Based on amino acid differences in hemoglobin, which organism is most closely related to humans?

The organism that is most closely related to humans based on amino acid differences in hemoglobin is the chimpanzee. Studies of molecular biology, particularly those involving the sequence comparison of hemoglobin and other proteins, have shown that the genetic and evolutionary relationship between humans and chimpanzees is very close.

Both species share a common ancestor, and their hemoglobin—the protein responsible for oxygen transport—has only a few amino acid differences. This stark similarity reflects a relatively recent divergence in evolutionary terms, making them more genetically similar compared to the other organisms listed. In contrast, while macaques, dolphins, and dogs also share common ancestors with humans, the degree of amino acid differences in their hemoglobin reflects a more distant relationship.