The September, 2005 issue of Analog carried my story, 'The Speed of Understanding'. There was a fair amount of science in the story: biology and genetics. The problem is, well--I'm a physicist and not a biologist.
After the story appeared, I got a (friendly) e-mail from a biologist. While she liked the story, she did have some trouble with the science. I thought her comments were well-taken and suggested to both her and Stan Schmidt that she give her critique of the science in this venue. Stan concurred.
And I thank her for offering to check for accuracy, the biology in any of my future stories (I've offered in return, to check her stories regarding the physics).
It is with genuine pleasure then, that I welcome Dr. Sue Linville.
Biological Concepts in Carl Frederick's “The Speed of Understanding”
By Susan Urbanek Linville
Carl Frederick’s “The Speed of Understanding” (Analog, September 2005) focuses on the biology and behavior of two alien species living on their home world, Rau. The canoids are dog-like herbivores that have evolved a peculiar habit of eating dead lucifish, an obvious non-vegetable food source. The lucifish are an underwater colonial species that communicate via bioluminescence and can work together in groups to create weapons. Lucifish also engage in a similar peculiar behavior—eating canoids who come to the shore to die. During the course of the story, the characters discover that memory molecules are being exchanged between the two species via a DNA-like memory molecule. The canoids are acting as living memory storage devices or “books” for the lucifish. This is obviously a unique idea, but as one delves into the issues of memory and cellular physiology and biochemistry, the believability of this sort of system falls short.
During the course of the story, the characters find that “the canoids and the lucifish both have brain organs that act like gene sequencers…they both seem to store memories-long-term, archival memories…in complex molecules rather like our own DNA. Many, if not most of these molecules end up in the blood stream.” One must ask first: what is the purpose of memory? Looking at it from an evolutionary perspective, memory allows an organism to learn, which in turn enables the organism to survive in an ever-changing and often inhospitable environment. For example, it allows an individual to remember the location of a food source so it can return to the same location to take advantage of that source. It allows a predator to learn how to hunt and becomes more efficient with the passage of time. It also enables prey to learn to identify predators so they can escape unharmed.
In order for memory to be of survival value, it needs to expeditious (especially in response to predators) and malleable. In Earth species, memory can be categorized into three main components. A sensory register maintains memories that flash briefly in the brain, but disappear after a second. This allows an organism to possess a continuum of thought and awareness. Short-term memory lasts for a few seconds to a minute and allows thoughts and ideas to be maintained as the individual, for example, works on a mathematical problem or composes a sentence. Long-term memory, the type discussed in this story, can last for minutes, weeks or even years. These memories are laid down by altering the biochemistry and physiology of brain cells. Neurotransmitters change the sensitivity of a brain cells to certain stimuli and new synaptic pathways are formed. The memory neurons are relatively swift, firing like a loaded gun when stimulated by specific sensory input or active recall. They are also malleable, in that the sensitivity and synaptic connections change as newer memories are deposited over older memories.
Now, let’s look at the possibility of the evolution of a molecule-sequence type memory where the molecules are stored in the blood stream. The first and foremost problem with this sort of memory storage is retrieval. In a neuron based memory, the neurons are primed to respond to specific stimuli. The memory is not an encoded “film sequence” of an actual event, but an imprint of important stimuli related to the event. The retrieval process can be instantaneous. In a molecule-sequence memory, when stimuli enter the brain via the sensory organs or active recall, there are no cells primed to respond. Instead, the memory molecules related to specific stimuli have to be located. They would probably be tagged in some fashion and incoming stimuli would need to trigger search molecules to seek out the correct memory molecule. When the correct tag is located, the molecule would then have to be sequenced to recover the memory. Speed of retrieval is a problem. Large molecules like DNA are not found in single open strands ready to be sequenced immediately because disruptive molecular bonds form between charged atoms on the strands, causing them to bind to other molecules, parts of themselves and other strands. Because of this problem, Earth DNA is a double stranded or closed molecule. In order for the DNA code to be read, sections of the molecule must first be un-zipped by a specific enzyme, then copied. One would expect that this would also be the case with memory molecules. Location of the molecules is also a problem. If the memory-molecules are being transported through the blood stream, the target molecule could be anywhere in the body and immediate recall would be impossible.
It seems doubtful there would be selection pressure for the evolution of a molecule-sequence form of memory storage unless this planet had no predators and its species lived in a slow, unthreatened existence. The whole process of a canoid learning to fetch a stick would be a slow and maybe impossible prospect. It is possible that the lucifish, if they are intelligent and capable, could have engineered this type of memory storage, but why store memories in another species, where memories may be lost, when you could have modified individuals in your own colony to hold extra memories. Ants have specialized individuals in their colonies, so specialization is not unprecedented.
Along with the problems of the efficacy of molecule-sequence memory, there are several problems of transferring memory-molecules from one species to the other. In the story, canoids acquire lucifish memory-molecules by eating the fish. “…when a lucifish eats a canoid, an enzyme breaks down those mitochondria and those lucifish memory molecules get released into the bloodstream.” The whole purpose of digestion is to break larger molecules down into smaller ones that can be transported from gut, through the circulation and into the tissues: carbohydrates breakdown to simple sugars, proteins breakdown into amino acids, fats reduce to glycerol and fatty acids, and DNA is broken down into nucleic acids. It would be difficult if not impossible to transport a molecule as large as DNA through the membranes of the gut and circulatory system—even an alien one. Many smaller molecules cannot even be transported in the blood without carrier molecules because of solubility problems.
After entering the canoid circulation, the memory molecules were said to have moved to the reproductive tissues where “the molecules apparently penetrate cell walls and attach themselves to chromosomes in the mitochondrial bodies-sort of like the introns, the junk, in our own DNA.” Molecules this large cannot penetrate a cell membrane (only plants have cell walls by the way). As a matter of fact, only a very few molecules can pass across cell membranes unimpeded. Because cells must maintain osmotic balance, prevent unwanted molecules from triggering unnecessary cellular processes, and keep out foreign pathogens, they cannot have molecules wandering in and out unchecked. Even alien cells would possess some sort of control mechanisms. The only way foreign DNA can be naturally introduced into a cell on Earth is by vectors (usually viruses). Viruses can break through the cell membrane and only retro-viruses can insert their genetic material into the existing cellular DNA. This process is not fool proof, of course. Insertions into already existing DNA can disrupt the normal cellular processes, causing cell death, or uncontrolled cell division like in the case of cervical cancer.
A final comment on memory molecule transfer deals with the reference to Mitochondria. Mitochondria are organelles found in cells of Earth species. Cells are protein factories: DNA is the cookbook that holds the directions for making proteins, the Endoplasmic Reticulum is the organelle where the protein is made using the recipe as a template, and proteins are packaged in a cell membrane for transport in the Golgi Body organelle. Mitochondria are powerhouses of the cell, breaking down sugar to create electrons to manufacture energy molecules known as ATP. Mitochondria are strange beasts, being the only organelles that have their own DNA. Most biologists believe that is the case because they were once prokaryotic (bacteria-like) cells that formed a symbiotic relationship with early eukaryotic (plant and animal) cells. It is doubtful the same symbiotic event would have occurred on an alien world, but if it did, Mitochondria are miniscule and have very small strands of DNA. They could hold some extra genetic material, but the probability is high that an insertion would disrupt normal cellular functioning, resulting in cell death.
Carl Frederick's biological oversights are not uncommon. I have read award winning stories with glaring biological errors. I don't think anyone expects SF writers to be expert in every scientific field, but there is a tendency to over simplify biological concepts. This is understandable, but often that simplification creates organisms that are automatons. Brains become computers and bodies become simple machines. The complex richness of biochemistry, genetics, endocrinology, neurobiology, anatomy, physiology, and behavioral mechanisms, and environmental interrelationships inherent in real organisms is lost. Can this tendency be overcome? Certainly. Writers do not have to become experts, they need to contact experts. There are many biologists at universities and local colleges more than happy to evaluate story concepts. The writer only needs to ask.
Susan Urbanek Linville has a PhD in biology from the University of Dayton. She currently works at the Center for the Integrative Study of Animal Behavior at Indiana University.
