Common Descent

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Lab 2: Common Descent

General Instructions


Be sure to read the general instructions from the Lessons portion of the class prior to completing this packet.


Remember, you are to upload this packet with your quiz for the week!



Key concepts from this lab to remember:

  • Species descend from other species. Even distantly related species, like humans and sponges, can trace their shared ancestry back to a common ancestor.
  • Evidence for common descent includes the fossil record and anatomical, genetic, and developmental homologies among organisms.
  • The fossil record provides a history of life on Earth. It includes fossils with features that are intermediate, or transitional, between those of major groups of animals.
  • When a series of transitional fossils are viewed together, they reveal the gradual sequence of change connecting one major group to another.
  • An organism’s DNA codes for proteins that result in an organism’s visible traits.
  • Scientists infer function and behavior from anatomical structures.
  • Natural selection is the process by which heritable traits that confer a survival and/or reproductive advantage to individuals that possess them increase in frequency within a population over generations.


Specific Lab Instructions

Part 1: Explore Your Inner Animals

Go to:Explore Your Inner Animal from HHMI Biointeractive


Notice the highlighted sections on the human:



When you click on each highlighted area, a list of animals with homologous structures appear on the right. For this portion of the lab, you must click on each animal to view the connection to humans.


When complete with one view, rotate the human, click on another anatomical structure in humans,explore the connection to other animals.



Repeat this click and rotate process until you have viewed all of the highlighted structures and associated animal connections.



Answer the following questions based on your explorations of the body:


The Eyes:

1.How do we know that Kramer cannot see the same way most humans can?

     Kramer is red/green color blind and only have 2 OPSIN and most humans have 3.


  1. Describe what the “clues” scientists found in our DNA suggest about how humans might have evolved enhanced color vision.
     Our ancestor only had 2 OPSIN and we evolved to 3 OPSIN through mutation



The Legs:

  1. Describe the anatomical features of Ardi’s upper and lower pelvis and what they indicate about how Ardi may have moved.
     The upper portion resembles human but the lower portion was designed to climb.


  1. Does Ardi’s foot structure support or refute the idea that Ardi was a creature in transition? Explain your answer.
     The foot structure was for walking and climb but the designed indicated that they didn’t walk as good as modern humans



The Ears:

  1. What are three bones are found in the middle ears of all mammals, including humans?
     Malleus, Incus, Stapes


  1. Explain why mammalian ears are more sensitive to sound than those of reptiles.
     We have all three bones that makes us better due to the fact reptiles only have one bone (Stapes).


The Hands:

  1. Describe what features the modern human hand shares with the hand of the 50 million year-old primate, Notharctus.


     Northarctus has thumbs that rotate inward, long fingers and finger nails not claws.



  1. How did Darwin explain common patterns like these among vertebrates?
     Through natural selection due to their environment.


The Brain:

     500 million years ago
  1. How many million years ago did the “first roots” of our modern human brain arise?


  1. Describe how our human brain is similar to the brains of other primates.
     We have a cord that goes down our body and connects to our brain/skull.


The Back:

  1. What is another word for coccyx?


  1. What is one of the easiest ways to distinguish an ape from a monkey?
     Apes do not have tails and monkeys do.


The Teeth:

  1. What is an advantage of chewing food over swallowing it whole?
     Better digestion system which gives them more energy to chase prey


  1. Why are teeth so important to paleontologists?
     It tells them how the animal live and what they ate.




Part 2:

Go toGreat Transitions Interactive: Exploring Transitional Fossils from HHMI Biointeractive


Review the Introduction, and then Begin the Simulation



A Quick Guide will pop up first – make sure to read it so you know how to navigate the page!



Excavate each fossil in the rock layers. When all are excavated, click each to view more details. Then, click on the underlined column headings for more information on structures. Finally, answer the questions below.



  1. Tetrapods first appeared in the fossil record how many million years ago?

365 million

  1. Of the fossils presented, which was the first to be discovered by humans? IchthyosteyaIn what year?1932 
From fish, their fossils were found in rocks over 500 million years ago
  1. What did Charles Darwin predict that tetrapods evolved from? What observations led him to that hypothesis?


  1. What is the purpose of gills in fish?
Use to breathe in water



  1. Why did lungs develop in fish, leading to tetrapods?
Living in water poor in oxygen


  1. What do we mean in biology when we use the term homology?
Shared ancestry traits


  1. To what are fins homologous?


  1. Explain the importance of a sturdy ribcage in tetrapods.
Supports the body on land and prevents lungs from collapsing.


  1. Why do many of the transitional fossils between fish and tetrapods have flat heads?
Shoulder bone separated from the neck to live in shallow waters or on land



  1. Why is Tiktaalik such an important transitional fossil?
First species in fossil record to show evidence of transitional neck


  1. What is the only surviving member of the lobe finned fish?



Part 1 Adapted from:

Click and Learn “Explore Your Inner Animals” (2016). HHMI Biointeractive Teaching Materials.


Part 2 Adapted from:

Click and Learn “Great Transitions Interactive” (2017). HHMI Biointeractive Teaching Materials.


Last Updated on June 16, 2019 by EssayPro