The Baby-Sling Hypothesis

for Human Evolution


Hair Distribution, Immuno-resistance and Adaptations to the First Baby Slings

This essay, which appeared in Anthropologie - International Journal of Human Diversity and Evolution (2013, Volume 51, Issue 3: 349-374), was first disseminated to advance readers in the UK, United States, South Africa and Australia in August 2008. It contains two hypotheses. The first postulates that infectious and parasitic conditions in the first baby-carrying devices or “slings” selected for changes in juvenile hair distribution and immuno-resistance, and that a convergence of datable mutations and osteological changes indicate that infants in our lineage adapted to the microenvironment between 1.2 and 2.8 million years ago - with evidence converging towards the older end of that range. Such slings, which might have been first used to carry gleanings, would have surrounded offspring in dangerous pathogens and parasites. Babies whose fetal body baldness had not disappeared would have had an advantage over infants with previously normal body fur, because adults could clean them better – probably resulting in the neotenic extension of the fetal trait.

The microenvironment might have selected for the elimination of infectious pathways as well. The inactivation of the CMAH gene, which could have provided a pathway for germs associated with ungulate and proboscidean hides to infect infants with deadly diarrhea, is explored as a candidate, and multiple ways of testing the hypothesis are described.

The related hypothesis, which is based partly on avian comparisons and milk chemistry, postulates that slings gradually forced adults to focus on the kind of nutrition needed by more slowly maturing infant brains by making their babies more altricial. This might have triggered more scavenging, hunting, and feedback mechanisms that slowly extended the new juvenile hair distribution to adults as part of a whole-body cooling system based on sweat and body baldness while contributing to speciation.

Even though the paper has been well received by numerous prehistorians and paleoanthropologists*, including the anonymous referees, its contention that infectious environments in the first baby-carrying devices caused selective infant mortality and a founder’s effect, which led to the speciation at the root of our genus, is bound to be controversial.

Please click on the following thumbnail photos, which I’ve used as icons, to see the web pages or PDFs described in the captions.

PDF: Hair Distribution, Immuno-resistance and Adaptations to the First Baby Slings. This article, which appeared in Anthropologie - International Journal of Human Diversity and Evolution (2013, Vol. 51, Issue 3: 349-374) proposes new mechanisms for the speciations at the root of the human genus, Homo.



  1. *Comments by advance readers include:

•    Robert Bednarik, the editor of Rock Art Research: “I think that your paper is very well argued, but will be hard to ‘sell’, because of its sophistication” (email, 10 Dec. 2008).

•    Francesco d'Errico, Director of Research CNRS, University of Bordeaux, France & Honorary Professor, Institute for Human Evolution, University of the Witwatersrand, South Africa: “... I found the idea and integrated interdisciplinary way you deal with the question fascinating. It is certainly worth publishing” (email, 12 Jan. 2010).

© 2008-2014 Duncan Caldwell on text © 2009 Duncan Caldwell on photos


Key words: Baby sling, Baby slings, human evolution, body baldness, evolution of human hair, human hair distribution, human body hair evolution, naked skin, human hairlessness, loss of fur, emergence of large brains, brain evolution, brain expansion, thermoregulatory control, sweat glands, evolution of sweating, aquatic ape theory, Peter Wheeler, Nina G. Jablonski, The Naked Truth, Scientific American, archaeology, paleontology, why humans have no fur, human brain evolution

Other Prehistory Pages

World's Oldest Optical Illusion Found?” -
National Geographic article by Andrew Howley about Duncan Caldwell’s discovery of one of the world’s oldest known intentional optical illusions (Dec. 22, 2010)

PDF: An historic sign, possible Mesolithic menhir, DStretch, and problems in dating rock art to the Sauveterrian in the Massif de Fontainebleau. Co-authored with my intern, Ulrika Botzojorns. Journal of Archaeological Science (2014, Vol. 42, February: 140-151)                     

PDF: The First Paleolithic Animal Sculpture in the Ile-de-France: The Ségognole 3 Bison & its Ramifications. L’Art Pléistocène dans le Monde / Pleistocene Art of the World / Arte Pleistoceno en el Mundo. Edited by Jean Clottes. Actes du Congrès IFRAO, Tarascon-sur-Ariège, septembre 2010, N° spécial de Préhistoire, Art et Sociétés, Bulletin de la Société Préhistorique Ariège-Pyrénées, LXV-LXVI, 2010-2011. ISBN 987-2-9531148-3-6

PDF: Supernatural Pregnancies:  Common features and new ideas concerning Upper Paleolithic feminine imagery. 2010. Arts & Cultures, Barbier-Mueller Museum

A Murder, Bombing, and Trip to “Dolmens”

The “prey-mother” hypothesis concerning Paleolithic feminine imagery & venus figurines

PDF: Observations et hypothèses sur le site du Paly : Milly-la-Forêt (Essonne). This article is the second of two papers about engravings at a megalithic complex around le menhir du Paly. After announcing the discovery of fingers, which confirm that a cruciform  motif on the menhir is really an anthropomorph, and not a Christian cross, it goes on to reveal other discoveries and interpret the “idol” in relation to the site’s possible structure and uses.  The paper speculates that the circle composed of nine white dots, which seem to form the anthropomorph’s belly, could represent the nine lunar months which occur between a woman’s last period and a full-term birth. If this supposition is correct, then the circle  may be one of the oldest known pregnancy calendars. The article goes on to describe a number of humanly modified features on the adjacent slab, including a pair of carved and polished basins, which probably began as solution cavities. The polishing may have been done to modify the shapes of the puddles, which form in them and double as mirrors of the sky. The puddle that forms in the larger one becomes almost perfectly circular, while the one in the smaller basin varies between an oblong and disc, depending on its depth, making it look like a changing moon. The smaller of these cavities, whose water flows to the larger one, also has four natural cracks, grooves, and accentuated cracks, which correspond perfectly to the four cardinal points, forming a cross. The second and larger of the polished bowls has an incision pointing due north, two natural cracks pointing east and west, and one heavy and two light incisions pointing northwest to 300 and 330°. The article goes on to discuss an oriented grid and other engravings at this crucial site for interpreting the Neolithic iconography of northwestern France. (Art Rupestre : Bulletin du GERSAR n° 63 - janvier 2013: 29-32)

PDF: Le Visage Gravé du Closeau 12 et ses Implications. Nanteau-Sur-Essonne (Seine-Et-Marne). This article, which revealed the existence of a huge, plumed, Neolithic face on a stele at Le Closeau, Nanteau-sur-Essonne, France,  appeared in Art Rupestre in July 2013. After comparing the iconography of statue-menhirs from Guernsey to Switzerland, it concludes that the Closeau stele may be one of the oldest ones in France. (Art Rupestre : Bulletin du GERSAR n° 64 - juillet 2013: 37-46)

PDF: A Possible New Class of Prehistoric Musical Instruments from New England: Portable Cylindrical Lithophones. This article, which appeared in the July 2013 issue of American Antiquity, argues that highly sculpted lithophones were used during funerals around 8,000 years ago (the early Archaic Period) in the Canadian Maritimes and New England. Reproduced by permission of the Society for American Archaeology from American Antiquity 78(3), 2013: 520-535.

The Foz Coa / Coa Valley prehistoric rock art scandal

Prehistoric Art Emergency &  Foz Coa /

Coa Valley home page

The Neanderthal / Neandertal insulation hypothesis concerning Neanderthal diets, behavior, extinction & adaptations to cold

Expedition Photos

Ancient & tribal feminine imagery

Prehistory home page

Historical & Biographical Pages


Spy Catcher, my father, Robert Caldwell’s, biography