- Evolution involves heritable changes in populations over time, which arise from mutations in DNA.
- Since DNA encodes proteins, evolutionary changes are recorded in:
- Base sequences of DNA and RNA
- Amino acid sequences of proteins
- By comparing these sequences between species, scientists can infer how closely related they are and reconstruct their evolutionary history.
By comparing base sequences in DNA and RNA or amino acid sequences in proteins, scientists can trace evolutionary relationships and confirm that all living organisms are connected through common descent.
DNA Sequence Comparisons
- DNA sequencing allows scientists to compare the order of nucleotides (A, T, C, G) in specific genes.
- Closely related species (e.g., humans and chimpanzees) have very similar DNA sequences, while distantly related species (e.g., humans and fish) have more differences.
- Conserved genes (genes essential for survival, such as those involved in respiration) change very slowly and are especially useful for long-term comparisons.
- Humans and Chimpanzees: Share 98–99% of their DNA, reflecting a recent common ancestor (~4–6 million years ago).
- Humans and Fruit Flies: Share about 60% of their DNA, indicating a much older common ancestor.
DNA from extinct organisms can sometimes be sequenced from preserved remains (e.g., Neanderthal DNA), allowing comparisons with modern humans.
RNA Sequence Comparisons
- RNA, especially ribosomal RNA (rRNA), provides another line of molecular evidence.
- rRNA is highly conserved across all life, meaning its sequences change very slowly.
- Small differences in rRNA base sequences reveal deep evolutionary relationships, such as the separation of Bacteria, Archaea, and Eukaryotes.
- rRNA studies were the foundation of the three-domain classification system.
If asked why rRNA is widely used, mention that it is found in all species, evolves slowly, and provides a universal marker for ancestry.
