Primate Traits and Trends
There is not a distinct trait that describes a primate, or divides them apart from other animals. As an alternative, there are trends in differing suites, which emerged throughout the flow of primate evolution and characterise a general pattern. For example, primates greatly differ from each other in their locomotor systems and manual dexterity; however, we primates have greater mobility in our hands, feet and limbs compared to other animal groups. Similarly, there are differences amongst primate brain sizes comparative to body sizes, although we tend to have bigger brains than other mammals with comparable body sizes. The evolution and artefact of such traits can be tracked via fossil records each time skeletal or cranial material is accessible. For example, in the human ancestry, relative cranial capacity only started to become distinguishable two million years. There are plenty of assumptions regarding the selection pressures, which led to our enlarged brains comparative to other primates, and to those of other primates compared to most other animals.
The Notable Neocortex
Primate brains are larger, compared to their body size, than those of other animals, and human brains are even bigger still. However, it is not our whole brains that are so comparatively huge. It is a specific part, called the neocortex that is responsible for cognitive capabilities like reasoning and perception, which makes up 50-80 per cent of the entire brain's volume in primates. In insectivorous mammals (insect eaters), the neocortex is approximately the same size as the medulla - an original section of the brain that controls basic body functions like respiration and heart rate. In prosimians (Lemurs, galagos, lorises, and tarsiers), the neocortex is ten times greater than the medulla, in monkeys and apes, and it is 20-50 times greater, and in humans, the neocortex is a massive 105 times larger than the medulla.
In a comparative analysis of primate brains, primatologist investigated the many hypotheses that have been progressed to clarify why evolution may have led to expansions in the size of the neocortex (Dunbar, 1998). Generally, anatomical characteristics that separate primates from other animals and that have clear functional gains are accredited to ecological selection pressures linked with negotiations between the necessity to search food and mates in addition to dodging predators. Nevertheless, Dunbar (1998) discovered a strong correlation between the size of the neocortex and the size of primate social groups that directed him to develop "the social brain hypothesis".
Comparing the size of the neocortex to the rest of the brain gives a neocortex ratio; this can be contrasted amongst primates that are different from each other in body size, shape of development, and energetic prerequisites. Dunbar (1998) discovered three different, matching groups equivalent to the relationship between group sizes and neocortex ratio in the prosimians, monkeys and apes. Prosimians have the smallest neocortex ratio for their social group sizes, monkeys are midway, and apes have the biggest. Moreover, inside each of these grades, the primates with the biggest grooming networks were those with the consistently larges neocortex ratios. Contemporary studies conforms that neocortical volume gradually rises from lemurs, lories, and tarsiers, to New World monkeys, to Old World monkeys, and to hominoids. Nevertheless, the brain structures of New World monkeys with the biggest groups and most complicated social structures, like squirrel monkeys, capuchin monkeys, spider monkeys, and woolly monkeys, are amazingly alike to Old World monkeys (Clark et al, 2001).
Dunbar understood the size of grooming networks to be revealing of the number of individuals that primates can sustain as trustworthy supporters, who will help them during struggles against other individuals. However, neocortex size also convincingly and directly forecasts the extent to which primates take part in tactical deception - deliberate dishonest signalling used to deceive one another (Byrne & Corp, 2004). Otherwise, acts that seems to intentionally delude other individuals, and therefore might be better measured of what is known as Machiavellian intelligence - whereby individuals perceive the world through their own and others' perspectives, and adjust their behaviour to advance their own fitness interests (Byrne & Corp, 2004).
The significance of keeping allies and the use of tactical deception infer that rivalry was a key selective force in primate social and cognitive evolution. However, other primatologists hold a gentler viewpoint whereby the unique cognitive abilities of primates are based on expedience - opportunistic use of different tactics for one's own benefit (Barrett & Henzi, 2005). This involved the ability to estimate whether supportive or aggressive strategies are called for, and consequently modify one's behaviour.
Having a large neocortex might be equally important for cooperating as it is for competing. Indeed, mutual cooperation stimulates the rewards centres of the brain, which are located in the neocortex (Riling et al 2002). A large neocortex might provide critical advantages under a range of ecological condition too, including remembering where food occurs over a large home range and extracting foods, such as termites, from a mound of dirt.
Actually, the majority of mammals have fully developed brains by the time they are weaned, although much of primate brain development happens throughout the long socialization time between weaning and adulthood (Joffe, 1997). Therefore, primate sociality might have been as necessary to the evolution of large brains in primates as large brains have been to the evolution of primate sociality. Whether social or ecological pressures were answerable for primate brain development, there is no qualm that primates have social brains, or that ours are the most social brains of all.
References
- Barrett, l & henzi, P (2005) The social nature of primate cognition. Proceedings of the Royal Society B272:1865-1875
- Bryne, R.W & Corp, N (2004) Neocortex size predicts deception rate in primates. Proceedings of the Royal Society of London B 271: 1693-1699
- Clark et al (2001) Scalable architecture in mammalian brains. Nature 411: 189-193
- Dunbar, R.I.M (1998) Primate Social Systems. Cornell Uni Press, Ithaca
- Joffe, T H (1997) Social Pressures have selected for an extended juvenile period in primayes. Journal of Human Evolution 32:593-605