September 18, 2006
Part II: What Makes Us Human?
The Origin of Adaptability and Human Beings
Rick Potts
Smithsonian Instituition
35 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)
Man's structural peculiarities only suffice to place him in a monotypic zoological family, with a single living species. His mental abilities are far more distinctive. If the zoological classification were based on psychological instead of mainly morphological traits, man would have to be considered a separate phylum or even kingdom.
— Theodosius Dobzhansky (1900 - 1975)
Species are often ecologically classified as adopting either an r-selected or K-selected strategy, where "r" is the instrinic rate of increase of the species and "K" is the carrying capacity of the environment.
An r-selected species is at its most competitive when it is invading disturbed habitat. It temporarily prospers because it can increase its numbers faster than any of its competitors, but such a strategy will eventually normally lose out to species that are more competitive once the resource space fills, should it remain stable.
R-selected species are often called "weed species" because they depend so heavily on disturbed habitat. Although Rick Potts never uses the term in this talk on the evolution of humans, that is the organism he is describing. Humans are now the sole surviving hominid species on the planet, but that wasn't true until quite recently.* From his work in his Turkana Basin and Olorgesailie sites in East Africa, as well as his more recent work in southern China, Potts outlines a compelling argument that Homo evolved to prosper best during periods of climatic instability.
Climatic instability affects all species. Generally, only three choices are offered a species:
- extinction in face of the changed environment
- migration to more clement environments
- adaptation to the broader range of environments
The genus Homo evolved — perhaps only by chance and not too much should be made of the fact — during a period of dramatically increasing climatic instability. Potts argues however that the recent increases in climatic oscillations lie at the core of the evolution of Homo.
While the increases in climatic variation appear in the fossil record to have suppressed populations of the more inertial hominins, Paranthropus and Australopithecus, the increased environmental stress apparently acted as an "intelligence pump" in Homo, forcing the lineage to become more inventive in its responses to a broader range of inclement environments.
In that, Potts' argument not only goes a long way in answering the question, "Why are we so smart?", it also recapitulates the "complexity pump" thesis that Andrew Knoll argued in an earlier lecture: evolution on a stable planetary surface would soon come to an end without episodic disturbances. Some degree of instability is necessary to cause life to become increasingly more complex.
Rick Potts presented his talk at an astrobiology conference, thus the question at the end was whether or not this level of instability is universally requisite to the evolution of intelligence elsewhere in the galaxy? Potts argues yes.
— Wirt Atmar
* This statement is only true if you accept an older taxonomy of the great apes. Up until the 1980's, the family Hominidae contained only humans, with the great apes placed in the family Pongidae. Recent comprehensive molecular studies have led to several reclassifications (see this diagram), with the chimpanzees, gorillas, and orangutans now moved into the hominid family. The classification, like all taxonomic revisions, remains controversial and somewhat chaotic (see Gyenis 2002).
About the Speaker
Dr. Rick Potts is Director of the Human Origins Program and Curator of Anthropology at the National Museum of Natural History, Smithsonian Institution. He received his B.A. in Anthropology from Temple University (1975) and his Ph.D. in biological anthropology from Harvard University (1982). He has been with the Smithsonian since 1985, developing a program of international collaboration among scientists interested in the ecological aspects of human evolution. Over the past decade, Rick has led excavations at early human sites in the East African rift valley, and currently directs a multidisciplinary research team at the famous handaxe site of Olorgesailie, Kenya.
In 1995, he also began a project in southern China, devoted to comparing evidence of early human behavior and environments from eastern Africa to eastern Asia. Rick has authored numerous research articles and three books. The three books are titled Early Hominid Activities at Olduvai, Terrestrial Ecosystems Through Time, and most recently a book written for a general audience titled Humanity's Descent: The Consequences of Ecological Instability.
His ideas and comments have been aired on several occasions on National Public Radio's All Things Considered and PBS's The Jim Lehrer Newshour, and he was awarded a Certificate of Honor by the Academy of Television Arts and Sciences for the Emmy-winning Tales of the Human Dawn on PBS.
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