Evolution: pattern of stasis and sprint (Introduction)

by David Turell , Saturday, June 04, 2022, 21:02 (693 days ago) @ David Turell

All through the period of evolution from start to now, he uses Chixculub extinction as an example:

https://aeon.co/essays/catastrophe-drives-evolution-but-life-resides-in-the-pauses?utm_...

"While dinosaurs get most of the attention, they weren’t the only ones to disappear. More than half of all life on Earth – from plankton to pterosaurs – perished following the impact of the Chicxulub asteroid that created a 150 km-wide crater in the Yucatán peninsula. It took 30,000 years for life to re-emerge in the fossil record, and another 4 to 9 million years to return to pre-impact levels.

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"This postapocalyptic period was characterised by novelty. New genetic combinations resulting from crossbreeding would have added to an array of anomalies caused by developing in a stressful environment. The first generation of the new world order wouldn’t copy the habits that had enabled their lineages’ survival for aeons; instead, they would copy habits their parents had improvised out of the necessity of the moment. Emerging from the ashes, the biotic world looked nothing like the one before the asteroid struck. It would take millions of years for pre-impact levels of species diversity to rebound and for ecosystems to stabilise.

"When things did settle back down, the pace of evolution would return to a virtual standstill. That’s the pattern we observe in the fossil record: disruption, change and then long periods of stasis.

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"But this persistent focus on natural selection as the sole mechanism of adaptive evolution has always been a sticking point. It can’t properly explain how anything new arises. After all, natural selection is a process that eliminates unfit variants – it doesn’t create, but changes the prevalence of what’s already there. Instead, novelty must come from the purely random process of genetic mutation. The problem is that when new mutations appear, they’re usually not a good thing. They are more likely to disrupt well-adapted systems than to improve them, especially if they have a big effect. The upshot is that the evolution of something new, such as eyes or feathers, requires a heck of a long waiting time. Not only is there a long wait for a beneficial mutation to come along, but then there’s the long process of accumulating enough of them to build up, step by step, a complex new structure. (my bold)

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"However, there’s been a growing acceptance of this pattern among evolutionary biologists and theorists over the years, as new studies and techniques reveal it again and again across diverse organisms. For example, Stevan J Arnold, an evolutionary biologist at Oregon State University, and his colleagues looked at patterns of body size evolution in vertebrates ...They found that bursts of body-size evolution occur only on the order of every million years or so.

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"The pervasiveness of this pattern means that modern-day evolutionary biologists now have two enigmas to explain. First, what prevents species from changing for the majority of their existence? And second, when they do change, how does it happen so fast?

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"At moderate scales, perhaps glacial cycles or other gradual environmental changes push populations back and forth around a mean, but over very long timescales, there is little net evolutionary change.

"Examples of such dynamic stability, where a system shows fluctuations around a mean but little net change over time, are everywhere...We see it in brain waves, or in ecological systems where the number of individuals in a population or species in a community fluctuates across years, but overall remains steady.

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"Such events are rare and occur only every million years or more – but when they do, the system must either change or cease to function. In evolutionary terms, that means it must evolve or go extinct. This suggests that macroevolutionary patterns can’t be understood by simply adding up microevolutionary changes over a long period of time because catastrophic events, such as the Chicxulub meteor, don’t occur on a constant gradual basis. In fact, all the evidence suggests that major evolutionary changes can occur in a blink of a geological eye and persist only when systems suffer a major disruption and are forced to massively reorganise.

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"The pattern of evolutionary stasis dominates the history of life on Earth.

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"Most importantly, viewing evolution through a systems lens fundamentally changes how we view the story of life on Earth. It’s not a story of the constant struggle for existence. Rather, it’s a story that resides in the pauses – the uneventful interludes, where components of the systems maintain the status quo, and change necessarily comes with painful and extreme disruption."

Comment: of course, he mentioned Punc-inc from Gould as being widely accepted. Note my bold with the true view of Natural selection being passive, not inventive. The author doesn't solve the problem of speciation nor does he recognize the possibility of a desgner running the show. The main point is evolution is filled with gaps.