Chapter 15

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Darwin became a naturalist on the HMS Beagle in 1831 and took a 5 year journey around the world.Darwin made many observations and collected evidence that led him to his theory of evolution.

Darwin collected many plant and animal specimens.

He found many fossils of organisms once alive that resembled organisms presently living.

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Fossils from the San Francisco Bay region. Mesozoic fossils are all marine, (J) Jurassic "clams" , (K) a Cretaceous ammonite, and (L) a Cretaceous ichthyosaur. Land-animal fossils are all Cenozoic in age, such as (M) part of the Miocene beaver skull, (N) a Pleistocene saber-toothed cat, and (O) a Pleistocene mammoth.

Darwin observed that the characteristics of Darwin observed that the characteristics of many animals and plants varied noticeably many animals and plants varied noticeably among the different Galapagos Islands.among the different Galapagos Islands.

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Dome shaped shell - Isabela Island

Saddle back shell - Hood Island

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Darwin observed the similarities and differences amongst these finches and noticed how their beaks varied and were suited for the type of food they ate.

(1785) (1785) James HuttonJames Hutton - Earth is shaped by - Earth is shaped by geological forces over long periods of time.geological forces over long periods of time.

(1798) (1798) Thomas MalthusThomas Malthus - more offspring are - more offspring are born than survive, limited by food and space.born than survive, limited by food and space.

(1809) (1809) Jean-Baptiste LamarckJean-Baptiste Lamarck - organism’s - organism’s acquire or lose traits by selective use or acquire or lose traits by selective use or disuse passing on the trait to the next disuse passing on the trait to the next generation. generation.

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Lamarck’s reasoning for his law of use and disuse

(1831) (1831) Charles DarwinCharles Darwin - evidence from - evidence from voyage around the world laid the groundwork voyage around the world laid the groundwork for his theory of evolution.for his theory of evolution.

(1833) (1833) Charles LyellCharles Lyell - processes occurring - processes occurring now shaped Earth’s geological features over now shaped Earth’s geological features over long periods of time.long periods of time.

(1858) (1858) Alfred WallaceAlfred Wallace - he also speculated - he also speculated that evolution by natural selection occurs. that evolution by natural selection occurs. This spurred Darwin on to publish his theory.This spurred Darwin on to publish his theory.

Origin of SpeciesOrigin of Species Darwin proposed that new species originate

from ancestral forms through the gradual accumulation of adaptations over very long periods of time.

In his book, Darwin describes descent with modification. Some heritable variations in populations are better

suited than others and since organisms tend to produce more offspring than the environment can support, competition for resources favors those better suited. These individuals reproduce and pass on their traits.

Darwin observed artificial selection in which nature provided variation and humans selected variations they found useful.

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Variation leading toNatural Selection

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Insect Resistance

Artificial Selection

Darwin proposed thisidea.

Descent with modification implies a common ancestor with a single tree of life linking all living things.

In humans: use of drugs selects for In humans: use of drugs selects for pathogens that through chance mutations pathogens that through chance mutations are resistant to the drugs’ effects.are resistant to the drugs’ effects.

Bacteria and viruses evolve rapidly due to Bacteria and viruses evolve rapidly due to rapid rates of mutation and reproductive, rapid rates of mutation and reproductive, posing a challenge to our society.posing a challenge to our society.

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HIV Resistance to 3TC

1.1. Fossil RecordFossil Record

2.2. Geographical distribution of living Geographical distribution of living speciesspecies

3.3. Homologous structuresHomologous structures

4.4. Similarities in embryological Similarities in embryological developmentdevelopment

5.5. Comparing DNAComparing DNA

Fossils Fossils provide the provide the strongest strongest evidence of evidence of evolution.evolution.Sedimentary Sedimentary strata reveal strata reveal the relative the relative ages of fossils.ages of fossils.

Absolute ages are determined by radiometric Absolute ages are determined by radiometric dating.dating.

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During his voyage, Darwin observed During his voyage, Darwin observed animals in similar environments on animals in similar environments on different continents that had similar different continents that had similar anatomy and behavior.anatomy and behavior.

All species of finch on the Galapagos Islands evolved from a common ancestor from Ecuador. Differing selective pressures on the each Island was the driving force for the evolution of beaks.

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During the past few decades scientists have demonstrated that what is now called South America was part of a large land mass called Gondwana, which included Australia and Antarctica.

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Horses have a complex evolutionary history. The earliest horses evolved in North America; many lineages arose and died out, and ancestors of several of these lineages crossed into Asia over the Bering land bridge and into South America over the Central America land bridge.

Organisms living in different geographical locations under similar ecological conditions are exposed to similar pressures of natural selection. Evolution of shared traits in unrelated species is convergent evolution.

Regardless of the appearance Regardless of the appearance of organisms, two species are of organisms, two species are closely related when they closely related when they share common ancestry. share common ancestry.

Homologous structures have different functions but Homologous structures have different functions but evolved from common ancestries.evolved from common ancestries. Forelimbs of all mammals show the same Forelimbs of all mammals show the same

arrangement of bones with different functions.arrangement of bones with different functions.

Analogous structures have a similar function but are anatomically different.

Humans also have vestigial Humans also have vestigial features, evidence of our features, evidence of our own evolutionary history. own evolutionary history. The appendix is believed The appendix is believed to be a remnant of a to be a remnant of a larger, plant-digesting larger, plant-digesting structure found in our structure found in our ancestorsancestors

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Cave-dwelling tetra fish are blind; they have small vestigial eyes that do not work. Why have them? Biologists have found a possible answer: genetic mutations that hamper eye development also may increase the number of taste buds. Thus, mutations that happened to give the fish an advantage in tasting and smelling—a huge benefit in a dark environment—might also have inadvertently, and harmlessly, caused the degeneration of their eyes.

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Pythons and boa constrictors have tiny hind leg bones buried in muscles toward their tail ends. These are vestigial. Vestigial legs are a clue that snakes descended from lizards. Over 100 million years ago, some lizards happened to be born with smaller legs, which, in certain environments, helped them move about unencumbered. As generation after generation survived and reproduced, this new form flourished.

All vertebrate embryos have a tail and pharyngeal All vertebrate embryos have a tail and pharyngeal pouches. pouches.

This This indicatesindicatesa commona commonancestor.ancestor.

Genes are not active at the same time. Genes are not active at the same time. Those that are active during early development Those that are active during early development

are less subject to change than genes that are are less subject to change than genes that are active later. active later.

This is because mutations occurring early in This is because mutations occurring early in development have a far greater chance of development have a far greater chance of being lethal and would not be passed on to being lethal and would not be passed on to future generations. future generations.

Mutations occurring later in development have Mutations occurring later in development have more limited effects, are less likely to be lethal more limited effects, are less likely to be lethal and are more likely to be passed on.and are more likely to be passed on.

That’s why humans and chickens are so That’s why humans and chickens are so different at later stages despite similarities as different at later stages despite similarities as embryos.embryos.

Comparing DNA sequences is the most Comparing DNA sequences is the most direct way to determine evolutionary direct way to determine evolutionary relationships.relationships.

The sequence of nitrogenous bases is The sequence of nitrogenous bases is more similar in closely related species more similar in closely related species than in species that are not as closely than in species that are not as closely related. related.

Scientists can use this information, with Scientists can use this information, with knowledge of mutation rates, to estimate knowledge of mutation rates, to estimate how long it’s been since 2 species shared how long it’s been since 2 species shared a common ancestor.a common ancestor.

1.1. Organisms differ and these differences may be Organisms differ and these differences may be inheritable.inheritable.

2.2. Organisms produce more offspring than Organisms produce more offspring than survive.survive.

3.3. Organisms compete for limited resources.Organisms compete for limited resources.4.4. Organisms best suited to their environment Organisms best suited to their environment

survive and reproduce, passing on these traits.survive and reproduce, passing on these traits.5.5. This process of natural selection causes This process of natural selection causes

species to change over time.species to change over time.6.6. Species alive today descended with Species alive today descended with

modification from a common ancestor uniting modification from a common ancestor uniting all organisms in a tree of life.all organisms in a tree of life.