Go to the Protein Data Bank (PDB) site and view human fetal Hemoglobin and bar-headed goose Hemoglobin. You may have to download one of the 3-D viewing support tools. PDB is the single worldwide repository for the processing and distribution of 3-D biological macromolecular structure data.
Use the structure screen tools and your mouse to explore the inner working and structure of this complex compound.
What do you notice about the "active site" in both molecules?