Problem 9: Neo-Darwinism Struggles to Explain the Biogeographical Distribution of Many Species
Editor's note: This is Part 9 of a 10-part series based upon Casey Luskin's chapter, "The Top Ten Scientific Problems with Biological and Chemical Evolution," in the volume More than Myth, edited by Paul Brown and Robert Stackpole (Chartwell Press, 2014). The full chapter can be found online here. Other individual installments can be found here: Problem 1, Problem 2, Problem 3, Problem 4, Problem 5, Problem 6, Problem 7, Problem 8, Problem 10.
Biogeography is the study of the distribution of organisms in time and space both in the present and past on Earth. It is often contended that biogeography strongly supports neo-Darwinian theory. For example, the National Center for Science Education (NCSE), a pro-Darwin advocacy group, claims that "consistency between biogeographic and evolutionary patterns provides important evidence about the continuity of the processes driving the evolution and diversification of all life," and "[t]his continuity is what would be expected of a pattern of common descent." However, the NCSE dramatically overstates its case and ignores the many instances where biogeography does not show the sort of "continuity" that would be expected under a pattern of common descent.
Evolutionary explanations of biogeography fail when terrestrial (or freshwater) organisms appear in a location (such as an island or a continent) where there is no standard migratory mechanism for them to have arrived there from some ancestral population. In other words, when we find two populations of organisms, Darwinian evolution claims that if we go back far enough, they must be linked by common descent. But sometimes it's virtually impossible to explain how these populations could have arrived at their respective geographical locations on the globe from some ancestral population.
For example, one of the most severe biogeographical puzzles for Darwinian theory is the origin of South American monkeys, called "platyrrhines." Based upon molecular and morphological evidence, New World platyrrhine monkeys are thought to be descended from African "Old World" or "catarrhine" monkeys. The fossil record shows that monkeys have lived in South America for about the past 30 million years.137 But plate tectonic history shows that Africa and South America split off from one another between 100 and 120 million years ago (mya), and that South America was an isolated island continent from about 80 - 3.5 mya.138 If South American monkeys split off from African monkeys around 30 mya, proponents of neo-Darwinism must somehow account for how they crossed hundreds, if not thousands, of kilometers of open ocean to end up in South America.
This problem for evolutionary biologists has been recognized by numerous experts. A Harper Collins textbook on human evolution states: "The origin of platyrrhine monkeys puzzled paleontologists for decades. ... When and how did the monkeys get to South America?"139 Primatologists John G. Fleagle and Christopher C. Gilbert put it this way in a scientific volume on primate origins:
The most biogeographically challenging aspect of platyrrhine evolution concerns the origin of the entire clade. South America was an island continent throughout most of the Tertiary...and paleontologists have debated for much of this century how and where primates reached South America.140
Primate specialist Walter Carl Hartwig is similarly blunt: "The platyrrhine origins issue incorporates several different questions. How did platyrrhines get to South America?"141 Such basic, vexing questions certainly don't lend credence to the NCSE's claims of "consistency between biogeographic and evolutionary patterns."
For those unfamiliar with the sort of arguments made by neo-Darwinian biogeographers, responses to these puzzles can be almost too incredible to believe. A Harper Collins textbook explains: "The 'rafting hypothesis' argues that monkeys evolved from prosimians once and only once in Africa, and ... made the water-logged trip to South America."142 And of course, there can't be just one seafaring monkey, or the monkey will soon die leaving no offspring. Thus, at least two monkeys (or perhaps a single pregnant monkey) must have made the rafting voyage.
Fleagle and Gilbert observe that the rafting hypothesis "raises a difficult biogeographical issue" because "South America is separated from Africa by a distance of at least 2600 km, making a phylogenetic and biogeographic link between the primate faunas of the two continents seem very unlikely."143 But they are wedded to an evolutionary paradigm, meaning that they are obligated to find such a "link" whether it is likely or not. They argue that in light of "[t]he absence of any anthropoids from North America, combined with the considerable morphological evidence of a South American-African connection with the rodent and primate faunas" that therefore "the rafting hypothesis is the most likely scenario for the biogeographic origin of platyrrines."144
In other words, the "unlikely" rafting hypothesis is made "likely" only because we know common descent must be true.
Indeed, the rafting hypothesis faces serious problems, as mammals like monkeys have high metabolisms and require large amounts of food and water.145 Fleagle and Gilbert thus admit that "over-water dispersal during primate evolution seems truly amazing for a mammalian order," and conclude, "[t]he reasons for the prevalence of rafting during the course of primate evolution remain to be explained."146 Or, as Hartwig puts it, "The overwhelming evidence for the late Cretaceous-Pliocene isolation of South America renders the mechanical aspect of platyrrhine dispersal virtually irresolvable" for "any late Eocene origins model must invoke a transoceanic crossing mechanism that is implausible (rafting) or suspect ... at best."147
And there are deeper problems: monkeys apparently made the journey from Africa to South America, but other smaller African primates never colonized the New World. If it was so easy for monkeys to raft across the proto-Atlantic ocean, why didn't these lower primates also make the voyage? The reason we're given by Fleagle and Gilbert is that there is no reason, and it all comes down to sheer chance. In their own words, rafting is "clearly a chance event" and "[o]ne can only speculate that by a stroke of good luck anthropoids where able to 'win' the sweepstakes while lorises and galagos did not."148
This is not the only case that appeals to rafting or other speculative mechanisms of "oceanic dispersal" to explain away biogeographical conundrums that challenge neo-Darwinism. Examples include the presence of lizards and large caviomorph rodents in South America,149 the arrival of bees, lemurs, and other mammals in Madagascar,150 the appearance of elephant fossils on "many islands,"151 the appearance of freshwater frogs across isolated oceanic island chains,152 and numerous similar examples.153 This problem also exists for extinct species, as a paper in Annals of Geophysics notes the "still unresolved problem of disjointed distribution of fossils on the opposite coasts of the Pacific."154 A 2005 review in Trends in Ecology and Evolution explains the problem:
A classic problem in biogeography is to explain why particular terrestrial and freshwater taxa have geographical distributions that are broken up by oceans. Why are southern beeches (Nothofagus spp.) found in Australia, New Zealand, New Guinea and southern South America? Why are there iguanas on the Fiji Islands, whereas all their close relatives are in the New World?155
After reviewing a number of "unexpected" biogeographical examples that require oceanic dispersal, the review concludes: "these cases reinforce a general message of the great evolutionist [Darwin]: given enough time, many things that seem unlikely can happen."156
Thus, neo-Darwinian evolutionists are forced to appeal to "unlikely" or "unexpected" migration of organisms, in some cases requiring the crossing of oceans to account for the biogeographical data. This kind of data may not necessarily absolutely falsify Darwinism, but at the least it challenges the simplistic argument that biogeography supports universal common descent through congruence between migration pathways and evolutionary history. In many cases, the congruence is simply not there.
[137.] Alfred L Rosenberger and Walter Carl Hartwig, "New World Monkeys," Encyclopedia of Life Sciences (Nature Publishing Group, 2001).
[138.] Carlos G. Schrago and Claudia A. M. Russo, "Timing the origin of New World monkeys," Molecular Biology and Evolution, 20(10):1620--1625 (2003); John J. Flynn and A.R. Wyss, "Recent advances in South American mammalian paleontology," Trends in Ecology and Evolution, 13(11):449-454 (November, 1998); C. Barry Cox & Peter D. Moore, Biogeography: An Ecological and Evolutionary Approach, p. 185 (Blackwell Science, 1993).
[139.] Adrienne L. Zihlman, The Human Evolution Coloring Book, pp. 4-11 (Harper Collins, 2000).
[140.] John G. Fleagle and Christopher C. Gilbert, "The Biogeography of Primate Evolution: The Role of Plate Tectonics, Climate and Chance," in Primate Biogeography: Progress and Prospects, pp. 393-394 (Shawn M. Lehman and John G. Fleagle, eds., Springer, 2006) (emphasis added).
[141.] Walter Carl Hartwig, "Patterns, Puzzles and Perspectives on Platyrrhine Origins," in Integrative Paths to the Past: Paleoanthropological Advances in Honor of F. Clark Howell, p. 69 (Edited by Robert S. Corruccini and Russell L. Ciochon, Prentice Hall, 1994).
[142.] Adrienne L. Zihlman, The Human Evolution Coloring Book, pp. 4-11 (Harper Collins, 2000).
[143.] John G. Fleagle and Christopher C. Gilbert, "The Biogeography of Primate Evolution: The Role of Plate Tectonics, Climate and Chance," in Primate Biogeography: Progress and Prospects, p. 394 (Shawn M. Lehman and John G. Fleagle, eds., Springer, 2006) (emphasis added).
[144.] Ibid. at 394-395 (emphasis added).
[145.] Ibid. at 404.
[146.] Ibid. at 403-404.
[147.] Walter Carl Hartwig, "Patterns, Puzzles and Perspectives on Platyrrhine Origins," in Integrative Paths to the Past: Paleoanthropological Advances in Honor of F. Clark Howell, pp. 76, 84 (Edited by Robert S. Corruccini and Russell L. Ciochon, Prentice Hall, 1994).
[148.] John G. Fleagle and Christopher C. Gilbert, "The Biogeography of Primate Evolution: The Role of Plate Tectonics, Climate and Chance," in Primate Biogeography: Progress and Prospects, p. 395 (Shawn M. Lehman and John G. Fleagle, eds., Springer, 2006).
[149.] John C. Briggs, Global Biogeography, p. 93 (Elsevier Science, 1995).
[150.] Susan Fuller, Michael Schwarz, and Simon Tierney, "Phylogenetics of the allodapine bee genus Braunsapis: historical biogeography and long-range dispersal over water," Journal of Biogeography, 32:2135--2144 (2005); Anne D. Yoder, Matt Cartmill, Maryellen Ruvolo, Kathleen Smith, and Rytas Vilgalys, "Ancient single origin of Malagasy primates." Proceedings of the National Academy of Sciences USA, 93:5122-- 5126 (May, 1996); Peter M. Kappeler, "Lemur Origins: Rafting by Groups of Hibernators?," Folia Primatol, 71:422--425 (2000); Christian Roos, J�rgen Schmitz, and Hans Zischler, "Primate jumping genes elucidate strepsirrhine phylogeny," Proceedings of the National Academy of Sciences USA, 101: 10650--10654 (July 20, 2004); Philip D. Rabinowitz & Stephen Woods, "The Africa--Madagascar connection and mammalian migrations," Journal of African Earth Sciences, 44:270--276 (2006); Anne D. Yoder, Melissa M. Burns, Sarah Zehr, Thomas Delefosse, Geraldine Veron, Steven M. Goodman, & John J. Flynn, "Single origin of Malagasy Carnivora from an African ancestor," Nature, 421:734-777 (February 13, 2003).
[151.] Richard John Huggett, Fundamentals of Biogeography, p. 60 (Routledge, 1998).
[152.] G. John Measey, Miguel Vences, Robert C. Drewes, Ylenia Chiari, Martim Melo, and Bernard Bourles, "Freshwater paths across the ocean: molecular phylogeny of the frog Ptychadena newtoni gives insights into amphibian colonization of oceanic islands," Journal of Biogeography, 34: 7-20 (2007).
[153.] Alan de Queiroz, "The resurrection of oceanic dispersal in historical biogeography," Trends in Ecology and Evolution, 20(2): 68-73 (February 2005). For a more detailed discussion, see Casey Luskin, "The Constitutionality and Pedagogical Benefits of Teaching Evolution Scientifically," University of St. Thomas Journal of Law & Public Policy, VI (1): 204-277 (Fall, 2009).
[154.] Giancarlo Scalera, "Fossils, frogs, floating islands and expanding Earth in changing-radius cartography - A comment to a discussion on Journal of Biogeography," Annals of Geophysics, 50(6):789-798 (December, 2007).
[155.] Alan de Queiroz, "The resurrection of oceanic dispersal in historical biogeography," Trends in Ecology and Evolution, 20(2):68-73 (February 2005).
Image: White-faced saki � Hans Hillewaert / via Wikimedia Commons.