June 7, 2019

WE ARE ALL DESIGNIST:

Why humans (or something very similar) may have been destined to walk the Earth: The paths available to evolving organisms are far from limitless (Evolutionary biologists James Horton and Tiffany Taylor, 6/07/19, Cosmos)

Many bacterial evolution studies have found, perhaps surprisingly, that evolution often follows very predictable paths over the short term, with the same traits and genetic solutions frequently realised. Consider, for example, a long-term experiment, in which 12 independent populations of Escherichia coli founded by a single clone, have been continuously evolving since 1988. That's over 65,000 generations - there have only been 7,500-10,000 generations since modern Homo sapiens appeared. All the evolving populations in this experiment show higher fitness, faster growth and larger cells than their ancestor. This suggests that organisms have some constraints on how they can evolve.

There are evolutionary forces that keep evolving organisms on the straight-and-narrow. Natural selection is the "guiding hand" of evolution, reigning in the chaos of random mutations and abetting beneficial mutations. This means many genetic changes will fade from existence over time, with only the best enduring. This can also lead to the same solutions of survival being realised in completely unrelated species. [...]

But what about the underlying physical laws - do they favour predictable evolution? At very large scales, it appears so. We know of many governing laws of our universe that are certain. Gravity, for example - for which we owe our oceans, thick atmosphere and the nuclear fusion in the sun that showers us with energy - is a predictable force. Isaac Newton's theories, based on large scale deterministic forces, can also be used to describe many systems on large scales. These describe the universe as perfectly predictable.

If Newton's view was to remain perfectly true, the evolution of humans was inevitable. However, this comforting predictability was shattered by the discovery of the contradictory but fantastical world of quantum mechanics in the 20th century. At the smallest scales of atoms and particles, true randomness is at play - meaning our world is unpredictable at the most fundamental level.

This means that the broad "rules" for evolution would remain the same no matter how many times we replayed the tape. There would always be an evolutionary advantage for organisms that harvest solar power. There would always be opportunity for those that make use of the abundant gases in the atmosphere. And from these adaptations, we may predictably see the emergence of familiar ecosystems. But ultimately, randomness, which is built into many evolutionary processes, will remove our ability to "see into the future" with complete certainty.

There's a problem in astronomy that acts as a fitting analogy. In the 1700s, a mathematical institute offered a prize for solving the "three-body problem", involving accurately describing the gravitational relationship and resultant orbits of the sun, Earth and moon.

The winner, Joseph-Louis Lagrange, essentially proved that the problem couldn't be solved exactly. Much like the chaos introduced by random mutations, a little bit of starting error would inevitably grow, meaning that you couldn't easily determine where the three bodies would end up in the future. But as the dominant partner, the sun dictates the orbits of all three to an extent - allowing us to narrow the possible positions of the bodies to within a range.

This is much like the guiding hands of evolution, which tether adapting organisms to familiar routes. We may not be entirely sure where we'd end up if we rewound time, but the paths available to evolving organisms are far from limitless. And so maybe humans would never appear again, but it's likely that whatever alien world replaced ours would be a familiar place.

Posted by at June 7, 2019 1:15 PM

  

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