AI depiction of the ancient retroviral DNA that is essential for embryo development but can help lung cancer cells survive too
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Post-gastrulation amnioids - models with mimic the development of the amniotic sac forming as expected (top panel). Amnioids without a key calcium-buffering gene and its accompanying switch don't form as expected (bottom two panels).
Some 13 million years before anyone could have written a creation myth, a retrovirus inserted its genetic material into the genome of an ancestral ape. Today, part of that viral legacy helps regulate early human development. This presents creationists with several difficulties at once: a history vastly older than their biblical chronology permits, genetic material acquired from a virus, and an evolutionary innovation produced by putting an existing sequence to a new use. There is also an uncomfortable sting in the tail for advocates of a benevolent intelligent designer: cancer cells can exploit the same biological machinery.
The research, reported in Science Advances, concerns a remnant of an ancient retrovirus known as HERVH. This sequence acts as a switch controlling a form of calbindin, a protein involved in buffering calcium inside cells. Removing the switch or calbindin disrupted the growth and developmental behaviour of human embryonic stem cells and the organisation of models of early embryonic structures.
The evolutionary distinction matters. The original acquisition of viral DNA represents horizontal genetic transfer: genetic material crossed from a virus into its host, rather than arriving through ordinary inheritance from a parent. Once incorporated into the germ line, however, that material could pass vertically through successive generations. Its recruitment to regulate a host gene is an example of exaptation — the co-option of an existing feature for a different function. The virus did not need to invent calbindin, nor did evolution need to create an entirely new protein from scratch. A new regulatory relationship could arise by combining material with different evolutionary histories.
This is precisely the sort of process obscured by the creationist slogan that new genetic “information” requires an intelligent author. Biologically useful novelty can involve changes in when, where and how an existing gene is expressed. Imported DNA can supply a regulatory element; subsequent evolution can preserve and modify its contribution. Calling the result “information” does not erase the natural processes that produced it, still less establish that someone intended the outcome.
The chronology is equally inconvenient. Comparative primate evidence places this insertion roughly 13 million years ago, after the lineage leading to humans and the African great apes had separated from the orangutan lineage. Orangutans are themselves great apes; the relevant event occurred within the broader great-ape family tree. Either way, this is inherited molecular history extending far beyond the few thousand years allowed by a literal young-Earth reading of Genesis.
Yet a mechanism useful during development need not remain beneficial in every context. Earlier research showed that lung squamous cell carcinoma can activate this viral switch, helping cancer cells avoid senescence — a state in which cells stop dividing. The cancer biology is complex, but the central evolutionary point is clear: machinery that supports normal development can also become available for malignant cells to exploit.
That is consistent with an evolutionary cost-benefit trade-off. Natural selection can preserve a developmental advantage despite a vulnerability elsewhere in life; it has no foresight with which to guarantee lifelong protection from every possible consequence. But if intelligent-design advocates insist that useful genetic arrangements demonstrate deliberate engineering, they must apply that reasoning consistently. A designer credited with the developmental benefit cannot simply be excused responsibility for the exploitable weakness. On their own premises, the result raises questions about competence, benevolence, or even malevolent design. Evolution requires no such theological contortions: an ancient infection, inherited variation and the opportunistic reuse of existing material are sufficient ingredients for the story.
Human history is written in more than ancient texts. It is also preserved in the genetic material passed from generation to generation, where migrations and changes in population size leave patterns that scientists can investigate. For creationists who would compress humanity’s ancestry into the descendants of a single family emerging from a mythical global flood, this presents a demanding test: their story must explain the actual distribution of genetic variation, rather than merely assert that people dispersed.
A new study published in Science on 8 October 2026 examines whole-genome sequences from 1,050 Polynesian people. It reveals successive founder effects associated with the settlement of Pacific islands: small founding groups carried only part of their source population’s genetic diversity, and subsequent departures repeated that sampling process.
The result is a nested pattern of inheritance. Particularly striking is the close genetic relationship between the populations of Hawaiʻi and Rapa Nui, despite their separation by roughly 7,000 kilometres. The researchers interpret this as evidence that both populations have deeper ancestral roots in Mangareva. Their reconstruction also involves repeated movement between islands, rather than a simple procession of isolated, one-way journeys.
These demographic events have medical consequences too. Variants that were rare in an ancestral population can become relatively common among descendants of a small founding group. The study identifies several disease-associated variants at elevated frequencies, showing how the legacy of settlement can remain relevant to health today.
This is also an accessible example of why evolution cannot be reduced to natural selection alone. Genetic drift — chance changes in the frequencies of genetic variants — can shape populations without making them better adapted. A variant does not have to be beneficial to become more common; sometimes its frequency reflects who happened to found a community and which descendants subsequently reproduced. The voyages were purposeful human achievements, but their genetic consequences required neither foresight nor a designer.
The challenge for biblical literalism is therefore more substantial than finding room for Polynesian voyagers somewhere after Noah. A scientific explanation must account for which populations share particular variants, how those variants are distributed, and which demographic history best explains the pattern. These findings do not, by themselves, constitute a test of every claim about a global flood. They do demonstrate what an evidence-based account of human dispersal looks like: a reconstruction open to scrutiny and revision, with consequences that can be checked against independent evidence. Simply invoking Genesis supplies none of that explanatory detail.
One of the strengths of science is that its conclusions remain open to revision. An assumption that once appeared reasonable can be tested against new evidence, found wanting, and replaced with something better. For creationists, who frequently portray such revisions as evidence that science cannot be trusted, this must seem a peculiar way of acquiring knowledge. Yet it is precisely how science improves its understanding: by allowing the evidence to correct the explanation, rather than requiring the evidence to conform to a predetermined answer.
A new study published in Science Advances provides another example. Researchers have challenged an assumption used in some recent estimates of when animals originated. Their analyses support an origin approximately 700–800 million years ago, potentially extending animal evolutionary history by around 200 million years beyond estimates based on a younger maximum-age constraint.
The issue is a deceptively simple one: if a fossil deposit preserves microscopic organisms in exquisite detail, but contains no definite animals, does that mean animals had not yet evolved? Some researchers have used the approximately 590-million-year-old Weng’an Biota of China in this way, reasoning that animals would have been preserved there had they existed. Its lack of unequivocal animal fossils has therefore helped set a proposed upper age limit for animal origins.
The new research exposes a difficulty with that reasoning. The younger Kheseen Biota of Mongolia also preserves exceptionally detailed microfossils, yet none can confidently be identified as animals. In this case, however, animals are known from other deposits of comparable age. Their absence from Kheseen therefore cannot demonstrate their absence from the world. Particular environments and conditions of fossilisation can leave animals out of the record, even when other organisms are beautifully preserved.
This matters because molecular clocks — methods that use genetic differences between living organisms to estimate when their ancestors diverged — require calibration against geological and fossil evidence. Change an unjustified age constraint, and the resulting estimates can change substantially. Using alternative constraints from older deposits, the researchers recovered a much earlier possible origin for animals. They have not discovered an 800-million-year-old animal, nor established a final date for the animal kingdom’s beginnings. They have shown why one argument for restricting those beginnings to a much later interval is unreliable.
For young-Earth creationism, neither chronology offers any comfort. The debate concerns events hundreds of millions of years ago, not whether animal history can be squeezed into the few thousand years allowed by a literal reading of Genesis. Uncertainty over precisely when animals originated does not make every proposed date equally credible, any more than uncertainty over a mountain’s exact height makes it plausibly a molehill.
An artist’s rendering of the Norellraptor after an “exquisitely preserved” fossil with a complete skeleton and parts of its plumage was unearthed in Liaoning province.
a Right hand. b Pubis. c Feet. am, acetabular margin; ap, apron; cs, claw soft tissue; gi, gastral impression; mcI-III, metacarpals I to III; mtI-V, metatarsals I to V; p, phalanx; pf, pubic foot; r, radius; sc, semilunate carpal; t, tibiotarsus; u, ulna; uI-III, unguals 1 to 3. Scale bar = 10 mm.
For creationists who insist that complex adaptations could only have appeared as complete, purpose-built packages, another feathered dinosaur has provided an awkward piece of evidence. Evolution does not require a finished flight apparatus to materialise in a single miraculous leap. It can modify inherited structures, combine them in new ways, and produce similar adaptations along different branches of the family tree. A newly described dinosaur from China adds evidence that even among the close relatives of birds, there was more than one evolutionary route towards an aerial lifestyle.
In a paper published in Nature Communications, Xuri Wang and colleagues describe Norellraptor barsboldi, a small microraptorine dinosaur from the Lower Cretaceous Jiufotang Formation of Liaoning, north-eastern China. Its remarkably complete, 57-centimetre skeleton preserves traces of plumage, including on its forelimbs and hindlimbs. It belonged to the group of feathered dinosaurs famous for their four-winged forms: evolutionary relatives of birds, rather than evidence that modern birds appeared fully formed and unrelated to other dinosaurs.
The crucial finding concerns the sequence in which adaptations arose. The researchers’ evolutionary analysis indicates that approximately 30 per cent of the derived anatomical features identified in microraptorine evolution also evolved independently in the bird lineage. However, they appeared in different orders. This supports the gradual assembly of flight-associated anatomy under different selective pressures, rather than the inheritance of an already completed flight apparatus from a common ancestor.
Two million years ago, southern Africa was home to different human relatives sharing the same landscape and following different evolutionary trajectories. That is the picture strengthened by newly described fossils from Drimolen Main Quarry in South Africa’s Cradle of Humankind. For creationists, the difficulties begin with the date: these hominins lived almost two million years before the supposed magical creation of the Universe out of nothing in a literal reading of Genesis. But the evidence also challenges the familiar caricature of human evolution as a single procession of increasingly human creatures, marching towards a predetermined destination.
In a paper published in Annals of Human Biology, Jesse M. Martin and colleagues describe 18 previously undescribed cranial and mandibular specimens from Drimolen. Among them is DNH 127, an adult skull fragment attributed to Homo erectus. This provides valuable support for the earlier identification of DNH 134, a young child’s partial skull from the same site. Identifying a species from an immature individual can be difficult because some diagnostic features develop during growth; an adult specimen provides an additional test of that interpretation.
The significance is therefore corroboration: DNH 127 strengthens the case that Homo erectus was present in South Africa approximately 2.04–1.95 million years ago. It does not, by itself, establish that the species originated there. The earliest fossil yet recognised is evidence of a species’ presence at a particular place and time, rather than a birth certificate identifying its evolutionary birthplace.
One of the recurring mistakes in creationist arguments is to assume that a complex biological system must always have performed its present function. If its components now work together, the argument goes, they must have been created together for that purpose. Evolution, however, can recruit existing machinery for new roles. Two papers in *Science* now provide evidence that this process may help explain the origin of an important form of microbial immunity—with the intriguing possibility that bacteria acquired the precursors of their antiviral weapons from viruses themselves.
To appreciate the discovery, it helps to understand what CRISPR immunity actually is. Although CRISPR is familiar as a tool for editing genes, its natural role is defence. Many bacteria and archaea possess CRISPR–Cas systems that retain molecular records of past invaders. Short pieces of foreign DNA are incorporated into the cell’s genome, between repeated sequences. These stored fragments provide templates for small RNA molecules, which guide CRISPR-associated—or Cas—proteins to matching genetic material during subsequent infections. Depending on the system, the resulting response can destroy invading DNA or RNA. This is adaptive immunity: protection directed against particular threats, with a genetic memory that can pass to descendants.
CRISPR stands for “clustered regularly interspaced short palindromic repeats”, a description of the DNA arrangement in which those memories are stored. The best-known gene-editing protein, Cas9, belongs to class 2, whose targeting machinery centres on one large protein. Class-1 systems instead use assemblies of several proteins to recognise their targets. It is the evolutionary origin of this latter machinery that the new research addresses.
The studies, published on 17 September 2026 investigate a compact system called VIPR, short for viral interference programmable repeat. Found in viruses and bacteria, it combines a small protein with a guide RNA. The researchers propose that an ancestral VIPR-like system involved in competition between viruses was recruited into bacterial defence, eventually contributing to the evolution of class-1 CRISPR. This would be evolutionary co-option: machinery favoured in one context becoming useful in another.
One of the problems with claiming that biological complexity proves intelligent design is that the argument cannot stop conveniently at butterflies, flowers and the human eye. If complex biological machinery requires a designer, then the same reasoning must apply to parasites and pathogens. A virus’s ability to infect us cannot become an unfortunate accident merely because crediting the supposed designer would now be embarrassing. Nor can the animal that carries it from host to host be excluded from the reckoning.
A newly identified tick-borne virus in China provides another uncomfortable example. Described in a correspondence in The New England Journal of Medicine, Asian longhorned tick nairovirus, or ALTNV, is associated with fever, fatigue, gastrointestinal symptoms and, in some patients, reduced platelet counts. Its vector is the already familiar Asian longhorned tick, Haemaphysalis longicornis; experiments demonstrated transmission to mice. “New” here means newly recognised by science, not shown to have come into existence recently.
The clinical findings deserve care. All 56 patients reported with ALTNV alone recovered without lasting effects. However, seven of 38 patients infected with both ALTNV and Dabie bandavirus died. These deaths do not establish that ALTNV alone is lethal, or determine its contribution to the fatalities. They do place the discovery within a system of tick-borne infections capable of causing serious illness and death.
Now apply the creationist rule that functional complexity and genetic information require an intelligent author. On that premise, the designer must take responsibility for the infectious agent and its means of delivery. Here is a blood-feeding animal whose activities provide a route for viruses to enter other animals, including humans. If every relevant adaptation was knowingly intended by an all-knowing creator, then the resulting suffering cannot be dismissed as an unforeseen side-effect. The alleged designer knew what its creations would do.
That is the force of the malevolent-designer argument. It does not require us to believe that a supernatural intelligence actually makes viruses. It asks why features that serve pathogens should count as evidence of loving craftsmanship when equivalent features serving their victims are routinely presented as precisely that. If the designer receives credit for our defences, it must also answer for the threats those defences sometimes fail to overcome. Deliberately creating the means of making people ill is hardly an obvious expression of benevolence.
One of the recurring problems for young-Earth creationism is that Earth’s history contains so much life before the supposed beginning of Earth’s history. A newly recognised fossil species from Illinois adds another example: a small, amphibian-like animal that lived approximately 309 million years ago, when the area around modern Chicago was a swampy river delta. That places it more than 300 million years before the creation event that biblical literalists insist accounts for all life on Earth. Explaining away a discrepancy of that magnitude requires rather more than pointing to an uncertainty in a scientific paper.
The animal is Jeanerpeton mazonensis, described by Allison J. Sefcovic, Payton J. Kohlberg and colleagues in a new paper in the Journal of Vertebrate Paleontology. Its recognition resulted from a fresh examination of a fossil already held in a museum collection. Previously assigned to Amphibamus grandiceps, the specimen proved sufficiently different in its skull and skeleton to warrant a genus and species of its own. The authors also suggest that other known specimens conceal more diversity among these early amphibamiforms than has previously been recognised.
The fossil comes from the exceptionally productive Mazon Creek deposits. Its preservation includes a body outline, scales, tiny abdominal skeletal elements called gastralia, and even impressions of the eyes. The genus honours the two student lead authors’ mothers, both named Jean. This is a reminder that important discoveries can begin with someone taking a closer look at a specimen collected long ago.
Left: Allison Sefcovic and Payton Kohlberg hold epoxy sculptures of their new species, Jeanerpeton mazonensis.
Of particular interest are structures previously interpreted as toe pads resembling those of living amphibians. Alongside the skeletal anatomy, such features help researchers investigate the combinations of characteristics present in these ancient animals. That does not establish Jeanerpeton as the direct ancestor of modern frogs or salamanders: resemblance and evolutionary relationship are not proof of direct ancestry. Its significance lies in adding another anatomically distinctive animal to the record against which explanations of amphibian evolution must be tested.
AI-generated impression of life in the Cretaceous Gobi. The mammal in the foreground is a generalised small mammal, not Tamirkhan balcarceli, for whom there is insufficient data for a reconstruction
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Field photos of the Khugenetsavkhlant badlands in the Eastern Gobi Desert of Mongolia today, where Tamirkhan balcarceli was discovered.
One of the most revealing differences between science and creationism is what happens when new evidence challenges an established explanation. In science, that is an opportunity to improve our understanding. In creationism, where the conclusion has already been declared unquestionable, it becomes a problem to explain away. A remarkable fossil from Mongolia’s Gobi Desert provides a particularly instructive example: a small mammal whose combination of teeth, skull and limb bones has prompted scientists to reconsider an enduring hypothesis about mammalian evolution. Predictably, there is no comfort here for anyone hoping that revising an evolutionary family tree means abandoning evolution.
The animal, Tamirkhan balcarceli, is described in a paper in Nature by Andres Giallombardo and colleagues. Discovered in 2004, the exceptionally informative specimen preserves a skull and part of a hind limb. This provides something researchers had previously lacked for the enigmatic mammals known as zhelestids: teeth and substantial skeletal remains belonging to the same individual.
Until now, zhelestids were known principally from teeth and fragmentary jaws. Their relatively low, rounded molar cusps resembled those of plant-eating hoofed placental mammals, encouraging suggestions that they represented an early radiation of placentals during the Cretaceous. The new fossil tests that interpretation against a much broader sample of anatomy. Its zhelestid-like molars occur alongside distinctive incisors, skull structures and hindlimb features characteristic of another ancient mammalian group, the zalambdalestoids. The researchers conclude that zhelestids belong within that group. Their apparently revealing resemblance to later herbivorous placentals arose through convergent evolution.
The significance extends beyond moving a name from one branch of a family tree to another. Identifying which ancient mammals belong within the placental radiation helps establish when that radiation began and how its early members diversified. An animal can possess teeth resembling those of a later group without belonging to that group: similar feeding demands can favour similar dental adaptations in separate evolutionary lineages. More complete fossils allow researchers to distinguish those similarities from the wider anatomical evidence of ancestry. This discovery therefore changes how an important set of Cretaceous fossils contributes to the history of placental origins; it does not, by itself, settle every question about their timing.
For young-Earth creationists, the chronological problem remains as severe as ever. This is a Late Cretaceous mammal, part of a world that existed tens of millions of years before the few thousand years into which they attempt to compress the history of Earth and its inhabitants. Revising its evolutionary relationships does nothing to bring that world within the biblical timetable. Nor does a previously mistaken interpretation of its teeth supply evidence for separately created “kinds”. To establish that claim would require positive evidence of separate creation, not merely the discovery that one proposed relationship needs correction.
For young-Earth creationists, some of the most troublesome evidence comes in the smallest packages. Microscopic fossils preserved in ancient Australian mudstones record organisms living approximately 1.75–1.4 billion years ago — an antiquity impossible to reconcile with the few thousand years allowed by a literal reading of the biblical genealogies. These organisms were already part of aLayers of 1.7 billion-year-old sedimentary rocks, Kakadu National Park, Northern Territoryn evolving biosphere more than a billion years before the supposed “Creation Week”. Their existence presents a chronological problem that no amount of argument about the meaning of “kind” can resolve.
These fossils are the subject of a paper in Nature, by Maxwell A. Lechte and colleagues, investigating the environments inhabited by some of the earliest known eukaryotes. Eukaryotes are organisms with structurally complex cells, typically containing a nucleus and specialised internal compartments; they include animals, plants, fungi and numerous microscopic organisms. Here, “complex life” refers to cellular organisation, not to miniature animals swimming through those ancient seas. Understanding these early cells helps explain the evolutionary foundations upon which much later forms of life depended.
Glossary.
Aerobes
Organisms that use oxygen in their metabolism. Obligate aerobes require it; facultative anaerobes can grow with or without it; microaerophiles require oxygen at concentrations below those in ordinary air.
Benthic
Living on, in or close to the bottom of a sea or lake. A “benthic habit” means a bottom-dwelling way of life.
Planktonic
Living suspended in the water and drifting largely with currents, rather than inhabiting the seabed.
Bottom waters
The water immediately above the seabed. It can lack oxygen even when the surface waters contain it.
Morphological complexity
Complexity of physical form or structure. Elaborate fossil walls, ornamentation and extensions can help researchers recognise probable eukaryotes.
Palaeontological, sedimentological and geochemical analyses
Studies of fossils, sediments and their formation, and the chemical composition of geological materials, respectively. Combining them helps reconstruct both ancient organisms and their environments.
Body fossils and molecular biomarkers
Body fossils preserve remains or impressions of organisms. Molecular biomarkers are chemical traces of biological molecules that can provide evidence of ancient life even without recognisable bodies.
Proterozoic eon
The interval from approximately 2.5 billion to 539 million years ago, encompassing much of the early history of eukaryotic life.
Neoproterozoic era
The final part of the Proterozoic, approximately 1 billion to 539 million years ago. The researchers propose that eukaryotes expanded substantially into planktonic habitats during this interval.
The research also illustrates something creationist caricatures of science routinely overlook: scientists continually test their explanations against evidence. Discoveries of living eukaryotes capable of surviving without oxygen, together with evidence that ancient seas were widely oxygen-poor, had raised questions about whether the earliest eukaryotes needed oxygen at all. To investigate, the researchers turned to rock cores drilled decades ago during mineral exploration and subsequently stored in Darwin. They examined more than 12,000 microfossils and analysed the sediments and their chemistry to reconstruct the organisms’ habitats. Old collections, approached with new questions, can still yield major discoveries.
The resulting pattern was revealing. Eukaryotic fossils occurred almost exclusively in sediments deposited beneath oxygenated waters, whereas sediments from oxygen-free settings still preserved other microbial fossils. Their distribution suggests that these early eukaryotes used oxygen and probably lived on the seabed. The researchers also propose that a much later expansion into planktonic habitats helped shape subsequent diversification. This connects evolutionary history with the availability of suitable environments: the opportunities for complex organisms to flourish depended on the physical and chemical conditions around them.
This does not establish every step in the origin of the eukaryotic cell, nor demonstrate that one particular rise in oxygen directly caused its appearance. It does strengthen the evidence that oxygen availability constrained early eukaryotic habitats. The broader picture is one of evolution unfolding within a changing planet, with environmental conditions opening opportunities and imposing limits. There is no requirement here for foresight or a predetermined destination.
Creationists may welcome any suggestion that scientists are reassessing an earlier interpretation, but the revision offers them no chronological refuge. Whether these organisms inhabited the seabed or drifted in the water, and precisely how they used oxygen, are questions within an ancient evolutionary history. Reconsidering those details does not compress that history into a biblical timetable. Science advances because its explanations remain answerable to evidence; a chronology fixed in advance can survive only by refusing the evidence that contradicts it.
In the following article from The Conversation, reproduced here under a Creative Commons licence, researchers Maxwell Lechte and Leigh Anne Riedman explain what these tiny fossils reveal about the early evolution of complex life.
Tiny fossils found in 1.7 billion‑year‑old mud yield clues to the evolution of complex life
Drill cores of sedimentary rock which contains microscopic fossils.
Stored in an open-air warehouse in tropical Darwin, Australia, are dozens of trays containing cylindrical cores of rock. They are from drill holes bored hundreds of metres below the surface by mineral exploration companies decades ago.
Some of these cores at the Northern Territory Geological Survey are mudstone – a type of sedimentary rock formed from hardened seafloor mud. The companies that drilled these cores were largely unaware that within these mudstones were fossils of microscopic organisms buried on the seafloor of an ancient inland sea that covered much of northern Australia over 1.5 billion years ago.
As our new study, published today in Nature, shows, these fossils are crucial for addressing a longstanding puzzle about the major evolutionary leap that led to all complex life on Earth: the origin of eukaryotes.
Layers of 1.7 billion-year-old sedimentary rocks, Kakadu National Park, Northern Territory.
Maxwell Lechte
Small but complex
All life on Earth can be placed into one of two types which are fundamentally different at the cellular level.
Prokaryotes (bacteria and archaea) have simple cellular organisation and are mostly single celled. Eukaryotes – including all animals, plants, algae and fungi – are very different. They have much more complicated cells featuring a nucleus and other specialised structures such as organelles which perform specific jobs.
The eukaryotic revolution transformed the planet. It led to the rise of animals and, eventually, to us. Based on observations from the genes of living organisms, it is now widely agreed that the last common ancestor of all living eukaryotes resulted from the symbiotic union of (at least) two prokaryotic microbes: an archaeon and a bacterium.
The first evidence for eukaryotic life comes in the form of these fossils of single-celled organisms. They show a level of cellular complexity not seen among prokaryotes, but common in eukaryotes.
Eukaryote fossils can be found around the world in rocks dating back at least 1.5 billion years. The fossils of the Northern Territory, the oldest of which date back to 1.75 billion years ago, are the oldest currently known eukaryote fossils globally.
But the ancient world in which early eukaryotes evolved remains shrouded in mystery. And so many fundamental aspects regarding their nature are unknown.
Oxygen – friend or foe?
Many types of bacteria can live and grow in places without oxygen. But nearly all eukaryotes alive today use oxygen for their survival. That’s because aerobic respiration – breaking down food using oxygen – provides the vast amounts of energy that complex life demands.
But the idea that oxygen has always been beneficial for all eukaryotes has come under fire in recent years. This follows the surprising discoveries of enigmatic eukaryotes that can thrive in conditions without oxygen.
There is also mounting evidence from the geological record that when eukaryotes were first evolving, oxygen was likely much scarcer. This means oxygen-free marine habitats would have been the norm. Collectively, these observations have called into question the assumption eukaryotes have depended on oxygen since their inception.
Genetic studies of living microbes belonging to groups considered closest to the ancestors of the first eukaryote can offer key insights into eukaryote ancestry. But only the fossil record can tell us about long-extinct lineages. And only geology can offer a window into the kind of world these organisms lived in.
Fossils of single-celled eukaryotic organisms with complex surface features such as extensions and plates.
Leigh Anne Riedman
More than 12,000 fossils
For our new study, we crushed up samples of the mudstone cores stored in Darwin, then dissolved them. We identified more than 12,000 fossils by analysing the organic residue left behind by this dissolution under a microscope.
We also studied the mudstones the fossils were preserved in to better understand what the environment was like when the sediments were deposited. This offered insight about the habitats in which these eukaryotes lived. And by analysing the chemistry of these mudstones, we could determine whether oxygen was present in the ancient seawater.
Our results show that eukaryote fossils were found in environments ranging from coastal mudflats to the open sea. But they were present only in samples deposited in oxygenated settings. Samples from oxygen-free environments contained only simple, prokaryotic forms.
This suggests that even the oldest known eukaryotes that lived on Earth 1.7 to 1.4 billion years ago were dependent on oxygen. These data lend support to a long-held hypothesis that oxygen played a key role in driving the evolution of early eukaryotes.
Resolving the drivers and context of the major evolutionary leap represented by early eukaryotes is one of the major outstanding questions in the life sciences. Ongoing studies of these enigmatic, ancient microfossils will no doubt tell us more about our own origins – and our place in the cosmos.
Maxwell Lechte, Research Associate in Geobiology, University of Sydney and Leigh Anne Riedman, Postdoctoral Researcher, Department of Earth Science, University of California, Santa Barbara
Published by The Conversation. Open access. (CC BY 4.0)
Abstract
The evolution of the eukaryotic cell paved the way for the emergence of all complex life on Earth. Despite its significance, the environmental context of early eukaryote evolution is largely unknown1,2. Here we use the geological record to reconstruct the habitats of the oldest known fossil eukaryotes, approximately 1.75–1.4 billion years old. Our integrated palaeontological, sedimentological and geochemical analyses show that although fossil eukaryotes are found in samples deposited in a range of environments from coastal to offshore, they are almost entirely restricted to those from settings with oxygenated bottom waters. This distribution suggests these organisms were aerobes (obligate, facultative and/or microaerophilic) and, given their size and morphological complexity, probably possessed mitochondria. Furthermore, their near absence from otherwise fossiliferous anoxic samples suggests a benthic habit, as planktonic eukaryotes would be expected to be present in both oxic and anoxic samples. We propose that eukaryotes were largely restricted to oxic benthic habitats for much of the Proterozoic eon, only expanding into planktonic habitats during the Neoproterozoic era (1–0.54 billion years ago). This late ecological expansion could account for the mismatch between the appearance of eukaryotic body fossils and molecular biomarkers3 and explain the stepwise increase in eukaryote diversity during the Neoproterozoic era4.
For young-Earth creationism, the fundamental problem remains the chronology. These microscopic organisms inhabited Earth more than a billion years before the supposed biblical creation. Debates about their metabolism or preferred habitat cannot make that immense span of time disappear. There is no evidence-based reconciliation between this geological history and a world only a few thousand years old; preserving the latter requires rejecting the former.
The study also illustrates how science progresses. Researchers revisit specimens, question assumptions and combine different kinds of evidence to distinguish between competing explanations. Whether early eukaryotes depended on oxygen is a question to investigate, not a doctrine to defend. Revising an interpretation in response to evidence strengthens our understanding; it does not render every alternative explanation equally credible.
What emerges is a history in which the evolution and distribution of complex life were constrained by environmental conditions. Oxygen availability helped determine where these early eukaryotes could flourish, while subsequent ecological expansion offered further opportunities for diversification. This does not mean that oxygen alone explains the origin of complex cells, but it places their history firmly within the workings of a changing natural world.
There is no need to imagine those ancient seas being prepared with humans in mind. Evolution has no foresight: organisms survive and reproduce under the conditions they encounter, and their descendants inherit the consequences. These tiny fossils preserve evidence of that long, contingent history — a history we can reconstruct by examining the rocks, rather than insisting that the rocks conform to an ancient creation story.
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Bats present creationists with a multitude of problems: firstly, there is the fact that they have a vastly more effective immune system than humans, so creationists need to explain why an omnibenevolent creator god would not give his favourite special creation, humans, the best available immune system. Secondly, there is the famous Bible blunder where, in most English language translations, bats appear to have been classified as birds (Leviticus 11:13-19) by the ignorant people who wrote it.
Now the facts have become even more difficult in the form of an awkward combination: remarkable adaptations that invite declarations of “design”, and an evolutionary history that researchers can investigate using evidence. Calling a bat a specially created “kind” explains neither its relationships with other bats nor when and where those relationships arose. Those are questions that require fossils, genomes and testable hypotheses.
Now, a major international study, published in Nature, has brought these questions into sharper focus. Researchers working within the Bat1K consortium assembled genomic data from 103 species, representing all 21 recognised living bat families, and combined this resource with anatomical evidence from 44 fossil bats. The university summarises their findings as pointing to a European origin for bats and mammalian powered flight around 65 million years ago — tens of millions of years before the supposed “Creation Week” of young-Earth creationism.
The research reconstructs a branching history of ancestry, migration and diversification. Its geographical model favours Europe as the ancestral region, followed by dispersal into Africa and subsequent expansion into other continents. These are historical inferences that can be tested and revised as further evidence becomes available.
The study also sheds light on echolocation: the ability to use returning echoes to detect surroundings and prey. The inferred position of the extinct bat Vielasia supports the conclusion that laryngeal echolocation — using calls generated in the voice box — arose before the diversification of the group containing all living bats. This places another celebrated bat adaptation deep within their evolutionary history.
