There are about thirty different types of animal. Each type is called a phylum, which is differentiated from other phyla by having a unique way to build a body, which naturally contributes to distinctive ways the animal lives, feeds, and reproduces.
All animals are multicellular and have multiple cell types. This excludes animal-like life forms like amoeba, which aren't multicellular, and colonial single-celled life forms like volvox, which don't have specialized cells. These animal-like life forms are called protistans. Animals most likely arose from a group of protistans called the choanoflagellates. Animals also have extra material between cells, generally used to help the cells stick together and communicate chemically, and this again is generally missing within the protistans.
There's another key point to understanding animals, and that's understanding where the multiple cell types come from: the position of the cells within the embryo and the process of embryo development determine the later identity of the cells. I've called the phenomenon of embryological development in animals the most complicated phenomenon in science. It depends on precise timing, exact position, and an enormous host of molecular signals, most of which are analog, not digital.
The simplest animal phylum is the sponges. Sponges are asymmetric (like plants) and have only two cell types, inside and outside. At the phylum level, one of the things you pay close attention to is the number and type of layers of tissue that an animal has. Sponges have only two.
There are two or three other phyla (including corals and jellyfish) at the next higher level of complexity. These also have only two layers of tissue, but they have a layer of goo in the middle, called a coelom. That's an important development. In addition to keeping track of the number and type of layers of tissue an animal has, you also keep track of the kinds of spaces between tissue it has, what those spaces are filled with, and what they're used for. In humans, for example, the space beneath our rib cage and abdominal muscles, where all our internal organs hang, that's our coelom. In other animals, different kinds of spaces may be filled with blood (hemocoels) or used like a hydraulic lift to provide the animal with a kind of skeleton made of water (hydrostatic).
All "true animals" (Eumetazoa) have three layers of tissue and one or more coeloms. They're also all symmetric. All eumetazoans display bilateral (right-left) symmetry sometime during their lives. Some, particularly the echinoderms, develop other types of symmetry.
The origin of the layers of tissue is important. At this level of organization, animal embryos early in their development form a hollow balls of cells. Cells on the inside of the ball form the endoderm, which goes on to form tissues like the stomach and intestines. Cells on the outside of the ball form the ectoderm, which goes on to form tissues like the skin. Cells that are in between form the mesoderm, which goes on to form tissues like muscle. It's possible to trace almost every bit of tissue in an adult animal back to its origin in one of those three layers.
At a point in development, the ball of cells forms a hole at one end. That hole determines the next great division in animal life. In one group of animals (the protostomes), that hole eventually goes on and usually becomes the mouth of the animal. In the other (the deuterostomes), the hole eventually goes on and usually becomes the anus of the animal (never the mouth). (Weasel words like "usually" are because there are occasional weird minor groups, simple and small in form, that are indisputably closely related to other protostomes but in which the hole doesn't become the mouth, and there are a few deuterostomes in which the hole doesn't become the anus.)
There are only four deuterostome phyla; all the twenty-odd others are protostomes, including insects, shellfish, and earthworms.
Humans are deuterostomes. From the perspective of the insects, we're talking out of our ass.
The phylum to which humans belong is call Chordata. It's distinguished by the possession of a stiff rod called a "notochord", which is used for muscles to push and pull against to swim. Almost all chordates are vertebrates, in which the notochord has become the vertebra, a cartilaginous or bony case for the brain and spinal cord. However, there's a minor group called the cephalochordates which don't have vertebra. In addition, chordates are distinguished by having gill slits in the pharynx (throat).
Our closest relative among the deuterostome phyla is probably the urochordates (sea squirts). The adult form of these guys is not very intersting; it's attached to the sea floor and basically consists of an empty sac with two siphons. It sucks water in, filters out some food, and shoots it out again, not very different from a sponge or a coral. However, the larval form of the sea squirts is almost indistinguishable from the cephalochordates: it's got gill slits and a notochord. (Some sources consider urochordata a subphylum within chordata, like the cephalochordates.)
The other two phyla within the deuterostomes are, according to molecular data, more closely related to each other than they are to us. The smaller group is the hemichordates (acorn worms), which have a distinctive anatomy that includes a notochord-like rod in the head region and pharyngeal gill slits. There is some doubt whether these are truly homologous to the corresponding features in chordates, particularly if the molecular data is believed.
The remaining phylum is the only other significant phylum in the deuterostomes, and that's the echinoderms, which includes starfish, sea urchins, sand dollars, and sea cucumbers. Echinoderms, as hinted above, start as bilaterally symmetric larva, but as adults, develop a new, five-fold kind of symmetry. Starfish have five arms, for example. There is no evidence of any kind of notochord-like structure or pharyngeal gill slits, but the molecular evidence confirms the embryological evidence that echinoderms are deuterostomes and more closely related to us than any of the protostomes.
So that's it for our animal family reunion: empty bags of water, worms with heads shaped like penises, and spiny things that hurt if you step on them. And all of us talk out of our ass.
Meanwhile, the protostome reunion down the road has three sub-clans each of which is larger than the deuterostome clan. At least they're mostly just weird worms and we have the biggest and smartest animals. Did you ever see a protostome President, huh? Didn't think so. Punk.
What the hell are you working on that this came out of it?
James Valentine's On the Origin of Phyla.
Man, this all sounds really complex. So complex, in fact, that only God could've done it! We all know that complex phenomena never occur randomly.
So we're more closely related to Starro the Star Conqueror than previously thought.
I'm intruiged by this sentence:
It's possible to trace almost every bit of tissue in an adult animal back to its origin in one of those three layers.Does this mean that there are tissues that do not originate in one of those layers, tissues that we do not know the origin of, or is that a weasel word?
There are tissues that we don't yet know the origin and complete history of. Embryonic development can become extremely complex: cells migrate all over the place in response to complicated molecular signals, tissues grow and curl and split and undergo planned die-offs, and so on. There are a host of minor birth defects, like sebaceous cysts and Rush Limbaugh's famous pilonoidal cyst, which are a result of tissues getting diverted and not quite migrating all the way to where they're supposed to be. You can end up with a bit of tooth enamel in a thing on your shoulder.
Tracing all the adult tissues through their embryonic development back to their origin in the original three-layered blastula is very difficult. Every year, a few more ambiguities are resolved, as extremely clever biologists painstakingly track another odd piece of tissue through its entire embryological history. Because that's how science WORKS, dammit, you don't just give up when confronted with a complex problem and say "The Designer [who we're not saying is God, but definitely isn't aliens or the Flying Spaghetti Monster] did it", you figure out how to solve the problem.
One final addendum: The deuterostome identity of echinoderms has been known a long time, so by the time Starro appeared (1960), its Earthly relatives were widely theorized to be relatively close to us.
However, it's not really until the last couple of decades that embryology and gene-typing have advanced far enough to confirm that the protostome-deuterostome split really is the major branch within eumetazoa and really cement beyond a shadow of a doubt the close relationship of chordata and echinodermata.
Within SCIENCE, that is. Creationists and crypto-creationists like the ID folk, of course, don't actually pay any attention to the actual science.
I'd be curious as to what you thought about the podcast novel "Ancestor", where the McGuffin is the race to grow human transplantable organs in other critters.
What the krunking infernal domain is a "podcast novel"?
The basic one-line premise as you say it sounds fine. You're going to have to a lot of work on the host animal to make long-term usable organs. You have to engineer the host animal to lack a cell membrane sugar that got knocked out in humans, just as an example.
It's the same thing as an audiobook, except you download the chapters as MP3 files (or use iTunes or some other podcasting client to grab each new chapter automagically as they're released) instead of buying the CD. Oh, and it's free. (You can buy print copies of his first podcast novel.)
Oh, and I just saw on his web page that he did some Champions work waaay back in the day.
Here's a quote from Ancestor's home page:
Dr. Claus Rhumkorrf seeks to recreate the ancestor of all mammals. By getting back to the root of our creation, Rhumorrf [sic] hopes to create an animal with human internal organs. Rhumkorrf discovers the ancestor, but it is not the small, harmless creature he envisions. His genius gives birth to a fast-growing evil that nature eradicated 350 million years ago -- an evil now on the loose, and very, very hungry.
Aside from the really confidence-inspiring typo, there's a fair amount of nonsense here.
First: The last common ancestor of all living mammals dates from around 150 mya, the late Jurassic. 350 mya, our ancestors were a bunch of big salamanders in swamps, and were also the common ancestors of reptiles, including dinosaurs and birds.
Second: The last common ancestor of all living mammals was almost certainly cat-sized at most, and more likely mouse or squirrel-sized. "Small" and "harmless" are exactly the words you'd use to describe it.
Third: He runs into a problem that most resurrect-the-extinct-monster plots run into, and that's that long-term evolution trends are progressive.[1] Today's predators are faster, bigger, smarter, better adapted, and more dangerous than any mammalian predator before the Pleistocene. There's a reason the creodonts went extinct, and that's that the carnivores kicked their asses. Even if the last common ancestor of mammals was a predator, there's every reason to expect that it couldn't compete with anything of the same mass living today, let alone be a threat to humans. It probably couldn't even feed itself--today's prey animals are adapted to avoid today's predators.
Fourth: I have no idea how reconstructing the basal mammal would lead to growing human organs for transplant in pigs. The basal mammal's immune system and signals would be at least as incompatible with ours as the pig's.
[1] Brains get bigger, size gets larger, species extinction rate gets smaller.
Oh, and sorry about the Whiggishness of "progressive evolution", but, y'know, it's true that the long-term evolution trends indicate pretty clearly that species are becoming better adapted in general, and that mammal lineages consistently produce bigger and smarter members.
No idea about how the technobabble works out, but he spends a lot of time going into the dirty details. The idea, from my layman's understanding, is that, once they get the "Ancestor", they'll have something that human bodies can't reject. Frankly, I thought the science was a little dodgy on a couple of levels. They're pulling DNA out of all living mammals and as much extinct animal DNA that they can scrape up, and creating a chimera that's got only common pieces of DNA. I'm not sure that all the common pieces would add up to a complete critter. Additionally, it sounds more like they're trying to create a generic "Mammal", when it would seem easier and more useful to me to create a generic "Human" as a universal donor (though that leads to a different SF novel). This so-called "Ancestor" would be, as I understand the concept, a master donor for all mammals, not just humans, and that seems like extra work. (Through, in their testing, they're only checking to see if human antibodies will attack their chimera.)
Either way, Sigler writes a mean thriller, and I'm willing to suspend disbelief in the service of a good story. (Warning to folks who might try it - there's lots of violence in both Ancestor and his completed podcast novel "EarthCore".)
It's a fast-growing evil! It was so evil that nature had to eradicate it! If we assume "evil" = "effective" in this context, that is, a good predator, then if nature eradicated it on the basis of that we are clearly talking about a new synthesis of evolution with reverse-creationism or as I call it "dialectical evodesign", where god and evolution operate in opposition to each other - as soon as some termite evolves a termite tower of babel, nature/god smacks him down, fragmenting his little termite language into a thousand different tongues (or whatever termites have for tongues), but then the termite evolves collective apotheosis and comes after god in heaven, leading to a sort of high-pitched, buzzy proto-Ragnarok. This implies an infinite hierarchy of meta-deities to pick up the slack as each level of His House is devoured by termites (or mold, or whatever is evolving its way up the ladder this week.)
There are typos in both versions of the name - it should be Ruhmkorrf, that's the name that was clearly intended. Compare 3 google hits for Rhumkorrf (two of which are this Ancestor story) with 26800 for Ruhmkorrf.
Anyway, purely on the basis of Greg's small quote from the descrption of the story, I will venture this free-floating ad hominem attack: the author is an idiot. People who like the story are suspect, so if you are one, Gentle Comments Reader, keep it to yourself.
Yeah, OK, based on Rick's description of the story, the author's an idiot.
Most of the stem cells lines that Bush approved aren't actually of any use, because they're contaminated by their growth medium--they've got a sugar on their cell membranes that humans don't normally have because the gene for it got knocked out sometime in our past.
That's just one example of a specific transplant-related human mutation.
In other words, the idea of transpecific transplantation doesn't depend on finding the common genetic origin of pigs and humans; it depends on replicating in pigs unique and very specific things in the human genome.
Wow, what a conversation! This is fun. Yes, I have a friggin' typo in my own book promo. Nice job on my part.
The "slugline" of the book doesn't touch on the reason for developing a new animal as an organ donor. Xenotransplantation moves animal parts into humans. The human immune system usually rejects this animal organ. Biotech firms are working on way to put human proteins into the animals, so that the human immune system accepts the transplant organs as "self."
The fear is that if this succeeds, we will have thousands if not millions of animal organs in humans that would otherwise die. This could be temporary, to keep someone alive until a human organ is available, or it could be a permanent solution, if the technology hurdles many obstacles. And with a large amount of animal tissue in humans, there is a possibility that viruses that can only infect pigs, for example, can mutate and infect humans. If this happens, we could have a new human virus for which we have little or no innate immune response. A common swine flu virus could wreak havoc, killing millions (read up on the 1918 influenza pandemic for a recent example of what a new virus can do).
So in the novel "Ancestor," they are trying to kill two birds with one stone. They are trying to create an animal from scratch, one protein at a time, to ensure there is no viral contamination. Simultaneously, they are using human DNA sequences to ensure that the animal's organs will be accepted by the donor's immune system. To do this, they are going as far back as possible to create the lion's share of the DNA, so that modern viruses will have a very difficult time infecting the new creature (assuming that viruses have mutated in lock-step with their respective evolving hosts).
This is why they want common DNA, because common DNA will provide a road-map for a creature that has existed. They take this code and tweak it to their needs: human DNA to solve immune system response, and a fast reproductive cycle so that they can create large herds of this creature.
Now here's the thing -- many people on this board are arguing about predators becoming gradually smarter and more efficient. However, the greatest predators that ever walked the Earth are all extinct. The dinosaurs were wiped out in an extinction event. Nature "removed" them. The premise of Ancestor is that if dinosaurs had to be removed for humans to evolve, what had to be removed for Dinosaurs to evolve? The extinction even prior to the Dinosaur's evolution was a massive one, wiping out as much as 90 percent of all species. Even the most advanced, intelligent, and successful species were knocked out.
So, Rhumkorrf (correct spelling, thanks) invents his Ancestor, which he thinks will be a peaceful herbivore. But oops, there's a lot going on with DNA that we still don't know, and just because you know what DNA is where doesn't mean you know what it codes for.
And ladies & gents, it's a fiction novel. There's not much fun to be had with a herd of peaceful herbivores, now is there? A pack of bloodthirsty carnivores, however, that's a good time in my book.
Of course I'm stretching current science. It's a fiction novel. Hack it to bits if you like. Just give it a listen at www.scottsigler.net/ancestor.
Ugh. I have always been a Typo King, and probably always will be.
The "Ancestors" were wiped out 250 million years ago, not 350 million years ago. Big difference.
That puts us to the Permian-Triassic extinction event, the most massive extinction event in the Earth's history. The Ancestors are based on a hypothetical Synapsid, one that became the dominant land predator just as the extinction hit. Synapsida had many predators, lion-sized and larger. They had teenie brains and were likely cold-blooded. So kick up the brain size via your computer-controlled OGLIO sequencer that lets you write entire DNA sequences (thanks to the fictional Billups IX supercomputer), throw in warm-blooded traits so the organs are compatible, and you've got the makings of a fun Dimetrodon-sized carnivore.
I'll leave the meat of this to Greg and just address your character name "Rhumkorrf". You may of course name your characters anything you want, but the names you choose do convey something. The fact that there are plenty of people named "Ruhmkorrf" and none named "Rhumkorrf" in the real world suggests that you started from Ruhmkorrf and either deliberately or accidentally changed it. Or, you could have made up a name that randomly happened to differ from a 9-letter real name only by the transposition of two letters. I refer to the arguments of Intelligent Design for the discrediting of that last hypothesis - only this time they're right, because you didn't evolve the name Rhumkorrf (presumably - or maybe you did, who am I to say how you pick your character names.)
My favorite theory right now (based on the meager information on this topic from your post) is that you switched the u and h deliberately, because you thought that Rhumkorrf would be less disturbing to the palate of the American reader, who has no doubt seen the word "rhombus", than Ruhmkorrf. "Rumkorf" is not exotic enough for what I presume is some sort of mad, or at least jerk, scientist.
Ah, that's much more sensible. Building a bigger brain and homeothermy into a Permian synapsid might be dangerous. Cynodonts might be a better choice, though; you'd end up with something like a reptilian wolf instead of something that's basically a komodo dragon or crocodile, and they're a lot closer to the basal mammal.
Of course you know that the P-T event didn't really clear the way for the dinosaurs; the therapsids were in charge for most of the Triassic. (Admittedly, once the archosaurs showed up, they immediately started to gain ground.)
They are trying to create an animal from scratch, one protein at a time, to ensure there is no viral contamination. Simultaneously, they are using human DNA sequences to ensure that the animal's organs will be accepted by the donor's immune system. To do this, they are going as far back as possible to create the lion's share of the DNA, so that modern viruses will have a very difficult time infecting the new creature (assuming that viruses have mutated in lock-step with their respective evolving hosts).
There's something wrong with this, even if I can't articulate quite what it is, but I think it goes back to Rick's point up above, that what you really want is a basal human. (Which raises a whole bunch of ethical questions and lives in an entirely different branch of SF.) You don't need to go all the way back to the basal mammal (or synapsid) to avoid viral cross-contamination, you just want something that doesn't have its own set of infectious agents living today.
Me, I'd take a chimp and overwrite its immune system with a human's (and strip out any suspicious looking endoviruses not present in the human genome), and grow the first one in a human womb. That ought to give you a critter with human-compatible organs and no novel vulnerability to chimp diseases. Also, I'd probably be burned at the stake by the religious nuts.
I think you answered why Rhumkorrf is going farther back to the primal mammal instead of primal primate. You can grow these Ancestors in cows or pigs until you have a breeding stock and then they're self-replacing. No way humans are going to volunteer, no matter how many zeroes you put on the check, to be hosts for a nonhuman birth, at least in the numbers that you'd need for breeding the first batch. Even if you did, no country would allow you to sell your parts, even if they didn't burn you at the stake.
Growing non-human critters and then harvesting the bits allows the companies researching into it to get around all sorts of stake-burning. (Though I suspect that certain sects would still have their matches and kindling ready.)
And hey, it's great to listen to on a long commute.
Addendum: Saying that you're putting the human immune signals into the Ancestor makes a lot of points of objection go away; it's not a universal mammal donor, it's designed for human donation.
If the critter is grown in a non-human's womb, you're going to expose it to some of the kinds of infectious agents you're worried about exposing humans to in transpecific transplants. It'll certainly be a good test of your immune system redesign.
However, if we're going all the way back to synapsids, you're golden; they're grown in eggs, and it's a heck of a lot easier to gin up an artificial egg than an artificial womb. (Heck, even the basal mammal was oviparous.)
Great points, this is good stuff.
RHUMKORRF: Jason's points are riveting, but I admit all I did was flip through a phonebook to find cool names. But, God may have made me flip through the book, and may have stopped on the "R" page, and may have made me choose that name, so it could be intelligent design after all.
HUMAN HOST/SEMI-HUMAN DONORS: No way would this happen. Ethical issues would bog down any corporation's profit motive -- sci-fi is full of the "semi-human" creations and the subsequent ethical debate over their rights as individuals. Genada (the corporation in the novel) knows this, and is intentionally going for something that is a) not human, b) not human-looking, c)not primate-looking) d) not "cute".
HOST MOTHER: In the book cows are the host. Cow eggs are enucleated, then filled with the artifical DNA. The two are fused and coaxed into mitosis. The cow's womb can handle the large creature. So the immune system problem is two-fold, have to be compatible with humans, AND have to be compatible enough with cows to beat their immune system.
LISTEN TO THE BOOK: It's free. I cover a lot of stuff I don't cover here. My goal is to create a plausible scenario to entice willing suspension of disbelief -- and you guys are a FAR tougher crowd than most readers.
I think you're going to want to modify the cow-hosts as well. Starting with an unmodified cow egg and cow host, you're already exposing yourself to a lot of contamination issues. I gather that development depends strongly on environment as well as genetics; a cow womb is going to do a lot of "cow-like" things to the embryo.
I have no idea if you need to worry about using cow, human, or ancestral organelle genetic material (mitochondrial DNA, ribosomal RNA, etc.). ISTR that there's evidence that mitochondria have tended to lose genes very slowly over time (the nuclear DNA picks up the slack).
This occurred to me far later than it should have: Not a heck of a lot of top predators survive mass extinctions, but the Ancestor (by definition) must have survived P-Tr. But in order to match up to protomammal evolution, it must have undergone rapid radiation into smaller and less carnivorous forms. I'd doubt it was hypercarnivorous like cats.