What if we were Opabinids?
Let’s turn on our science fiction circuits today and imagine: What would earth look like if evolution had gone differently in the Precambrian? Suppose instead of boring bilateral creatures, the five-eyed Opabinia had been the way of the future? What if the ultimate intelligent species on our planet turned out to be an Opabinid?
Known only from fossils in the Burgess Shale, Opabinia had a segmented body, but no jointed legs. Its proboscis had a unique unjointed claw at the end that apparently was used to capture prey, based on the sight of its five mushroom-shaped eyes. The proboscis then had to place the prey in the backwards-facing mouth.
How do you think Opabinids would have radiated; would there be opabinid birds? Primate equivalents? Would having five eyes have taken their intelligence in a different direction? What would intelligent society look like from an opabinid point of view?
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Ultraphyte 
The extra upward-facing eyes would have been useful for a bottom-dweller (c.f. modern flatfish) but I think that once they emerged on land the extra eyes would have disappeared in favor of (now highly-efficient and useful) binocular vision. (Why would humans need an eye on top of their head. Heck, we don’t even have an eye on the BACK of our head where it would be useful, presumably because our brains can’t handle the information overload.)
The proboscis looks like it would be suitable for tool-makers, so the modern Opabinoids (assuming they developed bones and legs) might look like intelligent baby elephants, perhaps even with donkey’s tails.
Speaking of elephants, is there any good reason why humans need to be as large as they are? Most people no longer need brute strength to survive (merely the ability to use a mouse, keyboard, stylus, or power steering), and 90-pound wimps (male or female) not only fit into modern society just fine, they use half the oxygen and food. Certainly the “blue marble” shows we live on an island called Earth, and we all know what evolution does to dwellers on islands with limited resources. (Due to the square-cube law, petite humans also will fare better in our all-too-probable high-heat future.) If I was in charge of a brand-new space habitat (or an expedition to Jupiter), my first rule would be, “Nobody over 120 pounds need apply.)
The radiation will depend on how the body plan could evolve. No doubt the basic body plan would allow for some very interesting forms. But what if limbs couldn’t evolve from this plan, could efficient land locomotion and even flight evolve? If Opabinia is more like an arthropod, then I could imagine that eventually the earth could have been dominated by descendents of this form.
“Why would humans need an eye on top of their head”
Actually multiple eyes could be useful to ward off predators. Perhaps we don’t have it just because it didn’t evolve? African monkeys have no prehensile tail–but all the South American ones do. If we’d evolved in South America, we’d all have a jointless fifth limb.
The idea of miniaturization is interesting. There is a debate now whether bigger brains are more intelligent; it used to be thought that brain/body ratio was what mattered. I’m not sure though; I wonder if we need to be any bigger than a Rhesus monkey.
“If limbs couldn’t evolve” — I don’t see why not. Jointed limbs not, but why not flexible ones like the octopus? Or multiple prehensile tails? Sometimes I wonder what’s all the fuss about thumbs. Octopi open jars without thumbs.
Sometimes I wonder what’s all the fuss about thumbs. Octopi open jars without thumbs.
Impressive as cephalopds are, they do not have the dexterity of humans. And so far, cephalopods have not emerged onto land, although their phylum, the molluscs, have, in a limited way, with limited distribution.
The bigger question is, are there very definite limits to phenotypic space that can be occupied from any given starting point. Niles Eldridge thought there were, but we really don’t know.
Chances are the result could come close to our shape. This ancestor already had what appear to be distinct nerve/muscle/skeletal segments so enlarging/customizing segments that would prove more useful would probably also occur. The direction and degree of change would depend on a trade-off between flexibility/suppleness and brute mechanical strength (rigid bones/stronger better defined muscles) for whichever habitat (marine vs. land vs. air) it settled. As an example, our hands/fingers are both fairly dexterous and suitable for working with rigid objects – probably why they’re actually quite complicated as compared with our arms and legs which are used mostly for leverage/stability – but they’re pretty similar to the general 5-point body plan of reptiles/dinosaurs.
As for key features — the placement and direction of the proboscis is probably not a characteristic that is set in stone. That is, gradual changes could occur so that the proboscis could be moved farther down toward the body, farther up closer to the eyes or it could even end up coiled inside the mouth. The proboscis’ size and apparently considerable functionality suggest that even then it took up a lot of ‘brain’ space which suggests that further modifications enlarging this brain region might be possible thereby making the proboscis useful for communication (by clacking and/or waving/signing) as well as for tool handling. If, as in our case, the proboscis also enables smell and taste, its greater share-of-brain means that these two senses would be useful for exploration and communication. (Perhaps it makes survival sense to keep most of one’s “senses” in a central location such as a well-protected head versus having control of senses distributed.)
Interesting notion – evolutionary might-have-been’s if mass extinctions hadn’t happened as they did. I suppose to really figure out these possibilities, one would need to know what the climate/atmosphere was like, what life forms existed, etc. and extrapolate from these. And based on such linear extrapolations, I wonder what global climate changes/crises would have arisen ‘naturally’. Would oxygen breathers have ever even been a possibility? It seems possible to move bits of the body and brain about – much like a gardener shaping a topiary – so there’s a pretty good chance that the end result regardless of which ancestor selected wouldn’t be that far off from us in terms of overall anatomy/physiology … assuming that the larger planetary physical environment was similar to ours. For example, flying means that you need air masses that don’t move too quickly along with a body part/shape/muscles that can get to at least glide. I don’t imagine that Earth’s gravity would have been changed by any of the mass extinctions – none of the meteors were that large – but our atmosphere/air certainly did which makes some potential evolutionary paths more or less likely.
Chances are the result could come close to our shape.
Chances are that if we reran evolution even with vertebrates this would not happen. It is a fallacy of perception that humans are the apex of evolution. A form as divergent as Opabinia would be very unlikely to result in descendents taking our basic shape. To believe otherwise you have to assume the human shape factor is a huge attractor for convergent evolution. What evidence would you cite to suggest this?
I don’t mean humanoid, just 4-limbs-and-a-head plan with multiple senses probably the same types as ours and centrally organized. Everything else is window dressing.
As far as an apex of evolution, i.e., survive anything/anywhere goes, the cockroach probably holds that spot.
Yeah, our body plan is weird even relative to other tetrapods. At some point you have pretty standard arboreal apes that switch to endurance walking and running as a lifestyle. It’s not the sort of thing one should expect to be a natural outcome of the process. Even other bipeds don’t share our body plan.
Ack, lemme rephrase “natural” as “inevitable” — not meaning to suggest the human form is anything but. >>
Interesting article about HOX genes and what they mean in terms of overall body plans.
http://www.sciencedaily.com/releases/2011/12/111215141609.htm
Here’s where Alex and SFreader may intersect.
The interesting thing about Hox genes is that they appear to have evolved by a long series of duplications: 1 –> 2 –> 4 –> 8 –> 16, then twice more to get sets Hox-A, B, C, D.
For example, human Hox-A13 is the 13th gene of set A:
http://en.wikipedia.org/wiki/HOXA13
But not all organisms have all 4 x 16 genes, since many got lost at random through evolution; and others swapped functions. So I’m not so impressed about the lost HoxC in sharks.
However: If this duplication process is so powerful, could it provide the answer “yes” to Alex, is the four-limbed human shape a strong “attractor” for convergent evolution? In other words, would any organism, even Opabinia, be highly likely to evolve a 4×4 limbed body plan like humans? As an SF writer I sure hope not, since that would rule out a lot of interesting possibilities.
On the other hand the trilobites (three-part body plan) and the five-limbed South American monkeys argue (at different levels) for other possibilities. I once started a novel about prehensile-tailed polyamorous primates but I thought it was too far ahead of its time.
“I once started a novel about prehensile-tailed polyamorous primates but I thought it was too far ahead of its time.”
Exactly WHAT they were doing with their tails? Enquiring minds want to know. 🙂
In any case, I think that calling New World monkeys, sloths, opossums, etc. “five-limbed” is stretching things. I’d say they are every bit a member of the standard four-limbed pattern as anything else. Now if you can show me an animal developing digits (or even an Opabinid-style claw) at the end of its tail….
Enquiring minds have more than enough imagination to guess, I’m sure. 🙂 If my Frontera series does well, I’ll dig out the old prehensile MS and see if Tor can handle it.
Is a prehensile tail a limb? Not sure that digits have much to do with it. Who uses individual toes for anything? Even for hands, most people nowadays type/keyboard by hunt and peck. (Aside from us piano players)
Take a look at these–Is the tail a limb or not?
All those pictures show the tail being used as an anchor. To my knowledge, monkeys don’t use their tails to feed themselves, manipulate tools, or whatever. I can find just as many pictures of circus acrobats or bulldogs hanging by their teeth. Does that make the jaw an extra limb for THEM?
My original comment about tail digits was to imply that an extension of the spinal column is quite different from a limb, and it would take quite a mutational leap to get that last vertebra in the tail to do something useful. (Monkey’s tails have bones. They’re not like tentacles, which are pure muscle assemblies called hydrostats.)
BTW, a good poser is asking people what is the most prominent tentacle (in the octopus sense) in the human body. Most people will hem and haw and guess the penis, but not even porn stars can do the dexterous things one associates with tentacles. The correct answer is the tongue.
Overall the actual number of limbs doesn’t matter as much as the functions that limbs can provide as evolution seems to be pretty plastic. For example, eyes cropped up several times using different evolutionary road maps and, like limbs, there’s no consensus on the optimal number of eyes: anything from one to many (compound eyes) is okay depending on your species. The same seems to apply to our senses.
It seems to me that our 5 senses are actually 2 overarching/super senses: (1) touch/hearing/sight allow us to perceive/interpret different wavelength scales; (2) smell/taste allow us to perceive/interpret the chemistry of our environment. I assume that perceiving wavelengths is probably more fundamental therefore these senses should be present at even the lowest ‘life’ form, e.g. virus, whereas perceiving chemical compounds is more difficult and requires a more complex sensory apparatus/life form. However all of these particular senses are passive. We have only one active sense, speech. So assuming that humans, thanks to our ability to speak, represent the first part of a 2.0 evolutionary cycle, what would be the next evolutionary stage of sensory development? The ability to affect/alter/emit wavelengths other than those that produce sound and become our own WiFi sources. (If only we’d held onto like the ability to detect electromagnetic fields as sharks and birds are able to do – this might be feasible.)
Eyes evolved many different ways–and through various intermediate steps. There are many fascinating examples of convergent eye evolution, such as the vertebrate and octopus eyes.
For the senses, it’s interesting that you group them in 2. There are other ways to group them; such as near (taste, touch) versus distant.
The “lowest” (simplest, or single-celled) forms of life such as microbes actually have taste/smell (chemical sense) as their fundamental means of signal detection. Touch and light-sensing come next.
Electromagnetic field detection, we still have (internally) through our nervous system; and electrodes can tap into that.
But the human tendency to group things in 2 may be related to our bilateral symmetry, and 2 eyes.
The “lowest” (simplest, or single-celled) forms of life such as microbes actually have taste/smell (chemical sense) as their fundamental means of signal detection. Touch and light-sensing come next. —
That’s really fascinating and intuitive if one considers that the ‘lowest’ life forms are probably closest to being only a couple of steps up from a chemical equation .. as in a virus.
I believe that microbes are generally classed as ‘animals’. Out of curiosity, how do the “senses” diverge/differ based on whether the organism is a plant, animal or fungus? Does the sequence of the appearance of senses determine which route an organism will evolve – animal vs. plant?
how do the “senses” diverge/differ based on whether the organism is a plant, animal or fungus? Does the sequence of the appearance of senses determine which route an organism will evolve – animal vs. plant?
The simplest, unicellular eukaryotes whether protozoa or algae are very similar with regard to senses. However, the kingdom of animals evolved a mostly motile way of life, in contrast to the plant kingdom. Motility required organs to move and senses to operate in real time to operate the movements. Plants, in contrast, operate at much slower time scales. The few plants that demonstrate rapid movements, e.g. Venus Flytraps, use a very different approach to animals to “move”.
I would suggest that evolution drove the development of senses depending on the organisms way of life, rather than the reverse.
The classification of microbes is mind-boggling.
Based on DNA sequences and molecular biology:
There are two whole “domains” of microbes, the bacteria and the archaea, that are mostly single-celled or modestly multicellular (slime mold). But bacteria and archaea differ profoundly from each other and from all other life, in aspects like their cell membrane (archaea have ether membranes).
Then there are the “eukaryotic” microbes, which have a cell with a nucleus like we do. Paramecium, fungi, amebas etc. all fall under this group. The amebas and other “protozoa” used to be called “single-celled animals” because they move about. But genetically, we have more in common with fungi. So we are motile multicellular fungi.
How the senses fit in is hard to say. Light detection evolved so many times in many different forms, from chloroplast to protozoan eyespots to invertebrate and vertebrate eyes. I suspect the same is true for “hearing” (vibration detection).
BTW at my college I am responsible for teaching all of the above plus viruses and immunology. It only gets worse, as more of them are discovered all the time.
“But genetically, we have more in common with fungi. So we are motile multicellular fungi.” — Egads! You mean there’s a scientific basis for the enduring popularity of ‘mushroom management’? The C-Suites will be thrilled.
Would enjoy learning more about our relationship/commonality with mushrooms – including which animal species have closer links.
From popular health-media sites/newsletters, mushrooms seem to be increasingly mentioned as anti-cancer therapies. Since most cancers seem to stem from a gene/cell running amok, this suggests that mushrooms confer some sort of genetic stability or provide a mechanism for auto-correction despite mushrooms also exhibiting the widest variations/spans of types and behaviors (as per the Wiki entry) of the various kingdoms. Very interesting symmetry going on here.
“which animal species have closer links.”
That’s hard to say because all the animals we know of, including sponges and corals, evolved from a common proto-animal ancestor. That proto-animal ancestor evolved from a common ancestor with fungi.
Mushrooms are interesting because they have a complex multicellular form, below ground as well as above ground. Below ground, mushrooms form a nutritional internet linking all kinds of tree roots. Kind of like the gloval tree net of Avatar.
But the multicellularity of mushrooms (and other fungi) evolved completely independently of multicellularity in animals. And even more distantly from plants–whose branched stalks superficially resemble the form of fungi. So multicellularity evolved many times, including the various stalked forms of bacteria.
Have to be careful of the terms I use 🙂
So to re-phrase my question — which animals have closer links (straighter line of evolutionary descent) and/or share greater commonailty (more genes in common).
As a microbiologist and SF author, which microorganisms would be your top picks to test a planet/ecology for potential use as a human habitat? (Sort of a low-level in vivo trial – and this could be for a planet in a different star system or within our solar system, i.e., Mars, Io?) On Charlie’s Diary a lot of people mentioned robotics related to a Mars colonization scenario he presented, but considering the range of microorganisms available, why not use Earth-based life to test livability?
If you’re asking about animal phylogeny, according to DNA sequence similarity it looks like this:
The green line “chordata” includes all vertebrates (including us). So, on this time scale, we vertebrates are all about the same, whereas sponges and starfish branch more distantly from the tree.
As for which microbes to pick, that sounds like a new post to me. Will work on it. 🙂