2: Introduction to Evolution

Evidence for Evolution

Universally shared features.

Hierarchical classification.

Geographic distribution.

Direct observation.

Fossil record.

Universally shared features

DNA, DNA replication, and the cell cycle are universal by across different domains of life.

The shared biochemistry within the genetic code is largely arbitrary.

Hierarchical classification

Groups within groups.

Explained by “descent with modification.”

Reflects shared ancestry.

Homology

Biological similarity due to common ancestry.

Embryonic similarity and molecular homology (homeobox genes).

Example: humans, cats, whales, and bats have the same bones in different shapes and sizes.

Analogy

Shared morphological trait that results from convergent evolution.

Example: fish and whales have fins; butterflies and birds have wings.

Geographic distribution

Geographic proximity, not ecological similarity, is the strongest predictor of relatedness.

Direct observation

Artificial selection — humans have bred a single species (dogs) to look very different; meanwhile, lemurs of different species look very similar.

HIV resistance — ritonavir kills off all drug-sensitive HIV, drug-resistant HIV survives and reproduces, and the virus evolves resistance.

Polyploidy

Occurs when two species, each with a specific number of X chromosomes, are crossbred to create a hybrid with both sets (two homologous sets of chromosomes).

Fossil record

Continuous evolutionary change.

Groups that have diverged more recently appear later in the record.