Forehead Aliens, Rishathra, and the Ecology of Alien Worlds
As long time watchers of the various Star Trek series and movies know, the galaxy seems to be populated by humanoid aliens, which differ mainly in the arrangement of bumps, ridges, and other patterns on their head. These are generally termed “rubber-forehead aliens,” for the prostheses used to give each their distinctive appearance. It seems that below the neck the differences must be minor, since not only do individuals from ostensibly different species find each other physically attractive, they engage in sex and somehow produce viable hybrids. There are mixed Human-Vulcans, Human-Klingons, Human-Romulans, Bajoran-Cardassian, and so on. In Larry Niven’s Ringworld novels, he calls “sexual practice outside one’s own species but within the intelligent hominoids”: rishathra. The prevalence and reproductive success of rishathra in the Star Trek universe was explained in The Next Generation episode The Chase, where a hologram of a hominoid species extinct for billions of years explains that they seeded their DNA throughout the galaxy. “”So…four billion years ago someone scattered this genetic material into the primordial soup of at least 19 different planets across the galaxy?” “The genetic information must have been incorporated into the earliest lifeforms on these planets and then passed down through each generation.”
As a Star Trek fan, I appreciate the writers attempt to explain within their universe what were actually constraints produced by the need to use human actors and save on CGI. Personally, I don’t think it was necessary (don’t get me started on their contortions to explain changes in the appearance of the Klingons). But as an evolutionary biologist, I am appalled. Even given that the original DNA of all nineteen planets was identical, the odds that the end result billions of years later would be nearly identical interfertile hominid species is zero. In the context of Steve Gould’s Wonderful Life, each of these are separate runs of the tape of life. Given the length of geological time and the role of chance, and that the initial starting conditions of each planet are different, contingency dictates that the end results would be widely disparate. Even if, as Simon Conway Morris has insisted, the rise of intelligence is inevitable, a human would still have a better chance of producing a fertile offspring with a starfish than with some hypothetical Romulan.
That said, there may still be some inevitable similarities among the species or at least among the biosphere of their planets. These similarities come from, as Steve Vogel (1998: Cat’s Paws and Catapults) stated: “inescapable physical rules and environmental circumstances;’’ the unavoidable uniformitarian assumption that physics is physics and chemistry is chemistry throughout the universe. We see evidence of this on Earth in the ubiquity of convergence, the recurrence of form by unrelated organisms (see Improbable Destinies: Fate, Chance, And The Future of Evolution by Jonathan Losos for an excellent recent summary). Porpoises, sharks, and the extinct ichthyosaurs have similar forms dictated by the hydrodynamics of rapid movement in water. It can be predicted that some organisms swimming through the ocean of an alien planet would also have a streamlined shape. You can also predict that would have visual organs that produce an image and are tuned to the wavelengths of light that penetrate the atmosphere.
It is not just form that would be expected to converge in some manner. We now recognize that the ecological roles played by organisms have not changed for hundreds of millions of years, even if the players themselves have come and gone. If some organisms find a way to directly tap the ambient energy and nutrients in the environment, some other organism will develop that survives by ingesting the first one or its waste products. Other organisms will find ways to remove particles from moving fluid or from the substrate. If nutrients become spatially isolated, perhaps in a living or dead organism, then methods for detecting their presence and moving towards will develop.
What I am suggesting here is that alien ecosystems with complex life will be on the base level be familiar to any ecologists. There will be filter feeders and deposit feeders, there will be food chains and food pyramids; there will be trophic interactions of all sorts. I strongly suspect there will be populations and communities. Even if life on another planet, as it was for most of Earth history, dominated by single-celled organisms, it would not be surprising if microbial ecology is quite similar, with organisms taking advantage of familiar chemistry to produce energy and obtain nutrients.
Given the numerous exoplanets that have been discovered over recent years, I think the discovery of one that supports life will happen sooner rather than later. It won’t have aliens that find the women and men of our species irresistible. And it won’t have organisms that share our DNA. But in some very fundamental ways, its biosphere will be quite familiar.
(after I wrote this, I became aware of a book that covers some of the same themes: Live Long and Evolve: What Star Trek Can Teach Us about Evolution, Genetics, and Life on Other Worlds by Mohamed Noor. I look forward to reading it).