Thursday, December 18, 2008

One World, Many Minds: Intelligence in the Animal Kingdom

A very cool article on animal intelligence appears in this month's Scientific American Mind - here is the beginning of it.

One World, Many Minds: Intelligence in the Animal Kingdom

We are used to thinking of humans as occupying the sole pinnacle of evolutionary intelligence. That's where we're wrong

By Paul Patton

Key Concepts

  • Despite cartoons you may have seen showing a straight line of fish emerging on land to become primates and then humans, evolution is not so linear. The brains of other animals are not merely previous stages that led directly to human intelligence.
  • Instead—as is the case with many traits—complex brains and sophisticated cognition have arisen multiple times in independent lineages of animals during the earth’s evolutionary history.
  • With this new understanding comes a new appreciation for intelligence in its many forms. So-called lower animals, such as fish, reptiles and birds, display a startling array of cognitive capabilities. Goldfish, for instance, have shown they can negotiate watery mazes similar to the way rats do in intelligence tests in the lab.

We were talking about politics. My housemate, an English professor, opined that certain politicians were thinking with their reptilian brains when they threatened military action against Iran. Many people believe that a component of the human brain inherited from reptilian ancestors is responsible for our species’ aggression, ritual behaviors and territoriality.

One of the most common misconceptions about brain evolution is that it represents a linear process culminating in the amazing cognitive powers of humans, with the brains of other modern species representing previous stages. Such ideas have even influenced the thinking of neuroscientists and psychologists who compare the brains of different species used in biomedical research. Over the past 30 years, however, research in comparative neuroanatomy clearly has shown that complex brains—and sophisticated cognition—have evolved from simpler brains multiple times independently in separate lineages, or evolutionarily related groups: in mollusks such as octopuses, squid and cuttlefish; in bony fishes such as goldfish and, separately again, in cartilaginous fishes such as sharks and manta rays; and in reptiles and birds. Nonmammals have demonstrated advanced abilities such as learning by copying the behavior of others, finding their way in complicated spatial environments, manufacturing and using tools, and even conducting mental time travel (remembering specific past episodes or anticipating unique future events). Collectively, these findings are helping scientists to understand how intelligence can arise—and to appreciate the many forms it can take.

The Tree of Life
To understand why a new view of the evolution of brains and minds is only now coming to full fruition, it is useful to review historical notions. Medieval naturalists placed living things along a linear scale called the great chain of beings, or scala naturae. This hierarchical sequence ranked creatures such as worms and slugs as lowly and humans as the highest of earthly beings. In the late 1800s the enormous mass of evidence contained in Charles Darwin’s masterwork, On the Origin of Species, convinced most of his scientific contemporaries that evolution was a reality. Darwin explained that modern species were related by physical descent and saw the relations among species as resembling the diverging branches of a family genealogical tree. Few, however, fully grasped the revolutionary implications of this tree of life—in which modern species represent the tips of the branches and inner branches represent past species, forming junctions where two lineages branch from a common ancestor.

So when comparative neuroanatomy first blossomed at the end of the 19th century, most researchers interpreted its findings in terms of the old linear scale. They believed modern invertebrates (animals without backbones), fish, amphibians, reptiles, birds, mammals and humans to be living representatives of successive evolutionary steps toward a more complex brain, with new brain components added at each step. Given the relative lack of interest in comparative neuroanatomy during the mid-20th century, these ideas persisted unchallenged for decades. The traditional ideas about sequential brain evolution appeared, for example, in the late neuroscientist and psychiatrist Paul D. MacLean’s triune brain model, formulated in the 1960s. Mac­Lean’s model promoted the belief that the human brain contains a “reptilian complex” inherited from reptilian ancestors.

Beginning in the 1980s, the field of comparative neuroanatomy experienced a renaissance. In the intervening decades evolutionary biologists had learned a great deal about vertebrate evolutionary history, and they developed new and effective methods of applying Darwin’s concept of the tree of life to analyze and interpret their findings. It is now apparent that a simple linear hierarchy cannot adequately account for the evolution of brains or of intelligence. The oldest known multicellular animal fossils are about 700 million years old. By the Cambrian period, about 520 million years ago, the animal kingdom had branched into about 35 major groups, or phyla, each with its own distinctive body plan. As a separate branch of the tree of life, each lineage continued to evolve and diversify independently of the others. Complex brains evolved independently in multiple phyla, notably among the cephalopod mollusks of the phylum Mollusca and, of course, among various groups of vertebrates. Vertebrate evolution has likewise involved repeated branching, with complex brains evolving from simpler brains independently along numerous branches.

Read the rest of the article.

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