How can comparisons of hemoglobin genes reveal evolutionary history?

Comparisons of hemoglobin genes reveal evolutionary history through the study of homology, which identifies features derived from a common ancestor. Because hemoglobin chains are modified descendants of a single ancestral sequence, their nucleotide and amino acid sequences provide a molecular record of evolutionary change.12

Researchers use two primary methods to reconstruct this history:

• Interspecies Comparison: By comparing the same hemoglobin chain (such as the $\alpha$ chain) across different species, scientists can measure the degree of divergence. This reflects the evolutionary distance between the organisms, as these chains have evolved independently since the lineages diverged.2
• Intraspecies Comparison: By comparing different hemoglobin chains within a single organism (such as the $\alpha$ and $\beta$ chains), researchers can trace the history of gene duplication events. These comparisons reveal how ancestral genes duplicated and subsequently evolved into distinct, specialized forms, such as those used in fetal versus adult hemoglobin.12

This molecular evidence, including the presence of non-functional pseudogenes, allows biologists to map the timeline of gene duplications and the phylogenetic relationships between species.12