Evidences for Evolution Lab

Introduction:

Unfortunately, we cannot repeat nature’s experiments of evolution; however there is a vast amount of evidence, mostly indirect, to support the theory. If modern organisms descended from ancestral organisms then we should see similarities between organisms in the fossil record. Also, we should be able to see more similarities amongst different types of organisms that live today if they have evolved from a common ancestor more recently. Each part of this lab will explore one of the major sources of evidence that support the theory of evolution.

PART A: The Fossil Record and the Age of the Earth Fossils are the remains of long-dead organisms that have escaped decay and become part of the Earth’s crust. Thus, fossils are evidence of organisms that lived long ago. Paleontologists, scientists who study ancient life, use fossils to understand events that happened long ago. They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behaviour. For example, fossil bones and teeth can indicate the size of animals, how they moved, and what they ate. Paleontologists also study fossils to gain knowledge about ancient climate and geography. For instance, if they find a fossil which resembles a present-day plant that lives in a mild climate, they may reason that the ancient environment was also mild. Use the information above and at Station A to answer the following questions:

1. Define fossil:

2. What normal processes must permanently stop for fossils to form and how can this happen?

3. Explain how each of the following preservation processes can result in formation of fossils:

a. Amber

b. Tar Pit

4. How could fossils be used to determine an animal’s diet?

5. Proboscideans’ ancestors were small and . Why did the group become larger as they evolved?

6. What is meant by a transitional fossil?

7. Recent fossil discoveries support the idea that modern birds evolved from one of the groups of dinosaurs near

the end of the Mesozoic Era. Observe the picture of the fossil Archaeopteryx, a prehistoric bird. List 2 Reptilian features and 2 Avian features:

PART B: Embryological Comparisons By the time a new individual has developed from an egg and has grown some recognizable body parts it is called an embryo. These basic structures are due to the most basic genes that even organisms that were ancestral to it must have had in order to begin growth. So, it was assumed that organisms that are closely related must also have similar structures as they develop.

A vertebrate is an animal with a backbone. At this station are photos of various vertebrate embryos at similar stages in development. Use the station info to help you determine the species of each embryo below.

A.____________ B.______________ C. ____________ D. ____________ E. ____________ F. ____________ Now look at the actual photographs of some of the embryos and compare them to the diagrams.

Questions:

1. Compare the actual photographs of developing vertebrate embryos. Do you see any similarities between

them? Explain.

2. Explain how embryological comparisons be used as evidence for the process of evolution.

PART C: Anatomical Comparisons Section 1 – Homologous Structures Homologous organs are ones that are similar in structure but may not be similar in function. For example, a human’s arm has the same basic positioning of bones in the arm as does a cat but a cat does not use its front limbs to grasp. The structure and organs of organisms, (anatomy) is determined by the genes that they inherit. All members of the same species have very similar genes for all structures, which is why they are so similar in appearance. Therefore, by examining the similarities and the differences between homologous organs which have the same embryonic origins, in two different organisms, we can observe their genetic and thus evolutionary relationships. Analogous organs (those which have similar functions and appearance but different genetic origin) can’t be used. The early land vertebrates were amphibians and possessed a limb structure called the pentadactyl limb; a limb with five fingers or toes. All vertebrates that descended from these early amphibians, including reptiles, birds and mammals, have limbs that have evolved from this same basic pentadactyl pattern. They also illustrate the phenomenon known as adaptive radiation, since the basic limb plan has been adapted to meet the requirements of different niches. There are two diagrams of the forelimbs of several different vertebrates. Figure 1 (you’ll find at the table) shows the generalized pentadactyl limb of an early land vertebrate. Note the names and relative position of the bones in this diagram. Figure 2 (on the following page) shows the forelimbs of several modern vertebrates. Compare each modern forelimb to that of the early vertebrate and colour the bones as indicated below: Humerus Upper arm Red Radius Lower arm on “thumbs-side” of limb Blue Ulna Lower arm opposite to radius Yellow Carpals Wrist Green Metacarpals Palm Orange Phalanges Fingers Violet These bones are all examples of homologous structures and are therefore derived from similar genes. You can see that the basic physical pattern of bones composing the forelimbs is the same in all the animals. This is explainable is we accept that all of the vertebrates living today, including the examples shown here, are descended from the first ancestral vertebrates, which have passed along the basic gene pattern for forelimbs structure from generation to generation.

Questions: 1. Briefly describe the purpose of the major anatomical change that has taken place in each of the limb

examples below (ie. What is the function of the forelimb?):

a) Human: ______________________________________________________________________

b) bird: ________________________________________________________________________

c) Seal: ________________________________________________________________________

d) Horse: ______________________________________________________________________

e) Sloth: _______________________________________________________________________

f) Bat: _________________________________________________________________________

Forelimbs of Modern Vertebrates Note: the radius and ulna are fused together in some animals

(Figure 2)

2. Observe the metacarpals and the carpals of the sloth and human. These bones perform the same function

in these animals. Do you expect them to be similar? Are they?

3. Compare the metacarpals and carpals of the bird and bat. Are these bones modified in the same ways? Describe how these modifications support the… Bird wing: Bat wing:

4. Based on your observations in questions 3 and 4, which pair of organisms (birds and bats or humans and sloths) are more closely related? Support your answer.

5. How are homologous structures, such as forelimbs of vertebrates evidence for evolution?

6. Now examine the skeletons of a human, turtle, snake, dog and chicken. Use the rating scale to compare the

skeletons to the human skeleton. Compare the shape, number of parts, and other characteristics as you see fit. Add one feature of your own choosing.

a) Which animal is most like the human? b) In the space that follows, write the names of each animal in the order that you think they are related to humans. (put

the most related first and the least related last)

Anatomical Feature

Dog Snake Turtle Chicken

Teeth

Ribs

Thumbs

Collar bones

Rating Scale: 5 = most like the human skeleton 4 = very similar to human 3 = somewhat like the human 2 = only slightly like the human 1 = dissimilar to the human skeleton

Section 2 – Vestigial Structures Vestigial structures are body structures in present-day organisms that no longer serve the original purpose, but were probably useful in an ancestor. A structure becomes vestigial when the species no longer needs the feature for its original function, yet it is still inherited as part of the body plan for the species. For example, vampire bats have molars, yet they are useless as these bats only drink blood. The eyes of blind mole-rats and cave fish are vestigial as they are no longer used for sight. Flightless birds, such as the ostrich and extinct elephant bird have extremely reduced forelimbs. Their ancestors probably foraged on land for food and nested on the ground. As a result, over time, the ancestral birds became quite large and unable to fly. Questions:

1. Give 2 examples of vestigial structures in animals.

2. Describe how the vestigial hind limbs of modern whales provide anatomical evidence for their evolution.

3. In terms of natural selection explain how structures that were once useful to an organism could become vestigial.

CHALLENGE

4. Suggest why a vestigial structure, once it has been reduced to a certain size, may not disappear altogether.

PART D: Biochemical Comparisons This is the newest and in some ways the best and most powerful evidence to establish evolutionary relationships. The previous methods each studied the end result of an organisms gene being expressed, ie. a one or shell or embryo. This method studies the immediate product of gene action, a protein molecule. You will learn in detail how a gene (a piece of DNA) makes a specific protein molecule in a cell in our next unit and in Biology 12. For now, all that you need to know is that the order of nucleotides in DNA determines the type and order of amino acids in a protein molecule. Any change in the order of nucleotides in the DNA will result in a change in the amino acid sequence of the protein that the piece of DNA (a gene) codes for. A change in the DNA is called a mutation and mutations occur randomly and unpredictably. Organisms which are the same species, and thus reproduce together, will all possess the same mutations after a few generations. Organisms which don’t reproduce with each other (and therefore separate species) will have different, unique mutations. If one species evolved into two separate species, their gene pools become isolated and they begin to accumulate their own mutations. The longer they have evolved apart, the more differences in their gene pools one would expect. Therefore, when we study amino acid differences in the same protein between species (which is technically fairly simple to do) we are really studying changes in DNA over time. A protein molecule common to all vertebrates is the blood protein hemoglobin. Look at the amino acid sequences shown on the chart. These sequences are portions of the hemoglobin molecule of five organisms. You will analyze this data to see how biologists use this technique to measure evolution and evolutionary rates and then answer the questions below.

Questions 1. Compare the amino-acid sequence of hemoglobin molecules of the human, gorilla, chimpanzee and horse.

Count the number of amino acids that differ between the organisms and list them in the table below. 2. Based on these results, which two animals appear to

be most closely related in terms of amino acid sequences?

3. What biological process results in changes in DNA?

4. If two organisms have very similar but not identical DNA sequences in their genes, what could you conclude and why?

5. If two organisms have some DNA in common, but a lot that are different, what would you conclude and why?

6. If two organisms have few DNA sequences in common, what would you conclude?

Number of Amino Acid Sequence Differences

Organisms

Number of Differences in the Sequence

Man and gorilla

Man and Horse

Gorilla and Horse

Gorilla and Chimpanzee

Chimpanzee and Man

Embryological Comparisons Actual Photographs

Human embryo at 7 weeks Fish Embryo

Chicken embryo Cat embryo

dolphin embryo

(Figure 1)

Vestigial Structures