Hemoglobin: Structure, Function and Oxygen Transport in Mammals - Integrating Epidemiological, Genomic, Environmental, Evolutionary and Recent Morphological Findings

Hemoglobin represents one of the most extensively studied proteins in mammalian biology, yet recent advances in genomics, environmental physiology, and evolutionary biology continue to reveal new insights into its structure, function, and adaptive significance. This comprehensive review synthesises current understanding of hemoglobin morphology and function in mammals, integrating epidemiological data, genomic analyses, environmental adaptations, and evolutionary perspectives with the most recent findings in hemoglobin research. The tetrameric structure of mammalian hemoglobin, comprising two α-globin and two β-globin subunits, each containing a heme prosthetic group, facilitates cooperative oxygen binding essential for efficient oxygen transport from respiratory surfaces to metabolically active tissues (Safo & Bruno, 2020). Recent genomic studies across 97 vertebrate species have revealed that purifying selection has been the dominant evolutionary force shaping hemoglobin genes, with dN/dS ratios ranging from 0.057 in teleosts to 0.359 in reptiles (Mao et al., 2023). Environmental adaptations to altitude, temperature, and pH demonstrate remarkable plasticity in hemoglobin function, with high-altitude mammals exhibiting modified oxygen affinity through both genetic and physiological mechanisms (Storz, 2021). Epidemiological studies of hemoglobin variants reveal significant populationlevel variations that reflect both adaptive responses to environmental pressures and pathological conditions. The integration of structural biology, functional genomics, and environmental physiology provides unprecedented insights into the mechanisms underlying hemoglobin's role in mammalian oxygen transport and its evolutionary optimisation across diverse ecological niches.