Freeman Dyson among others has speculated about the physical changes that could occur as the human species spreads into the cosmos. How will evolution deal with a colony world in a distant star system, and how long will it take before serious differentiation begins to occur? For that matter, what about the crew aboard a multi-generational starship — will humans have adapted so thoroughly to a space-borne environment when they arrive that some opt to make their planetary excursion no more than a brief research stop before pushing on to yet other solar systems?

Or will they one day adapt to the vacuum itself?

Such questions are called to mind by recent work from Virginie Millien (McGill University), whose new paper in the open source journal PLoS Biology examines islands as test beds for evolution on Earth. It has long been assumed that isolation would create selective pressures unique to an island environment. A so-called ‘island rule’ has small animals evolving into outsized versions of their counterparts on the mainland, while larger animals tend to shrink. But although systematic evidence has been scarce, Millien’s work now confirms that island species do undergo accelerated evolutionary changes in small time frames.

How small? Anywhere from thousands of years down to decades, depending on the species. But the accelerated rate of evolution tends to slow down, until for intervals over 45,000 years the difference in evolutionary rates between mainland and island species becomes statistically insignificant. The big changes seem to involve the initial adaptation. Truly remote islands show the most interesting effects, but habitat destruction on the mainland can force equally quick changes. From the paper:

The commonly proposed mechanisms that govern evolution on islands — a founder event followed by slower evolution — can be compared to the mechanisms that operate after a drastic change in the environment on the mainland. However, the present data suggest that the peculiar ecological environment on islands — lack of predators, reduced interspecific competition, resource limitation — favours faster evolution, even over several thousands of years. Species surviving in fragmented landscapes are also confronted with a modified environment characterised by a reduced area and an increased isolation relative to their undisturbed habitat. These new environmental conditions parallel those seen in true island habitats, and one may suspect that morphological changes in response to fragmentation are similar to changes in island species.

Thus evolutionary rates vary with circumstances, as we would expect. Which brings to mind some of Dyson’s speculations about the evolution of future species adapted to space itself. But a shorter range outlook ponders what could happen even on places as relatively nearby as Mars once human colonies take hold there. Millien’s work offers the possibility that evolutionary changes to, for example, differing gravitational pulls will begin to produce serious species changes in fairly short time frames. Then throw in genetic engineering for some truly interesting effects. Here’s Dyson in Disturbing the Universe:

The Mongolian nomads developed a tough skin and a slit-shaped eye to withstand the cold winds of Asia. If some of our grandchildren are born with an even tougher skin and an even narrower eye, they may walk bare-faced in the winds of Mars. The question that will decide our destiny is not whether we shall expand into space. It is: shall we be one species or a million? A million species will not exhaust the ecological niches that are waiting the arrival of intelligence.

And a bit later:

When life invades a new habitat, she never moves with a single species. She comes with a variety of species, and as soon as she is estabished, her species spread and diversify still further. Our spread through the galaxy will follow her ancient pattern.

The above quotes are from my 1979 hardcover edition of Disturbing the Universe (New York: Harper and Row), both on p. 234. Millien’s paper is “Morphological Evolution Is Accelerated among Island Mammals, PLoS Biology Vol. 4 Issue 10 (September, 2006). And although I don’t have time to get into this today, the open access movement which PLoS Biology exemplifies is part of an ongoing revolution in science publishing that we’ll continue to examine in these pages.