In the referenced publication Robert Bednarik makes several important points that are quite illuminating. Regarding the roundness (shape) and size of the shell beads, he states in the second paragraph of the Discussion section:

"...The first observation we can make concerns the considerably finer workmanship of these Acheulian specimens in comparison to those we have of the Upper Palaeolithic. This may be unexpected, but it mirrors an experience we had recently with European rock art: the most sophisticated we have found so far, that of Chauvet Cave in France (Chauvet et al. 1995) turned out to be also the earliest we know of in the European Upper Palaeolithic (Clottes et al. 1995). Hence the idea of evolution towards increased sophistication is a Eurocentric myth in rock art development, and may well be so in other areas of archaeology.”

Though it could be argued, and with exceptions, the general tendency toward earlier “finer or higher quality” art or crafts-person-ship in any given medium is readily observed in a pre-industrial historic and generational sense - the latter being recognizable over a single life-span - but Bednarik notes the phenomenon also exists in the archeological record. I find this observation fascinating (from the ‘60s, mind-expanding), and cannot fathom, from a natural human-tendency perspective, why it may be so. I’m sure the answer is on the www. though. :)