The Bone Hunters: The Heroic Age of Paleontology in the American West by Url Lanham

Author:Url Lanham [Lanham, Url]
Language: eng
Format: mobi, epub
ISBN: 9780486144443
Publisher: Dover Publications
Published: 2012-05-23T04:00:00+00:00

A scene in the miniature Table Mountain Badlands near Denver. The black arrow below and to the left of the summit of the lightcolored ridge marks what is sometimes given as the Cenozoic-Mesozoic boundary in this formation.

Probably the most significant difference between reptiles and mammals is the higher intelligence—the ability to profit from experience—of the mammals. Intelligence is correlated mainly with increased brain size. Within the different groups of mammals, brain size has generally increased during the Cenozoic, but even the earlier mammals usually had larger brains than their reptilian contemporaries.

It is interesting that many of the other characteristics of mammals contribute directly or indirectly to the evolution of larger brains. The warm blood of mammals is important mainly as a device for maintaining a constant body temperature. Given the methods of heat regulation available to a mammal, it is easier for the animal to maintain a constant temperature if that temperature is usually higher than that of the environment. The fur is, of course, an important factor in maintaining this high temperature. The chief advantage of the constant body temperature is that it creates the proper internal environment for the accurate functioning of the central computer for the body—the brain. Apparently the different chemical processes that go on in the brain have dif ferent temperature characteristics, so that their coordination is destroyed if the normal operating temperature is abolished. The mammalian brain is quite sensitive to temperature changes, and becomes incompetent in fever or hypothermia. Constant temperature thus was a necessary condition for the evolution of the large and complex brain.

The close link between mother and offspring established by the evolutionary origin of milk glands also produces a situation that favors the evolution of large brain size. There is the establishment of a parent-offspring group, a family, in which the experienced parent can teach the young, or the young profit from emulation of the parent. Thus it becomes possible to take advantage of variation in the direction of increased brain size, creating a situation in which natural selection acts relatively swiftly on the evolution of a better brain. Throughout the mammals, as opposed to the reptiles, parent-young communication, is a prominent feature of life.

If superior intelligence was a mammalian characteristic even during the Age of Reptiles, then perhaps it was some change in the environment that got the Age of Mammals underway. This is the most generally accepted explanation. The change in the environment was a biological change—the disappearance of the major reptilian groups—which was probably a result of changes in the physical environment. According to this view, before the mammalian revolution could take place, there had to be a harvest to clear away the old order. Mammals could then become larger (which in fact they did at the beginning of the Cenozoic), and thus even more intelligent. The brain of a mouse can accomplish little by way of learning. It requires an appreciably large mammal, with a correspondingly large brain, to take good advantage of the potential for increased intelligence that exists in mammals.

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