Coon argued the fossil record showed the major races (Caucasoid, Mongoloid, Australoid, Capoid, and Congoid) date back at least as far as Homo erectus. Coon believed these five races transitioned to Homo sapiens independently and at different times, with the mutations responsible for the transition either happening multiple times in the different populations or being spread by peripheral gene flow.
Our races jumped from Homo erecus to Homo Sapiens brain size by saltation. Stated more specifically, the essential difference between Homoerectus and Homosapiens lies in the total area of the cerebral cortex of the brain. The cortex is a thin sheet of nerve cells (neurons) twisted and bent to fit its mostly globular container, the skull. Our races moved from the Homoerectus to the Homosapiens state by a doubling of the number of nerve cells in this sheet. [. . .]In Coon's view:
At least one race of Homo erectus and possibly all five evolved by saltation into Homo sapiens. From available evidence we may surmise that the appropriate threshold was crossed by each race in response to local opportunities, either by its own mutations or by impregnation of its women by Homo sapiens invaders. In such a case the women would transmit to the new generation their own most useful local climatic adaptations.
[Racial Adaptations, pp. 137-139]
When the brain size of Homo erectus increased by a doubling of the cerebral cortex, some of their races got more neurons than their environmental and cultural requirements warranted. The brain sizes of all races rose from about 1,200 cc (in the males) to between 1,450 cc and 1,700 cc, and then fell back to the Homo erectus level or a little higher in the tropics, and to about 1,400 to 1,500 cc in the temperate and polar zones. As far as we know, no Homo erectus are alive today.Coon based his belief that "the Caucasoid [is] the oldest sapiens race" on the Swanscombe and Steinheim skulls.
While the oldest Homo erectus skulls have been found in the tropics, the oldest Homo sapiens come from Europe, where Caucasoids lived during a warm interglacial well over 250,000 years ago. After interruptions, they were followed by the cold-adapted Neanderthals, whose fate is still a mystery. Some say that while the earliest Homo sapiens' vocal apparatus let them speak, Neanderthal's repertoire of semantically useful sounds was limited. The Neanderthals may have become extinct, they may have been absorbed into the Caucasoid ranks, or they may have moved eastward to sire the American Indians, and, in part at least, the Mongoloids.
[Racial Adaptations, p. 149]