Evolution of Longevity in Ungulates and Carnivores

Abstract

Evolution of maximum lifespan potential (MLP) and its possible relation to the evolution of extra-brain functions are investigated for the ungulates and carnivores. MLP defines a species’ characteristic aging rate and is considered a basic biological property of an organism. It is related to postnatal developmental rate, length of time general vigor is maintained, length of reproductive period, generation time and the time available for learning behavior. In addition to MLP, two other parameters were studied: MLP calorie consumption (MCC) and the Jerison encephalization quotient (EQ). MCC, the product of MLP and specific metabolic rate (SMR), is considered to represent total ‘life-capacity’ of an organism, and EQ the degree of brain development beyond that required for normal body functions. MLP, SMR and MCC were calculated from brain and body weight estimates of fossil and living species for 59 ungulates and 32 carnivores. MLP and MCC were compared to the EQ values previously calculated for these species by Jerison. Mammalian species of the Mesozoic era have low MLP, MCC and EQ values, and those remaining in a Mesozoic-like niche have shown little change over the past 150 million years. However, MLP, MCC and EQ do show a progressive increase along the ancestral-descendant sequence of the horse and camelid over the past 50 million years. Analysis of other ungulates and carnivore species indicates that MLP and MCC have progressively increased on the average, accompanied by a substantial increase in dispersion. Species along an ancestral-descendant sequence known to become extinct (archaic) show little or no increase in these parameters. These results are similar to those reported by Jerison for the EQ of these species and suggest that the co-evolution of MLP, MCC and EQ involved mutually beneficial properties. Increase in MLP may reflect a progressive decrease in mutation rate; and the rapid rate of increase in MLP, MCC and EQ suggests that simple genetic changes (probably of a regulatory nature) are involved. Similar findings for primate species suggest that evolution of longer lifespan, increased metabolic efficiency and increased extra-brain functions represent major characteristics describing the evolutionary success of the mammalian species.