William H. Calvin, A Brain for All Seasons (University of Chicago Press, 2002) Chapter Notes)

Recommended Reading

For background reading on climate change in general, there are two recent books which are especially good. Neither really explores the abrupt climate flip-flops that I focus on here, but they are exactly what you might want to give policymakers to help them sort through the more general issues of climate change. Anyone who wishes to speak intelligently about ozone, greenhouse, and El Niño needs to read both of them.

George H. Philander, Is the Temperature Rising? The Uncertain Science of Global Warming (Princeton University Press 1998). Written with grace and understatement for general readers, by someone deeply involved with modeling the climate, it covers much of a Princeton introductory course in the earth sciences.

Brian Fagan, Floods, Famines, and Emperors: El Niño and the Fate of Civilizations (Basic Books 1999). See also his The Little Ice Age (Basic Books 2000). Archaeologists have this wonderful perspective on what’s gone wrong in the past, both with climate and human institutions.

There are two books on a more direct lineage with this one; although neither book on anthropology and climate emphasizes the abruptness aspects, they are much better on the Miocene-Pliocene climates and the slow aspects of the Pleistocene:

Steven M. Stanley, Children of the Ice Age (Harmony 1996). Much more on the non-abrupt aspects of anthropology and paleobiology in the ice ages.

Rick Potts, Humanity’s Descent (William Morrow 1996). And for an excellent review of paleoclimate indicators, see his “Environmental hypotheses of hominin evolution,” Yearbook of Physical Anthropology 41:93-136 (1998).

There is now a new paleoclimate book, by one of the experts on the abruptness seen in the ice cores, that more directly addresses the present abruptness issues:

Richard B. Alley, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future (Princeton University Press 2000). It is written for nonspecialists (Alley has gotten a lot of practice as a frequent commentator for Science news articles). The book contains far more detail on abrupt climate change than the others. So if you find yourself asking, “But how could they possibly know that?” you’ll find most of the answers in Alley’s excellent book. Its final chapter about the future is conventional economic extrapolation, not the more relevant perspective of high-risk management seen in medicine, re-insurance, and disaster planning.

If anyone needs a quick reference about the importance with which the scientific community views the revelations about abrupt climate change, see the Perspectives in the 15 February 2000 issue of the Proceedings of the National Academy of Sciences. In particular, see

Richard B. Alley, "Ice-core evidence of abrupt climate changes," Proceedings of the National Academy of Sciences 97(4):1331-1334 (15 February 2000) at http://www.pnas.org/cgi/content/full/97/4/1331.

For a good textbook on the earth sciences, covering atmospheric sciences, geology, and oceanography, let me suggest:

Brian J. Skinner, Stephen C. Porter, Daniel B. Botkin, The Blue Planet: An Introduction to Earth Systems Science, second edition (Wiley 1999).

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For the paleoanthropological side of things, there are many choices. In general, climate makes an appearance only in its usual uplift-encouraging-the-savannas role or in the gradualist simplification of the Ice Ages. Except within the range of tree-ring dating, events that last for only a few centuries often cannot be seen in the archaeological record because of bioturbulence smoothing the record out, and the abruptness implications of the ice cores have generally not been digested yet. Besides Potts and Stanley, there are many other excellent books for general readers about anthropology:

Jared Diamond, Guns, Germs, and Steel: The Fates of Human Societies (W. W. Norton 1997). The focus is on the last 13,000 years and biogeography’s influence on domestication.

Donald Johanson, Blake Edgar, From Lucy to Language (Simon & Schuster 1996).

Richard E. Leakey, Roger Lewin, Origins Reconsidered: In Search of What Makes Us Human (Doubleday 1992).

Richard E. Leakey, The Origin of Humankind (Basic Books Science Masters Series 1995).

Christopher Stringer, Robin McKie, African Exodus: The Origins of Modern Humanity (Holt 1996).

Ian Tattersall, The Fossil Trail (Oxford University Press 1995), a history of fossil finding which has excellent fossil hominid illustrations.

Ian Tattersall, Becoming Human (Harcourt Brace 1998).

Ian Tattersall & Jeffrey Schwartz, Extinct Humans (Westview Press 2000).

Alan Walker and Pat Shipman, The Wisdom of the Bones (Knopf 1996).

The relevant textbooks, both of which cover hominids well, are:

John G. Fleagle, Primate Adaptation and Evolution, second edition (Academic Press 1999). Has more of the comparative anatomy perspective of physical anthropology.

Richard G. Klein, The Human Career: Human Biological and Cultural Origins, second edition (University of Chicago Press 1999). Has more of the cultural perspective of archaeology.

For aspects of the great apes, start with:

Dean Falk, Primate Diversity (W. W. Norton 2000). Her book is aimed at anthropology undergraduates, with an excellent glossary.

Frans de Waal, Good Natured: The Origins of Right and Wrong (Harvard University Press 1996). Together with his other books for general readers, such as The Ape and the Sushi Master, Bonobo, Peacemaking Among Primates, and Chimpanzee Politics, you get a good view of what the ape-human transition might have been from.

Frans de Waal, editor, Tree of Origin: What Primate Behavior Can Tell Us about Human Social Evolution (Harvard University Press 2001). An excellent, readable collection of chapters by nine primatologists.

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For the brain side of things, you will find many of the references in my earlier books, The Cerebral Code, How Brains Think, Lingua ex Machina (with the linguist Derek Bickerton), and Conversations with Neil’s Brain (with the neurosurgeon George Ojemann), all at http://faculty.washington.edu/wcalvin. For the connection with behavior, see:

Melvin Konner, The Tangled Wing: Biological Constraints on the Human Spirit (W. H. Freeman 2001).

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Especially for evolutionary biology, some fine writers have also been at work, adding to the books written by the biologists. It is, after all, one of the grand stories of all time – and nothing else makes much sense unless you understand the evolutionary process.

Helena Cronin, The Ant and the Peacock (Cambridge University Press 1992).

Richard Dawkins, Climbing Mount Improbable (Norton, 1996).

Daniel C. Dennett, Darwin’s Dangerous Idea (Simon & Schuster 1995).

Jonathan Miller, Darwin for Beginners (Pantheon 1982 but much reprinted) is a fine place to get up to speed, helped by the illustrations by Borin van Loon. Called Introducing Darwin in some editions.

John Maynard Smith and Eors Szathmary, The Major Transitions in Evolution (W. H. Freeman 1995).

Ernst Mayr, This is Biology: The Science of the Living World (Harvard University Press 1997).

Jonathan Weiner, The Beak of the Finch: A Story of Evolution in Our Time (Knopf 1994).

Christopher Wills, Understanding Evolution (W. H. Freeman 2002).

Edward O. Wilson, Consilience (Knopf, 1998).

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The gradual climate change story, about the only aspect of climate change that has reached a large audience, is not covered adequately by the present book. Few realize how strong the case is for global warming, so let me repeat here some of the items from the IPCC summary of where gradual climate change seems to be going, “Climate Change 2001: The Scientific Basis.”

· The global-average surface temperature has increased over the 20th century by about 0.6°^C.

· Globally, it is very likely that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861 . . . the increase in temperature in the twentieth century is likely to have been the largest of any century during the past 1000 years.

· On average, between 1950 and 1993, night-time daily minimum air temperatures over land increased by about 0.2°^C per decade. This is about twice the rate of increase in day-time daily maximum air temperatures (0.1°^C per decade). This has lengthened the freeze-free season in many mid- and high-latitude regions.

· Satellite data show that there are very likely to have been decreases of about 10 percent in the extent of snow cover since the late 1960s, and ground-based observations show that there is very likely to have been a reduction of about two weeks in the annual duration of lake- and river-ice cover in the mid- and high-latitudes of the Northern Hemisphere, over the twentieth century.

· There has been a widespread retreat of mountain glaciers in non-polar regions during the twentieth century.

· Northern Hemisphere spring and summer sea-ice extent has decreased by about 10 to 15 percent since the 1950s. It is likely that there has been about a 40 percent decline in Arctic sea-ice thickness during late summer to early autumn in recent decades and a considerably slower decline in winter sea-ice thickness.

· Tide-gauge data show that global-average sea level rose between 0.1 and 0.2 meters during the twentieth century.

· It is very likely that precipitation has increased by 0.5 to 1 percent per decade in the twentieth century over most mid- and high-latitudes of the Northern Hemisphere continents, and it is likely that rainfall has increased by 0.2 to 0.3 percent per decade over the tropical (10°N to 10°S) land areas.

· In the mid- and high-latitudes of the Northern Hemisphere over the latter half of the twentieth century, it is likely that there has been a 2 to 4 percent increase in the frequency of heavy precipitation events [thunderstorms and large-scale storm activity].

· Warm episodes of the El Niño-Southern Oscillation (ENSO) phenomenon… have been more frequent, persistent and intense since the mid 1970s, compared with the previous 100 years.

· In some regions, such as parts of Asia and Africa, the frequency and intensity of droughts have been observed to increase in recent decades.

· A few areas of the globe have not warmed in recent decades, mainly over some parts of the Southern Hemisphere oceans and parts of Antarctica.

· The atmospheric concentration of carbon dioxide has increased by 31 percent since 1750. The present CO₂concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years.

· About three-quarters of the anthropogenic emissions of CO₂ to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation . . . .

The entire document is at http://www.ipcc.ch.

Chapter Notes

When a reference is briefly given as Author (year), it means that the full reference will be found nearby or in the Recommended Reading section.

page
3 Alley (2000). The several-year figure is apropos of the suddenness with which the last ice age ended about 15,000 years ago in the Northern Hemisphere, e.g., “the last ice age came to an abrupt end over a period of only three years.” But “big changes in less than a decade” is how paleoclimatologists typically characterize all of the abrupt warmings and coolings in the best ice cores, though the full time course from one stable state to another may take a few decades.

3 Even in ordinary dry spells such as the summer of 2000, “We have the hottest driest weather in perhaps 50 years, we have thousands of lightning strikes an hour, we have 300 new fires every day in the West, largely because of lightning strikes,’’ a senior forest service official said. Reuters news story, 27 August 2000, datelined Boise, Idaho, USA.

3 Episodes this brief are seldom detected later by scientists studying the layers, as the worms churn the evidence, mixing up the layers from an entire millennium. Such smoothings make it impossible to tell whether a cooling developed abruptly or more slowly, and it totally hides many of the century-long abrupt coolings and droughts, which become little bumps in the record.

4 Phoenix Generation: Ovid didn’t describe ashes in the Assyrian version but Hans Christian Andersen added fire in The Phoenix Bird (1872) version.

7 Jared Diamond, The Third Chimpanzee (HarperCollins 1992).

7 Besides the brain enlargement two million years ago, there was a further shift away from ape-like specializations; marathon-like endurance likely developed and childhood became even longer. See Leakey (1995).

11 Loren Eiseley, The Night Country (Scribners 1971), p.159. Alley (2000), p.83.

Darwin’s home

13 Solene Morris, Louise Wilson, Down House: The Home of Charles Darwin (English Heritage 1998). Directions to Down House can be found at http://WilliamCalvin.com/bookshelf/down_hse.htm

An excellent biography in two volumes is Janet Browne’s Charles Darwin (Jonathan Cape 1995, 2002). For Darwin’s correspondence, see http://www.lib.cam.ac.uk/Departments/Darwin/.

14 Dennett (1995), p.21.

16 “Swinging gait,” see Francis Darwin, “A character sketch by Darwin’s son,” pp. 88-107 in his The Life and Letters of Charles Darwin (1887).

16 There is a nice summary of the modern synthesis and punctuated equilibria in Tattersall (1998), ch. 3.

18 Repeating catastrophes: the impact catastrophe at 65 million years ago was also a series of events and, while the extinction of the dinosaurs is one result, the adaptive radiation of mammals was another.

18 I don’t know who used the phrase first, but George Orwell wrote “Catastrophic gradualism” in the Common Wealth Review (November 1945); see Collected Essays, Journalism and Letters, vol. 4 (Harmondsworth 1978), p.35.

19 Cronin (1992), p.7.

20 Mayr (1997), p.189.

Evolution House, Kew Gardens

21 John Burnet, “Empedocles of Acragas” at http://plato.evansville.edu/public/burnet/ch5b.htm.

23 Darwin’s 1838 insight upon reading Thomas Robert Malthus, Essay on the Principle of Population (1798), is covered in Browne (1995) at pp.385-388.

24 A biography of Alfred Russel Wallace is at http://www.wku.edu/~smithch/index1.htm.

24 Memes are discussed in Richard Dawkins, The Selfish Gene (Oxford University Press, revised edition 1989); Susan Blackmore, The Meme Machine (Oxford University Press 1999); and William H. Calvin, “The Six Essentials: Minimal Requirements for the Darwinian Bootstrapping of Quality,” Journal of Memetics 1 (1997) at http://WilliamCalvin.com/1990s/1997JMemetics.htm.

My six essentials build on the three which Alfred Russel Wallace listed in 1875 (“. . . the known laws of variation, multiplication, and heredity . . . have probably sufficed. . . . ”); I make explicit the pattern, the work space competition, and the environmental biases. See Wallace’s “The limits of natural selection as applied to man,” chapter 10 of Contributions to the Theory of Natural Selection (Macmillan 1875).

25 Between a third and a half of an infant’s cortical connections present at eight months of age seem to disappear by adulthood, although few neurons are lost; essentially, some axon branches are retracted. The best data is in monkey: P. Rakic, J.-P. Bourgeous, M. F. Eckenhoff, N. Zecevic, and P. Goldman-Rakic, “Concurrent overproduction of synapses in diverse regions of the primate cerebral cortex,” Science 232:232-234 (1986). But the figure reflects the balance between creation of new synapses and breaking of old ones – and we don’t yet know the rate of either creation or destruction, just some estimates of the cumulative differences. For all we know, there could be a turnover of five percent every month, with the rate of destruction only slightly greater than the rate of creation leading to the observed differences.

26 Mutations are also needed to restore variation to an inbreed population like the cheetahs who, while they might have gene-shuffling and recombination, don’t have very many alternative alleles to shuffle.

Down among the fossils

27 Why ocean bottoms remain cold, see Philander (1998), p.128. A dramatic example of trapped CO₂ bubbling out in the manner of an uncapped bottle of seltzer occurs in volcanic lakes such as Lake Nyos in the mountainous region of northwestern Cameroon, where 1,700 people were killed in 1986. A strong wind causes the stratified lake to turn over; the gas-rich bottom waters, upon reaching the surface, release their gas in huge quantities. In the case of Lake Nyos in 1986, the jet of gas and water shot up about 260 feet. Moving at about 45 miles an hour, the gas reached villages 12 miles away. The lake released about a cubic kilometer of carbon dioxide.

It is also a sterling example of a recurring natural disaster that, now that scientists understand its mechanism, can be prevented via appropriate technology. Michel Halbwachs, Jean-Christophe Sabroux, “Removing CO₂ from Lake Nyos in Cameroon,” Science 292(5516): 438 (20 April 2001; http://www.sciencemag.org/cgi/content/full/292/5516/438a; see the 27 February 2001 New York Times news story, “Trying to tame the roar of deadly lakes,” at http://www.nytimes.com/2001/02/27/science/27LAKE.html.

28 Flow through clouds, see Philander (1998), p.84. For “latent heat,” see the glossary.

28 Tom Lehrer, see http://www.keaveny.demon.co.uk/lehrer/lyrics

31 Concealed ovulation, see Jared Diamond, Why is Sex Fun? (Basic Books 1997).

31 The C word: William H. Calvin, “Competing for Consciousness: A Darwinian Mechanism at an Appropriate Level of Explanation,” Journal of Consciousness Studies 5(4)389-404 (1998).

Frans de Waal, Frans Lanting, Bonobo: The Forgotten Ape (University of California Press 1997) . For more bonobo information, see http://WilliamCalvin.com/teaching/bonobo.htm.

Musée de l’Homme in Paris
35 An excellent web starting point for paleoanthropology and its terminology is at http://www.becominghuman.org. You can find various dates for common ancestors, depending on the method and particular genes being used. Two recent references, with citations of other dating attempts, are:

F. C. Chen and W. H. Li, “Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees,” American Journal of Human Genetics 68(2):444-456 (February 2001).

S. L. Page and Morris Goodman, “Catarrhine phylogeny: Noncoding DNA evidence for a diphyletic origin of the mangabeys and for a human-chimpanzee clade,” Molecular Phylogenetics and Evolution 18(1):14-25 (January 2001).

35 Sonia Ragir, “Diet and food preparation: Rethinking early hominid behavior,” Evolutionary Anthropology 9:153-155 (2000).

Sonia Ragir, Martin Rosenberg, Philip Tierno, “Gut morphology and the avoidance of carrion among chimpanzees, baboons, and early hominids,” Journal of Anthropological Research 56:477-512 (2000) at http://www.unm.edu/~jar/v56n4.html#a3.

Mark F. Teaford and Peter S. Ungar, “Diet and the evolution of the earliest human ancestors,” Proceedings of the National Academy of Sciences (U.S.) 97: 13506-13511 (5 December 2000).

Richard W. Wrangham, James Holland Jones, Greg Laden, David Pilbeam, and NancyLou Conklin-Brittain, “The raw and the stolen: Cooking and the ecology of human origins,” Current Anthropology 40(5):567-594 (December 1999).

36 Frans B. M. de Waal, “Apes from Venus: Bonobos and human social evolution,” in Tree of Origin, edited by Frans B. M. de Waal (Harvard University Press 2001), pp. 39-68.

36 Richard Wrangham, Dale Peterson, Demonic Males: Apes and the Origins of Human Violence (Houghton Mifflin 1996).

37 Kaye E. Reed, “Early hominid evolution and ecological change throughout the African Plio-Pleistocene.” Journal of Human Evolution 32:289-322 (1997). Says australopithecines are found associated with faunas suggesting wooded habitats.

37 Yves Coppens, “The East Side story,” Scientific American, pp. 88-95 (May 1994).

38 Monkeys out-competing chimps is just the latest version; there used to be lots more ape species, many more than Old World Monkeys. But the monkeys have been gaining with the Pleistocene climate changes, showing that being smarter is not always better. The Uganda story is from Michael P. Ghiglieri, East of the Mountains of the Moon: Chimpanzee Society in the African Rain Forest (Free Press 1988).

39 Leo Gabunia, Abesalom Vekua, David Lordkipanidze, Carl C. Swisher III, Reid Ferring, Antje Justus, Medea Nioradze, Merab Tvalchrelidze, Susan C. Antón, Gerhard Bosinski, Olaf Jöris, Marie A.de Lumley, Givi Majsuradze, Aleksander Mouskhelishvili, “Earliest Pleistocene hominid cranial remains from Dmanisi, Republic of Georgia: Taxonomy, geological setting, and age,” Science 288:1019-1025 (12 May 2000).

39 C. C. Swisher, W. J. Rink, S. C. Anton, H. P. Schwarcz, G. H. Curtis, A. Suprijo and Widiasmoro, “Latest Homo erectus of Java: Potential contemporaneity with Homo sapiens in southeast Asia.” Science 274: 1870-1874 (1996).

40 The scaled-down version of the multiregional hypothesis is Milford H. Wolpoff, John Hawks, David W. Frayer, Keith Hunley, “Modern human ancestry at the peripheries: A test of the replacement theory,” Science 291:293-297 (12 January 2001).

Yuehai Ke, Bing Su, Xiufeng Song, Daru Lu, Lifeng Chen, Hongyu Li, Chunjian Qi, Sangkot Marzuki, Ranjan Deka, Peter Underhill, Chunjie Xiao, Mark Shriver, Jeff Lell, Douglas Wallace, R Spencer Wells, Mark Seielstad, Peter Oefner, Dingliang Zhu, Jianzhong Jin, Wei Huang, Ranajit Chakraborty, Zhu Chen, and Li Jin, “African origin of modern humans in east Asia: A tale of 12,000 Y chromosomes,” Science 292:1151-1153 (10 May 2001). “We came to a simple conclusion,” says Li Jin. “There are no old lineages left [from archaic Asians].”

One self-described “dedicated multiregionalist,” Vince Sarich of the University of California, Berkeley, said: “I have undergone a conversion – a sort of epiphany. There are no old Y chromosome lineages [in living humans]. There are no old mtDNA lineages. Period. It was a total replacement.”

41 Wisteria and Out of Africa, see Kenneth Kidd.

42 H. Thieme, “Lower Paleolithic hunting spears from Germany,” Nature 385:807-810 (1997).

43 Gordon H. Orians, “Human behavioral ecology: 140 years without Darwin is too long,” Bulletin of the Ecological Society of America 79(1):15-28 (1998).

43 The English landscape architects were good at keeping the large animals in the distance. They hid a fence in a “ha-ha,” a ditch through the landscape. From the customary viewpoint, the viewer didn’t see the ditch, looking right over the top of it at the distant pastoral landscape.

46 Category carryover from altruism to syntax: William H. Calvin, Derek Bickerton, Lingua ex Machina: Reconciling Darwin and Chomsky with the Human Brain (MIT Press, 2000), chapter 10.

Bockenheim.........................................................

48 Sanborn C. Brown, Benjamin Thompson, Count Rumford (MIT Press 1979).

48 Quarter-century per generation: One sometimes sees 20 years given for the human generation time. But a reasonable definition is not the shortest possible interval but the age of the mother at the birth of a child, averaged over her children that survive. With menarche at 17 in Sweden only a century ago, and with the first baby having a lower chance of survival, I’d guess that the average surviving children were mostly born when the mother was between 20 and 30.

49 Richard Dawkins, The Selfish Gene (Oxford University Press 1976), p.214.

52 Jeremy R. Marlow, Carina B. Lange, Gerold Wefer, Antoni Rosell-Melé, “Upwelling intensification as part of the Pliocene-Pleistocene climate transition,” Science 290:2288-2291 (22 December 2000).

55 Leslie C. Aiello, Peter Wheeler, “The expensive tissue hypothesis: The brain and the digestive system in human and primate evolution,” Current Anthropology 36:199-221 (1995). And see Ann Gibbon’s news story, “Solving the brain’s energy crisis,” Science 380: 1345-1347 (29 May 1998).

Layover Limbo

59 “Enlarge one neocortical area, enlarge them all” paraphrased from: Barbara L. Finlay and R. B. Darlington, “Linked regularities in the development and evolution of mammalian brains,” Science 268:1578-1584 (1995).

59 Variation within and between species: As my colleague Joe Felsenstein is fond of pointing out (the “coalesce fallacy”), suppose you have two species A and B. You plot brain size vs body size for a hundred As, and perhaps you get a symmetrical scatter with no trend. Ditto for B, except that Bs are usually bigger than As. If you mix up As and Bs into one big scatter plot (and don’t plot the points in different colors), you get an impressive upwards trend: “bigger bodies have bigger brains,” someone shouts - all without being able to see the trend within either species by itself. Maybe the trend doesn’t exist at all, and is just an artifact of lumping when you should be splitting. Actually bigger bodies within a species usually do have bigger brains, but there are many situations where lumping groups can mislead you. Correlation is not causation, and sometimes correlation itself is – as with lumping the hypothetical As with the Bs – meaningless. The same caution applies, say, to plotting brain size vs. IQ scores for different geographic subpopulations, e.g., races. You need to establish the trend within the subpopulation and you constantly have to look out for a correlation which isn’t cause and effect but merely a mutual consequence of some third thing such as growth rates or hormone levels at critical periods during development.

61 I earlier discussed the r-K spectrum in chapter 6 of my The Ascent of Mind (Bantam 1990), at http://WilliamCalvin.com/bk5/bk5ch6.htm.

Life history analysis: Barry Bogin, Patterns of Human Growth, 2nd ed. (Cambridge University Press 1999).

63 The data in the figure is adapted from figure 8.3 of Klein (1999), which is based on the 1990 collection of Aiello and Dean.

The Sahara

65 J. Kutzbach, G. Bonan, J. Foley, S. P. Harrison, “Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene,” Nature 384:623-626 (19 December 1996).

J. E. Kutzbach, Z. Liu, “Response of the African Monsoon to Orbital Forcing and Ocean Feedbacks in the Middle Holocene,” Science 278(5337) 440-443 (17 October 1997).

Martin Claussen, Claudia Kubatzki, Victor Brovkin, Andrey Ganopolski, Philipp Hoelzmann, Hans-Joachim Pachur, “Simulation of an abrupt change in Saharan vegetation in the mid-Holocene,” Geophysical Research Letters 26(14):2037-2040 (15 July 1999).

Philipp Hoelzmann, Birgit Keding, Hubert Berke, Stefan Kröpelin and Hans-Joachim Kruse, “Environmental change and archaeology: Lake evolution and human occupation in the Eastern Sahara during the Holocene,” Palaeogeography, Palaeoclimatology, Palaeoecology 169:193-217 (2001).

Ana Moreno, Jordi Targarona, Jorijntje Henderiks, Miquel Canals, Tim Freudenthal and Helge Meggers, “Orbital forcing of dust supply to the North Canary Basin over the last 250 kyr,” Quaternary Science Reviews 20(12):1327-1339 (June 2001).