The scale independence of evolution.

In this paper, I argue that the ultimate causes of morphological, and hence developmental, evolution are scale independent. In other words, micro- and macroevolutionary patterns show fundamental similarities and therefore are most simply explained as being caused by the same kinds of evolutionary forces. I begin by examining the evolution of single lineages and argue that dynamics of adaptive evolution are the same for bacteria in test-tube evolution experiments and fossil lineages. Similarly, I argue that the essential features of adaptive radiations large and small can be attributed to conventional forces such as mutation and diversifying natural selection due to competition. I then address recent claims that the molecular features of metazoan development are the result of clade-level selection for evolvability, and suggest that these features can be more easily explained by conventional individual-level selection for the suppression of deleterious pleiotropic effects. Finally, I ask what must be known if we are to understand the ultimate causes of molecular and developmental diversity.