Page 129 - Introduction to Paleobiology and The Fossil Record

Chapter 5

Macroevolution and the tree of life

Key points

• Evolution by natural selection is a core scientific model that was set out by Darwin,

and has been confirmed again and again in every branch of biology.
• Creationist attempts to promote their religious beliefs, such as “intelligent design” or

belief in a flat Earth, are not testable and therefore are not science.
• Speciation often occurs by the establishment of a barrier, and the isolation of part of a
previously interbreeding population.
• Evolution takes place both within species lineages (phyletic gradualism) and at the time

of speciation (punctuated equilibrium); the first model is commonest among asexual
microorganisms that live in the open oceans, and the latter in sexual organisms that are
subject to environmental and geographic barriers.
• There may be a process of species selection, acting independently of natural selection,
but examples have been hard to fi nd.
• The evolution of life may be represented by a single branching phylogenetic tree.
• Cladistics is a method of reconstructing phylogeny based on the identifi cation of shared
derived characters (homologies).
• Molecular sequencing provides additional evidence for reconstructing and dating the
tree of life.
• DNA has been extracted from fossils such as woolly mammoths, but not from truly
ancient fossils.

Probably all organic beings which have ever lived on this earth have descended from
some one primordial form, into which life was first breathed . . . There is grandeur in

this view of life . . . that, whilst this planet has gone cycling on according to the fi xed
law of gravity, from so simple a beginning endless forms most beautiful and most
wonderful have been, and are being evolved.

Charles Darwin (1859) On the Origin of Species