(The following editorial first appeared in the May 2004 issue of Analog Science Fiction and Fact. Thirty-five others, on a wide range of topics, are collected in the 2002 Tor book Which Way to the Future? A different one (usually one not available in the book) will be posted here a few times a year. And, of course, brand-new ones appear in each issue of Analog.)
Copyright © 2004 by Stanley Schmidt
At the 2003 World Science Fiction Convention in Toronto, I participated in a panel called “Design a Truly Alien Alien,” ably moderated by the always imaginative and stimulating Ctein. The capsule description in the pocket program said, “In science fiction TV, aliens typically resemble humans with rubber face masks and behavioral patterns less bizarre than some members of your own family. In extreme cases, we may be presented with creatures that, while not human, are clearly inspired by terrestrial life-forms such as insects or octopi. Yet it is statistically ludicrous that actual aliens would be so utterly familiar. . . .”
Well, yes and no—but how much of each?
First of all, it’s not a purely statistical process. The form and functioning of organisms is not determined purely by chance. True, they evolve by random mutation of individual traits followed by natural selection of the ones best able to survive in their environment; but the result is that the ones that do survive are ones that function effectively in that environment. Which ones those are is determined by the same kinds of engineering principles that govern the design of any kind of machinery. L. Sprague de Camp wrote much more about this in his two-part article “Design for Life” (Astounding, May-June 1939); and I in my book Aliens and Alien Societies (Writer’s Digest Books, 1996 [especially Chapter 5, “Engineering Organisms”]). I don’t have room to repeat all those arguments here, but I will say that de Camp made a good case for believing that intelligent beings evolved in similar environments on an Earthlike planet are likely to look at least vaguely humanoid. He also did a good analysis of why practically all of the large swimmers on Earth are streamlined in similar ways, divisible into three subtypes depending on exactly how they swim.
It’s true that too many science-fictional aliens (especially in movies and television) are “humans in rubber suits” or impractical combinations of traits cobbled together from unrelated terrestrial animals. Nevertheless, it seems quite safe to say that you will very seldom encounter big swimmers in the form of sharp-edged cubes—anywhere. Nor will you find something that looks like a fish or an octopus living in a desert. That kind of design just doesn’t work for that job.
The similarity of swimmers to which de Camp devoted such attention is one example of “convergent evolution,” in which similar environmental problems independently lead to similar biological solutions in different places. Examples abound on Earth, and the similarities sometimes go even further than you might expect. The South American birds called jacamars, for example, look and act very much like the African bee-eaters, even though the two families are not closely related. Given that they both live in tropical climates and make their livings by catching flying insects and battering them to death against branches, it’s probably not surprising that they’re similar in size and shape. But why should their color schemes be so similar? I don’t know.
When, on that panel, I mentioned the many examples of convergent evolution on Earth, my esteemed colleague Ctein expressed skepticism about how much that implied about forms life might take on other worlds. After all, the same environment here can include spruce trees, club mosses, cardinals, otters, and moose. Does that not prove that many different kinds of organisms can evolve in the same kind of environment? And does that not imply that completely different ones might evolve in a similar environment elsewhere?
The answer to the first question is clearly yes, in a coarse sort of way—but not if you look closer. Spruce trees, club mosses, cardinals, otters, and moose all occupy different parts of the environment, or “microenvironments.” In fact, each of them is part of the environment for all the others. The whole collection of organisms in a region, and the ways they interact, constitute an ecosystem, and what I have called “microenvironments” are more commonly called ecological niches. Both cardinals and otters, for example, are parts of a common Canadian type of ecosystem; but a cardinal is not at all suited to functioning in the part of that environment, the niche, occupied by the otter—or vice versa. If anything else ever tried to occupy the otter’s niche, the otter has long since outcompeted it to extinction.
If you go to other parts of the planet at similar latitudes and with similar climates, you may find different species of conifers or lycopodia or seed-eating birds, but you’ll find similar species making up an ecosystem overall so much like the other that an untrained observer may not notice the difference. Boreal forests look and feel quite similar in widely separated places all around the globe, even if they’re made up of largely different species. So do tropical rain forests. So do coral reefs.
Etc. It can easily make one suspect that while many different kinds of organisms can evolve in a particular combination of terrain and climate, that combination will strongly tend to produce sets of such organisms that have large numbers of obvious similarities. But must it always be the same kind of set?
Even on Earth we can find examples to suggest that it doesn’t. Australia has been isolated from all the other continents longer than they have been separated from each other, and that isolation has allowed parts of its evolution to proceed in ways notably different from the ones that occurred elsewhere. The best-known example is the marsupials, a group of mammals using a significantly different form of reproduction than the placental mammals that predominate elsewhere (though it can be viewed as a variation on the same theme). Australian marsupials have branched out to exploit practically all the ecological niches available on their home continent, and some of those have developed different solutions to similar problems than their placental analogs on other continents. Where Europe, Asia, Africa, and the Americas have deer and/or antelope in the “large herbivore” department, Australia has kangaroos and wallabies. Deer and antelope run; kangaroos and wallabies hop, even in similar environments. So we know that solutions at least that diverse can occur.
On the other hand, hopping isn’t all that different from running. Both categories of critters use four legs, and choosing one mode or the other is principally a matter of changing the details—such as size and proportions—of bones and muscles. For that matter, similar changes, only more so, can change legs to arms, wings, fins, or flippers. How about more fundamentally different solutions to the “getting around” problem—like wheels? They work quite well, in suitable environments, so why don’t we see them (at least in largish, multicellular animals) on Earth? Probably the more important reason is that evolution works by single modifications of things that have already evolved. Legs, wings, and flippers are similar enough in their fundamental structures that it’s relatively easy to turn one of them into one of the others by a series of such incremental changes. It’s much harder to get from any of them to a wheel and axle. The structure is too fundamentally different; changing one to the other would require several simultaneous—and drastic—changes.
But what if you started from a fundamentally different point? All the examples we can point to so far are things that evolved on Earth and are based on DNA. That doesn’t necessarily mean that that’s the only way it can happen anywhere else. If the first organisms on a different planet made some different “choices” than the ones that were made here on Earth, subsequent evolution might have led to a whole cascade of approaches—and organisms—quite different from the ones that developed here. Such a thing conceivably may have even tried to happen here, but the version with the head start overwhelmed the upstart and squelched it before it could amount to much. Willy Ley said some decades ago that, “A prerequisite for life to start on a planet is that there be no already developed life forms there”—because if there are, they’ll be very hard for new beginners to compete with. One might imagine that life could start independently in two separate parts of a planet, if the first set hasn’t already spread to the second point of origin, but Ley’s point is basically sound. If there ever were fundamentally different approaches to life here, they were overwhelmed long before we got to see the results.
But different approaches may have happened—or may still happen in the future—on other planets. Biologist and writer Joan Slonczewski imagined such a situation in “Microbe” (Analog, August 1995): an ecosystem based on triple (rather than double) helices of DNA, in which pavement-like plants co-evolved with wheel-like animals.
So quite different kinds of organisms and ecosystems may indeed have evolved on other worlds—even under conditions otherwise similar to ones found on Earth. All it takes is a different starting point than we had on Earth, and a logical progression of subsequent evolution. The possibilities aren’t quite limitless—any organism anywhere must be a valid engineering solution to the problems posed by its environment—but they’re almost certainly wider than the range we see on our little planet.