Evolution review

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Evolution review

Name ________________________________ Period


When 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.


1.Give two similarities between each of the skulls that might lead to the conclusion that these are all related species. the pointy bone on top of the muzzle of the horse and the triangular shape of the head and the gap between front and rear teeth

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

Increase in the size of the skull; a shift from cusps to complex ridges on the grinding surface of the premolars and molars, elongation of the face and of the space between the incisors and cheek teeth, an anterior shift of the cheek teeth so they lie forward of the eye; a deep lower jaw bone;

3. What is the biggest change in leg anatomy that occur Fifty five million years ago, there was an animal the size of a small dog, called Hyracotherium (sometimes called Eohippus). Its front feet had four toes, and its back feet had three. Modern horse feet have a single hoof. We see the reduction and loss of the side toes and enlargement of the terminal phalanx (hood) elongation and enlargement of the central metapodial (the longest bone in the foot)

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


Organisms that are closely related may also have physical similarities before they are even born! Take a look at the six different embryos below:

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

Species Anatomical Changes From Early to Late Stages


Anatomical Changes From Early to Late Stages


Developed limbs, defined features in face, neck, ears, loss of tail, tiny fingers present


Developed beak, tail shorter, wings and legs developed, head quite large


Tail gone, developed limbs, detailed features in ears and mouth


Shell developed, limbs have developed, tail is thinner, large belly, long tail, beak


Has gills, tail and large underbelly


fins developed, gills, tail and scales

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

Same basic shape, circular spots (eyes) and underbelly, all have tails, tiny bumps on underside, hole for ear

2. 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.

Examination of vertebrate embryos reveals that during corresponding stages of early development, the embryos appear to be very similar. For example, all vertebrate embryos pass through stages in which they have gill pouches. The pouches eventually develop into the gill apparatus in fish; in later- evolving vertebrates that do not have gills, the gill pouches undergo further refinement and develop into structures associated with the head and neck. Similarly, all early vertebrate embryos have tails, which persist in some animals but regress during the later stages of development of humans. Thus, the individual development of an animal occurs through a series of stages that paint a broad picture of the evolutionary stages (phylogeny) of the species to which it belongs.
"Ontogeny recapitulates Phylogeny", Haeckel

Comparative Anatomy

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.

For each animal, indicate what type of movement each limb is responsible for.

Animal Primary Functions :

Human: Using tools, picking up and holding objects

Whale: swimming

Cat: running, walking, jumping

Bat: flying, flapping wings

Bird: walking, hopping,

Crocodile: swimming, walking/crawling

Comparison to Human Arm in Function :


Comparison to human arm in form

Comparison to Human Arm in function


Whale has a much shorter and thicker humerus, radius, and ulna. Much longer metacarpals.

Whale fin needs to be longer to help in movement through water. Thumbs are not necessary, as they don’t need to pick up and grasp things.


Curved humerus, shorter thinner humerus and ulna and radius, smaller metacarpals and phalanges

Movement of cat involves jumping and running, smaller for agility and balancing on small ledges, no thumbs for grasping since they use claws and teeth for this.


Thinner humerus, ulna, radius, smaller carpals, longer and thinner metacarpals and phalanges

Bones are smaller so that there is less weight in flight, long metacarpals and phalanges to extend wings


Slightly shorter humerus, ulna, radius; metacarpals fused together, fewer but pointy phalanges

Bones are thinner for flight, more aerodynamic and light


Shorter, thicker humerus, ulna and radius, larger carpals, pointy phalanges

Thicker legs to support heavy weight and long metacarpals for swimming

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

  1. Give an example of a homologous structure

: Following are some examples of homology: The arm of a human, the wing of a bird or a bat, the leg of a dog and the flipper of a dolphin or whale are homologous structures. They are different and have a different purpose, but they are similar and share common traits.

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.

  1. Give an example of an analogous structure:

Examples of analogous structures range from wings in flying animals like bats, birds, and insects, to fins in animals like penguins and fish. Plants and other organisms can also demonstrate analogous structures, such as sweet potatoes and potatoes, which have the same function of food storage.Apr 17, 2015

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

Below are some vestigial structures found in humans. For each, hypothesize what its function may have been. 


Possible function

Wisdom teeth

Extra grinding ability for vegetation


Store “good” bacteria to fight infections or digest cellulose like the caecum in rabbits

Muscles for moving the ear

Better hearing by changing direction of ears

Body hair

Keeping warm
Stop pathogens from getting to mucous membranes
Trap pheromones/oil on body

Little toe

Balance/clinging on rocks/trees


Rear stabilizing limb, balance

5. How are vestigial structures an example of evidence of evolution?

Vestigial organs are often homologous to organs that are useful in other species. The vestigial tailbone in humans is homologous to the functional tail of other primates. Thus vestigial structures can be viewed as evidence for evolution: organisms having vestigial structures probably share a common ancestry with organisms in with organisms in which the homologous structure is functional.

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