Xenobiology 3 — Growth
This is the third of a series of blogs on the subject of alien and monster biology. The first, which covers respiration, can be found here.
How does your creature increase in size and what restrictions does this place on the organism?
The size of an animal is important in terms of how it interacts with its environment and fits into the ecosystem of the planet you are creating.
Gravity limits the size of animals. Whales can survive in the sea where they are supported by the water, and can descend to some quite astounding depths and pressures, but cannot survive on land with Earth’s gravity.
If you have an environment with a higher gravity than Earth, it would be likely that your creatures would be smaller, to cope with such pressures, unless there is a very dense atmosphere to support the body. If you have a planet where there is less gravitational pull, larger creatures may be possible.
So how would these larger body sizes be reached?
For mammals, fish and birds, the basic shape of the creature is fixed shortly after birth or hatching.There may be some maturing in certain infants as proportions change, but in general terms, the body shape stays the same as the creature increases in size
The size reached in adulthood is a combination of genetics of the individual and the nutrition provided — this combination is the reason families tend to be tall or short and that for generations, children have been larger than their parents.
Other creatures e.g. snakes, have a moulting process where they shed their external skin allowing them to grow. They look similar for each step of the process, but have periods where their outer coating is softer, making them more vulnerable. Similar, but more extreme, is a hermit crab, where the soft, vulnerable animal within the shell finds a new house and then hauls itself out of its old home, getting in to the new, more spacious one which allows it to grow. Throwing off your outer shell and then having to withdraw from life for a few days whilst you are vulnerable creates and interesting societal structure.
Consider what would happen if there were a limited number of these larger shells. How would it be decided who accessed the precious, scarce resources? Would it come down to physical combat, or are there other ways to control progression within the hierarchy?
Transition between several, complex life stages are also common eg butterflies, insects and arthropods such as ticks where there is a life cycle involving egg, larvae, nymph and adult. This can take place over several years, with periods of dormancy in between. In ticks, it also includes the romantically named ‘questing’ period where the nymphs and adults run to the top of blades of grass, waving their antennae, looking for a host to jump onto.
What if your creatures had several separate and distinct lifecycle stages, but the explorers or heroes did not realise they were the same thing until it was too late. This is used to good effect in Speaker for the Dead, by Orson Scott Card.
An example of several distinct life stages in science fiction would be Ridley Scott’s Alien, with egg, facehugger, chest buster and adult. As parasitic creatures a host is required for the intermediate stages.
If you are planning to use parasitism, please consider what the creature used a host in the time before the protagonists arrived. Creatures do not evolve if there is a missing host in their lifecycle; it tends to act as an evolutionary dead end.
Do the young and the adults live in the same environment? If this is not the case, eg for turtles, the adults live in the sea, but the eggs are laid on land; it leads to a perilous (and dramatic) journey for the young to the next life stage. This basic fact of life was used to great effect for drama and pathos in the documentaries March of the Penguins and Frozen Planet.
Plants generally have the growing easier; they just get bigger and bigger in situ. Consider though, ecosystems such as a rainforest or coral reef, where the new creatures live on the bodies of the old (yes I know corals are animals). This reminds me of Mary King’s Close in Edinburgh old town, where there are five or so stories of houses and shops, just bricked up inside/below the more modern buildings.
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This is the third of a series of blog posts, which have been derived from a lecture I gave at Right on Paper, a one day conference of academic talks on various subjects, for speculative fiction writers, held in London on 3rd February 2018.
This talk, was in turn sparked by a conversation in the bar at Nine Worlds, a science fiction and fantasy convention, where I announced that there was a really interesting talk which could be given on Xenobiology and decided I’d better put my money where my mouth was.
I also blog on veterinary matters here.
