‘Mass extinctions accelerate evolution’

Evolution• Heavy metal pollution contributed to some of the world’s largest events
• Humans responsible for demise of gigantic ancient mammals 

SCIENTISTS have provided fresh insights on how mass extinction events accelerated evolution. Scientists in the first study published in Nature Communications presented evidence that malformed fossil remains of marine plankton from the late Silurian (415 million years ago) contain highly elevated concentrations of heavy metals, such as iron, lead, and arsenic.

These are well-known toxins that cause morphologic abnormalities in modern aquatic organisms; which led the authors to conclude that metal poisoning caused the malformation observed in these ancient organisms and may have contributed to their extinction and that of many other species.

Also, a computer science team at The University of Texas at Austin, United States (U.S.), has found that robots evolve more quickly and efficiently after a virtual mass extinction modeled after real-life disasters such as the one that killed off the dinosaurs.

Beyond its implications for artificial intelligence, the research supports the idea that mass extinctions actually speed up evolution by unleashing new creativity in adaptations.

Computer scientists Risto Miikkulainen and Joel Lehman co-authored the study published today in the journal PLOS One, which describes how simulations of mass extinctions promote novel features and abilities in surviving lineages.

Meanwhile, new research has revealed that early humans were the dominant cause of the extinction of a variety of species of giant beasts. Scientists at the universities of Exeter and Cambridge claim their research settles a prolonged debate over whether mankind or climate change was the dominant cause of the demise of massive creatures in the time of the sabretooth tiger, the woolly mammoth, the woolly rhino and the giant armadillo.

Lewis Bartlett, of the University of Exeter, led the research, which also involved the universities of Reading and Bristol and is published in the journal Ecography.

Known collectively as megafauna, most of the largest mammals ever to roam the earth were wiped out over the last 80,000 years, and were all extinct by 10,000 years ago.

An international team led by Thijs Vandenbroucke (researcher at the French CNRS and invited professor at UGent) and Poul Emsbo (US Geological Survey) initiated a study to investigate a little known association between ‘teratological’ or ‘malformed’ fossil plankton assemblages coincident with the initial stages of these extinction events.

Several Palaeozoic mass extinction events during the Ordovician and Silurian periods (ca. 485 to 420 to million years ago) shaped the evolution of life on our planet.

Although some of these short-lived, periodic events were responsible for eradication of up to 85% of marine species, the exact kill-mechanism responsible for these crises remains poorly understood.

Documented chemical behavior of these metals, which correlates with previously observed disturbances in oceanic carbon, oxygen and sulphur signatures, strongly suggests that these metal increases resulted from reductions of ocean oxygenation.

Thus, metal toxicity, and its expressions in fossilized malformations, could provide the ‘missing link’ that relates organism extinctions to widespread ocean anoxia.

As part of a series of complex systemic interactions accompanying oceanic geochemical variation, the mobilisation of metals in spreading anoxic waters may identify the early phase of the kill-mechanism that culminated in these catastrophic events.

The recurring correlation between fossil malformations and Ordovician-Silurian extinction events raises the provocative prospect that toxic metal contamination may be a previously unrecognized contributing agent to many, if not all, extinction events in the ancient oceans.

Miikkulainen, a professor of computer science at UT Austin said: “Focused destruction can lead to surprising outcomes. Sometimes you have to develop something that seems objectively worse in order to develop the tools you need to get better.”

In biology, mass extinctions are known for being highly destructive, erasing a lot of genetic material from the tree of life. But some evolutionary biologists hypothesize that extinction events actually accelerate evolution by promoting those lineages that are the most evolvable, meaning ones that can quickly create useful new features and abilities.

Miikkulainen and Lehman found that, at least with robots, this is the case. For years, computer scientists have used computer algorithms inspired by evolution to train simulated robot brains, called neural networks, to improve at a task from one generation to the next.

The UT Austin team’s innovation in the latest research was in examining how mass destruction could aid in computational evolution. In computer simulations, they connected neural networks to simulated robotic legs with the goal of evolving a robot that could walk smoothly and stably.

As with real evolution, random mutations were introduced through the computational evolution process. The scientists created many different niches so that a wide range of novel features and abilities would come about.

After hundreds of generations, a wide range of robotic behaviors had evolved to fill these niches, many of which were not directly useful for walking.

Then the researchers randomly killed off the robots in 90 percent of the niches, mimicking a mass extinction. After several such cycles of evolution and extinction, they discovered that the lineages that survived were the most evolvable and, therefore, had the greatest potential to produce new behaviors.

Not only that, but overall, better solutions to the task of walking were evolved in simulations with mass extinctions, compared with simulations without them.

Practical applications of the research could include the development of robots that can better overcome obstacles (such as robots searching for survivors in earthquake rubble, exploring Mars or navigating a minefield) and human-like game agents.

Bartlett said cutting-edge statistical analysis had helped solve the mystery almost beyond dispute, concluding that man was the dominant force in wiping out the creatures, although climate change could also have played a lesser role.

The researchers ran thousands of scenarios, which mapped the windows of time in which each species is known to have become extinct, and humans are known to have arrived on different continents or islands.

This was compared against climate reconstructions for the last 90,000 years. Examining different regions of the world across these scenarios, they found coincidences of human spread and species extinction which illustrate that man was the main agent causing the demise, with climate change exacerbating the number of extinctions.

However, in certain regions of the world – mainly in Asia – they found patterns which patterns were broadly unaccounted for by either of these two drivers, and called for renewed focus on these neglected areas for further study. “This is a good example of how evolution produces great things in indirect, meandering ways,” explains Lehman, a former postdoctoral researcher in Miikkulainen’s lab, now at the IT University of Copenhagen.

He and a former student of Miikkulainen’s at UT Austin, Kenneth Stanley, recently published a popular science book about evolutionary meandering, “The Myth of the Objective: Why Greatness Cannot Be Planned.

Even destruction can be leveraged for evolutionary creativity.” Meanwhile, widespread species are at just as high risk of being wiped out as rare ones after global mass extinction events, says new research by United Kingdom (UK) scientists.

There have been five mass extinction events in the Earth’s history, including climate change caused by volcanoes and an asteroid hit that wiped out the dinosaurs.

In general, geographically widespread animals are less likely to become extinct than animals with smaller geographic ranges, offering insurance against regional environmental catastrophes.

However, a study published in Nature Communications has found this insurance is rendered useless during global mass extinction events, and that widely distributed animals are just as likely to suffer extinction as those that are less widespread.

The research by Dr. Alex Dunhill School of Earth and Environment at the University of Leeds and Professor Matthew Wills from the University of Bath’s Milner Centre for Evolution, explored the fossil record of terrestrial (land-living) vertebrates (including dinosaurs) from the Triassic and Jurassic periods (252-145 million years ago).

They found that although large geographic ranges do offer insurance against extinction, this insurance disappeared across a mass extinction event that occurred around 200 million years ago (at the Triassic-Jurassic boundary) associated with massive volcanic eruptions and rapid climate change which caused the demise of around 80 per cent of species on the planet.

During this catastrophic event many groups of crocodile ancestors became extinct, which paved the way for the dinosaurs to rise to dominance in the subsequent Jurassic Period.

Dunhill and Wills mapped how the geographical distribution of groups of organisms changed through the Triassic-Jurassic periods. These distribution maps were then compared with changes in biodiversity to reveal the relationship between geographic range and extinction risk.

This is the first study to analyse the relationship between geographic range and extinction in the terrestrial fossil record and the results are similar to those obtained from the marine invertebrate fossil record.

Alex Dunhill, who started the work at Bath and is now at the University of Leeds, said: “The fact that the insurance against extinction given by a wide geographic distribution disappears at a known mass extinction event is an important result.

Many groups of crocodile-like animals become extinct after the mass extinction event extinct at the end of the Triassic era, despite being really diverse and widespread beforehand. “In contrast, the dinosaurs which were comparatively rare and not as widespread pass through the extinction event and go on to dominate terrestrial ecosystems for the next 150 million years.”

Co-author Matthew Wills from the University of Bath’s Milner Centre for Evolution commented: “Although we tend to think of mass extinctions as entirely destructive events, they often shake up the status quo, and allow groups that were previously side-lined to become dominant. “Something similar happened much later with the extinction of the dinosaurs making way for mammals and ultimately ourselves.

However, our study shows that the ‘rules’ of survival at times of mass extinctions are very different from those at ‘normal’ times: nothing is ever really safe!” Dunhill added: “These results shed light on the likely outcome of the current biodiversity crisis caused by human activity.

It appears a human-driven sixth mass extinction will affect all organisms, not just currently endangered and geographically restricted species.”

Bartlett, a researcher from the University of Exeter’s Centre for Ecology and Conservation, said: “As far as we are concerned, this research is the nail in the coffin of this 50-year debate – humans were the dominant cause of the extinction of megafauna. What we don’t know is what it was about these early settlers that caused this demise.

Were they killing them for food, was it early use of fire or were they driven out of their habitats? Our analysis doesn’t differentiate, but we can say that it was caused by human activity more than by climate change. It debunks the myth of early humans living in harmony with nature.”

Dr. Andrea Manica, of Cambridge University, was lead supervisor on the paper. He said: “Whilst our models explain very well the timing and extent of extinctions for most of the world, mainland Asia remains a mystery.

According to the fossil record, that region suffered very low rates of extinctions. Understanding why megafauna in mainland Asia is so resilient is the next big question.”



1 Comment
  • Peter_Edo

    interesting…

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