Engage: Evolution of Cells?
Evolution can be defined as "change over time." But does change over time really mean evolution? How would you define it? Download the resource document in "Related Items" below to record your definition of evolution as well as data from this resource so you can determine for yourself whether or not there is evidence for evolution.
To get started, play Cell Phone Evolution in this first activity.
Now that you've sequenced the cell phones in chronological order, would you consider the changes in cell phones over time to truly represent the concept of evolution? What evidence would you look for to determine if real cells have evolved? Start by reading the section below, which considers a theory of cell evolution.
You may have heard of the endosymbiotic theory. It's based on evidence that suggests eukaryotic cells evolved from larger prokaryotes internalizing smaller prokaryotes and forming symbiotic relationships. Because they have their own DNA and share similar characteristics with today's eubacteria, both mitochondria and chloroplasts are believed to have come from those smaller bacterial ancestors.
Click the cell image to open a link to access additional information about endosymbiosis and evolution. The link opens in a new window. Close the window when you are finished reading about the endosymbiont theory to return to the resource.
Explore/Explain 1: Are Cells Evolving Now?
When Charles Darwin was thinking about how to express his thoughts about species changing over time, he used the phrase "descent with modification" and sketched his ideas out on a page in his journal. Notice the number 1 circled at the bottom of the sketch. What do you think that means? What message was he trying to get across with the connected lines that branch? What about the labels of A, B, C, and D?
This image is in the public domain.
Does his sketch fit your ideas of evolution? Could you recognize evolution in a modern-day example?
Read through the cards below. They tell the story of how MRSA, a methicillin-resistant strain of Staphylococcus aureus, developed. The story won't make sense, though, until you arrange the cards in the appropriate sequence from bottom to top on the timeline.
Is Staphylococcus aureus diverging into a new species? How can you tell when evolution is taking place? What evidence should you look for? Click the image below for additional information about antibiotic-resistant bacteria. The link opens in a new window. When you have finished reading the page and watching the video, simply close the window to return to the resource.
This image is in the public domain courtesy of the CDC and Matthew J. Arduino, DRPH. Photo credit: Janice Haney Carr. Image # 11157 downloaded from //phil.cdc.gov/phil/details.asp.
Other populations of organisms, like bacteria, are also affected by environmental pressures. The organisms that survive or thrive under those pressures reproduce to pass their successful traits to the next generation. Scientists study fossils, compare genomes, and analyze relationship patterns of organisms to their environment and to one another to see if there is additional evidence for evolution. In the next section, you get to be a paleobotanist examining fossils for evidence of environmental pressures on plants.
Explore/Explain 2: The Fossil Record
Scientists examine and analyze fossils for various types of information, including evidence for evolution. Fossils alone may not provide a complete picture, but often patterns are observed that lead scientists to ask questions that, in turn, provide avenues for further research.
One such question might be "Does the environment provide selection pressure that determines which traits of a population contribute to survival and therefore to reproductive success?" Click the image of the fossilized leaf to investigate evidence of population success due to environmental change. You will need a calculator in order to analyze the data.
Note - Click the image to open the link in a new window. When you have completed the investigation, simply close the window to return to this site.
Humans, like plants, have a fossil record, too. Do fossils of human species provide information about evolutionary change? You decide!
Click the image above to view a video about research on the human record.
Note - Clicking the image a new window. When you have finished watching the video, simply close the window to return to this site.
Explore/Explain 3: Putting Evolution on the Map!
From left to right:
The three photos pictured here are in the public domain courtesy of CDC and downloaded from //phil.cdc.gov.
Could having the trait for sickle cell be an advantage in the game of survival of the fittest? Let's use the maps and information below to help answer the question.
Things you should know before you begin:
- Malaria is a disease caused by a parasite transferred into humans by the Anopheles mosquito. Part of its life cycle takes place in blood.
- Anopheles mosquitoes are prevalent in warm, moist environments.
- Sickle cell is a blood disorder that causes red blood cells to become misshapen.
- Sickle cell is an inherited trait that represents a mutation where a single nucleotide base change, known as a point mutation, changes the genetic code for hemoglobin in red blood cells.
- People who are heterozygous (Tt) for sickle cell are carriers of the trait but don't have the physical issues that a homozygous recessive (tt) person does.
- People who are carriers of the sickle cell trait are resistant to malaria.
For more information about malaria, mosquitoes, or sickle cell, click on the images above.
Mapping it Out
Is having the sickle cell trait an advantage in areas where malaria is prevalent? First analyze the areas on the map where malaria is prevalent, and then drag the smaller map representing sickle cell frequencies on top of it. Analyze the data and form your own conclusion about mutations as evidence for successful evolution.
Biogeography is a scientific field often used to study patterns of disease associated with different cultures, migration outcomes, and relationships between living organisms and their environments. For an interesting article about a genetic disease prevalent in populations along the Silk Road, click "Related Items" below.
Simply put, homologies are similarities. Homologies in organisms could mean similarities in bone structure, DNA sequences, or anatomical structures. Scientists believe that homologies indicate evidence for evolution.
Image courtesy of the University of California Museum of Paleontology's Understanding Evolution (//evolution.berkeley.edu).
Click the image to analyze data scientists have gathered to see if you agree that homologies are evidence of evolution. Once you are on the website, click through the four screens that focus on homologies. Use the questions below to guide your analysis of the data.
- Which examples of anatomical homologies provide evidence of evolution? Explain your reasoning.
- What do a hummingbird and whale have in common? Is this evidence for evolution? Explain your reasoning.
- Why do scientists hypothesize that today's snakes have an ancestor with legs? Is this evidence for evolution? Explain your reasoning.
- Are there homologies in cells and genes? Do these homologies provide evidence for evolution? Explain your reasoning.
Click "TEKS B(7)(A) Data Sheet" to download and/or print the document in order to record your observations and justifications as you research homologies.
Now that you've had a chance to look at the evidence, it's time to see what you remember. Take the self-check quiz below to match the areas of evolutionary study with the evidence cited by scientists.