Wednesday, August 24, 2016

Arrival and "Starfish Aliens"

Arrival, the upcoming adaptation of Ted Chiang's wonderful science fiction short story, Story of Your Life, will be hitting theaters in November. I'm hoping audiences will get to see plausible aliens in this film, because realistic aliens are about as rare as realistic spacecraft in science fiction. Though I wrote an article explaining the quasi-plausible nature of some aspects of the xenomorphs from the Alien series, I can't honestly say the xenomorphs -- exactly as presented in the films -- are possible as real organisms. However, I do think the Heptapods of Story of your Life and Arrival are entirely believable as products of evolution on another world.

First I should reiterate why we shouldn't expect to see real aliens that are giant, albino human bodybuilders or "blue space babes" (sorry Liara fans). Consider this simple thought experiment: imagine that the earliest chordates, the ancestors of the vertebrates, were wiped out in the Cambrian by a natural disaster. If this had happened, there would be no humans, no mammals, birds, fish... no vertebrates would exist. Instead, the terrestrial world might be dominated by arthropods (it kind of is anyway, but still) and terrestrial mollusks, perhaps even some strange forms of terrestrial cephalopods. Instead of schools of fish, we might have schools of fish-like slugs. Real "fish slugs" actually exist today, they're just not as dominant or as diverse as modern fish. Our hypothetical alternate Earth would be surprisingly alien, all because of one evolutionary lineage being snuffed out in its early years!

Phylliroe, a pelagic, fish-like nudibranch slug. Image from Deep Sea News; Photo (c) Fabien Michenet /

So if one small change in the evolutionary history of life on our planet could have produced a surprisingly alien world, why should we expect aliens to look anything like a Klingon, Asari, or Engineer? Even if microbial life were seeded by some humanoid precursor, as was the case in Star Trek and Prometheus, the argument against humanoid aliens still holds. There's no way to "engineer" out random mutations and extinctions from billions of years of evolution.  Aliens are going to be weird, and the aliens of Arrival are pretty weird... but are they believably weird?

The Heptapods. Painting by Rachel Koning.

The illustration above is based on the description provided in Ted Chiang's short story. At a glance, one can see that he took the term "starfish alien" almost literally. The aliens are called heptapods because of their seven-way (heptaradial) symmetry and seven limbs that serve as both arms and legs. Their bodies consist of a barrel-shaped axial pod equipped with seven eyes arranged in a ring near the dorsal surface and surrounding a respiratory spiracle that doubles as the vocal organ. They have a ventral orifice lined by bony plates -- jaws presumably -- and no obvious anus, though the they could have a U-shaped gut with the anus opening near the throat. It could be argued that radial symmetry isn't the best design for an active, motile, terrestrial creature, but that doesn't mean the design is unrealistic. Evolution isn't a clever engineer that produces optimum designs, it's a mix of random and nonrandom processes often leading to the modification of preexisting structures away from one function and towards another, a process known as exaptation. This process often leads to the evolution of body plans or traits that are less than ideal for the function they perform. So when critiquing the design of an alien from a movie, one should be careful when pointing out perceived "design flaws", because if the alien is a product of evolution, it wasn't actually designed in the literal sense.

Radial symmetry is generally an adaptation for a pelagic or sessile lifestyle. A body plan with limbs and sense organs positioned radially has obvious benefits for an organism that cannot move under its own power. Imagine being buried up to your waist with something you need to reach placed directly behind you! For motile creatures, bilateral symmetry is more common. A streamlined body is better for actively moving through water or crawling along the seabed. Gravity provides an up and down, leading to the evolution of dorsal, ventral and lateral surfaces. A mouth at one end and anus at the other allows for a longer, more efficient gut. Sense organs tend to cluster around the mouth, and since nerve conduction is not instantaneous, enlarged ganglia, or a brain, tend evolve near the sense organs and mouth. This trend in some animal lineages is called cephalization. So why would the heptapods, which are motile, highly intelligent, presumably terrestrial animal analogs, evolve radial symmetry? We could say they evolved from sessile ancestors that evolved to be motile later. To make things more complex, we could say they are like some echinoderms, such as brittle stars, in that they evolved from bilateral ancestors which in turn evolved into sessile suspension feeders, which then reverted back to a motile existence while retaining their radial symmetry!

It's not difficult to imagine the ancestral heptapods filling niches analogous to those of some cephalopds, octopodes in particular, living as intelligent, opportunistic, benthic predators. Chiang suggests that the heptapods have an endoskeleton of some kind, with structures similar to vertebrae in their limbs, so it's not hard to imagine a terrestrial clade evolving from marine or aquatic heptapods. If they were like octopodes, their intelligence and tool use could, under the right conditions, evolve into something comparable to human intelligence and technology.

I'll refrain from discussing their language for the sake of avoiding excessive spoilers.

A heptapod hand from Arrival

Much the way the Interstellar gave us our first realistic wormholes and black holes, I'm hoping Arrival will show us aliens that feel as though they really evolved on distant planet. Perhaps it will inspire future film and video game writers to be a bit more imaginative with their alien designs.

We'll see on November 11th!


  1. YES! I went to see the movie yesterday without any previous information about the story or the movie argument. I really thought I was going to see an Interstellar/Independence day mix but I was surprised to see a movie that approached the alien physiognomy so accurately, diverging from the traditional humanoid shape. The language stuff was interesting and I think it got lots of things right too.

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  3. The Heptapods are awesome! They really felt and looked like visitors from another world.