SUMMARY. One of the key concepts in modern biology is metabolic theory, which links energy flows with genetic processes and evolutionary rates. Its key proposition — that metabolic rate determines mutation rate and evolutionary rate — remains largely intuitive. A solution to this problem is possible by switching to relative estimates. A promising approach is a comparative analysis of the transition-transversion bias of taxonomic groups with different metabolic rates. This is reflected in parameters such as body size, maturation rate, and fertility. The aim of this study is to establish a link between the scale of transition-transversion bias, paleontological age, average body size, life cycle period, and fecundity in placental mammals at the family level. There is a significant negative correlation between the magnitude of transition-transversion bias at the species and generic levels of divergence, paleontological age, body size, maturation rate, and lifespan, while a positive correlation exists with litter size. This pattern of correlations suggests that families with higher metabolic rates have higher rates of accumulation of transversion frequencies, indicating a higher level of mutational processes. The directionality of these correlations allows us to conceptualize placental mammals as a bipolar system, with families of different paleontological ages, alternative biological parameters, and distinct nucleotide substitution patterns at the poles. Strict evidence for the validity of a key proposition of metabolic theory and the justification for the «evolutionary rate ambiguity hypothesis». The study›s results complement the theory of r/K strategies, indicating that r-strategists are more metabolically active and have higher mutation rates.
Keywords: mammals, evolutionary rate, transition-transversion bias, metabolic theory, r/K-strategy theory, evolutionary speed hypothesis
