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What drove the Cambrian Explosion?

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The origin of animals occurred sometime during the Proterozoic Eon, perhaps as early as 2.1 Ga (billion years ago) after the Great Oxygenation Event. Available oxygen is a prerequisite for animal life, and that is about as far back as palaeobiologists can push it. More familiar are the trace fossils known as the Ediacaran fauna which emerged after the environmentally highly stressful Cryogenian Period that was marked by two Snowball Earth events. Traces of these animals may have been big enough to be easily found, but they were not particularly diverse and are difficult to place in any particular modern group. Most modern animals have front- and rear ends, tops and bottoms, and input and output orifices. The earliest of these bilaterian beasts may have emerged during the Ediacaran as well, but were not very prepossessing. It was during the Cambrian Period (541 to 485 Ma) that most modern animal phyla became recognisable to palaeobiologists. That carnival of diversification is widely known as the Cambrian Explosion. Yet it was later in geological time that the full panoply of Phanerozoic diversity among taxa below the level of the phylum truly exploded, punctuated by mass extinctions and the diversification that followed each of them. So, what lay behind the initial emergence of the characteristics that form the basic templates of the phyla themselves?

Cartoon of the Cambrian Explosion in benthic faunas. Credit: Gabriela Mangano and Luis A. Buatois, 2016 The Cambrian Explosion, Fig 3.15

A multinational team of modellers and geoscientists have moved the focus from long-term shifts in climate and atmospheric chemistry to what might change from day to night in an ecosystem during the diel cycle (Hammarlund, E.U. and 13 others 2025. Benthic diel oxygen variability and stress as potential drivers for animal diversification in the Neoproterozoic-Palaeozoic Nature Communications, v. 16, article 2223; DOI:10.1038/s41467-025-57345-0). During the Neoproterozoic oxygen levels in Earth atmosphere rose to about half the amount present today. But animals arose and evolved in sea water. The most prolific source of food for them would have been in shallow water (the benthic zone), simply because sunlight in the photic zone encourages photosynthesis. As well as a thriving base for animal life’s food chain shallow water is where oxygen is produced; but only during daylight hours. At night decay of organic matter on the seabed draws down dissolved oxygen. Emma Hammarlund and colleagues wondered if day-night changes in oxygen levels might have exerted sufficient stress to force early animals to adapt and thus diversify. Their model shows that in warm, shallow water the lower oxygen levels at the start of the Phanerozoic could change dramatically in the diel cycle. Algae at the base of the food chain would swiftly oxygenate the water in daylight, but at night would consume it to produce much lower levels. Animals that were better adapted to the stress of this daily ‘feast-and-famine’ cycle in oxygen availability would outcompete others that were less resilient for the available nutrients. Environmental stress had flipped from an obstacle to evolution to a catalyst for it. The earliest appearances of organisms in the 10 modern phyla seem to coincide with global warming at low latitudes to an air temperature of about 25° C at the start of the Cambrian, perhaps when this shift began.

Another empirical coincidence lies in the sedimentary rock record. On modern continents the base of Phanerozoic sediments is widely marked by shallow-water sandstones often at an unconformity. Often white and containing abundant burrows, the sandstones are signs of abundant life, though rarely contain body fossils. They represent global sea-level rise that flooded the existing continents, so the highly productive benthic environment became about four times more widespread at the end of the Cambrian than it was during the previous Ediacaran Period. Abundant life forms were under stress more or less everywhere. Thereafter these ‘shelf seas’ halved in total area, but the basic ‘templates’ for animal life were well-established and the numbers of classes, orders, families etcetera steadily burgeoned. By the end of the Cambrian oxygen production rose so that atmospheric concentration of the gas reached 25%, higher then it is at present.

See also: Hammarlund, E. 2025. How dramatic daily swings in oxygen shaped early animal life. The Conversation, 21 March 2025.

A cure for the Great British Pothole Plague?

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Anyone who read the manifestos of the mainstream political parties in the UK – there may not be many who did – would have been amused to see that all promised to resolve the plague of potholes in the countries roads, both major and minor. For decades road users have been alarmed when hitting a pothole and in some cases had damage inflicted on their vehicles, and in the case of those on two wheels, on themselves. The RAC (Royal Automobile Club) has estimated that there are, on average, six potholes per mile on Britain’s roads: the greatest density in Europe. The AA (Automobile Association) estimated that almost £0.6 billion was spent in 2024 repairing pothole-damaged vehicles. This is not a new phenomenon. Before the advent of turnpike trusts in the late 18th century, which maintained roads travelled by Britain’s mail coach services, it was not uncommon to encounter potholes up to two metres deep. Legend has it that on one such route through northern Nottinghamshire two coach horses fell into a pothole and drowned. Scottish engineer, John Loudon McAdam invented a solution around 1820: crushed stone laid on the road surface in slightly convex layers, the topmost being bonded with stone dust. This ‘macadam’ surface created cambered highways that drained rainwater to the sides and downwards. Modern roads are still based on that principle, with the addition of tar or bitumen to the top layer to produce a hard, impermeable surface, which also prevents aggregate and dust being sucked from the surface by fast moving vehicles.

A spore of the club moss Lycopodium

So, why the potholes? Several reasons: increased traffic; heavier vehicles; less maintenance; patching rather than resurfacing. Most important: the materials and the weather. Dry, hot weather softens the bitumen and drives out volatile hydrocarbons making the bitumen less plastic. The pounding of tyres in cooler weather fractures the now stiffened bitumen, mainly at microscopic scales. Wetting of the tarmac seeps water into the microfractures. The formation of ice films jacks opens the microfractures and produces more in the cold stiff bitumen, eventually to separate the particles of aggregate in the asphalt. The wearing course begins to crumble so that aggregate grains escape and scatter. Thus weakened, the top layer breaks up into larger fragments and a pit forms to join up with others so that a pothole forms and grows. Wheels of traffic bounce when they cross a pothole, the shock of which causes the centre of degradation to shift and create more cavities. Simply filling the existing potholes merely serves to create new ones: a vicious cycle that can only be broken by complete resurfacing: the traffic cones come out!.

All this has been known for well over a century by civil engineers. Around the start of the 21st century – maybe slightly earlier – it dawned on engineers that the critical problem was degradation of bitumen. A petroleum derivative, occurring naturally as surface seeps in some oilfields, bitumen is chemically complex: a combination of asphaltenes and maltenes (resins and oils). Deterioration of bitumen through evaporation, oxidation and exposure to ultraviolet radiation decreases the maltene content and stiffens the binding agent in asphalt. So the earliest attempts at reducing pothole formation centred on rejuvenation by periodically adding substitutes for maltenes to road surfaces. Diesel (gas-oil) works, but is obviously hazardous. More suitable are vegetable oils such as waste cooking oils or those produced by pyrolysis of cotton, straw, wood waste and even animal manure. The problem is getting the rejuvenators into existing asphalt surfaces: clearly, simply spraying them on the surface seems a recipe for disaster! A solution that dawned on engineers around 2005 was to make bitumen that is ‘self-healing’.

Schematic of the production of microcapsules from club moss spores to contain sunflower oil to be used in self-healing asphalt (Credit: Alpizar-Reyes, E. et al. 2022)

Simply mixing rejuvenators into bitumen during asphalt manufacture will not do the trick, for the result would be a weakened binding agent at the outset. For the last 15 years researchers have sought means of adding rejuvenators in  porous capsules, to release them as microfractures begin to form: on demand, as it were. There have been dozens of publications about experiments that found ‘sticking points’. However, in early 2025 what seems to be a viable breakthrough splashed in the British press. It was made by an interdisciplinary team of scientists from King’s College London and Swansea University, in collaboration with scientists in Chile. They chemically treated spores of Lycopodium club mosses to perforate their cell walls and clear out their contents to be replaced by sunflower oil, an effective bitumen rejuvenator. Experiments showed that such microcapsules released the oil to heal cracks in aged  bitumen samples in around an hour. Mixed into bitumen to be added to asphalt they would remain ‘dormant’ until a microfracture formed in their vicinity released it, thereby making the asphalt binder self healing.

Will such an advance finally resolve the pothole plague? It may take a while …

See: Alpizar-Reyes, E. et al. 2022. Biobased spore microcapsules for asphalt self-healing. ACS Applied Materials & Interfaces, v. 14, p. 31296-31311; DOI: 10.1021/acsami.2c07301

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Apology

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Dear Followers

You will have noticed a 5-week break in my posting news items, for which I need to apologise and to explain.

Despite weekly searching all the leading journals that publish geoscientific papers, none have appeared that meet my criteria for commenting. That is, nothing has emerged that makes a significant breakthrough in any of the the Categories that Earth-logs covers. In fact, since Covid I have noticed a drop in the number of publications that do. Maybe there was a downturn in research during the pandemic, or perhaps some other reason such as a decline in the discipline, of journal policy changes.

There’s not much I can do other than wait patiently, and post when something turns up – you will be among the first to know about it, as ever!

In the meantime, maybe one or more of you have come across something interesting that I missed, or have a question about topics covered earlier. Either way, don’t hesitate to get in touch with me, either with a comment or using the Contact Author link in the Menu bar.

With regards

Steve Drury

Changing Atlantic Ocean currents may threaten Gulf Stream warming of Europe

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Climate during the last Ice Age was continually erratic. Generally fine-grained muds cored from the floor of the North Atlantic Ocean show repeated occurrences of layers containing gravelly debris. These have been ascribed to periods when ice sheets on Greenland and Scandinavia calved icebergs at an exceptionally fast rate, to release coarse debris as they melted while drifting to lower latitudes. These ‘iceberg armadas’ (known as Heinrich events) left their unmistakable signs as far south as Portugal. Their timing correlates with short-lived (1 to 2 ka) warming-cooling episodes (Dansgaard-Oeschger events) recorded in Greenland ice cores that involved variations in air temperature of up to 15°C. The process that resulted in these sudden climate shifts seems to have been changing ocean circulation brought about by vast amounts of fresh water flooding into the Arctic and North Atlantic Oceans. This lowered seawater density to the extent that its upper parts could not sink when cooled. It is this thermohaline circulation that drags warmer surface water northwards, known as the Atlantic Meridional Overturning Circulation (AMOC), part of which is the Gulf Stream. When it fails or slows the result is plummeting temperatures at high latitudes. The last major AMOC shutdown was after 8 ka of warming that followed the last glacial maximum. Between 12.9 and 11.7 ka major glaciers grew again north of about 50°N in the period known as the Younger Dryas, almost certainly in the aftermath of a flood to the Arctic Ocean of glacial meltwater from the Canadian Shield. Around 8.2 thousand years ago human re-colonisation of Northern Europe was set back by a similar but lesser cooling event.

The Atlantic Meridional Overturning Circulation (AMOC). Red – warm surface currents; cyan – cold deep-water flow. (Credit: Stefano Crivellari)

Three researchers at Utrecht University, the Netherlands have issued an early warning that the AMOC may have reached a critical condition (Van Westen, R.M., Kliphuis, M & Dijkstra, H.A. 2024. Physics-based early warning signal shows that AMOC is on tipping course. Science Advances, v. 10, article adl1189; DOI: 10.1126/sciadv.adk1189). Previous modelling of AMOC has suggested that only rapid, massive decreases in the salinity of North Atlantic surface water near the Arctic Circle could shut down the Gulf Stream in the manner of Younger Dryas and Dansgaard-Oeschger events. René van Westen and colleagues have simulated the effects of steady, long-term addition of fresh water from melting of the Greenland ice sheet. They ran a sophisticated Earth System model for six months on the Netherlands’ Snellius super computer. Their model used a slowly increasing influx of glacial meltwater to the Atlantic at high northern latitudes.

The various feedbacks in the model eventually shut down the AMOC, predicted to result in cooling of NW Europe by 10 to 15 °C in a matter of a few decades. Yet to achieve that required the model to simulate more than 2000 years of change. It took 1760 years for a persistent AMOC transport of 10 to 15 million m3 s-1 to drop over a century or so and reach near-zero. That collapse involved around 80 times more melting of Greenland’s ice sheet than at present. Yet their modelling does not take into account global warming: including that factor would have exceeded their budgeted supercomputer time by a long way. Melting of the Greenland ice sheet is, however, accelerating dramatically

Van Westen et al. have shown the possibility that steadily increasing ice-sheet melting can, theoretically, ’flip’  the huge current system associated with the Atlantic Ocean, and with it regional climate patterns. The tangible fear today is of a more than 1.5°C increase in global surface temperature, yet a warming-induced failure of AMOC may cause local annual temperatures to fall by up to ten times that. Rather than the currently heralded disappearance of sea-ice from the Arctic Ocean, it may spread in winter to as far south as the North Sea. The only way of forecasting in detail what may actually happen – and where – is ever-more sophisticated and costly modelling of ocean currents and ice melting in a warming world. Uncertain as it stands, the work by van Westen and colleagues may well be ignored: perhaps as a ‘thing we dinnae care to speak aboot’.

See also: Le Page, M. 2024. Atlantic current shutdown is a real danger, suggests simulation. New Scientist, 9 February 2024; Watts, J. 2024. Atlantic Ocean circulation nearing ‘devastating’ tipping point, study finds. The Guardian, 9 February 2024.

Extreme scientific showing-off: Hominin fossils in space

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Good illustrations of self publicity and soaring ambition are the private space programmes of oligarchs Elon Musk (SpaceX), Jeff Bezos (Blue Origin) and Richard Branson (Virgin Galactic). For a cool US$65 million a ‘civilian’ can get a trip to the International Space Station on SpaceX; a one-hour suborbital flight on Blue Origin will cost US$300,000, with luck having Bezos as a companion; a reservation on Virgin Galactic for a 1 hour trip to the ‘edge of space’ (~100 km up) now costs US$624,000. It’s a tourist trip for the very, very rich only … but even the long-dead can go … or bits of them. On 8 September 2023 aboard Virgin Galactic flight Tim Nash, a South African billionaire had in his pocket a sturdy tube containing a thumb bone of Homo naledi and the collarbone of Australopithecus sediba. Nash reportedly said afterwards, “I am humbled and honoured to represent South Africa and all of humankind as I carry these precious representations of our collective ancestors”.

Reconstructed head of a somewhat annoyed Homo naledi. Credit: John Gurche, Mark Thiessen, National Geographic.

Nash was entrusted with these unique fossils by Lee Berger, Professor in Palaeoanthropology at Witwatersrand University, South Africa and a National Geographic Explorer-in-Residence. Berger recovered fossils of both species from limestone caves in the UNESCO World Heritage Site grandly named the Cradle of Humankind near Johannesburg. He is no stranger to controversy, and this venture cooked up with Nash seems to aim at promotion of South African achievements rather than having any scientific purpose. It has backfired spectacularly (see: McKie, R. 2023. ‘Callous, reckless, unethical’: scientists in row over rare fossils flown into space. The Observer, 22 October 2023). Comments from the anthropological world, six national and international bodies and perhaps the leading hominin specialist Professor Chris Stringer of the Natural History Museum in London include the words and phrases “callous”, “unethical”, “extraordinarily poorly thought-out”, “a publicity stunt”, “reckless” and “utterly irresponsible”. The caper breaks the South African, indeed international, scientific rule that fossils can only be allowed to travel for scientific purposes, applied consistently by similarly hominin-rich African countries such as Ethiopia, Kenya and Tanzania.

But, Hey, that’s how you get on in the world … isn’t it?

Geochemical evidence for the origin of eukaryotes

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Along with algae, jellyfish, oak trees, sharks and nearly every organism that can be seen with the naked eye, we are eukaryotes. The cells of every member of the Eukarya, one of the three great domains of life, all contain a nucleus – the main location of genetic material – and a variety of other small bodies known as organelles, such as the mitochondria of animals and the chloroplasts of plant cells. The vast bulk of organisms that we can’t see unaided are prokaryotes, divided into the domains of Bacteria and Archaea. Their genetic material floats around in their cells’ fluid. The DNA of eukaryotes shares some stretches with prokaryotes, but no prokaryotes contain any eukaryote genetic material. This suggests that the Eukarya arose after the Bacteria and Archaea, and also that they are a product of evolution from prokaryotes, probably by several combining in symbiotic relationships inside a shared cell membrane. Earth-logs has followed developments surrounding this major issue since 2002, as reflected in some of the posts linked to what follows. 

While prokaryotes can live in every conceivable environment at the Earth’s surface and even in a few kilometres of crust beneath, the vast majority of eukaryotes depend on free oxygen for their metabolism. Logically, the earliest of the Eukarya could only have emerged when oxygen began to appear in the oceans following the Great Oxidation Event around 2.4 billion years ago. That is more than a billion years after the first prokaryotes had left their geological signature in the form of curiously bulbous, layered carbonate structures (stromatolites), probably formed by bacterial mats. The oldest occur in the Archaean rocks of Western Australia as far back as 3.5 Ga, and disputed examples have been found in the 3.7 Ga Isua sediments of West Greenland. The oldest of them are thought to have been produced through the anoxygenic photosynthesis of purple bacteria (See: Molecular ‘fossils’ and the emergence of photosynthesis; September 2000), suggested by organic molecules found in kerogen from early Archaean sediments. Later stromatolites (<3.0 Ga) have provided similar evidence for oxygen-producing cyanobacteria.

Acritarchs are microfossils of single-celled organisms made of kerogen that have been found in sediments up to 1.8 billion years old. Features protruding from their cell walls distinguish them from prokaryote cells, which are more or less ‘smooth’: acritarchs have been considered as possible early eukaryotes. Yet the oldest undisputed eukaryote microfossils – red and green algae – are much younger (about 1.0 Ga). A means of estimating an age for the crown group from which every later eukaryote organism evolved – last eukaryotic common ancestor (LECA) – is to use an assumed rate of mutation in DNA to deduce the time when differences in genetics between living eukaryotes began to diverge: i.e. a ‘molecular clock’. This gives a time around 2 Ga ago, but the method is fraught with uncertainties, not the least being the high possibility of mutation rates changing through time. So, when the Eukarya arose is blurred within the so-called ‘boring billion’ of the early Proterozoic Eon. A way of resolving this uncertainty to some extent is to look for ‘biomarker’ chemicals in the geological record that provide a ‘signature’ for eukaryotes.

A new study has been undertaken by a group of Australian, German and French scientists to analyse sediments ranging in age from 635 to 1640 Ma from Australia, China, Asia, Africa, North and South America (Brocks, J.J and 9 others 2023. Lost world of complex life and the late rise of the eukaryotic crown. Nature, v. 618, p. 767–773; DOI: 10.1038/s41586-023-06170-w; contact for PDF). Their chosen biomarkers are sterols (steroids) that regulate eukaryote cell membranes. Some prokaryotes also synthesise steroids but all of them produce hopanepolyols (hopanoids), which eukaryotes do not. The key measures for the presence/absence of eukaryote remains in ancient sea-floor sediments is thus the relative proportions of preserved steroids and hopanoids, together with those for the breakdown products of both – steranes and hopanesthat are, crudely speaking, carbon ‘skeletons’ of the original chemicals.

Proportions of biomarkers in sediments from present to 1.64 Ga. Cholesteroids – reds; ergosteroids – blues; stigmasteroids – greens; protosteroids magentas, hopanoids – yellows; unsampled – grey. Snowball glaciations are shown in pale blue. (Credit: Simplified from Figure 3 in Brocks et al.)

Interpretation of the results by Jochen Brocks and colleagues is complicated, and what follows is a summary based partly on an accompanying Nature News & Views article(Kenig, F. 2023. The long infancy of sterol biosynthesis. Nature, v. 618, p. 678-680; DOI: 10.1038/d41586-023-01816-1). The conclusions of Brocks et al. are surprising. First, the break-down products of steroids (saturated steranes) that can be attributed to crown eukaryotes (left on the figure above) are only present in sediments going back to about 200 Ma before the first Snowball Earth event (~900 Ma). Before that only hopanes formed by hopanoid degradation are present: a suggestion that LECA only appeared around that time – the authors suggest sometime between 1 and 1.2 Ga. That is far later than the time when eukaryotes could have emerged: i.e. once there was available oxygen after the Great Oxidation Event (~2.4 to 2.2 Ga). So what was going on before this? The authors broke new ground in analysis of biomarkers by being able to detect signs of the presence of actual hopanoids and steroids of several different kinds. Steroids were present as far back as 1.6 Ga in the oldest sediments that were analysed.

Steroids of crown eukaryotes are represented by cholesteroids, ergosteroids and stigmasteroids. All three are present throughout the Phanerozoic Eon and into the time of the Ediacaran Fauna that began 630 Ma ago. In that time span they generally outweigh hopanoids, thus reflecting the dominance of eukaryotes over prokaryotes. Back to about 900 Ma, only cholesteroids are present, together with archaic forms that are not found in living Eukarya, termed protosteroids.  Before that, only protosteroids are found. Moreover, these archaic steroids are not present in sediments that follow the Snowball Earth episodes (the Cryogenian Period).

Thus, it is possible that crown group eukaryotes – and their descendants, including us – evolved from and completely replaced an earlier primitive form (acritarchs?) at around the time of the greatest climatic changes that the Earth had experienced in the previous billion years or more. Moreover, the Cryogenian and Ediacaran Periods seem to show a rapid emergence of stigmasteroid- and ergosteroid production relative to cholesteroid: perhaps a result of explosive evolution of the Eukarya at that time. The organisms that produced protosteroids were present in variable amounts throughout the Mesoproteroic. Clearly there need to be similar analyses of sediments going back to the Great Oxygenation Event and the preceding Archaean to see if the protosteroid producers arose along with increasing levels of molecular oxygen. The ‘boring billion’ (2.0 to 1.0 Ga) may well be more interesting than previously thought.

Annual logs for 2020 and 2021 added

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For ease of access to annual developments within the general topics that Earth-logs covers I have now compiled all the Earth-logs posts from 2020 and 2021 into the categories: Geohazards; Geomorphology; Human Evolution; Magmatism; Palaeobiology; Palaeoclimatology; Physical Resources; Planetary Science; Remote Sensing; Sediments and Stratigraphy, and Tectonics. You can download them by ‘hovering’ over the Annual logs pull-down in the main menu and clicking on a category, whose index page will appear. Then scroll down to the 2020 or 2021 entry and click on the link to the PDF.

I hope that readers find this option useful in showing how each general topic has developed over the 21st century so far. Of course, it is based on my personal view of what constitute important developments published in international journals

Best wishes for 2023.

Steve Drury

The earliest upright ape

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Two decades ago the world of palaeoanthropologists was in turmoil with the publication of an account of a new find in Chad (see: Bonanza time for Bonzo; July 2002). A fossil cranium, dubbed Sahelanthropus tchadensis (nicknamed Toumaï­ or ‘hope of life’ in the Goran language), appeared like a cross between a chimpanzee and an australopithecine. The turmoil erupted partly because of its age: Upper Miocene, around 7 Ma old. Such an antiquity was difficult to reconcile with the then accepted ~5 Ma estimate for the evolutionary split between humans and chimpanzees, based on applying a ‘molecular clock’ approach to the difference between their mtDNA. The other point of contention was the size of Sahelanthropus’s canine teeth: far too large for australopithecines and humans, but more appropriate for a gorilla or chimp.

Cast of the reconstructed skull of Sahelanthropus tchadensis. (Credit: Didier Descouens, University of Toulouse)

In the absence of pelvic- and foot bones, or signs of the foramen magnum where the spinal cord enters the skull – crucial in distinguishing habitual bipedalism or being an obligate quadruped – encouraged the finders of a 6.1 to 5.7 Ma-old Kenyan hominin Orrorin tugenensis to insist that its skeletal remains – several teeth, fragments of a lower jaw, a thigh bone, an upper arm and of a finger and thumb but no cranial bones – were of ‘the earliest human ancestor’. In Orrorin’s favour were smaller canine teeth than those of later australopithecines. At the time of the dispute, centred mainly on absence of crucial evidence, doyen of hominin fossils Bernard Wood of George Washington University and an advocate of ‘untidy’ evolution, suggested that both early species may well have been evolutionary ‘dead ends’ (see: A considered view; October 2002). And there the ‘muddle’ has rested for 20 years.

In 2002 not only a cranium of Sahelanthropus had been unearthed. Three lower jaw bones and a collection of teeth suggested that as many as 5 individuals had been fossilised. A partial leg bone (femur) and three from forearms (ulna) cannot definitely be ascribed to Sahelanthropus but, in the absence of evidence of any other putative hominin species, they may well be. It has taken two decades for these remains to be analysed to a standard acceptable to peer review (Daver, G. et al. 2022. Postcranial evidence of late Miocene hominin bipedalism in Chad. Nature v. 608, published online; DOI: 10.1038/s41586-022-04901-z). The authors present convoluted anatomical evidence that Toumaï­’s femur, which had been gnawed by a porcupine and lacks joints at both ends, suggesting that it was indeed suited to upright walking. Yet the arm bones hint that it may have been equally comfortable in tree canopies. Yet it does look very like an ape rather than a hominin.

Much the same conclusion has been applied to Australopithecus afarensis, indeed its celebrated representative ‘Lucy’ met her end through falling out of a large tree ~3.2 Ma ago (see: Lucy: the australopithecine who fell to Earth?; September 2016). So, dual habitats may have been adopted by hominins long after they emerged. Yet Au afarensis was capable of trudging through mud as witnessed by the famous footprints at Laetoli in Tanzania. Only around 3 Ma has reasonably convincing evidence for upright walking similar to ours been discovered in Au africanus. The full package of signs from pelvis and foot for habitual bipedalism dates to 2 Ma ago in Au sediba. Even this latest known australopithecine seems to have had a gait oddly different from that of members of the genus Homo.

So, in many respects the benefits of full freeing of the hands to develop manipulation of objects, as first suggested by Freidrich Engels, may have had to await the appearance of early humans. Earlier hominins almost certainly did make tools of a kind, but the revolutionary breakthrough associated with humanity was more than 5 million years in the making.

See also: Callaway, E. 2022. Seven-million-year-old femur suggests ancient human relative walked upright. Nature (News)24 August 2022;

Handwerk, B. 2022. Seven Million Years Ago, the Oldest Known Early Human Was Already Walking. Smithsonion Magazine, 24 August 2022 (click the link ‘published today in Nature’ in 2nd paragraph to access complimentary PDF of Daver et al)

Neocolonial/economic bias of the fossil record and evolution

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Charles Darwin’s ideas on the evolution of species through natural selection became imprinted by his participation in the second survey expedition of HMS Beagle (1831-1836), commanded by Captain Robert Fitzroy. The voyage aimed at comprehensive surveys along its circumnavigation, Darwin having been engaged to provide geological expertise. At that time he would have been best described as a ‘natural historian’ and his only qualification was that he had an ordinary degree (BA) from Cambridge  and had read widely in natural science: had it not been for joining the Beagle he may have become a country parson.

The voyage was a maritime venture typical of British and other European imperialism and colonisation during the early 19th century – a survey not only of geodesy, geography and natural science but also of the economic potential of the places that it visited. European science benefitted immensely from such voyages and overland expeditions. Today, research in the natural sciences is still dominated by academics from the better-off nations. Significantly, the charting of the ocean floor during the 20th and 21st centuries has been conducted almost exclusively by those nations with a global reach: plate tectonics is a science for the very wealthy. It is only in the last 60 years that geological mapping of the bulk of the continental surface has been relinquished by former colonial powers to local surveys. In the majority of cases the geological surveys of these now independent countries are grossly underfunded and they still largely depend on maps produced more than half a century ago by their former rulers.

In the 19th century global palaeontology, botany and zoology, which lie at the roots of evolutionary studies, shipped specimens to the museums and universities of the colonising powers. Their scientists today still retain a near monopoly of access to those old collections. Now it is economic power that enables continued collection by researchers mainly from the former colonising countries and their institutions. There are a few exceptions, such as the rapid rise of Chinese natural science in a mere three to four decades, which has become a major ‘player’ in early and Mesozoic evolution. Gradually, hominin palaeontology has drawn in local scientists from countries well-endowed with productive sites, such as Kenya, Tanzania and Ethiopia, yet funding remains largely external. Nussaïbah Raja at Friedrich-Alexander University in Erlagen, Germany and colleagues from Britain, South Africa, Brazil and India  (Raja, N.B. et al. 2021. Colonial history and global economics distort our understanding of deep-time biodiversity. Nature Ecology & Evolution, v. 6, p. 1-10 ; DOI: 10.1038/s41559-021-01608-8) have used the vast Paleobiology Database (PBDB) to assess which countries are the main influence over global fossil collection.

Proportion of publications on national fossil data with a local lead author, for regions of the world. (Credit: Raja et al., Extended Data Fig 9)

Their findings are unsurprising. The 29 thousand papers referenced by PBDB that give fossil-occurrence data from the last 30 years involved 97% of authors who were resident in high- and upper-middle-income countries: more than a third from the US and the rest of the top ten from, in order, Germany, Britain, France, Canada, Russia, China, Australia, Italy and Spain: and 92% of the publications were published in English. Interestingly, it appears that old colonial ties still exert an influence on palaeontology research in former colonies: a quarter of that conducted in Morocco, Tunisia and Algeria was done by scientists based in France; 10% of work in South Africa and Egypt was authored by UK-based researchers; and 17% of Namibian palaeontology was conducted by scientists from Germany.  When it comes to first authors of papers about fossils, local scientists get increasingly short shrift as the overall wealth of their homelands decreases. The authors of the PBDB study devised an index of what they call ‘parachute science’, based on the proportion of a country’s fossil data that was contributed by foreign teams that lacked any local co-authors.

The ‘Parachute Index’ for the ten countries most exploited by external palaeontological researchers. (Credit: Raja et al., Fig 3b)

This lack of engagement with and assistance for local scientists ‘hinders local scientists and domestic scientific development, by favouring foreign input and exacerbating power imbalances between those from foreign countries and those located ‘on the ground’. Furthermore, this can also lead to mistrust by local scientists towards foreign researchers, affecting future collaborations’. Scientific ‘colonialism’ is still pervasive for much of the world, and is a major force in imposing opinions on evolution in particular. Raja and colleagues rightly call for external economic and ‘intellectual’ power over research to be replaced by ‘equitable, ethical and sustainable collaboration’. Without that, scientific expertise will advance at a very slow pace in less well-endowed regions, with the same-old, same-old beneficiaries getting the benefits.

See also: Callaway, E. 2022. How rich countries skew the fossil record.Nature News 13 January 2022. Adame, F. 2021. Meaningful collaborations can end ‘helicopter research’. Nature Careers, 29 June 2021.