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18th October 2017

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Life: from Sea to Land to Space

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A recent scientific paper caught my eye, “Evolution accelerated when life set foot on land,” by Elizabeth Pennisi. The abstract reads (in its entirety):

Life probably originated in water, but nature did some of its best work once organisms made landfall. That’s what Geerat Vermeij has concluded after surveying fossils and family trees to discover where and when some of life’s greatest modern advances evolved. He compiled a list of key innovations that showed up in several groups of organisms and provided a big competitive edge and was able to find existing fossil evidence to date the origins of a dozen. Nine innovations appeared first on land and later in the sea and two never made it back to the sea. The conclusion: Almost all these seemingly out-of-the-blue innovations, from fungus farming by insects to the water transport systems that made tall trees possible, came about after plants and animals learned how to survive on land some 440 million years ago, Vermeij, an evolutionary biologist at the University of California, Davis, reports.

Since the abstract referred to the work of Geerat Vermeij I looked him up and found his recent paper, How the Land Became the Locus of Major Evolutionary Innovations, which details the nine evolutionary innovations mentioned above. Apparently Vermeij has had an enduring interest in evolutionary innovations, as I also found his very interesting earlier paper,  Historical contingency and the purported uniqueness of evolutionary innovations. I will not discuss this paper here, but I will note that the abstract touches on many ideas that have been of great interest to me.

Suppose that the increase in the complexity of life as it makes the transition from an aquatic environment to a terrestrial environment is a pattern that points to a deeper evolutionary mechanism. If this is true, one would expect this deeper evolutionary mechanism to be expressed in every biosphere, so that biospheres that only consisted of a global ocean may be limited in the degree of complexity of life forms, while planets without large bodies of water may not evolve life at all.

The most complex life would arise on planets with a surface of both water area and land area. When we are someday able to reconstruct biosphere evolution, and are able to do so on many worlds with distinct biospheres, there may be an as-yet-unknown law that describes the optimal ratio between water surface area and land surface area. The distribution of land masses will also likely enter into any complexity of life calculation. A world of island archipelagos and no continental land masses may result in different evolutionary patterns than a world of one or a few continental land masses. We already know certain generalizations that apply to island biogeography, so that we may be able to scale up this approach in order to formulate a theory of planetary-scale island biogeography (and I once noted that astrobiology is island biogeography write large).  

Once life made the transition from water to land, not only did it begin to fill the newly emerging ecological niches on land, but life also launched itself beyond the land and into the air. Arthropods evolved wings and began to fly about 400 million years ago, which was not long after insects evolved. Thus we might extend the possible complexity of life from water to land to air. Those biospheres that do not evolve life that makes the transition to flying may also stagnate at lower levels of complexity.

The obvious extension of this line of thought (pointed out to me in a Tweet from Winchell Chung) is that life may evolve even greater complexity when it makes the transition from planetary endemism to space. As soon as I saw this comment, I realized that I had already formulated this, although with a different emphasis, in Transhumanism and Adaptive Radiation, in which I wrote that, once life makes the transition into space, we may experience a “Great Voluntaristic Divergence.” I conceived this primarily in social terms, as a condition of future civilization, but it is equally true in biological terms, as long as the expansion of civilization into the cosmos is not exclusively an AI virtual presence.

Any expanding civilization that brings a portion of its homeworld biosphere along with it as it settles other worlds will experience the adaptive radiation of the life is the expanding presence endures over biological scales of time. And the possibilities for complex life inhabiting countless worlds, as well as artificial ecosystems (space settlements) will provide orders of magnitude of additional ecological niches in which orders of magnitude of further biological complexity will be evolved.

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Tagged: Elizabeth PennisiGeerat Vermeijbiogeographyisland biogeographyastrobiology

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