Evolution__3rd_Edition

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Macroevolution
Part five
Part 5 is about macroevolution. Macroevolutionary changes are large: the kinds of
events that can be studied in the fossil record, such as the origin of new organs, or
body plans, or of new higher taxa (that is, taxa above the species level). These
large-scale changes can be distinguished from “microevolution,” which refers to changes in
gene frequencies within a population. The conventional dividing line between macro- and
microevolution is at speciation, so that events below that level are microevolution and those
above it are macroevolution.
As said in the Preface to this book, the distinction between micro- and macroevolution
has traditionally been not only between the timescales of the events but also between
the methods used. Microevolution has been studied with genetic techniques, and has used
observation and experiment on the timescale of human lifetimes. Macroevolution has
been studied with fossil evidence, comparative morphology, and phylogenetic inference.
However, modern biology has seen a breaking down of the methodological distinction
as genetic techniques are being used to study large-scale, macroevolutionary questions.
It is always interesting when two completely independent methods can be used to study
the same question. We shall see a series of such cases in Part 5, as molecular and fossil
evidence have been used to study the time of evolutionary events and the significance
of mass extinctions.
Chapter 18 is a short history of life, from the origin of life to the origin of modern humans.
The chapter begins with an introduction to paleontology (paleontology is the science that
studies fossils). The history of life will lead us into an abstract question: is macroevolution
really microevolution extrapolated over a long timescale or does macroevolution take place
by different, though not incompatible, mechanisms from microevolution? This general question
will recur at several points in the chapters of Part 5. Chapters 19 and 20 are about two
emerging subdisciplines of evolutionary biology: evolutionary genomics and “evo-devo.”
Evolutionary genomics uses sequence data from whole or partial genomes to reconstruct
the evolution of genomes. In a way, it is the DNA equivalent of the morphological history we