The field of biology is a diverse one that includes the study of organisms from the small and simple to the large and complex. From biological molecules to biomes, the one theme that remains consistent is evolution. All species of living organisms are descended from a common ancestor. Although it may seem that living things today stay much the same, this is not the case. Evolution is actually an ongoing process. Additionally, new species are discovered regularly. For example, scientists have used a method called fluorescent in situ hybridization, which uses fluorescent probes to locate specific genes on chromosomes, to discover a green sea slug that can perform photosynthesis just like a plant.1 The slug obtains genes related to photosynthesis from the algae it eats through a process called horizontal gene transfer. In this process, genes can be transferred directly from one cell to another. The algal genes code for products that repair and maintain chloroplasts eaten by the slug. You can read more about it at this website.
The ongoing process of evolution includes the repeated formation of new species (speciation), changes within species (anagenesis), and death of species (extinction). Patterns in shared morphological and biochemical traits, including shared DNA sequences, can be used in constructing a diagram that illustrates the biodiversity, taxonomic links, and evolutionary history of extinct and extant living things. Such diagrams are commonly called “The Tree of Life.”
You may wish to share a tree of life diagram with students and use the diagram alongside facts about the rates of extinction (historically and currently) and species estimates versus species documentation to guide a discussion about evidence for evolution as an ongoing process. Ask students to discuss where in their daily lives they are aware of evidence of speciation, anagenesis, and extinction. Through discussion, elicit from students the importance of considering scale (both temporal and physical) when considering evidence of evolutionary change. Ideas and thoughts shared during this discussion may prove to be helpful reference points when students read about misconceptions of evolution later in the chapter.
- 1Biol. Bull. 227: 300–312. (December 2014)