Elephant's sixth 'toe' discovered

A mysterious bony growth found in elephants' feet is actually a sixth "toe", scientists report.

For more than 300 years, the structure has puzzled researchers, but this study suggests that it helps to support elephants' colossal weight.

Fossils reveal that this "pre-digit" evolved about 40 million years ago, at a point when early elephants became larger and more land-based.

Lead author Professor John Hutchinson, from the UK's structure and motion laboratory at the Royal Veterinary College, said: "It's a cool mystery that goes back to 1706, when the first elephant was dissected by a Scottish surgeon."

Many people, he said, thought that the structure was a huge lump of cartilage, and over the years its purpose or lack of purpose has been debated.

"Anyone who has studied elephants' feet has wondered about it. They've thought: 'Huh, that's weird,' and then moved on," he added.

But Prof Hutchinson and colleagues used a combination of CT scans, histology, dissection and electron microscopy to solve the puzzle.

The researchers said the structure was made of bone, although bone with a highly irregular and unusual arrangement.

But closer examination also revealed that it showed a strong similarity with an unusual bone that is found in the front feet of pandas.

This bone - which is not quite an extra digit, but does the job of one - helps the panda to grip bamboo, and is called the panda's "thumb" or "sixth finger". Moles too have a bone masquerading as an extra digit, which helps them to dig.

Light (IR) sensitive cells. Advantage: knows something warm nearby. (for visible, knows if it's day or night, knows when a predator's shadow looms over).

OK. Development of a few IR sensitive spots might happen.

Gathered in a patch. Advantage: more sensitive detection.
Patch curved to make a cup. Advantage: self shadowing gives some sense of directionality.

However, cupping, until it is complete and protected, provides a place for dirt to gather, thus blocking the sensitive cells.

This requires a further change in biology (some sort of cleansing system such as tears) or behavior (instinctive grooming). These changes won't happen until the light sensitive spot has shown itself to be useful. And it cannot show itself to be useful until it is properly integrated into the brain. Which requires growth or specialization of nerves and brain structures to interpret the new data (heat). So everything has to develop at the same time for there to be any advantage to the new sensitive cells.

Cup pinches in to make a pin hole camera. Advantage: actual crude image formation. Pinhole gets transparent cover. Advantage: protects imaging surface from damage, accumulated crud.

Here's where it really goes wrong since we are dealing with IR. There is no transparent biological material to IR. (Most current IR devices use germanium lenses. There is a small body of other materials that are IR transparent, but I've not been able to find any biological ones.) No IR device can "see" through skin. (We can see the heat shadow cast upon the skin from objects in very close proximity to it. That is, if the object is touching the skin or within say 1/4" of it, further if hotter.)

So any "transparent cover" would totally negate any benefit derived from the IR sensitive cells. They'd die off in a few generations as utterly useless.

Transparent cover thickens into lens. Advantage: sharper image.

If we assume visual spectrum sensitivity instead of IR then this "transparent cover" also degrades performance (loss of fine directionality, loss of focus) of the light sensitive cells until a full lens is formed. Looking through a sheet of saran wrap is a whole lot worse than looking through a proper lens.

It is possible to have a light sensitive spot of cells. It is possible to have a fully functioning eye. There's just no way to gradually get from the first to the second.

Specialized skin muscles learn to distort lens.
Advantage: Ability to focus on details.

So we need to evolve muscles (which of course have a different cell type than skin does) where the DNA doesn't have any muscles. We need to grow more nerves and more brain structures to control these muscles. I just don't see this happening by accident.

We call the resulting miraculous structure an eye

About the only part of this you have correct is that the eye is "miraculous". Caused by a miracle. In other words, created.

These changes won't happen until the light sensitive spot has shown itself to be useful.

Being able to strike a mouse in utter visible light darkness clearly has no use to a predator.

And it cannot show itself to be useful until it is properly integrated into the brain.

A nerve cell that senses, say touch, already has all the plumbing to the brain. If a single mutation makes it sensitive to heat/IR the integration is already in place.

There is no transparent biological material to IR.

Zatso? I guess we'd better let all those doctors using trans-dermal IR lasers for cosmetic surgery know that factoid.

No IR device can "see" through skin.

I could fry your retinas to permanent blindness with IR without doing the slightest bit of damage to your corneas or lenses

Do yourself a favor. Never work with IR lasers.

*WINK* Can I do that??? Did I just use existing muscles in my skin, and existing nerves to distort my skin?? How could that be? (I will admit maybe puckering my lips would be a better model for focusing a lens)

Looking through a sheet of saran wrap is a whole lot worse than looking through a proper lens.

The evolutionary standard isn't "perfection", it's "better" a primitive eye with a saran wrap cover doesn't provide a better image than an open eye. It does provide a good enough image for the life of the animal, as opposed to good enough until the first piece of grit gets in the pocket vision.

Like all things in life it's a trade-off. In this case, a lifetime of good enough vision is more of an advantage than a few months of better vision followed by crud degraded vision.

It is possible to have a light sensitive spot of cells. It is possible to have a fully functioning eye. There's just no way to gradually get from the first to the second.

Ah, we've come full circle. Transitional forms/fossils never fill gaps, they create them.

About the only part of this you have correct is that the eye is "miraculous". Caused by a miracle. In other words, created.

Created one small and uncertain step at a time.

Being able to strike a mouse in utter visible light darkness clearly has no use to a predator.

Since evolution decrees that things happen slowly, it is safe to assume that the first mutation of these IR sensitive cells would be totally useless to the creature (assume snake) carrying them. No nerves carrying the IR signals, no brain structure to interpret these signals. etc.

So any behavior or structure to clean/protect these cells will not develop until the cells are useful. Without the cleaning behavior/structure the cells will never be useful as they will likely be blocked.

A nerve cell that senses, say touch, already has all the plumbing to the brain. If a single mutation makes it sensitive to heat/IR the integration is already in place.

so all the snake knows is it was touched over there. And ONLY if the number of mutated cells is relatively huge. The input from one mutated cell would be lost in the noise. The snake does not recognize that the particular touch from that one cell means a mouse is over there. It would get the same results from anything it brushed against (as the nerves and brain are still wired to touch for that cell)

me->There is no transparent biological material to IR.

Zatso? I guess we'd better let all those doctors using trans-dermal IR lasers for cosmetic surgery know that factoid.

I stand corrected. I forgot the cornea for wavelengths of 400-1400 nm.

I've still not found a medical laser that works through skin. they all either work through a small incision or topically. me->No IR device can "see" through skin.

I could fry your retinas to permanent blindness with IR without doing the slightest bit of damage to your corneas or lenses

Only at the specific wavelength mentioned above. And corneas are not skin. They are an extremely biologically complex tissue. Starting from skin (which is opaque to IR) how do we get to a transparent covering (will call it a cornea since that is the term for it in vertibrates)?

Since the cornea has no vascular tissue it must be fed from the aqueous humor trapped behind it. Since it must be kept dehydrated in order to be transparent there must be a barrier of some sort to allow nutrients in and pump water out.

So, a simple skin covereing would have to be highly developed from the start in order for it to be of any use. Any vascular tissue and it would only block the mutated sensor cells. No vascular tissue and it would starve and die UNLESS there was already a liquid source of nutrients behind it.(as the nutrients diffuse into it.)

But a source of nutrients is not enough. There must be a barrier to pump excess water out of the cornea to keep it transparent. So we need a barrier layer between the nutrients and the cornea. Oxygen is another issue. The cornea receives all it's oxygen from the air. Oxygen in the air is absorbed into tears and then diffused into the corneal tissue. No tears and the tissue dies of oxygen deprivation.

So in order to have a transparent tissue over the mutated IR sensor cells we need to have the tear system in place AND the nutrient-passing water-pumping system in place AND the liquid nutrient system in place.

Looks like we need just about the entire eyeball to be there just to maintain a transparent cornea!

Do yourself a favor. Never work with IR lasers.

15 years so far with no accidents and no exposures. Follow the basic safety rules (WEAR YOUR GOGGLES!) and you have no problems. *WINK* Can I do that??? Did I just use existing muscles in my skin, and existing nerves to distort my skin?? How could that be? (I will admit maybe puckering my lips would be a better model for focusing a lens)

So an IR sensitive spot in your mouth would be pretty useless. Perhaps on your nose. In any event, the muscles required to focus these mutated cells would not exist when the cells mutated and would have to be developed

me->Looking through a sheet of saran wrap is a whole lot worse than looking through a proper lens.

But saran wrap is also opaque to IR. Those mutated IR sensitive cells would be useless behind any layer of skin.

It's not a question of "perfection" vs "good enough". It's a question of "works" vs "doesn't work at all"

me->About the only part of this you have correct is that the eye is "miraculous". Caused by a miracle. In other words, created.

Created one small and uncertain step at a time.

Which, as we can tell just from the cornea, is impossible. Unless all those steps happen simultaneously the whole thing won't work. The eye is irreducibly complex.

(Excellent discussion by the way. I learned a bunch about the eye. And I haven't even gotten to the lens yet!)

Um, no. let's not.

Let's assume a single mutation in an existing nerve cell. This cell was supposed to grow up to detect touch.

Let's assume that since the nerve cell was supposed to tell the snake (for example) "hey, you bumped into something" that the nerve was already connected to the brain, and the brain already has enough wiring to process the signal as a sensory signal.

The brain reads that nerve's output as a tickle, it doesn't take even a snake brain all that long to figure out that tickle means there's something warm out there that we aren't actually touching.

If the snake is bright enough to start swinging its head side to side, a behavior it already has when trying to localize a scent, it can figure out "something warm" is more or less that-a-way.

Now the snake can spend less time sniffing its way to a cold rock a mouse has rubbed its scent on and more time going where scent+warm=food.

That is a distinct survival advantage from a single mutation on a sensory nerve, plus trivial adaptations of existing behavior.

I think you will agree that a single mutation is a slow step.

BTW, I was saddened to hear that you have no ability to sense the warmth of a fire through your skin without actually touching the flames. Sucks to be you.

so all the snake knows is it was touched over there. And ONLY if the number of mutated cells is relatively huge.

I'm also saddened to hear that you can't feel a pinprick. OTOH, I guess this is an advantage whenever you need to get a shot or a blood draw.

No IR device can "see" through skin.

Simply not true:

The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits

I won't belabor the point (much) but a typical snake's head isn't much thicker than a dozen mm or so.

Starting from skin (which is opaque to IR)

As Ayn would say, "Check your premise..."

Since it must be kept dehydrated in order to be transparent

I suppose a thin transparent dry scale is out of the question? Pity. Snakes already use them as eye covers.

So an IR sensitive spot in your mouth would be pretty useless. Only if I kept my mouth shut. (You may have noticed, I don't ;^P)

In any event, the muscles required to focus these mutated cells would not exist when the cells mutated and would have to be developed

Yeah, the poor snake would have to adapt existing skin muscles or go with a fixed focus camera.

You actually do work with IR lasers? Amazing.

But saran wrap is also opaque to IR. Those mutated IR sensitive cells would be useless behind any layer of skin.

No matter how thin, nor what range of IR wavelengths? I guess doctors gotta stop using heat lamps to teat muscle spasms.

Which, as we can tell just from the cornea, is impossible. Unless all those steps happen simultaneously the whole thing won't work. The eye is irreducibly complex.

Given that the fossil record says eyes were evolved in aquatic creatures, and we are trying very hard not to confound an existing visible light eye with a plausible future infra-red eye your very well reasoned IR cornea objections don't apply.

The eye is irreducibly complex.

No. Just very very very amazing!

Excellent discussion by the way.

Yes! It's been very thought provoking, seldom do I get such a good opportunity to question my premises.

I learned a bunch about the eye.

Me too! And I haven't even gotten to the lens yet!

A topic for another day, perhaps?

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