Here's a summary of some stuff gleaned from Wiztel's book so far. (I've only read the first 100 pages, which introduces and justifies his historical comparative method, akin to that used in linguistics, palaeontology, and genetics.)
First, he remarks that myth deals with eternal questions (who are we, why are we here, how'd we get here, what's our purpose, etc.). As such, it's easy to see why myths persist, taking into account what Gurdjieff wrote and the stuff in Schumaker's "Corruption of Reality". So if myths are as Laura, Clube, Napier, Baillie, etc. present them, important information can be passed on for thousands of years, even if it's buried in a lot of obfuscation from addition/deletion/changes.
First, I'll mention that Witzel doesn't cite Clube and Napier. He acknowledges the possibility of some myths passing on memories of real disasters/catastrophes (citing the Black Sea flood [5600 bce] and Toba explosion/tsunami [77,000 bce], as well as some recounted in American myths, as possible examples), but rejects the idea that the universal Flood myths recount an actual occurrence. He also rejects the idea of "mnemotechnical mechanics of myth formation as storage device of Stone Age 'scientific' knowledge" as the be-all-end-all explanation of myth. I think he's obviously wrong about the former, and kind of wrong about the latter. It may not account for every aspect of mythology, but it certainly explains a lot, as Laura shows in "Horns of Moses."
So I think his approach is partly flawed. It doesn't take into account just how influential shared astronomical events can be to world populations. But I think it is probably useful for figuring out earlier, more common versions of the varied myths.
He argues for 3 distinct historical layers of myth: Pan-Gaean > Gondwana > Laurasian (originating in Greater Southwest Asia some time between 50,000 [time Australian, New Guinean migration) to 20,000 ybp (American migration) - i.e., sometime after the second-last ice age). The rationale being that the common features can only be explained by common inheritance; they're too similar in structure to be explained as coincidence or based on archetypes, and too separated geographically and temporally to be explained by diffusion.
Laurasian myth is the main focus of the book, which added on unique features to the existing Gondwana myths (e.g., Gondwana myth has the emergence of humans into a preexisting and eternal world, contrasted with what's below). Witzel has identified 15 or so motifs common to Laurasian mythology, forming a common story line.
The Storyline (the 15 motifs are numbered [in brackets])
-primordial emergence / creation: often from water/darkness/chaos/non-being [1], or the breaking up/dismemberment of an egg, giant, or bull (comet imagery!) [2], or the emergence of a hill or island, often with help of a diver [3].
-subsequent four generations ("ages") of gods: Father Heaven and Mother Earth giving birth to various generations of children/gods (often 4 generations or ages) [4]; this 'primordial intercourse' results in groups of gods like the Titans/Olympians or Asura/Deva, for example, and there's usually some godly incest going on. There's also the 'pushing up of heaven' (and origin of the Milky Way) [5]. Gods like Indra and Atlas act as 'poles' between heaven and earth. The 'hidden light of the sun' is revealed' [6].
These changeovers are violent, e.g., the Near Eastern (adopted by the Greeks) castration mytheme (e.g. Kronos and Ouranos, Kumurbi, Indra). These are separate from the original killing of the primordial giant, however (the original giant comet?). In the Mesopotamian version, the 4 ages are progressive (more optimistic), contrasted with the Greek, for example, which just gets worse. The Mesopotamian one may be older, but it's hard to say.
-age of monsters / semidivine heroes, where the new gods defeat or kill their predecessors [7]; killing the dragon [8] (e.g., Indra, Beowulf, Sigurd, Siegfried, Herakles, etc., who overlap with semidivine heroes like Achilles, Hector, Odysseus, Romulus and Remus, David, Xbalanque, etc.). Only the Earth fertilized by the blood of the dragon can support life (i.e., humans). (Panspermia?) The 'sun' (comet?) deity is the father of humans [9]. Interesting here is the 'solar' origin (often via the world tree) of various chiefs and kings, e.g., the 'descent' of the 1st Japanese 'emperor' from heaven.
-emergence of humans, their evil deeds, and the flood [10]. The flood results in a new generation (e.g., Gilgamesh, Noah, Pyrrha).
-heroes and nymphs [11]: a culture hero or shaman brings culture, fire, food; origin of rituals; spread of humans, start of 'noble' lineages, beginning of human history [12]. ([13] is missing from his chart.)
-violent end to present world (humans, world, gods), often preceded by prophecy [14], sometimes with the hope of a new heaven and earth [15].
Some other features that struck me as interesting:
-the oldest, most universal myth is the Flood myth (especially with the 'sky falling' mytheme), which only ever occurs after humans behave in a way displeasing to the gods; similarly, the 'dragon' is only slayed after the first male/female deities appear (as it is their offspring); this should make a lot of sense after reading "Horns of Moses."
-views the world/universe as analogous to a body or organism; an analogy Laura also makes in "Horns of Moses," making clear cause and effect, and our obligations to the universe
-more patriarchal than Gondwana (but Witzel notes that we often only have the male versions of myths, females often had their own versions, which were rarely recorded)
-shamanism is a common feature, and variations on the Orpheus myth are common
-in Japanese myth, the child of the primordial deities Izanami and Izanagi, Hirago, is set adrift, like Moses.
-again, drawing from "Horns of Moses", Witzel mentions that originally only the Pharaoh was 'reborn' (like the original pharaoh/comet?), before that rule was relaxed and more could have the privilege. Even though it's not reincarnation per se, it could support the idea that the view of comets returning is what gave rise to the idea.
-while Witzel doesn't agree with Jung and Campbell's archetype theories fully (the don't explain story lines, for example), he acknowledges that the human mind makes some important contributions to myth: we think in largely binary structures, make analogy based on experience, and anthropomorphize.
-discussing Zoroaster, Witzel points out that he telescoped the idea of the renewal of time and society at the new year into the life of the individual: one had to make the individual choice between right/truthful action and evil, right action restoring the universal order. Witzel sees this as an 'optimistic' feature of Laurasian myth: the possibility of renewal within mini-cycles. This brings to mind the idea of the world reflecting the thought of the human population.