Evidence for EvolutionRM 6

Station 1: Fossils

Fossils are preserved evidence of prehistoric life. Fossils are either body fossils, likebones, teeth, or shells, or trace fossils, like footprints or burrows. Scientists study fossilsto understand the evolutionary history of life.

Since the shape of an animal's teeth depends on what it eats, studying fossil teeth cantell you about a prehistoric animal's food and habitat. Herbivores that eat grasses havea high crown above the root of the tooth. This adaptation is an advantage because theteeth of grass-eating herbivores constantly get worn down by abrasive silica particles inthe cells of grass leaves. Herbivores that eat the relatively soft leaves of trees and shrubshave a low crown above the root.

Looking at the pattern of change in horse teeth over the past 50 million years,paleontologists have hypothesized that today's grassland herds of zebra and other horsesevolved from forest-dwelling animals that ate the leaves of trees or shrubs.

Ouestions:

1. Do you think the pattern of change shown by the horse teeth supports thishypothesis? Why or why not?

2. How would you test this hypothesis?

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Figure 1. Hyracotherium(approx. 52 million years old)

Figure 2. Mesohippus (approx.32-24 million years old)

Figure 3. Merychippus (approx.15 million years old)

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Figure 4. Equus (approx. 5million years old to present)

Evidence for EvolutionRM7

Station 2: Biogeography

Biogeography is the study of species distribution patterns across geographical areas.With the introduction of new technologies, biogeography now also includes the study ofgene distribution patterns across geographical regions.

Sickle cells are abnormally shaped red blood cells caused by a recessive mutant genethat codes for an abnormal form of the hemoglobin protein. People who inherit a copy ofthe mutated gene from each parent develop sickle cell disease, which causes fatigue,pain, stroke, organ damage, and often death before adulthood. People who only have onecopy or no copies of the mutant hemoglobin gene are generally healthy.

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Percent of PopulationWith the Sickle-Cell Allele

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Since the disease caused by the homozygous condition is deadly, doctors workingin Africa were puzzled by the abnormally high rate of the mutant gene found therecompared to the rest of the world.

(go to next card)

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Evidence for EvolutionRM 7 continued

Station 2: Biogeography (continued)

Working in the 1950s, British doctor Anthony Allison noticed a pattern: populations withelevated rates of the mutant sickle-cell gene are located in the same geographical areasas the organism that causes severe malaria. Malaria is an infectious disease caused by aparasite transmitted by mosquitos. Severe malaria often causes coma and death.

Dr. Allison hypothesized that the evolution of this gene must provide an advantage inregions where malaria is present.

_ Geographical Range of Malaria(most severe forms)

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Questions:1. Do you think the information and map data support Allison's hypothesis? Why or why

not?

2. How would you test this hypothesis?

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I

Evidence for EvolutionRM 8

Station 3: Molecular HomologiesIn biology, a homology is defined as a similar trait shared among organisms that evolvedfrom a common ancestor. The trait may have changed over time depending on whetherthe variation provided an advantage for survival. Scientists look for homologies aspart of the evidence for evolution. With careful study, scientists can support or reject ahypothesis about a common origin.

Scientists have discovered a protein found in the cells of most eukaryotic organismscalled cytochrome c. It is a critical part of cellular energy transfer and thus necessaryfor life. This makes cytochrome c an ideal molecule to study evolutionary relationships.The more closely related two species are, the fewer the differences in the aminoacid sequence. The more distantly related two species are, the larger the number ofdifferences in the amino acid sequence.

Use the table "Amino Acid Sequences of Cytochrome c in Four Organisms" to analyzethe evolutionary relationship between three organisms of your choice. To get started,choose two of your organisms and count the number of amino acid differences. Recordyour data in your notebooks on a data table similar to this one:

Number of aminoacid differences

Organism A vs. Organism B Organism A vs. Organism C

Note: Amino acid sequences that are identical among all four organisms are illustrated bya dash in the table.

Questions:1. Which organisms did you choose to analyze?

2. Based on your analysis, hypothesize which two organisms are more closely related.

3. How would you further test your hypothesis?

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Evidence for EvolutionRM 8 continuedStation 3: Molecular Homologies (continued)

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1 x x x Ala 57 Thr Thr Thr Ser2 X x x Ser 58 Asp Ala Asp Ala3 x x x Phe 59 - - - -4 x x x Ser 60 - - - -5 x x x Glu 61 - - - -6 x x x Ala 62 - - - -7 x x x Pro 63 - - - -

8 x x x Pro 64 Glv Glv Glv Ala9 - - - - 65 lie lie lie Val10 Asp Asp Asp Asn 66 Thr lie Thr Glu11 Val Val Val Pro 67 - - - -12 Glu Glu Glu Asp 68 Glv Glv Glv Glu13 Lvs Lvs Lvs Ala 69 Glu Glu Glu Glu14 - - - - 70 Asp Asp Asp Asn15 Lvs Lvs Lvs Ala 71 - - - -16 - - - - 72 - - - -17 - - - - 73 Met Met Met Tvr18 - - - - 74 Glu Glu Glu Asp19 Val lie Val Lvs 75 - - - -20 Gin Met Gin Thr 76 - - - -21 - - - - ~~ "I.. Glu Glu 1 •....••• ,

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22 - - - - 78 - - - -23 Ala Ser Ala Ala 79 - - - -24 - - - - 80 - - - -25 - - - - 81 - - - -26 - - - - 82 - - - -27 - - - - 83 - - - -28 Val Val eve Val 84 - - - -29 Glu Glu Glu Asp 85 - - - -30 Lvs Lvs Lvs Ala 86 - - - -31 - - - - 87 - - - -32 Glv Glv Glv Ala 88 - - - -33 Lvs Lvs Lvs Glv 89 lie lie lie Val34 - - - - 90 - - - -35 - - .... 91 Ala Val Ala Pro36 Thr Thr Val Gin 92 - - - -37 - - - - 93 lie lie lie Leu38 - - - - 94 - - - -39 - - - - 95 - - - -40 - - - - 96 Lvs Lvs Lvs Pro41 Asn His Tvr His 97 Glv Glu Glv Gin42 - - - - 98 Glu Glu Glu Asp43 lie Leu Leu Leu 99 Ara Ara Arc Arc44 Phe Phe lie Phe 100 Ala Ala Gin Ala45 - - - - 101 - - - -46 - - - - 102 - - - -47 Lvs Lvs Lvs Gin 103 - - - -48 Thr Thr Thr Ser 104 - - - -

49 - - - - 105 - - - -50 Gin Gin Gin Thr 106 - - - -51 Ala Ala Ala Thr 107 - - - -52 Pro Pro Ala Ala 108 Lvs Lvs Ser Lvs53 - - - - 109 - - - -54 Phe Tvr Phe Tvr 110 Thr Thr eve Thr55 Thr Ser Ser Ser 111 Asn Asn Ser Ser56 - - - - 112 Glu Glu Lvs Ser

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Evidence for EvolutionRM 9

Station 4: Anatomical Homologies

In biology, a homology is defined as a similar trait shared among organisms that evolvedfrom a common ancestor. The trait may have changed over time depending on whetherthe variation provides an advantage for survival. Scientists look for homologies as part ofthe evidence for evolution. With careful study, scientists can support or reject a hypothesisabout a common origin.

Scientists who have compared the skulls, teeth, and tusks of different elephant fossilshypothesize that the tusks of modern elephants evolved from teeth.

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The skull of Moeritherium, anelephant that lived about 55

million years ago

The skull of Gomphotherium,an elephant that lived about

20 million years ago

The skull of the mammoth,Mammuthus, an Ice Age

relative of Hving elephants

Questions:

1. Do you think the illustrations support this hypothesis? Why or why not?

2. How would you test this hypothesis?

Note: artist renderin not to scale

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