Primate Evolution
Life History Theory: Why bigger brains for Primate and How it came to be?
Introduction
Complex behaviors and intelligence are the trademark of the primate order and this has been attributed in part to relative large brain to body mass ratio (Reader and Laland, 2002). Defining intelligence, however, is a highly problematic issue; an operational definition used points to the primary component of intelligence to flexible problem solving and the ability to cope with any difficult situations (Jerison, 1973). Arriving at an agreement for the driving factors favoring primate intelligence is very difficult. Many theories have been posed as selective mechanisms for the trends toward increased intelligence in primate evolution. Some emphasize complex ecological pressures, mainly foraging strategies as the primary forces driving an evolutionary increases in cognitive abilities, and other suggest that increased social complexity favored the evolution of primate intelligence (Tomasello and Call, 1997). Across the animal kingdom, brain size increases with increasing body size, however, despite the common scaling principle, brain size to body weight ratios differ from one taxonomic group to another (Jerison, 1973; Gould, 1975). In primates, for example, the brains of apes are generally larger relative to body weight than the brains of monkeys, whereas the brains of monkeys are larger than those of prosimians (Jerison, 1973). Structural differences are also apparent. In chimpanzees, a larger proportion of the brain is devoted to neocortex than in monkeys, who in turn have proportionately more neocortex than prosimians (Martin, 1990; Passingham, 1982).
Despite the fact that it is metabolically costly, there has been increase in primate brain size (Harvey et al, 1987). What selective pressures have overcome these costs? When the question is applied to humans, answers typically refer to the adaptive advantages of technology – initially stone tools and language. But monkeys and
Introduction
Complex behaviors and intelligence are the trademark of the primate order and this has been attributed in part to relative large brain to body mass ratio (Reader and Laland, 2002). Defining intelligence, however, is a highly problematic issue; an operational definition used points to the primary component of intelligence to flexible problem solving and the ability to cope with any difficult situations (Jerison, 1973). Arriving at an agreement for the driving factors favoring primate intelligence is very difficult. Many theories have been posed as selective mechanisms for the trends toward increased intelligence in primate evolution. Some emphasize complex ecological pressures, mainly foraging strategies as the primary forces driving an evolutionary increases in cognitive abilities, and other suggest that increased social complexity favored the evolution of primate intelligence (Tomasello and Call, 1997). Across the animal kingdom, brain size increases with increasing body size, however, despite the common scaling principle, brain size to body weight ratios differ from one taxonomic group to another (Jerison, 1973; Gould, 1975). In primates, for example, the brains of apes are generally larger relative to body weight than the brains of monkeys, whereas the brains of monkeys are larger than those of prosimians (Jerison, 1973). Structural differences are also apparent. In chimpanzees, a larger proportion of the brain is devoted to neocortex than in monkeys, who in turn have proportionately more neocortex than prosimians (Martin, 1990; Passingham, 1982).
Despite the fact that it is metabolically costly, there has been increase in primate brain size (Harvey et al, 1987). What selective pressures have overcome these costs? When the question is applied to humans, answers typically refer to the adaptive advantages of technology – initially stone tools and language. But monkeys and