Deep Divergence

Notes

1. Meyer, 2013, p. 106: “In addition to the studies I have already cited, a 1997 paper by Japanese biologist Naruo Nikoh and colleagues examined two genes (aldolase and triose phosphate isomerase), and dated the split between eumetazoa and parazoa—animals with tissues (like cnidarians) from those without (like sponges)—at 940 million years ago.  Compare that to a 1999 paper by Daniel Wang, Sudhir Kumar, and S. Blair Hedges based on the study of 50 different genes, showing that “the basal animal phyla (Porifera, Cnidaria, Ctenophora) diverged between about 1200-1500 Ma.””  p. 105-106: “There is a second, more telling reason to doubt the deep-divergence hypothesis: the results of different molecular studies have generated widely divergent results. … For example, comparing th ewray-led study and the Erwin-led study generates a difference of 400 million years.  In the case of other studies, even greater differences emerge.  Many other studies have thrown their own widely varying numbers into the ring, placing the common ancestor of animals anywhere between 100 million and 1.5 billion years before the Cambrian explosion (some molecular clock studies, oddly, even place the common ancestor of the animals after the Cambrian explosion).” ↩
2. Meyer, 2013, p. 119: “Just as the molecular data do not point unequivocally to a single date for the last common ancestor of all the Cambrian animals (the point of deep divergence), they do not point unequivocally to a single coherent tree depicting the evolution of animals in the Precambrian.  Numerous papers have noted the prevalence of contradictory trees based on evidence from molecular genetics.  A 2009 paper in Trends in Ecology and Evolution notes that “evolutionary trees from different genes often have conflicting branching patterns.”  Likewise, a 2012 paper in Geological Reviews acknowledges that “phylogenetic conflict is common, and frequently the norm rather than the exception.”  Echoing these views, a January 2009 cover story and review article in New Scientist observed that today he tree-of-life project “lies in tatters, torn to pieces by an onslaught of negative evidence.”  As the article explains, “Many biologists now argue that the tree concept is obsolete and needs to be discarded,” because the evidence suggests that “the evolution of animals and plants isn’t exactly tree-like.”” ↩
3. Meyer, 2013, p. 122-123: “Then, in the mid-1990s, a very different arrangement of these animal groups was proposed based on the analysis of a molecule present in each (the 18S ribosomal RNA).  The team of researches who proposed this arrangement published a groundbreaking paper in Nature with a title that surprised many morphologists: “Evidence for a Clade of Nematodes, Arthropods, and Other Moulting Animals.”  The paper noted the conventional wisdom, based on Hyman’s hypothesis, that arthropods and annelids were closely related because both phyla had segmented body plans.  But their study of the 18S ribosomal RNA suggested a differeng grouping, one that placed arthropods close to nematodes within a group of animals that molt, which they call “Ecdysozoa.”  This relationships surprised anatomists …” ↩
4. Meyer, 2013, p. 124: “My point in summarazing these disputes is simply to note that the molecular and anatomical data commonly disagree, that one can find partisans on every side, that the debate is persistent and ongoing, and that, therefore, the statements of Dawkins, Coyne, and many others about all the evidence (molecular and anatomical) supporting a single, unambiguous animal tree are manifestly false.” ↩