Phenomenon
We see that life on this planet reflects an amazing amount of diversity, and yet all life has certain characteristics in common.
Question
How did there come to be so many different kinds of living things on Earth, and why do they all have so much in common?
(But reference YOUR question generated at the beginning of the year in Unity and Diversity Part 1.)
Model Ideas
In coming to the close of the year and returning to our Big Question, we already have many (if not all) of the ideas we need to explain the patterns of unity and diversity of life we noted during our launch into MBER-Bio. The ideas below represent extensions of ideas we already developed in Natural Selection. The difference here is that the time scale--as we began to explore in the last unit, Speciation--is huge. The materials for this unit therefore frame the "model-building" as a summary and extension of previous ideas we've already figured out. Therefore, you will not see prompts to offer new model ideas as you have in past units. We try to provide guidance where appropriate, but in truth, we expect that your students should be the guides. If they feel like they can answer the question using ideas from Natural Selection, follow their lead. If they feel there is a new model to capture, follow their lead. The slide deck provides the content needed for these conversations. As you engage in this final series of lessons, keep in mind the central sensemaking goal: we want to come to some kind of satisfying moment where we (as a class) have figured out an explanation for the patterns we engaged with in Unity and Diversity Part 1--that all life has some things in common and that we also see incredible diversity where organisms seemingly "fit" their environments. We have the ideas to explain this phenomenon, so let's get to work!
Summarized Ideas (as presented in the PowerPoint):
- There are many different species on Earth. They all have a great deal in common, because they all evolved by Natural Selection from a common ancestor.
- But they are also very different because they were each shaped by their own particular environment – and there are an almost infinite variety of environments on Earth. Darwin called the process by which Earth was populated by new species, each adapted to its own environment, “Descent with Modification”.
Overview
Transition in: Now that we understand how species arise, we have an explanation for the diversity portion of our Big Driving Question, and perhaps even some ideas about unity. We are now ready to formally address our Big Driving Question about Unity and Diversity in the final unit.
This final unit is really about “pulling the pieces together”. Explanatory ideas to answer the Big Question for the year may vary, but two new ideas will be introduced explicitly to explain the Unity and Diversity of life on our planet. Student understanding, however, will be grounded in the models and model ideas that have generated previously in the curricular year.
We tackle the Big Question in two pieces, first addressing the diversity aspect, “How did there come to be so many different kinds/species of living things?” Building directly on the last model we generated, our Model for Speciation, we revisit (once again) our Galapagos finches. But instead of asking how 17+ species came into existence, we shift our lens a bit asking WHY there are 17+ species of finches? Isn’t one finch good enough? We engage in an activity looking at the variation in diet, habitat and geography among six members of the ground finch group endemic to the Galapagos. We recognize that the variation in the environment (and how each finch species engages their environment) plays a big part in generating and supporting this biodiversity. We of course directly leverage our Model for Change Over Time / Natural Selection to remind ourselves that the “how” question and “why” question are intertwined.
We then turn to the unity aspect of our question, “Why does all life share certain characteristics in common?” Leveraging our exploration of the finch lineage’s common ancestor, we “zoom out” on the tree of life infer that all life has a common ancestor. This is the core idea we leverage to explain unity.
Finally, we offer Darwin's idea of "descent with modification" as a means to describe how that unity became diverse--variations on a theme in some sense--and offer three pieces of evidence scientists use to support this concept. We end with a celebratory recognition of all we have accomplished. (There is an optional "model-integration" activity that can be used as a means to review connections among our various models and a core model, Natural Selection. The activity also provides a great opportunity for students to prepare for any assessment/final exam.)
Advanced Planning
Please be certain that you have your previous models posted in your classroom (or easily available to students in some other manner).
You will also need to prepare the Ground Finches Cards and read over the Teacher Guide for that activity. See materials for further details.
1. We once again return to the Big Driving Question (from Unity and Diversity Part 1), now convinced we are ready to tackle it. We leverage our recent Model for Speciation as a means to explain HOW diversity arose, but we also find we need to explore WHY: Why are there so many different kinds of species?
We recognized that we understand how new species arise, and yet we still have a questions about the diversity piece of our Big Question: why so many species?
2. We dive into the “why” question through an exploration of the distribution and ecology of the six species of ground finches from the Galapagos islands. In looking over the data, we recognize that each species has changed over time to fit its particular environment and habits.
We generated our first model idea. Diversity arises through natural selection and speciation, but it is truly the diversity of our planet’s environments that allows for so much diversity. Each species has been shaped by natural selection to its particular environment or “niche”.
3. We return to our Big Driving Question to explore our question about unity. With all of the diversity we’ve now explained, why do we think all life has certain traits in common?
We recognized that all life has a common ancestor, and that common ancestry explains our observation that all life has certain characteristics.
4. We explore Darwin’s concept of “descent with modification” as a means to understand the two patterns—unity and diversity—together. We review key pieces of evidence for the concept, and use the idea to add to or revise our model.
We’ve elaborated on our understanding of how unity and diversity are related through descent with modification and we’ve revised and finalized our model.
5. Optional Learning Segment.
We return to a handful of slides from Unity and Diversity Part 1 to recognize and celebrate the understanding we have built together over the year. You can decide how you would like to have a moment of recognition. For many classes, the last moment of the previous segment will be enough.
We’ve realized that we made real progress in developing an understanding of the big patterns in biology, the big patterns of life on this planet.
6. Optional Activity: Model Integration
We explore the connections between our central ideas from Natural Selection and many of the other models we’ve built during the year. In “mapping models to models”, we highlight and reinforce connections among the ideas and review what we’ve learned.
We reinforced our understanding of the connections between models and perhaps managed to do some preparation for end-of-year exams.
Download Resources
| Attachment | Size |
|---|---|
| All MBER-Bio Unity and Diversity Part 2 Materials (Download) | 21.07 MB |