Evidence for Evolution - Fossils & DNA
Biology: IB Diploma Higher Level, topic 3.2.1
The Evidence for Evolution by Natural Selection
The theory of evolution by natural selection has evidence from multiple scientific fields. Here we will go through geological, molecular, biochemical, and physical evidence.
Evidence from fossils
- Fossils are the remains or traces of ancient life.
- Fossils are found in rocks and have been preserved by natural processes.
- Fossils show the gradual changes in organisms over vast periods of time.
- They can help us to see physical similarities in organisms, but not all organisms leave a fossil behind when they die.
- This means there are big gaps in the fossil record that we have.
Dating fossils
- Three main techniques can be used to date fossils:
- Determining how old the rocks near to the fossil are. This can be done by looking at geological records or through techniques like stratigraphy, which dates rocks based on layering.
- Radiometric dating, which dates fossils based on the rate of decay of radioactive isotopes such as carbon-14.
- Geographical data. This can involve techniques like palaeomagnetism, which correlates changes in the Earth's magnetism to site age.
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Evidence from DNA
- Genomes of different species can be sequenced and compared to see how similar they are.
- Even distantly related organisms share a surprising amount of the same DNA, implying that organisms shared a common ancestor.
- The more similar the genomes are to each other, the more closely related they are; this often confirms what fossil evidence tells us.
- In eukaryotes, we can also sequence mitochondrial DNA, which has been used to examine human evolutionary relationships through the maternal line.
Molecular evidence
- Molecular evidence includes any evidence from biological molecules, including DNA, but also comparisons of RNA, amino acid sequences, and overall protein structure.
- Some proteins, like cytochrome c (used in respiration), are highly conserved across organisms. By looking at small changes in highly conserved proteins, we can work out relatedness of different taxa.
- The highly conserved nature of such proteins and processes provides evidence for common ancestry of organisms.
Test yourself on Evidence for Evolution - Fossils & DNA
Which of the following is NOT a form of molecular evidence for evolution?
Which of the following statements about evidence for evolution are true?