Evidence supporting evolution includes similarities in DNA, RNA and amino acid sequences, changes produced by selective breeding, and comparisons of homologous and analogous structures. These lines of evidence are assessed at both SL and HL in IB Biology subtopic A4.1.
How the Evidence Supports Evolution
Evolution is a change in the heritable characteristics of a population. Multiple independent forms of evidence support the conclusion that populations change over generations and that different species share common ancestors.
Evidence | How it supports evolution |
|---|---|
DNA and RNA base sequences | Species with more similar nucleotide sequences are inferred to share a more recent common ancestor. Differences accumulate through mutation after populations diverge. |
Amino acid sequences | Similarities in the primary structure of proteins indicate that the genes coding for those proteins were inherited from a common ancestor. Greater sequence similarity generally indicates a closer evolutionary relationship. |
Selective breeding | Humans select individuals with desired heritable traits to reproduce. The rapid development of distinct domesticated breeds and crop varieties demonstrates that selection can change populations over generations. |
Homologous structures | Structures such as the pentadactyl limbs of humans, whales and bats have the same underlying structural plan but different functions. This supports divergent evolution from a common ancestor. |
Analogous structures | Structures with similar functions but different evolutionary origins, such as bird and insect wings, result from convergent evolution under similar selection pressures. |
A common misconception is that organisms evolve because they “need” a particular trait. Evolution is not goal-directed: existing heritable variation is acted on by selection, so individuals with advantageous traits may leave more offspring.
Exam Technique
For an explain question, do not merely list evidence. State the observation and link it explicitly to evolution, for example, “similar amino acid sequences indicate inheritance from a common ancestor.” When comparing structures, distinguish clearly between homologous structures, which indicate common ancestry, and analogous structures, which indicate convergent evolution.
