7.6 Evidence of Evolution
- Syllabus
- 2025
- Topic
- 7.6
- Level
- —
Learning objectives
7.6A—Describe the types of data that provide evidence for evolutionDescribe the types of data that provide evidence for evolution.• Evolution is supported by scientific evidence from many disciplines (geographical, geological, physical, biochemical, and mathematical data).7.6B—Explain how morphological, biochemical, and geological data provide evidence that organisms have changed over timeExplain how morphological, biochemical, and geological data provide evidence that organisms have changed over time.• Molecular, morphological, and genetic evidence from extant and extinct organisms adds to our understanding of evolution.- i. Fossils can be dated by a variety of methods. These include 1) the age of the r ocks where a fossil is found; 2) the rate of decay of isotopes including carbon-14; and 3) geographical data.- ii. Morphological homologies, including vestigial structur es, provide evidence of common ancestry.• A comparison of DNA nucleotide sequences and protein amino acid sequences provides evidence for evolution and common ancestry.
Five Complementary Sources of Evolutionary Evidence
Evolution is supported by scientific evidence from multiple disciplines. Each data type records a different feature of life or Earth history, and compatible patterns across disciplines strengthen the evolutionary explanation.
| Data type | Example of what is observed or measured | Evolutionary contribution |
|---|---|---|
| Geographical | Where organisms or fossils occur | Links distribution patterns to population history |
| Geological | Fossils, rock layers, and ages | Places biological forms in a time sequence |
| Physical | Organismal structures and measurable traits | Reveals structural similarities, differences, and change |
| Biochemical | DNA, proteins, and other molecular features | Reveals inherited molecular similarities and differences |
| Mathematical | Quantified patterns and statistical comparisons | Tests whether observed patterns fit or depart from stated expectations |
A geographical pattern alone may have several explanations. When it agrees with fossil chronology, structural homology, molecular similarity, and quantitative analysis, the combined evidence supports a more coherent history of descent and change.
Data are observations or measurements; common ancestry and evolutionary change are inferences supported by those data. One data type need not answer every evolutionary question.
How Fossils, Structures, and Molecules Reveal Evolution
Evidence from extant and extinct organisms supports evolution when dated or comparable features reveal a consistent pattern of biological change and inherited similarity over time.
| Evidence | Observation | Evolutionary reasoning |
|---|---|---|
| Fossils and geology | Fossils occur in rocks of different ages and places | Dating by rock age, isotope decay including carbon-14, and geographical context orders organisms through time |
| Morphological homology | Organisms share underlying structural patterns | Shared structures, including vestigial structures, support inheritance from common ancestors |
| DNA and protein sequences | Nucleotide or amino-acid sequences can be compared | Patterns of molecular similarity and difference support evolutionary relationships and common ancestry |
Fossil sequences document extinct as well as living forms, while homologies and molecular sequences connect those forms through shared features. Agreement among chronology, morphology, and molecules is stronger than relying on appearance alone.
A similar-looking feature is not automatically a homology, and greater molecular similarity is evidence of a closer relationship only when comparisons are made appropriately. Evidence supports an evolutionary model; it is not a claim that living species descended directly from other living species.