspring were born –with longer necks

Lamark’s theory was not totally disproved Lamark’s theory was not totally disproved until decades later until decades later with the discovery that genes cannot be altered by any effort by an organism during its lifetime with the discovery that genes cannot be altered by any effort by an organism during its lifetime Lamarck’s Theory

Basic Types of Evolution Macroevolution = speciation – the formation of new species. The change in species over long periods of time. Not immediately observable. Macroevolution = speciation – the formation of new species. The change in species over long periods of time. Not immediately observable. Microevolution = changes in genes/alleles within a population. Microevolution = changes in genes/alleles within a population. Can be observed in a human lifetime. Can be observed in a human lifetime.

Macroevolution/Microevolution Macroevolution 1. Large-scale changes in gene frequencies 2. Occurs over a longer (geological) time period 3. Occurs at or above the level of species in separated gene pools 4. Consists of extended microevolution Microevolution 1. S mall-scale changes in gene frequencies 2. Occurs over a f ff few generations 3. Occurs w ww within a species or population in s ss same gene pool 4. Refers to s ss smaller evolutionary changes

Macroevolution/Microevolution Macroevolution 5. Has not been directly observed 6. Evidence based on remnants of the past 7. M M M More controversial 8. Example: Birds from reptiles Microevolution 5. O bservable 6. Evidence produced by e ee experimentation 7. Less controversial 8. Example: Bacterial resistance to antibiotics

If all existing organisms descended with modification from ancestors that lived during the past, If all existing organisms descended with modification from ancestors that lived during the past, all life forms should have fundamental similarities: all life forms should have fundamental similarities: all living things consist mainly of carbon, nitrogen hydrogen and oxygen all living things consist mainly of carbon, nitrogen hydrogen and oxygen their chromosomes consist of DNA their chromosomes consist of DNA all cells synthesize proteins all cells synthesize proteins in essentially the same way in essentially the same way Biological Evidence Supporting Evolution

Biochemistry provides evidence for evolutionary relationships Biochemistry provides evidence for evolutionary relationships Blood proteins are similar among all mammals Blood proteins are similar among all mammals Humans’ blood chemistry is related Humans’ blood chemistry is related most closely to the great apes most closely to the great apes then to Old World monkeys then to Old World monkeys then New World monkeys then New World monkeys then lower primates such as lemurs then lower primates such as lemurs Biochemical test support the idea Biochemical test support the idea that birds descended from reptiles that birds descended from reptiles a conclusion supported by evidence in the fossil record a conclusion supported by evidence in the fossil record Evolutionary Relationships

Organisms in all populations Organisms in all populations possess heritable variations such as possess heritable variations such as size, speed, agility, visual acuity, size, speed, agility, visual acuity, digestive enzymes, color, and so forth digestive enzymes, color, and so forth Some variations are more favorable than others Some variations are more favorable than others some have a competitive edge some have a competitive edge in acquiring resources and/or avoiding predators in acquiring resources and/or avoiding predators Not all young survive to reproductive maturity Not all young survive to reproductive maturity Those with favorable variations Those with favorable variations are more likely to survive are more likely to survive and pass on their favorable variations and pass on their favorable variations Natural Selection—Main Points

In common nonscientific usage, In common nonscientific usage, natural selection is sometimes expressed as natural selection is sometimes expressed as “survival of the fittest” “survival of the fittest” “Survival of the Fittest” This is misleading because natural selection is not simply a matter of survival - but involves differential rates - but involves differential rates of survival and reproduction

One misconception about natural selection One misconception about natural selection is that among animals only the biggest, strongest, and fastest only the biggest, strongest, and fastest are likely to survive are likely to survive These characteristics might provide an advantage These characteristics might provide an advantage but natural selection may favor but natural selection may favor the smallest if resources are limited the smallest if resources are limited the most easily concealed the most easily concealed those that adapt most readily to a new food source those that adapt most readily to a new food source those having the ability to detoxify some substance those having the ability to detoxify some substance and so on... and so on... Not only Biggest, Strongest, Fastest

Darwin observed Galapagos finches showing variations in beak shape and size from island to island. He reasoned these differences made the finches better adapted to the food in their particular local environment. Each finch population had developed beaks which were suitable for that particular environment.

Phylogenic Tree Phylogenic trees trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

Natural selection works Natural selection works on existing variation in a population on existing variation in a population It could not account for the origin of variations It could not account for the origin of variations Critics reasoned that should a variant trait arise, Critics reasoned that should a variant trait arise, it would blend with other traits and would be lost it would blend with other traits and would be lost The answer to these criticisms The answer to these criticisms existed even then in the work of Gregor Mendel, existed even then in the work of Gregor Mendel, but remained obscure until 1900 but remained obscure until 1900 Limits of Natural Selection

Evidence of Change Fossil Record Fossil Record Embryology Embryology Molecular Biology-Amino Acids, Nucleotides, DNA sequencing, mitochondrial DNA Molecular Biology-Amino Acids, Nucleotides, DNA sequencing, mitochondrial DNA Anatomy commonalities Anatomy commonalities Various adaptations Various adaptations

EVIDENCE OF EVOLUTION STRUCTURAL ADAPTATIONS STRUCTURAL ADAPTATIONS MIMICRY MIMICRY CAMOUFLAGE CAMOUFLAGE

Fossil Record Fossils are a major source of information about changes in life during the Fossils are a major source of information about changes in life during the distant past distant past In general, fossils In general, fossils show that life has show that life has increased in increased in diversity and complexity diversity and complexity over time over time

Fossil Record Interpretation of the distribution of fossils in the rock initially based on the principle of superposition Interpretation of the distribution of fossils in the rock initially based on the principle of superposition - in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils - in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils -radiometric dating confirms this -radiometric dating confirms this In general older life forms tend to be less complex In general older life forms tend to be less complex Periods of diversity are interrupted by mass Periods of diversity are interrupted by mass extinctions – followed by new life forms extinctions – followed by new life forms Fossil Record is incomplete – estimated only 1 in 10,000 extinct species are represented – Why? Fossil Record is incomplete – estimated only 1 in 10,000 extinct species are represented – Why?

Embryology All vertebrate embryos have Gill slits on sides of the throat Gill slits on sides of the throat Post anal tail Post anal tail The fact that organisms without gills, or tails have them as embryos is taken as evidence of a common ancestry with organisms that had both Which is the fish, rabbit, human, chicken, tortoise?

Comparative Anatomy Similarities in structure between organisms was used Similarities in structure between organisms was used to determine evolutionary relationships to determine evolutionary relationships

Other Proof From Anatomy Vestigial structures – structures that are greatly reduced with little or no function Vestigial structures – structures that are greatly reduced with little or no function - they are thought to be left over from - they are thought to be left over from ancestors ancestors Pelvis and leg bones in snakes Pelvis and leg bones in snakes Reduced toe in horse Reduced toe in horse Appendix in human Appendix in human Coccyx (tail bone) in humans Coccyx (tail bone) in humans

Vestigial Structures

Comparative Anatomy Analogous Structures Analogous Structures Similar function but different structure - Similar function but different structure - Insect’s wing, Bird’s wing and Bats wings Insect’s wing, Bird’s wing and Bats wings – all allow flight, but are structurally different – all allow flight, but are structurally different Eyes of Mollusks and Vertebrates – both allow sight, but are different in structure Eyes of Mollusks and Vertebrates – both allow sight, but are different in structure

Comparative Anatomy Homologous Structures Homologous Structures Have a similar structure but different function Have a similar structure but different function The forelimbs of vertebrate animals all have the same structural design, but they have different functions The forelimbs of vertebrate animals all have the same structural design, but they have different functions This similarity of structure shows a common ancestry This similarity of structure shows a common ancestry

Homologous Structures Analogous structures

Molecular Biology Comparisons of the sequences of amino acids in proteins or nucleotides in DNA can show the relationships between organisms the number of differences in the sequences of amino acids or nucleotides indicates how closely related two organisms are

Hemoglobin Comparison Species AA differences from humans Gorilla1 Rhesus Monkey 8 Mouse27 Chicken45 Frog67

Hemoglobin Cladogram

Cladogram (family tree) created from a fossil record

Bird Evolutionary Tree Phylogenic Trees and Cladograms are also created using comparative DNA sequences. If the DNA is very similar to each other, it means they share a fairly recent common ancestor.

During his voyage, Darwin observed fossil mammals in South America that are similar to yet different from present day animals. Ex. Llamas, sloths, and armadillos. The finches and giant tortoises lining on the Galapagos Islands vary from South America, even though they differ in subtle ways. These observations convinced Darwin that organisms descended with modification from ancestors that lived during the past which was his central claim of the theory of evolution. Darwin Developed the Theory

Charles Darwin Alfred Wallace Descent with modification. The Origin of Species Species were not created in their present forms but evolved from an ancestral species. Natural selection, the mechanism by which change occurs (Explanation of how evolution occurs).

Darwin and Alfred Russel Wallace ( ) Darwin and Alfred Russel Wallace ( ) read John Malthus’ book read John Malthus’ book and came to the same conclusion, and came to the same conclusion, that a natural process that a natural process was selecting only a few individuals for survival was selecting only a few individuals for survival Darwin’s and Wallace’s idea Darwin’s and Wallace’s idea called natural selection called natural selection was presented simultaneously in 1859 was presented simultaneously in 1859 Darwin and Wallace