ANSWER KEY

ASSIGNMENT – THE EVIDENCE FOR EVOLUTIONBackgroundWhen Charles Darwin first proposed the idea that all new species descend from an ancestor, he performed an exhaustive amount of research to provide as much evidence as possible. Today, the major pieces of evidence for this theory can be broken down into the fossil record, embryology, comparative anatomy, and molecular biology.

A.FOSSILSFossils are formed when organisms become buried in sediments, causing little decomposition of the organism. As time progresses various sedimentary layers get deposited, with the oldest on the bottom and the youngest on the top.Fossils are also formed through freezing, being embedded in amber, preserved in tar, or even footprints and imprints.Early fossils are fairly simple organism, while later fossils become increasingly complex. This supports our more recent understanding of genetics and evolution; new alleles and genes develop from existing genes by mutation, and it seems unlikely that more complex organisms (those with many different genes) would develop first and then become more simple (having fewer genes).

This is a series of skulls and front leg fossils of organisms believed to be ancestors of the modern-day horse.

1. Give two similarities between each of the skulls that might lead to the conclusion that these are all related species. [2]

Triangular shape of the skull

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Gap between teeth Pointy bone on top of nose

2. What are the biggest changes in skull anatomy that occurred from the dawn horse to the modern horse? [2]

Increase in the size of the skull Elongation of the face Deep lower jaw bone Deeper set eyes

3. What are the biggest changes in leg anatomy that occurred from the dawn horse to the modern horse? [2]

Shift from four toes to one Elongation of leg bone

B.EMBRYOLOGYEmbryology is the study of the development, structure and function of embryos. When comparing vertebrate embryos in the early stages of development, you will see striking similarities. Even species that bear little resemblance in their adult form may have strikingly similar embryonic stages.

Let’s take a look at the six different embryos below:

4. Hypoth

esize which embryo is from each of the following organisms. [3] 6 x 0.5 = 3

Species EmbryoHuman Answers will varyChickenRabbitTortoiseSalamanderFish

These are older, more developed embryos from the same organisms.

5. Hypothesize which embryo is from each of the following organisms. [3] 6 x 0.5 = 3Species Embryo

Human Answers will varyChickenRabbitTortoiseSalamanderFish

These embryos at their most advanced stage, shortly before birth.

6. Describe how the embryos changed for each of these organisms from their earliest to latest stages.[6]

Species Anatomical Changes From Early to Late Stages (at least three)Human Loss of tail, development of arms/legs, loss of gill slits, formation of ear

Chicken Developed beak, shorter tail, wings and legs developed, large head.

Rabbit Tail gone, developed limbs, development of snout and ears.

Tortoise Shell developed, longer thinner tail, limbs developed, large belly

Salamander Gills, tail, and limbs developed.

Fish Fins, gills, and tail developed.

7. Look again at the six embryos in their earliest stages. Describe the patterns you see. What physical similarities exist between each of the embryos? [3]

Same shape Same eye spots All have tails All have bumps (ear hole)

8. Does this suggest an evolutionary relationship? Explain how these embryos can be used as evidence of a common ancestor between each of these six organisms. [2]

Yes, at same stage of development the embryos appear to be similar.

C.COMPARATIVE ANATOMYComparative anatomy compares the structures of organisms of both living species and fossils. Comparisons of anatomical features in different organisms often provide evidence to support the theory of evolution. Organisms are often classed together according to similarities in their structures. It was through comparing the anatomy of organisms that scientists discovered phylogeny, meaning the evolutionary history of a group of organisms. Comparative anatomy includes homologous and analogous structures as well as vestigial features.

HOMOLOGOUS STRUCTURES Homologous structures evolved from a common ancestor. Examples of homologous structures include the forelimbs of a variety of mammals. For example, the human and frog arm. These species show the same skeletal elements in the humerus, radius and ulna and share a common origin. However, these skeletal elements have been modified over time to suit the different functions suitable for the type of mammal, bending and grasping for humans and hopping and swimming for frogs. Homologous structures result from divergent evolution (to be discussed later).

ANALOGOUS STRUCTURESAnalogous structures serve the same function between organisms but are different in internal anatomy. For example, the fin of a shark, wing of a penguin, and flipper of a dolphin all function to help these marine organisms swim but are different in their internal form. These structures are of no use in classifying organisms or in working out their evolutionary relationships with each other.

VESTIGIAL STRUCTURESVestigial structures are structures in an organism that has lost most or all of its function. Vestigial structures are usually dwarfed and useless to the organism. Sometimes vestigial structures may be adapted for new uses e.g. penguin wings can’t be used for flight, yet they are adapted for swimming. Even though organisms have these structures there is no significant disadvantage to the organism. Examples of vestigial structures include the pelvic bone in whales.

Shown here are images of the skeletal structure of the front limbs of 6 animals: human, crocodile, whale, cat, bird, and bat. Each animal has a similar set of bones.

9. Colour code each of the bones according to this key [6]:

(you can choose the colour)

Humerus

Ulna

Radius

Carpals

Metacarpals

Phalanges

1. For each animal, indicate what type of movement each limb is responsible for. [5]Animal Primary Functions

Human Using tools, picking up and holding objectsWhale swimmingCat Running, jumping, walkingBat flyingBird Walking, hoppingCrocodile Swimming, walking

2. Compare the skeletal structures of each limb to the human arm. Relate the differences you see in form to the differences in function. Be specific! [10]

Animal Comparison to Human Arm in Form Comparison to Human Arm in FunctionWhale Whale has a much shorter and thicker

humerus, radius, and ulna. Much longer metacarpals. Thumb has been shortened to a stub.

The whale fin needs to be longer to help in movement through water. Thumbs are not necessary as the fins are not used for grasping.

Cat Curved humerusSmaller metacarpals and phalanges

Movement involves jumping and running. Thumbs are not necessary for grip

Bat Smaller humerus, ulna, and radiusMetacarpals and phalanges much longer

Bones are longer and spread out for flying

Bird Humerus, ulna, and radius are smallerPhalanges are fused and pointy

Bones smaller and lighter for flying

Crocodile Humerus, ulna and radius are all shorter and thickerMetacarpals and phalanges are longer

Thick strong bones support weight of crocodileLong metacarpals and phalanges for swimming.

Compare the anatomy of the butterfly and bird wing below.

3. What is the function of each of these structures? [1] Flying and gliding

4. How are they different in form? Give specific differences. [2] Butterfly wings don’t have bones, come in two pieces, and have no feathers

Compare the overall body structure of the cave fish and the minnow below.

5. What is the biggest, most obvious difference between the body structure of these two fish? [1] Cave fish missing eyes

6. Assume the two fish came from the same original ancestor. Why might the cave fish have evolved without eyesight? [2] Cave fish live in an environment without light so there is no need for sight. This adaptation

would have not given an advantage to the cave fish and therefore wasn’t selected for.

7. What kind of sensory adaptation would you hypothesize the cave fish has to allow it to navigate in a cave, including catching and eating food? [2] Sensory adaptation for motion, vibration, sound, smell or taste

You have now studied three different types of anatomical structures: Homologous structures – show individual variations on a common anatomical theme.

These are seen in organisms that are closely related. Analogous structures – have very different anatomies but similar functions. These are

seen in organisms that are not necessarily closely related but live in similar environments and have similar adaptations.

Vestigial structures – are anatomical remnants that were important in the organism’s ancestors but are no longer used in the same way.

8. For each type of anatomical structures, give an example from this activity. [3]

Anatomical Structures Example from ActivityHomologous Structures Similarities in legs of human, cat, crocodile, bird, whale, and bat

Analogous Structures Bird and butterfly wings

Vestigial Structures Four toed horse or “thumb” in whale

9. Below are some vestigial structures found in humans. For each, hypothesize what its function may have been. Be specific! [5]

Structure Possible Function?

Appendix Aid in digestion*Important Note – although the appendix is considered a “vestigial organ” in many textbooks/online, new research suggests that the appendix plays a vital role in our immune system.

Wisdom teeth Chewing – chewing more plant materials

Muscles for moving the Ear

Hearing - Listening for predators

Body hair Warmth – keeping warm

Little toe Stability – for balancing, perhaps clinging to trees

Tailbone Stability – for balancing, perhaps climbing or clinging to tress

10.How are vestigial structures an example of evidence of evolution? [2] Vestigial structures are often homologous to structures that are functioning normally in

other species. Vestigial structures show that we all evolve from a common ancestor and natural selection

allow us to keep traits that are useful to us and lose traits that are not.

D.MOLECULAR BIOLOGY – DNA and PROTEIN STRUCTUREDarwin, and other early scientist such as Wallace and Lamarck based their understanding of evolution on what they could see with the naked eye. More recently though, we have also been able to look at our DNA and protein structures, and by comparing DNA sequences of genes from one organism to another, we can learn an enormous amount about their relationships. All living cells have the same basic DNA structure and use the same genetic code. Proteins produced from genes all come from the

same set of amino acids. Comparing sections of DNA in different species has shown that even organisms that seem to be different, actually have large sections of identical DNA. Organisms that seem fairly similar on the basis of comparative anatomy, show more genes in common than organisms that aren’t much alike. For example, 96% of the genes in humans and chimpanzees are identical. That two species and their common ancestor have similar DNA is strong evidence supporting evolution. Protein amino acid sequences can also be used to compare similarities between species. Proteins are made from amino acids and the sequence of these amino acids is controlled by genes. Comparing how many of the amino acids are in the same positions on the protein chain can provide some idea of how closely related two species are. For example, humans and chimpanzees only have one position where they are different on the amino chain, while humans and moths have 31 different positions.

Cytochrome c is a protein found in mitochondria. It is used in the study of evolutionary relationships because most animals have this protein. Cytochrome c is made of 104 amino acids joined together. Below is a list of the amino acids in part of a cytochrome c protein molecule for 9 different animals. (Note - Any sequences exactly the same for all animals have been skipped).

1. For each non-human animal, take a highlighter and mark any amino acids that are different than the human sequence. When you finish, record how many differences you found in the table below. [8]

2. Record how many differences you found in the table.[8]

Animal Number of Amino Acid Differences Compared to

Human Cytochrome C

Animal Number of Amino Acid Differences Compared to

Human Cytochrome CHorse 5 Shark 14

Chicken 7 Turtle 8

Tuna 11 Monkey 1

Frog 9 Rabbit 4

3. Based on the Cytochrome C data, which organism is most closely related to humans? [1]

monkey

4. Do any organisms have the same number of differences from human Cytochrome C? In situations like this, how would you decide which is more closely related to humans? [2]

No organisms have the same number of differences To decide which is more closely related to humans comparing anatomy would help

determine which is more closely related.

E. BIOGEOGRAPHYAll the places where species live is known as species distribution. The study of the geographic distribution of these species (both living and fossilized) is known as biogeography. When looking closely at distributions it is clear that many unique species occur in isolated pockets or islands. When looking at these unique species through the lens of evolution, we would expect unusual species in isolated areas because isolation is necessary before speciation can occur. The theory of the movement of the Earth’s tectonic plates was supported by the distribution of the fossils of particular species. Moving continents also explains why Australia has most of the world’s marsupials and the only two monotremes; the platypus and the echidna.

CONCLUSION1. Charles Darwin published his book On the Origin of Species in 1859. Of the different types of

evidence that you examined, which do you think he relied upon the most, and why? [2]

Darwin relied upon anatomy and some fossil evidence

2. Given the amount of research and evidence available on evolution, why do you think it is classified as a theory? [2]

It is a theory because it is based on a hypothesis that is corroborated by evidence.

Resources:Dauray, James. Evidence for Evolution. 1cdn.edl.io. Retrieved April 28, 2020.Evidence for Evolution Factsheet. coolaustralia.org. Retrieved April 28, 2020.