R’il’nian Teeth

My science fiction is based on two species, the R’il’nai and Humans, and their crossbreds, the Ril’noids, living together. One of the major differences between the two parent species is in life span. The Humans have what we would consider a normal life span. The R’il’nai, while not immortal, do not age beyond maturity. A number of my characters have been alive for millennia. Crossbreds can show either pattern.

This leads to all kinds of interesting situations in the society. How do the two species interact, for instance? How many Humans would want to marry someone who would never grow old? How does a R’il’nian act toward someone he or she knows will grow old and die while the R’il’nian is still young? This is in the background of all of my plots.

Here, however, I am addressing a different problem.

Most of the cells in our bodies are constantly turning over. I can imagine a creature that looks and acts human with a near-infinite life span, except for one thing. Teeth.

Tooth enamel wears, and unlike skin, it is not constantly replaced from within. Modern dentistry can do a lot to repair wear, but I’m having to have enamel repairs already. Young mammals are born with two sets of tooth buds, one that grows into teeth suited for the small jaw of a juvenile; the second set adult sized, and that’s it. People who lived thousands of years would wear out their teeth. How to handle the problem?

The R’il’nai would have to have an essentially infinite number of replacement teeth. When a tooth was worn out, it would be shed much as a child sheds its milk teeth, and replaced by a new tooth. How? They must have some tooth stem cells in their jaws, just as we have blood stem cells in our bone marrow. Assuming that a tooth would last for 50 or 60 years, this would mean that the R’il’nai and non-aging R’il’noids are teething roughly every two or three years. I don’t think I’ve actually mentioned that, but if a R’il’noid seems to be in a particularly bad humor, he or she may be teething.

Jarn’s Journal Year 2, Day 325

Year 2, Day 325

Even the predators are hungry.

Not that I let that stop me from stealing two of their fresh kills and teleporting them to the vicinity of the camp I found yesterday. The shaman, who goes by the name of Lion, begged me to stay, and share my wisdom with them as I had with Storm Cloud’s group. Wisdom? Knowledge perhaps, thanks to the computer library, but it is these people who seem able to adapt that knowledge to their environment. Was it not Songbird who combined her knowledge of basketry with the information in the computer to devise the fish traps?

Well, I could teleport in enough food to keep them from starving from areas where the drought had not been so extreme—but visiting them occasionally would be sufficient for that. I pointed to the half-moon, visible in the daylight sky. “I will return when the moon is full,” I told Lion. “And I will join you at the Gather. But for now, I need to find Storm Cloud’s band.” I was perhaps going too far with the promise to join them at the gather—I still didn’t know were that was! But if I could find Storm Cloud, I could follow that band, no longer constrained by my inability to walk any distance.

Neither Lion nor any member of his band could tell me exactly where to find Storm Cloud’s band. They did, however, have considerable awareness of the regions each band roamed over. Not teleport coordinates, not a map, but a general awareness of landmarks, and distance (in days’ travel) and direction between them. By the time I left Lion’s band, late in the evening, I had a much smaller area to search in hopes of finding Storm Cloud and Songbird.

I can only hope they are in better condition than Lion’s band.

Why an Index?

With 550 posts as of today, I’ve started to have problems remembering what I’ve already put on here. This is particularly a problem with posting existing content such as poems, short pieces from the Summer Arts Festival, or science explanations originally written for the Alaska Science Forum. I can’t remember which books or DVDs I’ve posted reviews on. It also is starting to be a problem when I want to link to a previous post and can’t remember when it was put up or what the title was. And there are posts on this blog that have permanent information, like the series on planet building and the one on horse color genetics, or the book and DVD reviews. I want to make it easier for my readers as well as myself to find things.

I made a start some time ago by adding an index page, which can be accessed from the menu at the top of any page. Right now, the only links are to index pages on my author site. This takes you out of the site and sometimes back in, which is rather clumsy. The index list is also incomplete.

I’m going to start posting an occasional entry which is strictly an index of past posts on a particular topic. These posts will be linked from the index page, and will link forward to the individual blog posts. As it takes a while to find all the posts that belong together, this will be a slow process—probably extending over the next few months. The first in this series, on DVD reviews, is already queued for January 3. Others will follow, most on Thursdays.

I probably won’t be indexing every post. Some, like those early posts which were simply glossary entries for my books, are on the author site and really belong there. Others, like the regular Monday updates on North Pole weather starting in November 2010, can be found easily enough just by using the calendar on the site. But I hope that by the time I have finished this, older posts of interest will be easier to find.

The Cambrian Explosion

I’ve been taking an OLLI (Osher Life Long Learning institute) class this month, titled Major Evolutionary Transitions. The presenters are two of my favorites: Dr. Sarah Fowell and Dr. Patrick Druckenmiller, who gave a wonderful course on dinosaurs last year. This time we’re skipping the dinosaurs and looking at eight topics, two a week. The first two were the Ediacaran fauna, soft-bodied animals that lived before animals evolved hard parts that are fossilized in conventional ways, and the Cambrian explosion, the first animals with hard parts.

To look at this transition, we have to look at fossils as more than fossilized bone or shells. That kind of fossil does indeed start with the Cambrian, about 542 million years ago. But there are other kinds of fossils.

Anomalocaris.

Chemical fossils are chemicals produced by life processes, and those go back over 3 billion years. Traces resembling microbes can be found in rocks dated to 3.5 billion years of age. Stromatolites — limestone structures similar to those built today by cyanobacteria — date back to 3.5 billion years ago. (Cyanobacteria? Ever had a fish tank? Think blue-green algae, though they’re not really algae.)

By the late Precambrian multi-celled animals were common, but they had no hard body parts. It takes really exceptional conditions to fossilize a jellyfish or a sponge, but rare fossils of these animals can be found. Then, 542 million years ago, there was a rapid increase first is the number of trace fossils—such as burrows or tracks—and then in actual hard parts. What caused this?

Most likely, a change in sensory input. The senses of smell/taste, being chemically based, are probably very old. I have imagined a planet in Homecoming, Mirror, at a very early stage of evolution where the only hard parts are those secreted by the stromatolite-like land corals. At least one of the soft-bodied animals will swim up-gradient to a particular chemical and attempt to ingest the source of the odor. Chances are that some of the Precambrian animals had similar abilities, and enough nervous system to use them.

Light sensing cells might also have been useful, in avoiding excessive light or in seeking light. (Moving up or down in the water column.) But the evolution of lenses and the compound eyes they made possible may well have set off the evolutionary arms race.

Precambrian animals, as far as we know, did not hunt each other. They may well have eaten each other, as anemones do today. But how could they find each other? And what is the use of armor or skeletons if there is nothing trying to eat you and you don’t need to move rapidly?

Then something evolved the first primitive eyes. It probably wasn’t the best-known predator of the Cambrian, the Anomalocaris, though it may well have been one of its ancestors. Once the eyes were there, even in very primitive form, the hunter could find its prey. The prey animals, such as trilobites, had to evolve eyes as well, to see the predators coming, and hard coverings, to make them harder to eat when caught. The prey animals got bigger to avoid being eaten, and the predators got bigger to catch them. The resultant arms race both speeded up the pace of evolution and produced increasingly large hard parts to be fossilized.

It’s worth pointing out that it took a long time for the Anomalocaris to be recognized as a single animal. Initially, the “arms” near the mouth were thought to be a shrimp-like creature, the ring of plates that made up the mouth were seen as a sort of jellyfish, and the body was thought to be a kind of sea cucumber. The animal was not put together until the 1980’s.

The photos are screenshots from an aquarium program, Aquazone Blue Planet which, in addition to conventional aquariums, has several Cambrian animals and backgrounds.

Garnet (Homecoming Glossary)

GARNET: #scifi Jewel tineral infant, the offspring of Ruby and an amethyst male native to Windhome.

Forest (Homecoming Glossary)

FOREST: #scifi Nature tineral, feathers laced in shades of green, who adopts Roi as his person.