Wednesday, August 24, 2016

Arrival and "Starfish Aliens"

The Heptapods. Painting by Rachel Koning.

Arrival is the adaptation of Ted Chiang's wonderful science fiction short story, Story of Your Life. I had hoped audiences would get to see plausible aliens in the 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 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 are entirely believable as products of evolution on another world. Unfortunately, despite my initial hopes, I cannot say the same about the creatures we see in the film.

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 remarkably 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 Story of Your Life are pretty weird... but are they believably weird?

The illustration at the top top of this post 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 a 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 large brains and tool use could, under the right conditions lead to the evolution of intelligence comparable to that of humans. Such conditions could include a diverse environment, complex social cooperation, and lack of speed and natural weapons.

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 had hoped the film adaptation, Arrival, would show us aliens that feel as though they really evolved on distant planet. Unfortunately, after I got the blue ray and got a better look at the concept art and the creatures in the film, I realized that, once again, the alien's anatomy was heavily derived from the human form. This is a large departure from the source material.


As you can see in the concept art above, the creature design is rather Giger-esque, and like many of Giger's designs, it consists heavily of distorted human anatomy; in this case, a vague human torso attached to a large, human-like hand. It resembles surrealistic art more than a work of speculative exobiology. Frustratingly, many of the concept pieces are considerably more believable.

The designs by Meinert Hansen shown above are considerably closer to the source material and is at least devoid of humanoid features. 

We are starting to see more realistic approaches to space and spacecraft in science fiction, hopefully we'll see a similar "hard sci-fi" approach to aliens in the near future as well.

Note: This is a revised version of an post written prior to the release of the film. It has since been updated to reflect my current opinion of the film's creature design.  


  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.

  2. This comment has been removed by the author.

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