Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record the population will become stable, showing little evolutionary change for most of its geological history. This state of little or no morphological change is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.
Punctuated equilibrium is commonly contrasted against phyletic gradualism, the idea that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous
____Wikipedia, April 29, 2018
Although I agree with punctuated equilibrium, I sometimes think Stephen Jay Gould (one of the co-authors of this theory) specifically came up with it for the purpose of discrediting HBD.
Richard Klein is a clear believer in the punctuated equilibrium theory. On pages 23 and 24 of his book The Dawn of Human Culture, he writes:
Each of the three or four punctuation events that we propose led up to the dawn of modern human culture occurred when human populations were small and geographically limited by modern standards. Each apparently occurred in Africa, and on present evidence, each appears to mark a coincidence of major biological and behavioral change. The first event occurred around 2.5 million years ago, when flaked stone tools made their initial appearance. These comprise the earliest enduring evidence for human culture, and their emergence probably coincided closely with the evolution of the first people whose brains were significantly larger than those of apes. The second event took place around 1.7 million years ago. The people this time were the first to possess fully human as opposed to ape-like body proportions, and they invented the more sophisticated stone artifacts that archeologists call hand axes. They may also have been the first to venture out of Africa. The third and most weakly documented event occurred around 600,000 years ago, and it involved a rapid spurt in brain size, together with significant changes in the quality of hand axes and other stone tools. The fourth and most recent event occurred about 50,000 years ago and it was arguably the most important of all, for it produced the fully modern ability to invent and manipulate culture. In its wake, humanity was transformed from a relatively rare and insignificant large mammal to something more like a geologic force.
I think Klein is more or less correct, but I might make a few revisions to his model in an imminent post.