Archive for November, 2011

Just eat it, or something

In the US, many of us are thinking about eating and digestion right now, after a holiday devoted to food. We usually think about digestion the way we do it, with food going in the mouth and into the gut, where the nutrients are extracted, and the waste products coming out the other end: a big tube, essentially. But we don’t have to resort to science fiction to come up with other ways to obtain nutrients: there are lots of options right here on Earth. Some of those methods might even inspire your next aliens.

Some very simple animals don’t have digestive systems at all. The single-celled Paramecium scoops in food particles and surrounds them with a membrane forming a vacuole, a space sealed off from the rest of the Paramecium cell. That separation is needed so the enzymes that break down the food particles don’t also digest the Paramecium.

Many sponges and other aquatic organisms do something similar, filtering food out of the water and getting the nutrients out without a distinct digestive system. This system doesn’t work if the animal doesn’t live in the water, or is big enough that all its cells aren’t directly immersed. Bigger, terrestrial, and faster animals (being active requires taking in more resources) had to come up with more efficient solutions.

Some of those solutions are pretty weird, at least from our perspective.

How about external digestion? Fungi do this, and spiders. Release digestive enzymes into the environment, let them do their thing, slurp up the predigested food. Fungi are unspecific about it, digesting all or most organic matter in the general area (decomposers, very important!). Spiders are more selective: they inject the enzymes into their prey and wait. That’s why a spider bite can be such a horrid experience: your flesh is being digested while you’re still using it.

Or how about coprophagy? Feces eating can be a normal part of the digestive process, not just a disgusting habit of your pet dog. Grasses are very hard to digest, since vertebrates can’t break down cellulose, so they need help from microbes that can break it down. Coprophagy is one method for making this system work. Rabbits partially digest their food, then excrete it. They eat the partially digested pellets and finish the digestive process. The feces after the second digestion is really a waste product, not an intermediate step, and isn’t eaten.

Ruminants such as cows took the opposite approach to having multiple digestions. They eat grass and start to digest it, then regurgitate the cud and chew on it for a while to further break it down. The second time it’s swallowed, it’s thoroughly digested and the nutrients extracted.

So which alien would you rather sit down to a diplomatic dinner with: a ruminant or a coprophage? And what would they find disgusting about our eating and digestion?

I don’t think a filter feeder is likely to evolve intelligence, but how about trying to design a system where that works. Nonsentient aliens with different digestions could be helpful or harmful to people trying to colonize a planet.

Memory, Habits, and Doorways

Tis the season to NANOWRIMO. Fa la la la la la la la lahhhh.

For several years in a row, I’ve signed up to write fifty thousand words in the month of November. I do so knowing that my life is not conducive to such output. I am not setting myself up for failure. I am hoping to foster the habit of writing daily. I am not alone, and while I’ve already seen some of my friends cross the 50K finish line, I know many more of them are trucking along or even puttering along with a mumble mumble current word count. Read the rest of this entry »

Two and a Half Cultures

Recently I was in Washington, D.C., and attended a local “Science Cafe” event featuring visual artists whose art is inspired by science.  (A theme for the evening was Leonardo da Vinci, whose restless mind not only created some of the greatest art ever but also pondered flying machines, tanks, and other investigations into technology and nature. The cafe even specially created a namesake drink, a mixture of beer, vodka, and wine which didn’t taste nearly as vile as it sounded.)  Naturally the question came up of the reverse: how does art informs science?

Read the rest of this entry »

Leaf it to me

I live in the northeastern United States, so this time of year I think about leaves a lot. The color changes are the most obvious reason to be thinking about leaves, of course. In the autumn, the trees slow down and then stop producing chlorophyll, the green pigment needed for photosynthesis, so the yellow pigments also in the leaf become more prominent.


But it’s probably more complicated (and more interesting) than that: yellow leaves are a sign of disease during most of the year, so some insects are attracted to plants with yellow leaves. If a tree is already ill, it might be more vulnerable as insect food. It appears that some trees actually produce red pigments to hide the yellow pigments since the green pigments are no longer doing so, and it’s all to protect themselves from insects.


And it’s probably really even more complicated than that, too.

(I love science: it’s always more complicated, and we’re always wrong, but it’s so much fun to try to figure it out.)

So there’s one thing to think about when world-building: does your local plant-equivalent have seasonal changes in the coloration of its leaf-equivalents? If so, why? Does that have any other effects that matter in the ecology of the world, like attracting or repelling other organisms?

For that matter, are they green to start with? Most planets with life will need some way to convert solar energy into biochemical energy, which is what photosynthesis does. There are organisms that use geothermal energy or non-biological chemical energy, but most energy comes from the sun through photosynthesis. It seems likely that other planets will have the same energetic basis (but there’s plenty of room for speculation here).

And what else do leaves do? They’re flat so they can maximize sun exposure, and they’re thin so they can maximize gas exchange.

Except where conditions are less than ideal.

Desert plants have all sorts of leaf adaptations to make sure that they don’t lose too much moisture from that flat surface. Waxy coatings hold moisture inside, and hairs cut down on air movement across the surface of the leaf, reducing evaporation. Smaller leaves help reduce water loss too.

(Leaves have to take in carbon dioxide for photosynthesis, but that creates a way that water can be lost. Grasses and cacti have evolved different physiologies to deal with that problem, but I want to stick to shape instead of biochemistry.)

Very cold can be a lot like very dry, and some of the same leaf adaptations show up in arctic climates: hairs, waxy coatings, and especially having small leaves such as like pine needles.

Leaves in wet climates tend to have fewer teeth on the edges, while leaves from cold areas have more teeth.

In places where it’s warm and wet year-round, there isn’t usually a season when most plants lose their leaves simultaneously. In temperate climates, it’s cheaper for the plant to shed them than it is to maintain them through the winter. In seasonally-dry areas, plants might drop their leaves for the dry season, again to save resources. But in very hard environments, especially if they are low in nutrients, plants often keep their leaves year-round, even through the winter, because resources might not be available to replace them.

These are broad generalizations, and there are lots of exceptions, but for the world-builder matching leaf shape to climate can provide a quick hook for a realistic world. We’re used to certain kinds of plants in certain places, even if we don’t think about it.

Putting spruce tree-equivalents in cold areas, plants with small hairy leaves in deserts and plants with large leaves in jungles makes those areas feel right to the reader, so you can save the weird stuff for where it matters. Getting the little subtle things correct keeps from jarring the reader out of your world, and makes the big things seem more believable.