Evidence of Evolution ActivityBackgroundWhen 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. Remember, evolution in short means “change over time”. Examine all of the examples below that show the evidence that scientists use to know how species have changed over time.FossilsFossil sequences connect different species into a lineage of ancestors and descendants and reveal the changes over time in living things. These fossils help us to explain how every species that exists on Earth is a descendant of an ancient ancestor.The image below is a series of skulls and front leg fossils of organisms believed to be ancestors of the modern-day horse.  

  

 

 

Equus(modern horse)

Pilohippus Merychippus Mesohippus Eohippus

(Dawn Horse)

Source:  http://www.iq.poquoson.org

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

 

 

2.  What is the biggest change in skull anatomy that occurred from the dawn horse to the modern horse?

 

3. What is the biggest change in leg anatomy that occurred from the dawn horse to the modern horse?

 

Skull Comparison:

Hippopotamus Skull

Human Skull

Beluga Whale Skull

Cat Skull

Dolphin Skull

4. Through your skull observations, which two organisms share the most recent (very closely related) common ancestor? What observations/evidence are you using to bring you to that conclusion?

5. Through your skull observations, which two organisms share the most distant (not very closely related) common ancestor? What observations/evidence are you using to bring you to that conclusion?

EmbryologyOrganisms that are closely related may also have physical similarities before they are even born!  Embryos of differing species often resemble each other and indicates a common ancestry. Vertebrate (animals with a backbone) embryos show features like gills and a tail, that are reduces or are transformed as the embryo matures. These similar traits in embryo form only could occur if they originally came from a common ancestor. Take a look at the six different embryos below:

Source: 

http://www.starlarvae.org

6. Hypothesize which embryo is from each of the following organisms:

Species Embryo (letter)

Human  

Chicken  

Rabbit  

Tortoise  

Salamander  

Fish  

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

7. Hypothesize which embryo is from each of the following organisms:

Species Embryo (letter)

Human  

Chicken  

Rabbit  

Tortoise  

Salamander  

Fish  

These are embryos at their most advanced stage, shortly before birth.8. Describe how the embryos changed for each of these organisms from their earliest to latest stages. 

Species Anatomical Changes From Early to Late Stages

Human  

Chicken  

Rabbit  

Tortoise  

Salamander  

Fish  9.  Look again at the six embryos in their earliest stages.  Describe the patterns you see.  What physical similarities exist between each of the embryos? (i.e. how do they look the same?)

   

10.  Which makes more sense: all of these embryos have similar features because they evolved from a similarly looking common ancestor or these organisms do not share a common ancestor and happened to evolve separately to look like this? Explain your answer.Comparative AnatomyComparative anatomy is the study of similar structures on distantly related organisms. The similar structures/body parts are used in unrelated activities (not the same function) but since they are the same bones in the same locations it is evidence that they must have come evolutionarily from a common ancestor. Shown below 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.  Color code each of the bones according to this key: 

Humerus    [   ] 

Ulna           [   ] 

Radius        [   ]

Carpals                   [   ] 

Metacarpals            [   ] 

Phalanges               [   ]

Compare the skeletal structure of each limb to the human arm. Relate the differences you see in form to the differences in function.

Animal Comparison to Human Arm in Form Comparison to Human Arm in Function

Whale 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  

 

 

Bat    

Bird  

 

 

Crocodile  

 

 

 

11. Are these front limb anatomy examples of homologous or analogous structures? Explain how you know?

Evolutionary Scientists study the following types of comparative anatomy: Homologous Structures: show individual differences but have a common anatomical theme. These are seen in organisms that are

closely related evolutionarily. Analogous Structures: have very different anatomies (body parts) but similar functions. These are seen in organisms that are not

necessarily related, but live in similar environments and have similar adaptations.

Compare the anatomy of the butterfly and bird wing below.

 

  12.  What is the function of the butterfly and bird wings? Are these functions the same or different?   13. How are these two sets of wings different in form (structure)? (Are they made out of the same material or the exact same structure?)  Give specific differences. 

 

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

 

Minnow

Cave Fish

14.  What is the biggest, most obvious difference between the body structures of these two fish?   

15.  Assume the two fish came from the same original ancestor.  Why might the cave fish have evolved without eyesight?    

16.  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?

 

You have now studied two different types of anatomical structures: 

         Homologous structures show individual variations on a common anatomical theme.  These are seen in organisms that are closely related.

 17.  Give an example of a homologous structure from this activity: ________________________________ 

         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.

 18.  Give an example of an analogous structure from this activity: ________________________________

 Here is one more type of anatomical structure:         Vestigial structures are organs or body parts that are reduced or not used anymore. These structures were important in the organism’s

ancestors, but are no longer used in the same way and act as a relic of an organism’s past ancestor. Vestigial structures are good evidence of evolution because it shows an organism’s evolutionary origin and how it has evolved since.

 Read about various traits in current organisms and their functions. Use this information to fill out the table to determine original vestigial structure function and possible organism it shares a common ancestor with.Tailbone: A Monkey uses a tail to aid in balance both in the air and on the ground.

Swim Bladder: Most fish have a special organ called a swim bladder. This organ fills with gas which allow fish to remain buoyant in the water, this is why fish do not sink or float in the water.

Nictitating Membrane: Alligators have a extra eyelid called a nictitating membrane. When alligators go under water the nictitating membrane covers the outside of the eyelid protecting the alligator’s eye and allowing them to view under water.

Appendix: Horses have a very large appendix that aids in the digestion of grasses, hay, etc.

Body Hair: Monkeys have a lot of body hair to help with body heat.

Muscles for moving ears: Cats are able to use muscles that allow them to move their ears in many different positions. This ability aids in helping cats catch prey and avoid predators. 

19.  Fill out the following table about vestigial structures: 

Vestigial Structure Possible Original Function and Organism Possibly Shared a Common Ancestor With:

Humans have the remnants of a fused tailbone

 

Sharks do not use a swim bladder but have a remnant of one.

 

Cats have a remnant of a small nictitating membrane on the corner of their eye.

 

Humans have a small appendix that has no function (except maybe in immunity)

 

Humans either do not have or use body hair.

 

Humans have muscles for moving their ears but cannot use them.

 

 20.  How are vestigial structures an example of evidence of evolution? (Hint: how does it show an organism’s evolutionary past?)

 

  

Molecular BiologyThe degree of genetic similarity between organisms reflects the degree of relatedness. On other words, the closer or more similar two organisms’ DNA is shows they shared a more recent common ancestor.

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 protein molecule for 9 different animals.  Any sequences exactly the same for all animals have been skipped. For each non-human animal, count the number of amino acids that are different than the human sequence.  When you finish, record how many differences you found in the table on the next page. 

  42 43 44 46 47 49 50 53 54 55 56 57

Human Q A P Y S T A K N K G I

Chicken Q A E F S T D K N K G I

Horse Q A P F T T D K N K G I

Tuna Q A E Y S T D K S K G I

Frog Q A A F S T D K N K G I

Shark Q A Q F S T D K S K G I

Turtle Q A E F S T E K N K G I

Monkey Q A P Y S T A K N K G I

Rabbit Q A V F S T D K N K G I 

  58 60 61 62 63 64 65 66 100 101 102 103 104

Human I G E D T L M E K A T N E

Chicken T G E D T L M E D A T S K

Horse T K E E T L M E K A T N E

Tuna V N N D T L M E S A T S -

Frog T G E D T L M E S A C S K

Shark T Q Q E T L R I K T A A S

Turtle T G E E T L M E D A T S K

Monkey T G E D T L M E K A T N E

Rabbit T G E D T L M E K A T N E Animal Number of Amino Acid Differences

Compared to Human Cytochrome CAnimal Number of Amino Acid Differences

Compared to Human Cytochrome C

 Chicken  7 Differences  Shark  

Horse   Turtle  

Tuna   Monkey  

Frog   Rabbit  

 21.Based on the Cytochrome C data, which organism is most closely related to humans (most similar DNA= least number of differences)?   

 22.  Based on the Cytochrome C data, which organism is the furthest related to humans (least similar DNA= highest number of differences)?  

  The data table below compare the amino acid sequence in the same part of the Hemoglobin Molecules of a human, horse, gorilla, chimpanzee and zebra.

23. Based on the amino acid sequence data above, which organism shares the most recent common ancestor with humans? Explain how you came to this conclusion.

24. Based on the amino acid sequence data, which organism shares the most recent common ancestor with horses? Explain how you came to this conclusion.

Phylogenetic Trees and Evolution Phylogenetic Trees, or Evolutionary Trees (sometimes also referred to as Cladograms), is a branching diagram showing the

evolutionary relationships among a set of organisms or groups of organisms, called taxa. In the past, biologists would group organisms based solely on their physical appearance. Today, with the advances in genetics and biochemistry, biologists can look more closely at individuals to discover their pattern of evolution, and group them accordingly.

In a phylogenetic tree, the species or groups of interest are found at the tips of lines referred to as the tree's branches. For example, the phylogenetic tree below represents relationships between five species, A, B, C, D, and E, which are positioned at the ends of the branches:

Image modified from Taxonomy and phylogeny: Figure 2 by Robert Bear et al., CC BY 4.0 The pattern in which the branches connect represents our understanding of how the species in the tree evolved from a series of common

ancestors. Each branch point (also called an internal node) represents a divergence event, or splitting apart of a single group into two descendant groups.

At each branch point lies the most recent common ancestor of all the groups descended from that branch point. For instance, at the branch point giving rise to species A and B, we would find the most recent common ancestor of those two species. At the branch point right above the root of the tree, we would find the most recent common ancestor of all the species in the tree (A, B, C, D, E). 

Image modified from Taxonomy and phylogeny: Figure 2 by Robert Bear et al., CC BY 4.0

Each horizontal line in our tree represents a series of ancestors, leading up to the species at its end. For instance, the line leading up to species E represents the species' ancestors since it diverged from the other species in the tree. Similarly, the root represents a series of ancestors leading up to the most recent common ancestor of all the species in the tree.

Which species are more related? In a phylogenetic tree, the relatedness of two species has a very specific meaning. Two species are more related if they have a more

recent common ancestor, and less related if they have a less recent common ancestor. We can use a pretty straightforward method to find the most recent common ancestor of any pair or group of species. In this method, we start

at the branch ends carrying the two species of interest and “walk backwards” in the tree until we find the point where the species’ lines converge.

You may see phylogenetic trees drawn in many different formats. Some are blocky, like the tree at left below. Others use diagonal lines, like the tree at right below. You may also see trees of either kind oriented vertically or flipped on their sides, as shown for the blocky tree.

Image modified from Taxonomy and phylogeny: Figure 2 by Robert Bear et al., CC BY 4.0 The identical information in these different-looking trees reminds us that it's the branching pattern (and not the lengths of branches) that's

meaningful in a typical tree.

Examine the two cladograms below:

Cladogram 1: Cladogram 2:

According to Cladogram 1:

25. Who shares the most recent common ancestor and traits with leopards? __________________________

26. What traits do the turtle and leopard have in common? (there are 4 of them)

27. What trait evolved in leopards after the common ancestor branched off and evolved into turtles? (Hint: leopards have this trait but turtles do not) ________________________________________

28. What is one trait the common ancestor of lampreys, tuna, salamanders, turtles and leopards possess? (but lancelets do not have this trait) ____________________________________

According to Cladogram 2:

29. What trait evolved after the ancestor of primates, rodents and rabbits diverged/evolved from the rest? (Hint: only crocodiles and birds have this trait but not primates, rodents and rabbits) _________________________

30. The common ancestor of all of the organisms in this cladogram possesses what trait? ___________________________

31. Which organisms diverged first from the rest of the organisms and would thus share the least number of traits with the birds? _____________________________________

32. What traits do primates, rodents, crocodiles, and birds all possess? (there are 5 of them)