The final installment of this series is going to lend itself to a bit more conjecture than the previous two posts. We based our hypothetical sea of alien life on some hard chemistry and a bit of logic, but from here it becomes harder to say anything for certain.
A lot depends on the world in which our aliens live. The inhabitants of an icy ocean planet will be quite different from an irradiated moon, but that’s really neither here nor there. But, assuming the life follows some of the same patterns on earth we can say:
Part III: The Size of Aliens
Most multicellular aliens will be small. There is a theory known as r/K selection that divides life into either quick, prolific reproducers (r-selected) or slow, careful reproducers (K-selected). The theory is currently being reviewed and updated as it doesn’t cover all aspects of a species life history but is, in general, a decent rule of thumb.
r-selected creatures (rats, bugs, small birds) tend to:
- Have many offspring, but put little investment into each one
- Grow quickly, reproduce young, and die early
- Be small and numerous
- Adapt to change well
K-selected creatures (elephants, whales) tend to:
- Have few offspring, but put a lot of resources into each one
- Grow slowly, reproduce later in life, and live longer
- Be somewhat bigger, but more rare
- Do better in stable environments
The biggest, most impressive aliens will likely be K-selected creatures, like humans, but the majority will be the smaller, more adaptable r-selected ones. The exact ratio depends on the stability of the environment – on a hostile death-world it wouldn’t make evolutionary sense to invest time and energy into a single offspring, but a calmer planet would make it easier for large creatures to grow and thrive.
An interesting note on intelligence is that, at least on Earth, cognitive ability tends to run in the K-selected species. Brain-power is very expensive when compared to other organs (up to 20% of your daily energy goes to your brain), which means that it tend to occur only in the species that have the time and energy to invest in it.
Part IV: The Alien Ecosystem
Similar to their personal ecology, alien food chains can be broken down by ratios and trade-offs, especially the ratio of producers to consumers. On Earth, ecosystems tend to follow something called the Ten-Percent Rule. The idea is that with every step up the food chain, 90% of energy is lost. Only ten-percent remains.
Take a field of grass, for example. Sitting happy under the sun, the grass creates 1,000 calories worth of sugars. It’s a nice life for grass, up until a cow comes along and eats it. Now, the cow isn’t a perfect engine, far from it. Most of the grass’ energy can’t be absorbed (it’s either tied into indigestible cellulose or lost to heat), so the cow only really gets 100 calories worth of energy out of their meal, even though they consumed 1,000 ‘sunlight’ calories. A human, then, eating the cow, would only receive 10 calories.
What this means is that, for life to stay sustainable, there must always be more producers than consumers. Our alien forests may have a thousand alien trees, a hundred alien deer, and a dozen alien hunters. Anything more and the ecosystem wouldn’t be energetically possible – the populations would crash. Of course, the numbers aren’t exact, but the pattern will stay the same.
It is worth nothing, however, that this alien forest will probably look nothing like Earth’s. Photosynthetic life needs not be green and, in fact, it’s not completely clear why green is the primary color of Earth plants. Physically, we know that it’s because chlorophyll, the photosynthetic pigment, primarily absorbs red and blue wavelengths while reflecting green ones. But different pigments could work just as well. Certain Earth bacteria and lichens absorb infrared light instead, appearing purple or orange and an alien life form that perfectly absorbs all wavelengths of light would look black – useful perhaps on a planet orbiting a dim star or under constant cloud cover.
Alternatively, there may be no photosynthetic producers. Take Europa, one of Jupiter’s moons. There is an intriguing idea that life could exist underneath the moon’s icy exterior, locked within a lightless ocean. Down there the food chain would be based on chemosynthesis. If that’s the case, an organism’s color wouldn’t matter a whit.
Part V: The Extra Bits
Now, I’ve skipped over a bit of information. For instance, one of the concepts Mass Effect integrated was chirality, which they used to great effect (although they made a few mistakes in the execution). It’s energetically more efficient to pick one side, rather than try to use both: we use left-handed amino-acids and right-handed sugars, but aliens could differ. Another divergent area would be the senses. Some of our senses, like smell, are likely to exist in some form everywhere, but that doesn’t mean aliens couldn’t have their own bizarre array of senses, depending on their environment and evolutionary history.
From here our hypothetical aliens become the realm of fiction, not science. Whether they are intelligent, friendly, evil, or just really really strange, we’d have to start to base our guesses on what we’d want to see, instead of what we could expect. And that’s okay, half the fun of Mass Effect and Avatar is seeing our own human flaws and stories projected on a strange new world. But if you had to design a new setting or creature, you can’t go wrong by starting with some science.