3 Some principles that underpin evolutionary change
Section 3 consists of several subsections of quite concentrated reading, describing some fundamental principles of biology. It shows how biologists need to use language very carefully and how commonly used words can take on a new and precise meaning. You will gain maximum benefit if you can read the whole of Section 3 in a single session, to follow the 'thread' that runs through it. In fact, you may find it beneficial to read this section through more than once, to satisfy yourself that you have a good understanding of the topic.
For the next part of the course, I'll be adopting a different and broader perspective. I want to introduce some underlying principles that you need to understand if the processes of evolutionary change discussed throughout this series of units are to make sense to you. LoM Chapter 3 and the TV programme provide a wealth of examples that illustrate my points. When I return to the main storyline again (in Section 4) the examples explored there are all the more meaningful if we follow an evolutionary perspective.
What you have been watching is the situation as it is today. However, the programme talks of 'an arms race' between plants and their predators and DA refers to plants 'strengthening the coats of their seeds', whilst mammals 'responded by developing powerful armour-piercing tools' [p. 61]. Whilst these shorthand ways of talking about evolution are commonplace, they are not accurate reflections of scientific understanding of the processes that underlie evolutionary changes. Scientists have to be careful that they express their understanding unambiguously. So in this section, I will show that scientists do not believe that these adaptations arise as a response to a challenging situation and explain why such a view of purposive change cannot be supported by scientific evidence or reasoning. I must first define adaptation and then consider the factors that could account for the evolution of protective seed coats and chisel-like teeth.