Rapid human genetic changes after the last Ice Age

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Our hominin ancestors in Africa first fashioned tools about 3.5 Ma ago. Since then regular intake of animal protein through hunting, followed by the later discovery of fire and cooking, may progressively have encouraged the evolution of larger hominin brains. Both behavioural leaps would have reduced the length of the ‘working day’ needed to sustain hominin groups. That would have lengthened opportunities for cognitive reflection. social life and culture, and thus further evolution. They also expanded the opportunities for migration, beginning with Homo ergaster venturing beyond Africa at least 1.8 Ma ago. Hominins evolved to such an extent that several separate species occupied our home world at any one time until about 45 thousand years ago. After that only H. sapiens occupied Africa, Eurasia and Australasia.

Such protracted and meandering evolution and dispersal clearly involved episodic physiological and cultural changes, but all we have to go on are fragmentary fossil remains and artifacts of various kinds. DNA has yet to be extracted from hominin bones older than 400 ka (an early Neanderthal from northern Spain). Though H. sapiens first appeared in Morocco about 300 ka ago, DNA from our species dates back to only 45 ka (western and central Europe). What is today termed ‘ancient’ human DNA, is actually very young and restricted to climate zones where its decomposition has been slow. At present there is little point in analysing fossil material from tropical and subtropical latitudes; the DNA is degraded beyond recovery by even the most up-to-date techniques. Fascinating as discussion of human evolution is, in reality most is merely inferred from comparative anatomy and anthropological interpretation.

By 45 ka the heavy evolutionary lifting had been done, resulting in anatomically modern humans, but we have little, if any, chance of explaining in genetic terms how it was achieved. There has been much speculation about the conditions, particularly climatic ones, which may have driven the changes. During the last 2.6 Ma – the Quaternary Period – global climate has been the most changeable in the last 300 Ma. Ice ages have come and gone, first in 40 ka cycles and during the last million years every 100 ka. Much more rapid changes, such as millennial Dansgaard-Oeschger cycles, appeared during each glacial episode, the last being the Younger Dryas between 12.9 and 11.7 ka. For a long while ideas on the drivers of human evolution have been dominated by those concerning environmental stress. Unsurprisingly, genetic change has also been ascribed to such a Darwinian-ecological cause: adaptability to adversity. To test such a hypothesis requires genetic data, of course. But, except for the climatically more stable Holocene Epoch since 11.7 ka, ancient human genomes are in very short supply.

Renowned researcher into ancient human genetics David Reich of the Harvard Medical School in Boston, USA has collated more than 15 thousand ancient human genomes extracted from the remains of individuals who lived and died in Europe and parts of the Middle East during the last ten thousand years. These have been analysed statistically in the context of ‘directional selection’. This is a type of natural selection that occurs when one version of a gene – an allele – confers an extreme form of a trait. If it proves advantageous it rapidly gets passed on to more descendants than do less advantageous alleles, and thus rises in frequency across a population. This differs from other causes of gene frequency changes, such as human migration, population mixing, and random genetic fluctuations that occur in small populations. Well-known examples of directional selection are rapid changes among European Peppered moths, African cichlid fish, Alaskan Sockeye salmon and Big Cats which change over time in response to variations in their habitats. A human example is a genetic variant that maintains the ability to digest the sugar lactose in milk beyond infancy, which enables many modern Europeans to digest milk throughout their lives. The algorithm needed to separate signs of directional selection from other types of genetic change was developed by Ali Akbari, a computational geneticist also at Harvard Medical School. A recent paper by Akbari, Reich and colleagues in the US, Iran, Germany, and Austria (Akbari, A. and 15 others 2026. Ancient DNA reveals pervasive directional selection across West Eurasia. Nature, advance online publication; DOI: 10.1038/s41586-026-10358-1) seems set dramatically to change the research into recent human evolutionary genetics.

Akbari et al. discovered that directional selection has driven the spread or decline of hundreds of gene variants in human populations throughout Western Europe in the last ten millennia. In particular, selection accelerated with the adoption of farming rather than a hunter-gatherer lifestyle.  Among the gene variants are those connected with light skin, red hair, risk of celiac disease – linked to gluten in cereals –  susceptibility to gout, resistance to leprosy, baldness, rheumatoid arthritis and alcoholism. There are many more (see Figure 3 in the paper): the team identified 479 gene variants affected by directional selection, some that can be explained by changes in lifestyle, others less explicable and yet more that underlie complex traits such as mental illness and cognition. Some of the variants sprang up and were sustained in the population, others rose and then dwindled. The Neolithic began a period of fundamental life style changes in Europe, summed up as a shift from hunting and foraging to farming of cereals and livestock, as early as about 10 ka ago in what is now Türkiye. The pace of genetic changes of this kind reached a peak around the Bronze Age, perhaps because human activities in Europe became more complex then with the mass migration westwards of Yamnaya horse- and wagon-using people from the steppes to dominate Europe

The shift from small wandering bands to living in settlements was a drastic change from a lifestyle that had continued throughout all previous human history. So, it is hardly surprising that there was a major shift in humans’ genetic makeup. But such a change in human labour was not unique to Europe and is known to have occurred on all inhabited continents, with the exception of Australia, at different times during the Holocene. Other regional genetic databases can be analysed in much the same way, once sufficient ancient DNA is collected in Asia, Africa and the Americas. Yet not much is available. The authors comment: ‘A variant that now correlates to household income or years of schooling [remarkably, there are some!] had to have meant something different in the Stone Age. So these results do not mean that Europeans evolved to be smarter or healthier.’  Moreover, the research results in the paper seem likely to be amplified as the data set is so large and complex.

See also: Dutchen, S. et al. 2026. Massive Ancient-DNA Study Reveals Natural Selection Has Accelerated in Recent Human Evolution. Harvard Medical School: News & Events. 15 April 2026; Callaway, E. 2026. Landmark ancient-genome study shows surprise acceleration of human evolution. Nature, v. 652, News, 15 April 2026

What caused the Younger Dryas frigid spell: case closed?

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Around 20 thousand years ago, the Earth began to emerge from the grip of the Last Glacial Maximum (LGM). Huge ice sheets had locked up so much water that sea level was then about 125 m lower than it is today. At 12,870 years ago the warming and sea-level rise were reversed for 1,170 years in the Northern Hemisphere: an episode of near-full glacial conditions known as the Younger Dryas (YD). The adjectives ‘sudden’ or ‘abrupt’ grossly understate the pace of initial cooling – 3°, 6° and 15° C in North America, Europe and Greenland, respectively. Isotopic evidence from Greenland ice cores suggest that the cooling took place over three years or less. Such a degree of precision stems from the continuous annual layering in the Greenland ice cap. As far as humans were concerned, this would have been catastrophic for hunter gatherers following game northwards in Eurasia and North America as conditions ameliorated during the seven thousand years since the LGM. The archaeological record, or rather the lack of one, for what are now temperate zones suggests humans either retreated south or were blotted out.

There is no counterpart for the YD in the end stages of early glacial episodes. Some authors have suggested that it was the outcome of an appropriately catastrophic geological event, such as a large meteorite strike, as proposed in 2007 (See: Whizz-bang view of Younger Dryas; July 2007). This hypothesis gained traction in 2013, at least for its authors, with the discovery of anomalously high concentrations of the noble metal platinum (Pt) and other platinum Group metals, such as iridium (Ir) at or around the start of the YD in the GISP2 ice core. New research on this anomaly (Green, C.E. et al 2025. A possible volcanic origin for the Greenland ice core Pt anomaly near the Bølling-Allerød/Younger Dryas boundary. PLOS One, v. 20, article  e0331811; DOI: 10.1371/journal.pone.0331811) offers a different scenario. Charlotte Green of Royal Holloway, University of London and colleagues from universities in the UK, Germany and Austria examine the timing of this Pt spike and its detailed geochemistry.

The ‘killer’ observation is that the anomaly occurs in ice that formed 45 years after the onset of the Younger Dryas and has a spread of about 14 years. Whatever kind of event released the platinum, it definitely did not somehow trigger the onset of the YD. Moreover, the anomaly was significantly deficient in iridium compared with a wide range of meteorites and terrestrial igneous rocks. It also differed markedly in other elements, such as lutetium and hafnium, and in all three elements in melt rocks and ejecta sediments associated with five proven impact structures. The closest match is to volcanic gas condensates from a recent eruption of a submarine volcano near Tonga

Both the GISP2 and NGRIP cores through the Greenland ice also record a large, 12-year long spike in sulfate of volcanic origin spread across the very start of the YD. That roughly matches the age of an explosive eruption, which formed the circular Laacher See in the Eifel volcanic field in Germany. That eruption is thought to have blasted 6.3 km3 of highly alkaline magma into the atmosphere: about the magnitude of the 1991 Pinatubo eruption, but insufficient to yield the size and duration of the sulfate spike that coincides with the start of the YD. The sulfate anomaly suggests a far larger, currently unknown eruption at 12,870 years ago. The Pt and Ir data from the Laacher See event rule it out as a source for the younger Pt anomaly in the GISP2 ice core. One possibility is a nearby Icelandic subglacial fissure eruption at that time.

So, as regards what started the Younger Dryas, there is support for a very large, but so-far unknown volcanic event, and an as yet unresolved, perturbation in the Atlantic Meridional Overturning Circulation (AMOC) resulting from drainage of a huge glacial lake in northern North America (see: The Younger Dryas and the Flood; June 2006), but no support whatever for an impact event. Climatology of the distant past is always likely to be difficult to pin down. That is because, as now, it involves linkages between a large number of variables: not only physical ones, but issues of biogeochemistry, the inner Earth, the rest of the solar system and even cosmology. That is, it is as complex as human affairs and their history. Common sense, linear thinking and the like, simply will not do.

See also: Scientists solve 12,800-year-old climate mystery hidden in Greenland ice. Science Daily, 20 March 2026

How do subducted slabs accumulate at different mantle depths?

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Seismic tomography provides no evidence that slabs of oceanic lithosphere descend intact through the whole mantle to the core-mantle boundary. It might once have happened when they were capped by abundant high-density rocks, such as Precambrian banded-iron formations. A great many actively descending slabs have been shown to cease sinking, slide sideways and accumulate at depths around 660 and 1000 km. Until recently these discontinuities were been generally ascribed to transitions in the structure of the dominant mafic mineral olivine (Mg2SiO4) in mantle peridotite induced by increasing pressure and temperature. The resulting increases in mantle density supposedly form barriers to further slab descent. Pressure-induced mineral transitions in the slabs themselves that increase their density, such as pyroxene to garnet, may somehow be inhibited thereby leading to stagnation in slab descent. That may be true for the 660 km discontinuity, but for stagnation at 1000 km deep no such density-changing mineral transitions have shown up in high-P high-T mineralogical experiments. Some other process must therefore be responsible for slab descent to that depth. Recent work by geoscientists at several universities in China gives insights into what may be going on (Li, J., Li, K., Li, J. et al 2026. Dual slab stagnation depths controlled by grain-size-induced sporadic low-viscosity zones at around 1000 km depth. Nature Communications DOI: 10.1038/s41467-026-69987-9).

Four different modes of subduction at island arcs. Credit: Li et al. Fig 6

Jing Li and colleagues have focussed on the possibility that changes in the bulk viscosity of the mantle may play an important role. Their approach is twofold: experimental mineral physics and geodynamic modelling. Results suggest that recrystallization in the mantle when deeply penetrating slabs pass through it may patchily reduce the mantle’s grain size and thus its viscosity; the more so with larger volumes of subducted slab material. In turn, the resulting physical heterogeneity probably disrupts the steady downward passage of the slabs; fine-grained, less viscous zones ‘lubricating’ slab penetration, unchanged zones hindering it. The authors link such hypothetical micro-structural processes to modes of subduction that are currently active. They consider four modes of active subduction beneath island arcs with either a slow or a fast rate of trench retreat (see Figure). A slowly retreating trench system combined with low-viscosity patches at depth (Mode 1) results in penetration below 660 km and slab stagnation at 1000 km. Slow trench retreat with a homogenous lower mantle (Mode 2) gives rise to penetration and buckling of the descending slab between 660 and 1000 km. Fast trench retreat with a deeper low-viscosity zone (Mode 3), or with a homogeneous lower mantle (Mode 4) both result in slab stagnation at 660 km.

The models developed by Jing Li et al convincingly simulate various results of seismic tomography beneath island arcs. Interestingly, they suggest that the eventual assimilation of older slab materials into the deeper mantle (‘fossil’ slabs) may play a major role in mineral comminution and reduced mantle strength. That may leave behind low viscosity zones that later subduction may exploit. In fact, there are signs of possible fossil slabs in seismic tomograms more than 1000 km below the present Pacific Ocean floor in the form of zones of high P-wave velocity.

This work shows that plate tectonics is far from ‘done-and-dusted’, the mantle being far from uniform in its properties. Li et al’s results potentially open up new insights into whole-mantle convection, in which older tectonic events influence plate motions that are currently operating and the triggering of plumes rising from the deepest mantle. It also hints that such complex physical mixing of subducted material into the mantle may have resulted in the geochemical heterogeneities that increasingly emerge from analysis of magmas with ultimate origins in the mantle.

See also:Grain Size Creates Dual Slab Stagnation Zones at 1000 km. Scienmag 3 March 2026

Annual logs update

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Sorry for the lack of posts over the last few weeks.

I have finally updated all annual logs from 2022 to 2025.

You can download the new PDF compilations using the menu bar, if you wish.

Hopefully, normal service will be resumed soon, depending on the journals’ contents, of course …

Cheers

Steve Drury

Annual logs update

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Followers can now download newly posted annual logs for Human Evolution and Migrations covering the years 2022 to 2025. By downloading them you can get a clear idea of how palaeoanthropology has moved forward since the Covid pandemic.

Enjoy the experience if you have the time and inclination!

Steve Drury

Vanished continents of the Hadean Eon: the zircon key

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Over the last few decades improved analytical techniques have made it possible to analyse tiny mineral grains for a variety of trace elements and several isotopes. Zircons obtained directly from crushed granitic igneous rocks vary in chemistry according to the magmatic processes that generated them and their tectonic context. Elevated ratios between uranium and niobium (U/Nb) and scandium and ytterbium (Sc/Yb) are characteristic of zircons in intermediate granites. These contain 52 to 63 % SiO2 – between mafic and felsic magmas – which formed by melting of hydrated mafic crust in settings akin to modern continental arcs; i.e. in subduction zones. But such partial melting can also take place where the base of continental crust delaminates and ‘drips’ into the mantle. That process is part of what is known as stagnant lid tectonics, believed by many to have been important in the Palaeoarchaean and Hadean. Such a process would have involved nearly anhydrous conditions and thus different geochemical partitioning of elements in the magmas and minerals that crystallised from them. Exposures of crystalline continental crust become increasingly rare further back in geological time, and there are none older than 4.0 Ga – i.e. of Hadean age – with a granitic component. Consequently studying the generation of continental crust in the Hadean and the early Archaean is almost entirely dependent on ancient zircons that found their way into much younger sedimentary rocks. The most famous of these occur as detrital grains in the 3.6 Ga Jack Hills conglomerate of Western Australia. Others have been extracted from similar ~3.3 Ga sedimentary rocks in the Barberton Greenstone Belt of South Africa and Eswatini.

Cartoon of possible Hadean stagnant lid tectonics, dominated by mantle plumes. (Credit: Bédard, J.H. 2018, Fig 3B, DOI: 10.1016/j.gsf.2017.01.005)

John Valley of the University of Wisconsin-Madison, USA, and co-workers from the US, Germany, Australia and France have worked on a large number of zircons newly extracted from Jack Hills. They have radiometrically dated them, and analysed Nb, Sc, U and Yb trace elements and hafnium (Hf) and oxygen isotopes Together with data from earlier studies, including Barberton zircons, they have teased out some remarkable insights into  ‘continent-forming’ magmatism as far back in time as 4.4 billion years ago (Valley, J.W. and 11 others 2026. Contemporaneous mobile- and stagnant-lid tectonics on the Hadean Earth. Nature, Open access; DOI: 10.1038/s41586-025-10066-2). More than 70% of the >4.0 Ga Jack Hills zircons have elevated U/Nb and Sc/Yb ratios, which suggest that they formed in a setting akin to continental-arc subduction (CAS) zones, to produce now-vanished Hadean continental crust. The remainder seem to represent processes at mid-ocean ridge (MOR) and oceanic island (OI) settings. In contrast, the bulk of Barberton zircons of Hadean age show OI affinities, with only around 22% showing Nb–Sc–U–Yb signatures of probable CAS origins. From about 4.4 to 3.8 Ga two distinct forms of continental crust generation seem to have operated on Earth. In the erosional source region for the Barberton zircons their host granites seem to have formed during the Hadean and Eoarchaean by remelting of foundered lower crust, i.e. probably in a stagnant-lid-like tectonic setting. But at around 3.6 Ga they ‘flip’ to a subduction-like setting. The zircons yielded by Jack Hills conglomerates suggest substantially different conditions: alternating CAS and OI settings during the Hadean and a fall-off in crust generation during the Eoarchaean (4.0 to 3.8 Ga).

Plots of Sc/Yb and U/Nb against ages of zircons (vertical scale logarithmic). Black points are from Jack Hills, red from Barberton. The yellow field represents zircons formed in subduction zones; green suggests stagnant lid tectonics; grey the overlap between the two settings. Credit: Valley et al. Fig 3 a and b.

The mixed Hadean zircon signatures from Jack Hills possibly indicate that they were derived by erosion and transport from several distinct terranes that had been generated by two different processes: some kind of upper crustal recycling and stagnant lid tectonics. Meanwhile, that part of the Hadean Earth represented by the Barberton zircons may have been a long-lived regime of stagnant lid tectonics, replaced by dominant subduction at the end of the Eoarchaean.  Yet the data suggest that into the Palaeoarchaean (3.6 to 3.2 Ga) and perhaps later, lid tectonics continued to operate somewhere, but at no time after 4.4 Ga was the Earth entirely subject to lid tectonics. Likewise, the authors insist that subduction was not of the plate-tectonic style, referring to some form of recycling of hydrated upper crustal mafic and ultramafic rocks into the mantle to undergo partial melting. Plate tectonics as we know it probably developed later in the Archaean. The early Earth had much higher heat flow than in later times, and thus the lithosphere was more ductile rather than brittle. The essence of modern tectonics is a series of rigid plates that extend down to the asthenosphere. When they deform it is largely through brittle failure of the entire lithosphere.

Stonehenge: the geologists’ last word?

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A sunset at Stonehenge

The great megalithic structure is the centrepiece of a vast ritual landscape on a 780 km2 plateau known as Salisbury Plain, underpinned by Cretaceous limestone: the largest remaining area of calcareous grassland in northwest Europe. The earliest sign that the Plain was used for ritual purposes dates to ten thousand years ago (8,000 BCE), when Mesolithic hunter gatherers erected large wooden posts to define by an E-W line the Sun’s rise and setting at the equinoxes. The area seems to have been continuously populated until 4,000 BCE when the first Neolithic farmers settled the Plain and began building burial mounds (barrows) to celebrate notable individuals and families.

The Stonehenge monument began as a circular cemetery around 3,100 BCE. Its development to the astonishing structure that remains largely intact today occupied the Neolithic populace and succeeding Bronze Age immigrants for the next 1,600 years. This involved setting up and then repeatedly shuffling around several kinds of boulders or megaliths. The first, around 2,600 BCE, were 2 to 3 tonne blocks mainly of igneous rock (the ‘bluestones’), now known to have originated from outcrops of Ordovician volcanics in Pembrokeshire about 230 km to the west. Next to arrive was a 6 tonne grey-green sandstone slab, now lying flat (hence its being named the ‘Altar’ Stone) beneath a fallen, far bigger megalith,. Once thought to be of Welsh provenance – in the Brecon Beacons 150 km to the west – the Altar Stone is now beyond a shadow of doubt to have come from Devonian strata in northern Scotland, possibly Orkney. The final erection of 30 truly enormous ‘sarsens’ to create Stonehenge’s signature circle and inner ‘horseshoe’ of vertical slabs capped by lintels took place between 2,600 to2 400 BCE. Weighing up to 50 tonnes, the sarsens are locally derived from remnants of Lower Eocene (~55 Ma) sands cemented by chemically precipitated silica (SiO2) that once covered much of southern England.

After 1,600 BCE, serious fiddling with the various stones, the bluestones in particular, ceased. The monument may have remained in some form of use during the Iron Age: it could hardly have been ignored. The first record of antiquarian interest is from the late 17th century and continued sporadically until systematic excavation of archaeological features on the Plain got underway during the 19th century and continues to the present.

Much recent literature has concentrated on what Stonehenge was for and how it was built, leading to a rich eclecticism and a little experimentation. But given the size of its stones and the obviously exotic nature of some of them, there have been disputes between those who consider them to have been brought by natural means and those who suggest collective human endeavour. The latter would have involved vast amounts of labour, shifting the bluestones over 250 km, entire community muscle power to drag the locally occurring sarsens about 25 km from their probable source, and a journey of at least 700 km to get the Altar Stone in place. Since none of the stones could conceivably have been moved by river flow, the only natural alternative for their transport is by glacial action.

Such an ice-transport theory rests on at least one of the several known advances of Pleistocene ice sheets having reached as far south as Salisbury Plain and deposited upon it glacial till that contains material from NE Scotland and South Wales. The most obvious indicators of glacial transport are large erratic boulders strewn far from their source down a previous ice stream that their distribution helps to reconstruct. In Northern Britain a great many megaliths that people erected long ago are glacial erratics of one kind or another. Of course, glacial tills contain grains of all sizes ripped and ground from the course of glacial flow. No so obvious, but equally capable of revealing transportation paths. After ice sheets melt, the till that they dump is eroded so that exotic rock and mineral grains enter drainage systems, some to remain in stream sediments. Two geologists based at Curtin University in Perth, Western Australia collected river sands from four active drainage systems on Salisbury Plain to test the glacial-transport hypothesis for the Stonehenge megaliths (Clarke, A.J.I. & Kirkland, C.L. 2026. Detrital zircon–apatite fingerprinting challenges glacial transport of Stonehenge’s megaliths. Communications Earth & Environment, v. 7, article 54; DOI: 10.1038/s43247-025-03105-3).

Using standard mineral-separation techniques – removal of low-density minerals (mainly quartz and feldspar) and those that are magnetic – Anthony Clarke and Christopher Kirkland mounted and polished samples of the remaining high-density grains embedded in resin. Using automated X-ray spectroscopy they identified grains of two minerals, zircon and apatite, that can be dated using uranium and lead isotopes. Zircons are virtually absent from the underlying Chalk although phosphorus-rich horizons in that rock sometimes contain apatite, a complex calcium phosphate. Both minerals are commonly found in igneous and metamorphic rocks and, being chemically resistant and hard, are often present in sediments derived by erosion of such parent rocks. The authors analysed U-Pb isotopes using laser ablation plasma mass spectrometry of suitable grains of each mineral. The U-Pb data from 250 apatite grains revealed a dominant age peak at 60 Ma, roughly the base of the once overlying Palaeogene sediments. Far fewer grains hint at older ages (175, 215, 300 and 625 Ma) in the Mesozoic, Palaeozoic and Neoproterozoic. The 550 analysed zircons span an age range from the Silurian to Palaeoproterozoic (432 to 1870 Ma), with a few outliers as young as 285 Ma and as old as 3396 Ma.

These data seem to suggest that they can support virtually any glacial transport hypothesis, including that of the Altar Stone, let alone the Stonehenge bluestones. However, that would be to misunderstand the complexity of sediment transport in relation to their original provenance. Erosion from a bedrock source leads to transport and deposition in sedimentary rock. Later uplift and erosion of that secondary host rock is followed by later sediment transport to another rock repository and so on and so forth through the entire geological history of Britain, across  its jumble of many tectonic terranes and the effects of numerous orogenic episodes! The Salisbury Plain chalk lands were covered by Palaeogene sedimentary rocks of the London Basin. And, lo and behold, one of those younger sediments, the Thanet Formation sandstones, tell much the same U-Pb story as do the modern river sediments of Salisbury! Those Palaeocene sands elsewhere directly overlie the Chalk and, in some localities on Salisbury Plain, still do today in the form of the chemically cemented sarsens. About 50 Ma ago (early Eocene) the Palaeocene rocks and those beneath were broadly buckled by the outermost ripples of the Alpine orogeny. Once eroded from above the Plain they would certainly have delivered that signature to the mercy of subsequent back and forth river transport. And indeed the sarsens, hard to miss in that landscape, perhaps still do so. Yet no one has thought to examine their content of heavy-mineral grains.

It does seem to me that the authors, perhaps inadvertently, walked into a sedimentological minefield in a vain attempt to put the lid on the fractious debate about human- versus glacial-transport of the Stonehenge megaliths. It is not their data that fling down a ‘challenge’ to the latter hypothesis (see their Conclusions), but the widely accepted absence of even the tiniest nugget of bluestone or Devonian sandstone on the vast and heavily excavated ritual landscape of Salisbury Plain, or indeed in the gravels of the streams that currently drain the Plain. But this where the plot thickens. A recent paper by one of the proponents of the glacial hypothesis (John, B.S. 2024. A bluestone boulder at Stonehenge: implications for the glacial transport theory. E&G Quaternary Science Journal v. 73, p. 117-134;DOI: 10.5194/egqsj-73-117-2024) describes a small piece of bluestone (22 × 15 × 10 cm) that was found during excavations at Stonehenge in 1924 and mysteriously ‘rescued’ by a Robert Newall and stored in his attic for almost 50 years, eventually examined by geologists and then returned to the attic. In 1976, two years before his death Newall passed it to the curator of Salisbury Museum ‘for safe keeping’. Brian John claims that its shape and surface texture suggests glacial transport. It also has several percussion scars suggesting that it had been worked, perhaps by someone hoping to make a stone tool. Unsurprisingly, Johns succeeded in provoking a storm of criticism from archaeologists largely of the human-transport wing of the controversy. And then there is the Mumbles Erratic, found at the eponymous Mumbles headland to the west of Swansea Bay. It too looks like a ‘bluestone’, but is it an erratic or from a Neolithic ship wreck carrying bluestones from Pembrokeshire?

Maximum extent of glaciation in SW Britain during the Anglian Stage 478 to 424 ka ago (Credit: Wikipedia Commons)

A great deal of work by British glaciologists has established the flow patterns and extent of major ice sheets, but only for four onshore, even though there is offshore evidence for repeated glaciation back as far as 2.5 Ma ago. The most extensive of these was the Anglian Stage between 478 and 424 ka ago. The figure above shows that the Irish Sea Glacier did not reach the Stonehenge area, but it did cross Pembrokeshire to reach Somerset on the eastern side of the Bristol Channel. Bluestone erratics may have been much more easily available than blocks hewn at their source in SW Wales, an hypothesis that is currently in vogue. Nope, the quest is not over …

How vulnerable are coastal zones to sea-level rise?

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These days only a fool or a scoundrel would deny anthropogenic global warming and its primary outcome of inevitable sea-level rise. Yet no agency, either national or international, has set out to attempt a detailed global assessment of coastal vulnerability. There is no shortage of relevant data to do that – from remote sensing, digital elevation models, simulations of tides and wave height from meteorological data and much else. Thankfully, a team of geomorphologists, climate scientists, sociologists and economists from The Netherlands and France, led by Vindhya Basnayake of the University of Twente, The Netherlands, have taken up the challenge (Basnayake, V. et al. 2026. A global assessment of coastal vulnerability and dominant contributors. Nature Communications, in-press manuscript; DOI: 10.1038/s41467-025-67275-6).

About 10% of the world’s population – a bit less than a billion – live in coastal zones at less than 10 m elevation above mean sea level, and two-fifths that may bear the brunt of future rise. Coastal flooding and erosion threaten landforms, ecosystems and built infrastructure. Both physical effects of sea-level rise potentially may disrupt population centres, livelihoods and marine and coastal industries. More frequent and severe storms driven by global warming are also expected to increase the frequency and intensity of coastal hazards over time. Basnayake  et al. have developed a Coastal Vulnerability Index (CVI) to express the hazard presented by future flooding and erosion to all coastal areas. The CVI is based on geomorphology, geology, coastal slope, coastal relief, wave height, and relative sea level change. It also integrates the local adaptive capacity and community resilience from socioeconomic and geopolitical data. Importantly CVI values are calculated at 1 km intervals along the global coastline at over 350 thousand locations. The approach used by the team incorporates from previous analyses time series for wave and tide heights and for changing sediment supply. The fine spatial resolution of data allows for identification of critical micro-regions – even within generally less vulnerable countries. Such a nuanced approach shows up the complexity of coastal risk that one-size-fits-all approaches are destined to miss.

Steep coastal slopes are less vulnerable than gentle ones, which allow greater penetration by marine hazards. The more rugged coastal terrain, the less vulnerable the coast is by acting like a large scale breakwater. Mean wave height controls the energy impinging on a coast, and is affected by wave ‘fetch’, so that ocean-facing coasts are more vulnerable than more enclosed locations. Offshore seismicity, as in island arcs, increases vulnerability to tsunamis. Tidal range has a counterintuitive effect, large ranges reducing the time a coast is in direct contact with the sea, whereas low ranges place the sea next to land for much longer. Although global sea level is destined to rise uniformly, some coasts are rising through tectonic or glacio-eustatic uplift, while others are actively subsiding; so relative sea-level change is used to address vulnerability. Other considerations assessed by Basnayake  et al. are subsidence due to coastal groundwater extraction, the presence of protective coastal vegetation such as mangroves, and the influence of deltas and estuaries.

Coastal vulnerability by country: dark blue – very low; green – low; yellow – moderate; orange – high; dark red – very high. (Credit: Basnayake et al. Fig 2a)

The figure above summarises the results of the CVI study on a country-by-country basis. Eurasia is surprisingly the least vulnerable continent in this respect, especially Britain and Norway that are so exposed to the fierce North Atlantic. That is partly due to those countries high adaptive capacity and communal resilience, but mainly to their rugged and deeply indented western coasts; a legacy of glaciation. It’s important to note that coloration on the figure can be misleading. For instance, the higher resolution data pinpoint extremely high vulnerability of stretches of coast dominated by low-lying deltas, such as those of Pakistan, India, Myanmar and SE Asia. Equally surprising is the high vulnerability of North America at similar latitudes; somewhat ironic for the heartland of climate-change denial. High resolution also points to counterintuitive hazards; for instance coastal defences sometimes exacerbate vulnerability by increasing erosion on nearby undefended stretches and by hindering sediment movement. Increased onshore infrastructure boosts runoff and erosion in the coastal realm and displaces natural buffers, such as coastal forest, to storm surges: perhaps partly responsible for the high vulnerability of coasts around the hurricane belt of the Gulf of Mexico and Caribbean. Of the nineteen countries with greatest vulnerability 12 are in West Africa and NE South America and 2 in the Caribbean area. The paper is well worth reading, to get a flavour of the complexity involved and the vast magnitude of the task of ameliorating risk of coastal devastation that lies ahead in the next decades.

See especially: Global Coastal Vulnerability: Key Causes Revealed. Scienmag, 14 January 2026.

Advances in hominin evolution

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For decades, most of the news concerning our deep ancestry emerged from discoveries in sub-Saharan Africa at sites in Zambia, Tanzania, Kenya, South Africa, Ethiopia. The first week of 2026 decisively shifted that focus northwards to Chad and Morocco in two separate publications.

In 2002 ago the world of palaeoanthropology was in turmoil following the first discovery of fragments of what was then thought to be a hominid, or great-ape, cranium in Chad dated at around 7 Ma ago (Brunet, M. and 37 others 2002. A new hominid from the Upper Miocene of Chad, central Africa. Nature, v. 4418, p. 145-151;DOI:10.1038/nature00879). When pieced together the cranium looked like a cross between that of a chimpanzee and an australopithecine. Some suggested that the creature may have been a ‘missing link’ between the hominids and hominins; perhaps the ultimate ancestor of humans. Sahelanthropus tchadensis (nicknamedToumaï­ or ‘hope of life’ in the local Goran language) was undoubtedly enigmatic. The ‘molecular-clock’ age estimate for the branching of hominins from a common ancestor with chimpanzees was, in 2002, judged to be two million years later the dating of Sahelanthropus, so controversy was inevitable. Another point of contention was the size of Sahelanthropus’s canine teeth: too large for australopithecines and humans, but more appropriate for a gorilla or chimp. Moreover, Toumaï­ showed no indisputable evidence for having been bipedal. The Chadian site subsequently yielded three lower jaw bones and a collection of teeth, a partial femur (leg bone) and three fragmentary ulnae (forearm bones). The finds suggested that as many as five individuals had been fossilised. The femur gave an unresolved hint of an upright gait, yet the ulnas suggested Toumaï­ might equally have been arboreal; as could also be said for the australopithecines.

Reconstructed skull of Sahelanthropus tchadensis. (Credit: Didier Descouens, University of Toulouse)

All the limb bones of Toumaï­have now been anatomically compared with those of hominins and apes (Williams S.A. et al. 2026. Earliest evidence of hominin bipedalism in Sahelanthropus tchadensis. Science Advances, v. 12, article eadv0130; DOI: 10.1126/sciadv.adv0130). Scott Williams of New York University and co-workers from other US institutions show that although the leg bones are much the same size as those of chimpanzees, their proportions were more like those of hominins. They also showed features around the knees and hips needed for bipedalism and an insertion point for a tendon for the gluteus maximus muscle (buttock) vital for sustained upright locomotion, similar to the femurs of Orrorin tugenensis (see: Orrorin walked the walk; May 2008) and Ardipithecus ramidus. Unfortunately, an intact Sahelanthropus cranium showing a foramen magnum – where the skull attaches to the spine – continues to elude field workers. Its position distinguishes upright gait definitively.

See also: This ancient fossil could rewrite the story of human origins.  Science Daily, January 3, 2026)

The second new advance concerns the joint ancestry of Neanderthals, Denisovans and anatomically modern humans (AMH), whose ancient genetics crudely suggest a last common ancestor living between 765 to 550 ka. This had previously been attributed to Homo antecessor found in the Gran Dolina cave at Atapuerca in northern Spain, roughly dated between 950 ka and 770 ka. (Incidentally, Gran Dolina has yielded plausible evidence of cannibalism). A novel possibility stems from hominin fossils excavated from a cave in raised-beach sediments near Casablanca in Morocco (Hublin, JJ. and 28 others, 2026  Early hominins from Morocco basal to the Homo sapiens lineage. Nature, v. 649 ; DOI: 10.1038/s41586-025-09914-y). The fossil-bearing sediments contain evidence for a shift in the Earth’s magnetic field (the Brunhes–Matuyama reversal) dated at 773 ka, much more precisely than the Atapuerca age span for H. antecessor. Jean-Jacques Hublin of CNRS in Paris and his multinational colleagues report that the fossils are similar in age to H. antecessor, yet are morphologically distinct, displaying a combination of primitive traits and of ‘derived features reminiscent of’ later Neanderthal, Denisovan and AMH fossils. The differences and shared features suggest that there may have been genetic exchanges between the Moroccan and Iberian population over a considerable period. The most obvious route would have been across the Straits of Gibraltar, but would have required some kind of water craft.  An important question is ‘which population gave rise to the other?’

Artistic reconstruction of a juvenile Homo antecessor, Based on skeletal remains from Gran Dolina Cave

Larger and more robust hominin remains in Algeria dated at 1,000 ka – H. heidelbergensis? – resemble those found near Casablanca. They may have evolved to the latter. Similar possible progenitors to Iberian Homo antecessor have yet to be found in Western Europe. Homo erectus appeared in Georgia and Romania between 2.0 and 1.9 Ma, but the intervening million years or more have yielded no credible European forebears of H. antecessor. For the moment, incursion of a North African population into Europe followed by sustained contact is Hublin et al’s favoured hypothesis, rather than a European origin for Homo antecessor. For Neanderthals and Denisovans to have originated from such an African group, as has been suggested, requires finds of African fossils with plausible resemblance to what are predominantly Eurasian groups. The Iberian population migrated far and wide in Western Europe, as witnessed by stone tools and footprints dating to between 950 to 850 ka in eastern England. So it is equally possible that the Iberian group were progenitors of Neanderthals and Denisovans in Eurasia itself. At least for the moment, ancient genomes of the two H. antecessor groups are unlikely to be found in either Iberian or African fossils of the same antiquity. But, as usual, that will not stifle debate: a resort to the adage ‘absence of evidence is not evidence of absence’ seems appropriate to several research teams!

The oldest anatomically modern human fossils dated at ~300 ka, were also discovered in Morocco (see: Origin of anatomically modern humans, June 2017). Their isolation in the NW corner of the African continent poses a similar conundrum, as since then such beings went on to occupy wide areas of sub-Saharan Africa and then the world.

Asteroid Bennu: a ‘lucky dip’ for NASA and planetary science

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I must have been about ten years old when I last saw a ‘lucky dip’ or ‘bran tub’ at a Christmas fair.  You paid two shillings (now £0.1) to rootle around in the bran for 30 seconds and grab the first sizeable wrapped object that came to hand:. In my case that would be a cheap toy or trinket, but you never knew your luck as regards the top prize. There is a small asteroid called 101955 Bennu, about half a kilometre across, whose orbit around the Sun crosses that of the Earth. So it’s a bit scary, being predicted to pass within 750,000 km of Earth in September 2060 and has a 1 in 1,880 chance of colliding with us between 2178 and 2290 CE. Because Earth-crossing asteroids are a cheaper target than those in the Asteroid Belt, in 2016 NASA launched a mission named OSIRIS-REx to intercept Bennu, image it in great detail, snaffle a sample and ultimately return the sample to Earth for analysis. This wasn’t a shot in the dark, as a lot of effort and funds were expended to target and then visit Bennu. But unlike me at the fair ground, NASA will be very happy with the outcome.

The asteroid Bennu, showing its oblate spheroidal shape, due to rotation, and its rubbly structure. Source: NASA/Goddard/University of Arizona via Wikimedia Commons

Bennu is a product of what might be regarded as ‘space sedimentation’, indeed a kind of conglomerate, being made up of boulders up to 58 m across set in gravelly and finer debris or ‘regolith’. High-resolution images revealed veins of carbonate minerals in the boulders. They suggest hydrothermal activity in a much larger parent body – one of many proto-planets accreted from interstellar gas and dust as the Solar System first began to form over 4.5 billion years ago. Its collision with another sizeable body knocked off debris to send a particulate cloud towards the Sun, subsequently to clump together as Bennu by mutual gravitational attraction. The carbonate veins can only have formed by circulation of water inside Benno’s  parent.

The ‘REx’ in the mission’s name is an acronym for ‘Regolith Explorer’. Sampling was accomplished on 20 October 2020 by a soft landing that drove a sample into a capsule, and then OSIRIS-REx ‘pogo-sticked’ off with the booty. The capsule was dropped off by parachute after the mission’s return on 24 September 2023, in the manner of an Amazon delivery by drone to a happy customer. So, you can understand my ‘lucky dip’ metaphor. And NASA certainly was ‘lucky’ as the contents turned out to be astonishing, as related two years later by the analytical team in the US, led by NASA’s Angel Mojarro (Mojarro, A. et al. 2025.Prebiotic organic compounds in samples of asteroid Bennu indicate heterogeneous aqueous alteration. Proceedings of the National Academy of Science, v. 122, article e2512461122; DOI: 10.1073/pnas.2512461122).

The rock itself is made from bits of carbonaceous chondrite, the most primitive matter orbiting the Sun. It contains fifteen amino acids, including all five nucleobases that make up RNA and DNA – adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U) – as in AUGC and AGCT. Benno’s complement of amino acids included 14 of the 20 used by life on Earth to synthesise proteins. The fifteenth, tryptophan, has never confidently been seen in extraterrestrial material before. Alkylated polycyclic aromatic hydrocarbons, also found in Bennu, are seen in abundance in interstellar gas clouds and comets by detecting their characteristic fluorescence when illuminated by mid-infrared radiation from hot stars using data from the Spitzer and James Webb Space Telescopes. These prebiotic organic compounds have been suggested to have played a role in the origin of life, but exposure to many produced by human activities are implicated in many cancers and cardiovascular issues.  A second paper by Japanese biochemists and colleagues from the US was also published in early December 2025 (Furukawa, Y. and 13 others 2025. Bio-essential sugars in samples from asteroid Bennu. Nature Geoscience, v. 12, online article; DOI: 10.1038/s41561-025-01838). The authors identified several kinds of sugars in a sample from Bennu, including ribose – essential for building RNA – and glucose. Bennu also contains formaldehyde – a precursor of sugars – perhaps originally in the same brines in which the amino acids formed.

Yet another publication coinciding with the aforementioned two focuses on products of the oldest event in the formation of Bennu: its content of pre-solar grains (Nguyen, A.N. et al. 2025. Abundant supernova dust and heterogeneous aqueous alteration revealed by stardust in two lithologies of asteroid Bennu. Nature Astronomy, v. 9, p. 1812-1820; DOI: 10.1038/s41550-025-02688-3).  In 1969 a 2 tonne carbonaceous chondrite fell near Allende in Mexico. The largest of this class ever found, it contained tiny, pale inclusions that eight years of research revealed to represent materials completely alien to the Solar System. They are characterised by proportions of isotopes of many elements that are very different from those in terrestrial materials. The anomalies could only have formed by decay of extremely short-lived isotopes that highly energetic cosmic rays produce in a manner analogous to neutron bombardment: they are products of nuclear transmutation. It is possible to estimate when the parent isotopes produced the anomalous ‘daughter’ products. One study found ages ranging from 4.6 to 7.5 Ga: up to three billion years before the Solar System began to form. It is likely that the grains are literally ‘star dust’ formed during supernovae in nearby parts of the Milky Way galaxy. Bennu samples contain six-times more presolar grains than any other chondritic meteorites. Nguyen et al. geochemically teased out grains with different nucleosynthetic origins. These ancient relics point to Bennu’s formation in a region of the presolar cloud that preceded the protoplanetary disk and was a mix of products from several stellar settings.

The results from asteroid Bennu support the key idea that that amino acid building blocks for all proteins and the nucleobases of the genetic code, together with other biologically vital compounds arose together in a primitive asteroid.  Its evolution provided the physical conditions, especially the trapping of water, for the interaction of simpler components manufactured in interstellar clouds. Such ‘fertile’ planetesimals and debris from them almost certainly accreted to form planets and endowed them with the potential for life. What astonishes me is that Bennu contains the five nucleobases used in terrestrial genetics and 70% of the amino acids from which all known proteins are assembled by terrestrial life. But, as I try to explain in my book Stepping Stones: The Making of Our Home World, life as we know it arose, survived and evolved through a hugely complex concatenation of physical and chemical events lasting more than 4.5 billion years. The major events and the sequences in which they manifested themselves may indeed have been unique. Earth is a product of luck and so are we!

See also: Tabor, A. et al. 2025. Sugars, ‘Gum,’ Stardust Found in NASA’s Asteroid Bennu Samples. NASA article 2 December 2025. Glavin, D.P. and 61 others 2025. Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu. Nature Astronomy, v. 9, p. 199-210; DOI: 10.1038/s41550-024-02472-9