A Question For The Lone Ranger

[Watser?]

[Dingfod]

Originally Posted by Dingfod

What in the hell is this, a slime mold?

YouTube - Unknown Lifeform in North Carolina Sewer!

At least one biologist thinks these things are a cluster of tubifex worms.

[The Lone Ranger]

Clusters of tubifex worms, eh? I wouldn't have thought of that, but it does make sense. You can't see enough detail in the video to be sure, but with that in mind, it does look like there are "filaments" in the masses that might actually be individual worms.

The obvious way to find out for sure is to take some samples.


Cheers,

Michael

[Angakuk]

A great project for your next vacation.

[wei yau]

A question for you, Masked Man.

Is the science described for these toys accurate? Also, for each toy, is there an evolutionary link from one form to the other?

These are pretty neat plush toys that can "transform" from one ancient lifeform to another.

[The Lone Ranger]

Hmm. Well, I've certainly seen worse, but it could certainly be better. For one things, coelacanths most-definitely are not directly ancestral to tetrapods. In fact, ironically, the coelacanths are members of the only sarcopterygian group that has never left the oceans.


Where to start?

Let's start with the fishes in general. The first true craniates were the jawless fishes (Agnathans); as the name implies, these fishes lacked true jaws. Surviving jawless fishes include the Myxini ("hagfishes") and the Petromyzontidae ("lampreys"). (Hagfishes, by the way, are craniates, but not vertebrates -- a hagfish has a cranium surrounding and protecting its brain, but its spinal cord is not protected by vertebrae.)

Neither hagfishes nor lampreys were ancestral to "advanced" fishes, but jawless fishes were quite common in the seas of some 400 million years ago. You may have noticed in the lamprey photo that it has seven pairs of gill openings.

It's thought that a group of agnathans known as the Thelodonti were the ancestors of the gnathostomes -- the jawed fishes and all of their descendents. The gnathostomes, obviously, possess true jaws. Those jaws are derived from the supporting elements of the first pair of gills; the hyoid apparatus is derived from the second pair of gills. That's why, if you look at a shark or other jawed fish, it has five pairs of gills. (With the exception of some "primitive" sharks that have six pairs of gills and no hypoid apparatus.)

In addition to their jaws, the gnathostomes have two pairs of girdles of cartilage and/or bone that support two pairs of appendages. The first girdle is known as the pectoral girdle (our clavicles and scapulae) and supports the forelimbs, and the second girdle is the pelvic girdle, which supports the hindlimbs.


The gnathostomes divided into three major groups. The Chondrichthyes have internal skeletons made of cartilage, not bone -- surviving chondrichthyians include the sharks and their relatives. The Placodermi were a group of fishes with heavy bony armor, all of which eventually became extinct. The Teleostomi are the "bony fishes" and their descendents -- fishes (and amphibians, reptiles, birds, mammals) with internal skeletons of bone.


The bony fishes evolved into two main groups. The Actinopterygii are the "ray-finned fishes." Their pectoral and pelvic fins are relatively thin and are supported by thin "rays" of bone. While this makes many of them fast and maneuverable swimmers, their relatively fragile fins typically cannot support their weight, even in water.

The other group of bony fishes is the Sarcopterygii, the "lobe-finned fishes." These fishes have much thicker and more muscular pectoral and pelvic fins, supported by stout bones. Sarcopterygians typically use these muscular fins for walking along the floors of lakes or of the ocean; quite a few of them can come out of the water and walk (albeit rather awkwardly) on land.

Incidentally, quite a lot of bony fishes can breathe air, either across the skin surface or with modified swim bladders or even true lungs. Many can survive out of water for hours or even days at a time, in a sufficiently-wet environment.


Anyway, by the early Devonian (roughly 400 million years ago), the sarcopterygians had split into two major groups, the coelacanths and the rhipidistians. It's rather an exaggeration to claim that the coelacanths haven't changed much in 400 million years. (The plush toy is a representation of a modern coelacanth, a member of the genus Latimeria.) And coelacanths certainly weren't ancestral to land-living vertebrates.

The rhipidistians colonized freshwater rivers and lakes, and in turn, split into two main groups -- the lungfishes and the tetrapodomorphs. As the name implies, the tetrapodomorphs were the ancestors of the land-living vertebrates, the Tetrapods (the amphibians, the reptiles, the birds, and the mammals).


So, Ichthyostega was indeed an animal that can be thought of as "intermediate" between a fish and an amphibian in its characteristics. But it was descended from rhipidistians (specifically, tetrapodomorphs), not from coelacanths.



Cheers,

Michael

[JoeP]

Originally Posted by The Lone Ranger

It's thought that a group of agnathans known as the Thelodonti were the ancestors of the gnathostomes -- the jawed fishes and all of their descendants.

Today, we are all gnathostomes.

And Teleostomi etc. True?

[JoeP]

I need a picture, TLR.

Edit:
Is this about right?

[The Lone Ranger]

Originally Posted by JoeP

I need a picture, TLR.

Is this about right?

Heh. That's the gist of it.

We (that is, all of us tetrapods) are indeed gnathostomes and teleostomi -- the direct descendants of fishes.


Cheers,

Michael

[JoeP]

Well, I fully expected a longer answer. But I think you knew that I knew that .. wait ... that humans aren't winners any more than all the other groups, except the placodermi who actually died out. Aren't we all "evolved" the same "amount"?

I'm fascinated by evolutionary trees. Are there any readily available that are weighted by the number of individuals [estimated to be] alive today? Or at least by the number of different species within the leaf groups (families, classes or whatever)? That would be the measure of success.

[Ensign Steve]

It would be nothing but beetles!

[JoeP]

Bacteria!

[Ymir's blood]

library!

[Ymir's blood]

[Corona688]

Originally Posted by JoeP

Well, I fully expected a longer answer. But I think you knew that I knew that .. wait ... that humans aren't winners any more than all the other groups, except the placodermi who actually died out. Aren't we all "evolved" the same "amount"?

Not precisely. Some things like horseshoe crabs are so tightly jammed in their niche that nearly all changes end up being maladaptive -- even more so than usual. It doesn't put their genome in stasis, but has made sure that, for quite a long time now, they look and (at least appear to) act like horseshoe crabs did millions of years ago. Same for the coelcanth -- it has to have picked up mutations by now, but selecton keeps mutations that don't force it out of its niche.

And some things mutate far faster than others.

[JoeP]

But is it useful to talk about species that have changed a lot - mutated successfully - gone through more speciation events since the pre-Cambrian - as being "more evolved"? Technically, it makes sense. But if evolution keeps a species fairly unchanged, since it's fit for its environment and surviving, isn't that successful evolution too?

[Listener]

Originally Posted by JoeP

Well, I fully expected a longer answer. But I think you knew that I knew that .. wait ... that humans aren't winners any more than all the other groups, except the placodermi who actually died out. Aren't we all "evolved" the same "amount"?

I'm fascinated by evolutionary trees. Are there any readily available that are weighted by the number of individuals [estimated to be] alive today? Or at least by the number of different species within the leaf groups (families, classes or whatever)? That would be the measure of success.

It's all a matter of perspective. There is a serious point of view that says wheat is the most successful species of all with the human race slaving to ensure its multiplication.

[Corona688]

Originally Posted by JoeP

But is it useful to talk about species that have changed a lot - mutated successfully - gone through more speciation events since the pre-Cambrian - as being "more evolved"?

Biologists get irked when you use their technical terms creatively. ;p Evolution is not any sort of yardstick since the very concept of evolution as a measure instead of a process makes no sense -- how many milli-evos does it take to evolve a leg? "Specialization" and "speciation" might be closer to what you want, but they're not measures either, though their rates might be. Rate of speciation at least would be clearly defined and potentially measurable and by that measure, horseshoe crabs and coelcanth appear to have changed very little.

[The Lone Ranger]

Almost any textbook on Zoology or Botany will contain charts showing how species diversity within certain groups has changed over time. Such charts are very useful for showing the relative "success" of the various taxa. To take just one example, the Brachiopods were an extremely successful taxon (in terms of numbers of species and individuals) for millions of years. For a time, they practically dominated the seas. But today, they're a very small taxon, with only a handful of surviving species.

Any such chart made for modern animals will inevitably be dominated by the Class Coleoptera (beetles), as has already been pointed out.


Here's such a chart for some of the major plant taxa, to show what these sorts of charts look like. You can see how the Lycopsids ("club-mosses" and their relatives) and the ferns used to be the world's dominant plant taxa, but that they've been largely replaced by the seed plants. (Note the explosive growth in diversity of the seed plants, starting in the late Cretaceous. This corresponds with the rise of the flowering plants and especially of the grasses.)

Sorry I haven't been able to provide more detailed responses. I'm kind of swamped lately.

Cheers,

Michael

[Qingdai]

It must be the end of the term, finals and grading for you.
I'm surprised you can do anything at this juncture.
Cool chart.

[Ensign Steve]

Hey, Michael. Do you know how this illusion works?

[JoeP]

Hey TLR, can you explain this?

The class of problems that can be efficiently solved by quantum computers is called BQP, for "bounded error, quantum, polynomial time". Quantum computers only run probabilistic algorithms, so BQP on quantum computers is the counterpart of BPP on classical computers. It is defined as the set of problems solvable with a polynomial-time algorithm, whose probability of error is bounded away from one half.[26] A quantum computer is said to "solve" a problem if, for every instance, its answer will be right with high probability. If that solution runs in polynomial time, then that problem is in BQP.

BQP is contained in the complexity class #P (or more precisely in the associated class of decision problems P#P),[27] which is a subclass of PSPACE.

BQP is suspected to be disjoint from NP-complete and a strict superset of P, but that is not known. Both integer factorization and discrete log are in BQP. Both of these problems are NP problems suspected to be outside BPP, and hence outside P. Both are suspected to not be NP-complete. There is a common misconception that quantum computers can solve NP-complete problems in polynomial time. That is not known to be true, and is generally suspected to be false.[27]

From Quantum computer - Wikipedia, the free encyclopedia

I get probabilistically lost about half way through this.

[ceptimus]

Re the optical illusion. If you can keep your focus fixed on one 'leaf' the apparent movement stops. This is easier if you close or cover one eye and then stare at one leaf near the centre with your remaining eye.

The illusion of movement is caused by the dark and light shading on the opposite sides of the leaves - if you edit the palette with a paint program to remove those shadings then the 'movement' stops.

I suspect that it is due to the retina taking longer to register a light-to-dark transition than a dark-to-light one - so every time your eye moves and a new image settles on the retina you see the light parts of the leaves first. Then a fraction of a second later you see the dark parts. The brain interprets this as the leaves growing slightly and moving towards the dark edge.

[Ymir's blood]

I tried that and some of them stopped but the rest started coming right at me!

[The Lone Ranger]

JoeP: Not really my field, I’m afraid. While I think I can understand the gist of it, without taking the time to read more of the article, I couldn’t begin to explain what it’s talking about without knowing more of the terminology. There are probably people here who’re much more knowledgable about such things and could do a much better job.

Originally Posted by Ensign Steve

Hey, Michael. Do you know how this illusion works?

It appears to work on the same principles as Akiyoshi Kitaoka’s famous "Rotating Snake" illusion. There are two basic principles involved: how our eyes/brains deal with shadings, and how we perceive (or don't perceive) movement.



First off, keep in mind that, even though we're rarely aware of it, our eyes are constantly darting about. Illusions like this take advantage of that fact to generate the impression of movement where there is none.


Because your eyes are constantly darting about, and because we’re typically moving our heads, our eyes and brains must perform a considerable amount of processing on incoming visual data in order to distinguish between things that are apparently moving (the apparent motion being the result of movements of the eyes and head) and things that are actually moving within the visual field.


One way that the brain does this is to ignore visual inputs during rapid eye movements. Another mechanism allows the brain to compensate for movements of the head: as you turn your head, signals from the vestibular apparatus in the middle ear are fed to the brain and cause reflexive movement of the eyes in the opposite direction. This means that the image remains still. (This is actually a reflex action; it’s known as the vestibular-ocular reflex. Your eyes will automatically move counter to any head rotation at the speed necessary to counter the apparent motion induced by movement of the head, unless you consciously choose to override the reflex.)



You can easily test this for yourself. Try reading this while shaking your head from side to side. It’s easy to do, isn’t it? That’s because your eyes will automatically move counter to your head rotation, producing a more or less stationary image.

Now, if your monitor will permit it, try moving the monitor from side to side at the same speed you had been moving your head from side to side. It’s much harder to read the text, isn’t it?


You can demonstrate that this is a true reflex and not just conscious (or sub-conscious) compensation for apparent movement by having someone else (presumably, someone you trust) move your head for you. Unless you consciously suppress the reflex, your eyes will automatically counter-rotate to compensate for any movement of the head. In other words, you don’t need to know when and where your head is going to move (or how fast) in order to compensate for head movements; the vestibular apparatus in your ear feeds data to your brain stem in response to any movement of the head, and the eyes automatically move to compensate.



As an aside, this is part of the reason why someone whose "higher" brain centers have been completely destroyed can still behave in ways that eerily mimic consciousness. The eyes will automatically track movements; the eyes will automatically move counter to any rotation of the head and so will remain "fixed" on a stationary object in the person’s field of view; the person will flinch away if something moves toward the eye suddenly, or from loud noises; and so forth. Since these are reflex actions and mostly due to activity in the brain stem, the person can display behavior that can easily be mistaken for consciousness even if the cerebrum is all but gone (as was the case with Terry Schiavo) and there is no conscious brain activity whatsoever.



Now, despite the fact that the eyes automatically counter-rotate to keep images "static," the eyes themselves never stay still for very long. Even if your head is perfectly still and you’re trying to keep your attention focused on an un-moving object, your eyes will dart around at least a little.

This is actually necessary, because the receptors of the eye, like most sensory receptors will eventually stop responding to a constant signal. This is called sensory adaptation.

You’ve probably noticed this before. When you first walk into a freshly-painted room, the smell of the paint is very strong. But after 10 or 15 minutes, you probably won’t be able to smell the paint at all. This is due to sensory adaptation. It actually happens in two different ways: many sensory receptors will cease to respond to a constant signal after awhile; even if the receptors continue to send signals, the brain itself will typically cease to consciously register a constant signal after awhile.

If you completely paralyze a person’s eye muscles and prevent them from moving their head, if there’s nothing moving within his/her field of vision, (s)he literally goes blind after a few minutes. This isn’t due to any damage to the eyes or brain; the eyes simply stop responding to a constant stimulus after awhile -- as soon as something in the visual field changes, you’ll see it.

(You can do neat experiments with frogs along this line. If you hook up electrodes to a frog’s visual cortex and monitor its activity, when the frog is sitting still and there’s nothing moving within its field of view, there is literally no activity in the visual cortex. In other words, the frog is seeing nothing at all. As soon as something moves in its field of view -- or the frog is moved, creating the illusion of movement -- the frog’s visual cortex lights up with activity.)

People who have had their extrinsic eye muscles (the muscles that move the eyes) temporarily paralyzed while their heads were immobilized report the same phenomenon. If there’s no movement (real or apparent) or change within their visual field, after a few minutes, their vision "fades out" and that can’t see anything at all. It’s actually somewhat un-nerving, I’ve heard. But as soon as there’s any movement within their visual field, they can see again.




You don’t normally notice the fact that your eyes are constantly in motion because your brain automatically compensates for these eye movements when interpreting visual data. It becomes very apparent that this is the case when you deprive the brain of surrounding data with which it can compensate for random eye movements.


A common way that psychologists demonstrate this is to put test subjects into a completely darkened room and to shine a laser pointer onto one of the walls. Even though the laser pointer is completely stationary, test subjects more or less universally claim that the light is randomly moving about. That’s because when you deprive the brain of outside reference data, it can’t compensate for the random eye motions, and so it looks as if the laser dot is moving, even though it isn’t. (The apparent random motion of a stationary object when your brain lacks a frame of reference with which to compensate for random eye movements is called the autokinetic effect.)


The autokinetic effect, incidentally, is often cited as an explanation for why people often see rapidly-moving "UFOs" that typically turn out to be the planet Venus. If you’re looking at a bright light in the sky and there are no other nearby objects for your brain to gather data on in order to compensate for your eye movements, your random eye motions create the illusion that the bright light is rapidly darting about the sky, even though it’s perfectly stationary. (This works best at dusk, when the sky is still light-enough that no nearby stars are visible.)



So, we can now put this together to see why certain patterns can create the illusion of motion where there is none. Notice that these sorts of optical illusions are not symmetrical in the horizontal and vertical axes.

If most of the lines and shading are such that the lines (or apparent lines) are mostly in the vertical axis, then an upward or downward movement of the eye will create little or no apparent motion. But a sideways eye motion will create much more obvious apparent motion.

The reverse is true as well, of course. If the pattern is such that most of the lines (or apparent lines) are in the horizontal plane, then a side-to-side movement of the eyes will create little or no apparent motion, while an upward or downward movement creates much more apparent motion.


The fact that movement of the eyes in one direction generates much more apparent motion than does movement of the eyes in a different direction makes it impossible for the brain to properly account for the random movement of the eyes when deciding if there’s any motion within the field of view. And so, we see motion where there is none.

You can see that it is an illusion if you deliberately focus on just one element of the picture, holding your eyes as steady as you can. By focusing on just one small portion of the picture and ignoring the surrounding details, you deliberately deprive your eyes of "contradictory" information and so destroy the illusion.


Cheers,

Michael