Before revision:  In contrast to this, the upper peak of the distribution consists of the surviving species in the current diversity wave. The populations of the most abundant species in the upper peak exhibit a scale-free  distribution with a nearly universal exponent of about 1.7.
After revision:  In contrast to this, the upper peak of the distribution consists of the surviving species in the current wave. In most waves both upper and lower peaks are composed of several smaller peaks. This URLanized hierarchical peak structure has a long-term memory transmitted across several waves. It gives rise to a scale-free distribution with a nearly universal exponent of about 1.7.