The Evolution of Intelligence in Primates, Research Paper Example

In its December 2 edition, the New York Times reported on a story with the following headline: “Rights Group is Seeking Status of ‘Legal Person’ for Captive Chimpanzee” (Gorman, 2013). An organization billing itself as the Nonhuman Rights Project (NRP) has filed a writ of habeas corpus in a New York state courtroom; in its filing, the NRP argues that a captive chimpanzee held by a private owner should be granted the legal status of “personhood,” and should be removed from the custody of its owner and placed in a chimpanzee-rescue sanctuary. This is a legal argument that would have been inconceivable a century –or perhaps even a few decades- ago; the fact that the court has agreed to hear the motion is a sign of just how much our understanding of the nature of primate intelligence has grown in the wake of scientific discoveries related to genetics and evolution. Advances in the study of DNA and genetics has revealed that humans and great apes such as chimpanzees, gorillas, and orangutans share an astonishingly high amount of DNA, and studies of primates have revealed that the intelligence historically ascribed solely to humans is seen, in varying forms, in so-called “lower” primates as well. The development of cognition and intelligence is the single most important evolutionary advantage underpinning the human species; by studying and learning about the capacity for intelligence inherent in other primates we can gain insight into our own evolutionary development.

The issue of what defines or constitutes intelligence is itself a matter of debate. In its most basic sense, intelligence is defined as the capacity to solve problems and to respond, adapt to, and cope with new or novel circumstances and events (Roth and Dicke, 2005). The ability to solve problems is, at its core, a trait underpinning survival strategies, and the capacity to solve problems is seen in a wide variety of species that might not generally be considered to possess intelligence as we define it in humans (or in some other species). Beyond primates, there are several other “higher” mammals that are considered to possess some form of intelligence; among the most notable of these are elephants and cetaceans. In the context of problem-solving capacity, though, intelligence is seen in other animals as well, including birds, dogs, cats, and rodents (Reader, Hager, and Laland, 2010). Clearly, however, the nature of intelligence as seen in humans and other primates differs from, and is of a greater scope and range than, the simple problem-solving capacity found in these other animals.

The issue of intelligence in primates and other animals is considered within the framework of several key capacities; these include “problems related to feeding, spatial orientation, social relationships, and intraspecific communication” (Roth and Dicke). Within this framework, however, there are a range of capacities and abilities found in different species; defining what constitutes intelligence is further refined by considering the capacity for flexibility, and for dealing with situations and solving problems that are unique and out of the ordinary. The capacity to solve problems with this level of flexibility is associated with the ability to reason, and to make decisions and take actions based on past knowledge and on the ability to weigh alternatives (Dunbar and Shultz, 2007).

By such criteria, intelligence has evolved independently in a variety of different species, as primates are not the only animals capable of demonstrating such capacities. Human beings are, of course, the species with the greatest capacity to respond to novel situations, and the development and use of complex tools is seen as evidence of human intelligence that is of a higher order than that of other animals (King, 1986). Humans are not the only animals that use tools, however; other mammals and even birds using objects from their environments to access food and to perform other tasks, and primates such as chimpanzees have even been seen fashioning sticks and rocks into simple tools to crack open nuts or to reach insects to eat (Sayers, 2013). Despite this capacity for using tools and solving problems, scientists agree that the nature of intelligence found in primates is of a different, more complex type than that seen in other species; it is this form of intelligence that is of interest to researchers looking for connections between human intelligence and that seen in other primates.

The specific form of intelligence seen in primates evinces some specific traits and markers seen in few other animals (the aforementioned whales and elephants being the two other most notable examples). This higher primate intelligence is characterized by a number of social functions, such as the capacity to empathize with others of the species, the capacity for self-awareness, the capacity to form social bonds, and to solve problems in groups (Roth and Dicke). Humans and other primates are inherently social creatures, and the form of intelligence seen in primates is a fundamental component of this capacity for social interaction. The question of whether non-human primates have the same form of consciousness that humans have is still a subject of debate, though studies have determined that many of the brain structures and functions associated with consciousness are found in the higher non-human primates (Roth and Dicke).

The evolution of primate intelligence is closely linked with the development of larger brains. When measured in terms of brain size to body size, the ratio of the human brain is six times larger than that of the average mammal (Byrne, 2000). In humans, brain size is developed both during fetal development and in postnatal development. The human brain at birth is much smaller than it will become as it passes through later developmental stages. In primates such as chimpanzees and other higher primates, this is also true, but to a much smaller degree; the brains of higher non-human primates are much closer to their fully-developed size at birth than are the brains of humans. Across all higher primates, however, the sizes of their fully-developed brains are notably larger in terms of brain/body size ratio that in other animals (elephants and cetaceans included) (Byrne).

There are several notable theories put forth about how and why primates developed these larger brains; among the two most prominent theoretical categories are the ecological theories and the social theories. Each of these theoretical categories is predicated on observations about the behaviors and capacities of primates, and each has been developed to explain why such capacities developed and what evolutionarily-selective advantages they might provide. The first general type of theory, the ecological model, posits that intelligence developed concurrently with evolutionary growth in brain size because it conferred a selective advantage to members of primate species that were best able to secure food in their environments. In this model –sometimes referred to as the “foraging” model- the capacity to find new and greater sources of food provided a selective advantage (King; Sayers). The increased nutrition available to those with greater foraging capacities conferred a propensity to underpin greater physical development, including those individuals with larger brains.

The social models explaining why primates developed larger brains are built around the idea that the capacity to work in social groups conferred selective advantages (Reader, Hager, and Laland). At the higher functions of intelligence found in humans and non-human primates, this social intelligence is evidenced in a number of ways. Chimpanzees, for example, have been seen to engage in social behaviors that demonstrate a capacity for deception, as well as a capacity for empathy (Byrne). In the social theory model, intelligence includes the capacity to understand and consider what other members of the species are thinking, and to make predictions about how they will behave. This sort of cognitive awareness is believed to be exclusive to the few animals –primarily primates- that have developed relatively large brains, and is considered to be among the specific hallmarks of primate intelligence (Worden, 1996). In the context of social theory models, the capacity for self-awareness and awareness of what other members of the species are thinking is believed to rely on the relatively large capacity of primate brains.

Large brains are not entirely advantageous, however. An evolutionary increase in brain size is associated with death during the delivery of offspring. Moreover, the biological and physiological demands of prenatal brain development are quite taxing, requiring long relatively gestation periods and a significant nutritional intake by gestating females to support brain development. There is a marked difference between humans and non-human primates in this regard; in non-human primates the majority of brain development takes place in the womb, while in human beings the development of the brain and other aspects of developmental maturity are much slower, and much of this development is postnatal. Because so much of human development is postnatal, there are significant disadvantages from a selective standpoint. The capacity of human intelligence is the evolutionary trade-off for this longer developmental period, and is among the most significant ways in which humans and non-human primates diverged from our common ancestor (Roth and Dicke).

By studying the physiological structures of the brains of humans and nonhuman primates, and by researching the ways that intelligence is manifested in different primate species, we can gain insight into the evolutionary course humans have taken. As the evolutionary branch of the common primate ancestry split, the human species developed a form of intelligence that is both similar to and different from that seen in other primates. As we learn about the nature of these similarities and differences, we are better able to trace how human intelligence evolved. The lessons learned from such study and research allow us to understand not just the ways in which humans are different from other primates, but also the ways in which we remain inextricably linked through our evolutionary history.

References

Byrne, R. (2000). Evolution of primate cognition. Cognitive Science, 24(3), 543-570.

Dunbar, R., & Shultz, S. (2007). Understanding Primate Brain Evolution. Philosophical Transactions: Biological Sciences, 362(1480), 649-658.

Gorman, J. (2013, December 2). Rights Group Is Seeking Status of ‘Legal Person’ for Captive Chimpanzee – NYTimes.com. Retrieved from http://www.nytimes.com/2013/12/03/science/rights-group-sues-to-have-chimp-recognized-as-legal-person.html?pagewanted=1&_r=0

King, B. (1986). Extractive foraging and the evolution of primate intelligence. Human Evolution, 1(4), 361-372.

Reader, S., Hager, Y., & Laland, K. (2011). The evolution of primate general and cultural intelligence. Phil. Trans. R. Soc. B, 366(1567), 1017-1027.

Rotha, G., & Dicke, U. (2005). Evolution of the brain and intelligence. Trends in Cognitive Sciences, 9(5), 250–257.

Sayers, K. (2013). On folivory, competition, and intelligence: generalisms, overgeneralizations, and models of primate evolution. Primates, 54(2), 111-124.

Worden, R. (1996). Primate Social Intelligence. Cognitive Science, 20, 579-616.