Academic journal article Science Scope

Using Local Street Trees to Teach the Concept of Common Ancestry

Academic journal article Science Scope

Using Local Street Trees to Teach the Concept of Common Ancestry

Article excerpt

Most students do not notice the trees that they walk past, much less appreciate them as examples of the biodiversity that surrounds them. Trees that line sidewalks and fill public spaces provide a local context for student learning about biodiversity and evolution, even in an urban setting. This article describes a portion of a newly developed curriculum that encourages middle school students to explore the trees around them and develop an understanding of their evolutionary history. The curriculum, piloted by 15 New York City middle school teachers, is appropriate for use in an urban or a nonurban context. The full curriculum is freely available online (see Resource).

Curriculum goals

The goal of this curriculum is to help middle school students learn about the street trees they see daily and use their new knowledge of local trees to further their understanding of the common ancestry of all trees. Although students walk past trees and other plants every day, many cannot identify these plants. Implementing this curriculum helps students develop observation skills to:

* notice and identify local trees;

* group local trees based on relatedness;

* understand that related taxa in a group are similar because they share characteristics resulting from common ancestry, or shared evolutionary history;

* understand evolutionary constraint, meaning that organisms cannot change characteristics based simply on need;

* learn that most street trees have flowers and fruits, even if students do not notice them; and

* learn that flowers become fruits and that flowers and fruits are reproductive structures for fertilization and seed dispersal.

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To mirror the life cycle of local trees, the curriculum is divided into a 14-lesson fall unit and an eight-lesson spring unit. The fall curriculum focuses on identification, grouping, common ancestry, and fruits. The spring curriculum focuses on grouping, common ancestry, and flowers.

The curriculum moves students from being everyday observers of local trees to observing trees scientifically. When they finish the curriculum, students are able to recognize variations among tree species, such as leaf shape and arrangement and different fruit and flower structures. During curricular activities, students use their new observation skills to collect data to use as evidence to identify and group trees by relatedness. These curricular activities help students learn what it means to be related, from an evolutionary perspective. Students learn that related trees are similar because they share traits inherited over generations from a common ancestor that lived long ago.

Framing biodiversity in the patterns of evolution is an important concept highlighted in the Next Generation Science Standards (NGSS) (NGSS Lead States 2013). Charles Darwin contributed two major themes to our understanding of evolution: the unity of life and natural selection, a mechanism for the evolution of life's diversity. An almost exclusive emphasis on natural selection has led most students to have only a limited understanding of the relatedness of all life (Catley 2006). To counteract this deficiency, the NGSS incorporate a new emphasis on the unity of life through common ancestry (see p. 26 for full standards alignment). This curriculum is an attempt to take some of the basic themes of common ancestry, relatedness, and shared history to the middle grades, a place where these principles are largely absent (Catley 2006).

Curricular activities

To implement the curriculum's activities that focus on student understanding of naming, grouping, and common ancestry, students use a paper field guide or a freely available iPad app called Leafsnap, which is an electronic field guide that uses pattern-recognition software (Figure 1). Like paper field guides, Leafsnap includes images of tree leaves, leaf arrangements, bark, fruits, and flowers. …

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