Evolution of longevity in primates

Abstract

Evolution of maximum lifespan potential ( MLP) and its possible relation to the evolution of extra-brain functions are investigated in the primates. MLP is related to a species' characteristic aging rate and is considered a basic biological property of an organism. MLP may be of more importance than realized in the past in determining the evolutionary success of a species. It is related to the postnatal development rate, the length of time general vigor is maintained, the length of reproductive period, generation time and the time available for learning and teaching behavior. Three other parameters are considered to be importantly related to MLP: MLP calorie consumption ( MCC), encephalization quotient ( EQ) and extra number of cortical neurons ( N c ). MCC is calculated as the product of MLP and specific metabolic rate ( SMR) and is considered to represent total “life-capacity” of an organism. It is of potential value in studying the biological mechanisms involved in the evolution of MLP. Brain function is estimated by the Jerison EQ and N c parameters. These parameters estimate the “extra” brain capacity involved in functions beyond normal body requirements. The rate of change in MLP and N c per unit time occurring during an ancestral-descendant sequence is used to estimate the biological complexity of the genetic processes which have evolved in governing the rate of expression of the general aging process and increasing brain function. The average rate of change of MLP during the emergence of the primates was analyzed by the difference between MLP in closely related living primate species and the evolutionary time of appearance of a common ancestor. MLP, SMR, MCC, EQ and N c were estimated from fossil cranial capacity and body weight measurements. The rate of change in these values was calculated according to the time of appearance of the fossil species. MLP and N c were found to increase together and reached their highest rate of increase approximately 200,000 years ago along the hominid ancestral-descendant sequence leading to modern man. The high rate of increase of these parameters suggests that few genetic changes were responsible. The general increase in MLP during the evolution of the primate species indicates that a corresponding general decrease in mutation rate may have occurred. The high levels of MLP, MCC, EQ and N c represented in the living primates, as compared to other mammals, are considered to represent a major characteristic determining their evolutionary success.