Similarities Between Molecules and Genomes
Molecular Clocks
Arguably, some of the most significant evidence of evolution comes from examining the
molecules and DNA found in all organisms (Figure7.23). The field of molecular biology
did not emerge until the 1940s and has since confirmed and extended the conclusions about
evolution drawn from other forms of evidence. Molecular clocksare used in molecular
evolution to relate the time that two species diverged to the number of differences measured
between the species’ DNA sequences or protein amino acid sequences. These clocks are
sometimes called gene clocks or evolutionary clocks. The fewer the differences the less
time since the divergence of the species. For example, a chicken and a gorilla will have
more differences between their DNA and protein amino acid sequences then a gorilla and an
orangutan. Thisprovidesadditionalevidencethatthegorillaandorangutanareevolutionally
closer related than the gorilla and the chicken.
Molecular clocks, combined with other forms of evidence, such as evidence from the fos-
sil record, has provided considerable evidence to estimate how long ago various groups of
organisms diverged evolutionarily from one another.
Molecular Genetics
The development of molecular genetics has revealed the record of evolution left in the
genomes of all organisms (Figure7.24). It also provides new information about the re-
lationships among species and how evolution occurs.
Molecular genetics provides evidence of evolution such as:
- the same biochemical building blocks – such as amino acids and nucleotides - are
responsible for life in all organisms, from bacteria to plants and animals - DNA and RNA determines the development of all organisms
- thesimilaritiesanddifferencesbetweenthegenomes, thegenesequencesofeachspecies,
reveal patterns of evolution.
Lesson Summary
- Fossil evidence, depicted by the skeletal fragments, demonstrates evolutionary mile-
stones. - Fossils and the rocks they are embedded in provide evidence of how life and environ-
mental conditions have changed throughout Earth’s history. - The fossils and the order in which fossils appear is called the fossil record.