Explain how the scientific theory of evolution is supported by the fossil record, comparative anatomy, comparative embryology, biogeography, molecular biology, and observed evolutionary change (NGSSS SC.912.L.15.1; Reporting Category 2, Classification, Heredity, and Evolution).

What this topic is asking

The NGSSS benchmark SC.912.L.15.1 asks you to explain how the theory of evolution is supported by several lines of evidence: the fossil record, comparative anatomy, comparative embryology, biogeography, molecular biology, and observed evolutionary change. For the Florida Biology 1 EOC you need to know what each line shows and why it points to common ancestry. Items usually present one type of evidence (often homologous structures or DNA similarity) and ask what it demonstrates.

Evolution is a well-supported theory

The strength of evolution comes from the fact that independent lines of evidence all point the same way. The EOC expects you to recognize each line.

The fossil record

Fossils are the preserved remains or traces of organisms from the past. The fossil record shows that:

• Life has changed over time: older rock layers contain simpler or different organisms than newer layers.
• Transitional forms exist, fossils with features of two groups (such as fossils linking fish and amphibians, or showing the evolution of the whale from land mammals).

The order of fossils in rock layers matches the expected sequence of evolutionary change.

Comparative anatomy: homologous structures

(Contrast these with analogous structures, which do the same job but have different underlying anatomy, like a bird's wing and an insect's wing, and do not indicate close relationship. Vestigial structures, reduced parts with little or no function, such as the human appendix, are also evidence of evolution from ancestors that used them.)

Comparative embryology and biogeography

• Comparative embryology. Related species show similar patterns in early development. For example, vertebrate embryos look very alike in early stages (with similar features), reflecting shared ancestry.
• Biogeography. The geographic distribution of species reflects their evolutionary history. Species on isolated islands often resemble nearby mainland species (their ancestors), having evolved after becoming isolated. Darwin's observations of finches on the Galapagos Islands are a famous example.

Molecular biology: DNA and proteins

This is often considered the strongest modern evidence, and it is also what guides classification.

Observed evolutionary change

Evolution is not only in the past: it is observed happening now. Examples include antibiotic resistance in bacteria (resistant bacteria survive and multiply when antibiotics are used) and pesticide resistance in insects. These show natural selection and evolutionary change within human-observable timeframes.

Try this

Q1. State what homologous structures are and what they provide evidence for. [2]

• Cue. Body parts with the same underlying anatomy but different functions, inherited from a common ancestor; they are evidence of shared ancestry (evolution).

Q2. Explain how DNA similarity between two species indicates their evolutionary relationship. [2]

• Cue. The more similar their DNA, the more recently they shared a common ancestor, because related species have had less time to accumulate genetic differences.