The skeleton articulated

Jan Zalasiewicz enjoys Brian Switek’s exploration of how the human scaffold — and our ideas about it — evolved.

Jan Zalasiewicz

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Our bones have evolved over millions of years.Credit: Nick Veasey

Skeleton Keys: The Secret Life of Bone Brian Switek Riverhead (2019)

The bony scaffolding beneath our skin can move us emotionally as well as physically. In enabling our lives, yet enduring beyond them, our skeletons challenge our understanding of ourselves. This premise underpins Brian Switek’s Skeleton Keys, a thoughtful, engaging meditation on the origins of the human skeleton, how it functions (or malfunctions) and how we come to terms with our essential but unsettling osseous framework.

Bone’s potential for physical immortality reminds us all too vividly of our personal mortality. Switek conveys the Grand Guignol aspects of this with suitably horrified fascination — contemplating, say, the bones of England’s King Richard III, hacked and broken in his final hour on the battlefield. Dinosaur bones, however awe-inspiring, cannot chill the spine in quite the same way as the fleshless frames of our own kind.

A ênfase é assim muito no "nosso". Switek há muito entusiasmou e escreveu elegantemente sobre os ossos de nossos parentes distantes, não menos os dinossauros. E alguns, como o monstruoso Supersaurus, são abordados neste livro. A história ainda mais antiga dos vertebrados é bem delineada desde o início, suas origens no período Cambriano, exemplificado pelo Pikaia, um organismo marinho extinto parecido com uma enguia que não tinha esqueleto, mas provavelmente possuía uma notocorda, a precursora da coluna vertebral. O Pikaia foi encontrado nos cerca de 508 milhões de anos de idade Burgess Shale, um rico tesouro descoberto no Canadá em 1909 pelo temível paleontólogo Charles Doolittle Walcott.

As outras criaturas da cornucópia Burgess - e os muitos esqueletos sofisticados, principalmente externos, então sendo conjurados por grupos de invertebrados, como os artrópodes - são mencionados apenas brevemente. Esta é uma narrativa de osso, não de carapaça, e os primeiros organismos revestidos de carapaça são significativos aqui principalmente para efetivamente empurrar os vertebrados para os lados por mais de 100 milhões de anos. O esqueleto dos vertebrados finalmente prosperou, e Switek descreve alguns passos importantes ao longo do caminho, como a forma como passou de externa para interna entre os primeiros peixes.

Further towards our particular twig of life’s tree, dinosaurs make a guest appearance, with legendary nineteenth-century US bone hunters and sworn enemies Edward Drinker Cope and Othniel Charles Marsh in the spotlight. Obsessively driven, and each burning their way through a family fortune, they unearthed many iconic dinosaurs, such as Triceratops and Diplodocus. There is nothing on their UK counterpart Mary Anning, although she performed comparable palaeontological miracles in extracting ichthyosaurs and plesiosaurs from dangerous Dorset cliffs. This nascent scientific field had formidable female protagonists, too, working against tremendous odds.

Close to the bone

Os próximos 100 milhões de anos, nos quais os mamíferos floresceram, são cobertos rapidamente, para chegar à bonança óssea do Pleistoceno dos depósitos de alcatrão de La Brea, em Los Angeles, Califórnia. Descrevendo-os como o mais importante sítio fóssil do planeta (que é a luta entre os paleontólogos), Switek concentra-se no conjunto de ossos humanos encontrados entre os mamutes e leões e gatos com dentes de sabre. Chamada de La Brea Woman, seus restos de 10 mil anos permitem que Switek explique as complexidades físicas e químicas do osso em geral e dos ossos humanos em particular. E é uma coisa extraordinária, permitindo resiliência e força, e contínua remodelação interna. Os esqueletos dos vertebrados, ao contrário dos dos artrópodes, não precisam ser sucessivamente mudados à medida que o animal cresce, e assim podem alcançar vastas dimensões - como na baleia azul.

This narrative is neatly done, but the fascination exerted by human bone on human minds lies at the book’s heart. With Switek, we visit Neolithic tombs and medieval ossuaries, consider skull cults and muse on the bony personification of Death. The book makes extended explorations of how nineteenth-century anthropologists such as Samuel Morton in Philadelphia, Pennsylvania, used skull measurements to claim the existence of racial differences, a malign legacy that, although long discredited in science, lingers today in apologias for racism. Switek also describes the protracted tug-of-war between scientists and the Native American community around the Columbia River in Washington state over who owns the 9,000-year-old skeleton of the Ancient One, also known as Kennewick Man (D. H. Thomas Nature 531, 302–303; 2016). This is terrain most palaeontologists never navigate; Switek picks through it well.

In the book’s coda, the narrative gets up close and personal. Switek considers his own skeleton, and how it might follow those of the dinosaurs into geological immortality. Switek’s deep-time focus comes through a little too strongly, I think, in his assertion that it is mainly our skeletons that will be left to tell of our passing. Of the detritus that each of us casually scatters — thousands of ballpoint pens, polyester socks, aluminium cans and so on — much is a good deal more decay-resistant than the average cranium or femur. Our bones might be only a small part of our ultimate legacy.

Nevertheless, as this book shows, the skeletal side of life grips us now, and might enthral whoever excavates our remains in the far future. As Switek ponders the sediments in which his own bones might be fossilized, he needs to think of larger geological processes. The sea floor off the shore of New Orleans, Louisiana, might provide a good start: there are stagnant muds, and local tectonic subsidence will allow the fossil to be securely entombed. In the meantime, we should enjoy Switek’s talent for spinning compelling tales of old bones.

Nature 566, 452-453 (2019)

doi: 10.1038/d41586-019-00679-9

Esmalte do dente permite determinar sexo de esqueleto humano

Análise de fragmentos de proteína responsável pela formação da coroa dentária ajudou a atribuir o sexo de remanescentes humanos de cerca de 5 mil ano.

RODRIGO DE OLIVEIRA ANDRADE | Edição Online 20:17 27 de dezembro de 2017

© PAULA ELAINE SGOBBI

Análise de fragmentos da proteína amelogenina permitiu identificação do sexo de esqueletos humanos de cerca de 5 mil anos.

Um método desenvolvido por um grupo internacional de pesquisadores, entre eles a bióloga Raquel Gerlach, da Faculdade de Odontologia da Universidade de São Paulo (USP), em Ribeirão Preto, poderá auxiliar na identificação do sexo de partes de esqueletos em estudos em arqueologia, paleoantropologia e no âmbito das ciências médico-legais.

A técnica se baseia na análise de fragmentos (peptídeos) da proteína amelogenina, responsável pela formação da coroa dentária, a parte visível dos nossos dentes. A amelogenina é codificada no cromossomo X, presente nos homens e nas mulheres, e no cromossomo Y, apenas nos homens, com poucas diferenças quanto às sequências de aminoácidos.

No estudo, os pesquisadores identificaram 23 diferenças entre a amelogenina codificada nos cromossomos Y e X. Em seguida, analisaram, às cegas, amostras de dentes humanos de múmias cujo sexo já era conhecido encontradas na região de Durham, na Inglaterra.

Os pesquisadores usaram uma pequena amostra do esmalte dentário das múmias e, em cada uma delas, foi aplicada uma solução ácida. O material dissolvido foi analisado em um espectrômetro de massa, usado para separar e identificar proteínas.

© PAULA ELAINE SGOBBI

Após ser coletada, amostra do esmalte dentário foi dissolvida e analisada em um espectrômetro de massa, usado para separar e identificar proteínas.

“Com base em diferenças identificadas anteriormente, conseguimos atribuir corretamente o sexo desses remanescentes humanos de cerca de 5 mil anos”, explica Raquel, coautora do estudo descrevendo os resultados da técnica publicado em dezembro na revista Proceedings of the National Academy of Sciences (PNAS).


O novo método apresenta-se como uma alternativa aos métodos empregados atualmente. “Hoje, para identificar o sexo de esqueletos, é preciso triturar dentes e ossos em uma solução específica para conseguir detectar o DNA por análise de PCR. Isso acarreta na destruição da amostra”, explica. “A vantagem da nova técnica é que ela não é invasiva, por se basear apenas na análise de proteínas presentes em uma pequena parte do esmalte dos dentes, que são preservados.”
Segundo ela, o próximo passo é analisar o desempenho da nova técnica em situações em que os ossos foram submetidos a altas temperaturas. “Sabe-se que nesses casos é difícil recuperar amostras de DNA”, explica a bióloga. “Vamos verificar se os peptídeos se mantêm bem preservados no esmalte do dente quando submetidos a situações similares às de incêndios”, completa.

Projeto
 
Busca e identificação de peptídeos de isoformas de amelogeninas codificadas especificamente a partir do cromossomo X ou do cromossomo Y em dentes humanos extraídos (nº 11/23963-3); Modalidade Auxílio à Pesquisa – Regular; Pesquisador responsável João Paulo Mardegan Issa (USP/Ribeirão Preto); Investimento R$ 31.919,17 (FAPESP).

Artigo científico 
 
STEWART, N. A. et al. Sex determination of human remains from peptides in tooth enamel. PNAS. On-line. dec. 2017.

Skeleton plundered from Mexican cave was one of the Americas’ oldest

Rock-encased bone shard left behind by thieves allowed researchers to determine that the remains are probably more than 13,000 years old.

• Ewen Callaway

30 August 2017

Nick Poole/Liquid Jungle

A human skeleton — probably one of the Americas' oldest — was stolen from the Chan Hol Cave in Mexico soon after it was discovered in 2012. 

A human skeleton that was stolen from an underwater cave in Mexico in 2012 may be one of the oldest ever found in the Americas. Scientists have now put the age of the skeleton at more than 13,000 years old after analysing a shard of hip bone — left behind by the thieves because it was embedded in a stalagmite.

Cave divers discovered the remains in February 2012 in a submerged cave called Chan Hol near Tulúm on Mexico's Yucatán peninsula, and posted photos of a nearly complete skull and other whole bones to social media. The posts caught the attention of archaeologists Arturo González González at the Desert Museum in Saltillo, Mexico, and Jerónimo Avilés Olguín at the Institute of American Prehistory in Cancún.

By the time researchers visited the cave in late March, the remains were gone — except for about 150 bone fragments and a pelvic bone that had been subsumed by a stalagmite growing up from the cave floor. On the basis of these bones, the researchers think that the skeleton belonged to a young man who died when sea levels were much lower and the cave was above ground.

Dating techniques

To determine the age of human remains, researchers often measure levels of a radioactive isotope of carbon in collagen protein within bones. But in this case, most of the collagen had been leached out by water while the bones were submerged, making this method unreliable, says Wolfgang Stinnesbeck, a palaeontologist and geoscientist at the University of Heidelberg, Germany, who led the efforts to date the remains.

Instead, Stinnesbeck’s team collected a fleck of the pelvis bone and surrounding stalagmite, which contains a mineral called calcite. The team then dated the rock using the relative levels of uranium and thorium isotopes in the calcite. The deeper into the stalagmite the researchers sampled, the older the dates turned out to be; stone just 2 centimetres from the bone was 11,300 years old. Calcite closer to the bone gave conflicting results, Stinnesbeck says.
The team determined that the skeleton was older than 13,000 years by analysing the rate at which calcite had formed around the bone, and by matching the shifts in stalagmite isotope levels to those in other caves. The findings were published on 30 August in PLoS ONE¹.

Eugenio Acevez Nunez

A diver collects a portion of a cave stalagmite found in cave that contains ancient human bones.

Alistair Pike, an archaeological scientist at the University of Southampton, UK, notes that the stalagmite set over the bone during a time of profound climate change, which could have altered the stalagmite's rate of growth. He says he is therefore more comfortable considering the bones to be a minimum of 11,300 years old — still “very significant”, he notes.

Ancient company

Few other human remains from the Americas are older than 13,000 years. The skeleton of a teenage girl recovered from a different Yucatán cave was carbon-dated to more than 12,000 years old, and a skeleton found in another submerged cave near Tulúm was deemed to be around 13,500 years old, also using radiocarbon dating.
“They’ve done a really nice job determining the age of this thing,” says David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas. There is convincing archaeological proof that humans colonized the Americas before 14,000 years ago, but very old remains are precious. “These sites are rare as hen’s teeth,” Meltzer says.
Apart from the Yucatán finds, the next-oldest skeleton from the Americas is that of a 12,600-year-old boy found in Montana, whose sequenced genome places him on a lineage leading to present-day Native American groups. Researchers have sequenced only a few other human skeletons from the Americas that are older than 10,000 years, hindering efforts to unravel the region's ancient population history.

Wolfgang Stinnesbeck

A stalagmite had grown around a shard of ancient pelvic bone (bottom portion). 

Getting DNA from what remains of the Chan Hol skeleton will be hard. A sample sent to one of the world’s leading ancient-DNA labs, the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, did not contain enough DNA, Stinnesbeck says. He hopes to find DNA in the few teeth not taken by the thieves.

The theft still boggles Stinnesbeck, whose team is continuing to study the cave and its remains. The researchers recently reported the discovery of fossils in the cave that are of a new species of peccary² — a hoofed mammal related to pigs — as well as evidence that the cave's human inhabitants made fires.
“What would you want with a skeleton? Would you take it home?” Stinnesbeck asks. “If they had known it was very old, maybe just to have a souvenir, to have something special.”
“We went to the police and they did some inquiries,” he adds. “They never came up with anything substantial.” 

Nature

549,

14–15

(07 September 2017)

doi:10.1038/nature.2017.22521

References

1. Stinnesbeck, W. et al. PLoS ONE 12, e0183345 (2017).
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2. Stinnesbeck, S. R. et al. J. South Am. Earth Sci. 77, 341e349 (2017).
   
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