Many of the changes in biological systems can be seen at multiple levels of organization. While feedback is often considered when studying metabolism or signaling within cells, it could also happen at the level of macroevolution. Some groups prosper and others decline based on the demands of the overall environment of the biological community. When some groups are particularly well suited to the habitat, they increase in a process like positive feedback in metabolism, but when the habitat changes so that they are not well adapted (as with anaerobes when oxygen increased in the atmosphere), they decline, similar to negative feedback shutting down some metabolic process.
Work Step by Step
Review the idea of feedback as covered in earlier chapters. Then try to match both positive and negative feedback with what is described in this chapter for the changes in the abundance of different animal groups over long periods of time.