Eric H

Quote Happy Wonderer
That is explained well by the process of random mutation and natural selection. I can't see what point you are trying to make. Some subset of the decendents of particular individuals of the ancient single-celled family are still single-celled creatures. A tiny minority of those decendents are multi-celled. An even tinier fraction are vertabrates.
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This is how I see the mathematics of evolution working, starting with the tinier fraction of vertabbrates as you describe, there will be fewer with one leg, even fewer with two legs, fewer with four legs. Fewer with two teeth in their mouth, even fewer with a whole set of teeth.

Whatever degree of complexity you go for reduces the number that natural selection has to work with.

This seems more apparent with size, apparently for every human on Earth now there may be two hundred million insects.

When you go for bigger and more complex things you reduce the chance of it happening by the numbers

The laws of numbers seems to work in an opposite way to the needs of evolution, and they also seem to work against the laws of evolution.

Peace

Eric

pz

Are you considering the polar body?

Another trick question: when does the chicken zygote cease being a single cell?

pz

I think you are looking at everything completely backwards.

'Complex organisms' do not have a reduced potential for change. You must understand that they are built on all the features that their ancestors had; they have a large toolbox or set of molecular subroutines that can be coopted and modified.

You also can't quantify complexity by simply counting the number of elements, like legs. Is a centipede more complex than a fruit fly? I'd say it is not.

Eric H

Quote RufusAtticus, Umm, Eric, bones came much later in the evolution of life, after fish evolved in fact.
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Sorry yes I wrote that in haste, start again,
Start of with an earliest life form floating around in the sea any shape or size but without anything that science would describe as the earliest stages of bone.

Introduce two or three of these earliest cartilages or whatever you would call the predecessors of bone to this life form.

If these bone like growths did nod help the life adapt to its surroundings, it could be a hindrance, in the same way as an unwanted tumour or growth might be to us today. It could slow or restrict movement, add weight, or even be an unwanted biological intrusion, and it could cause illness.

My point is would natural selection prevent it passing this growth on to the next generation?


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quote Happy Wonderer, Bonus question: is a fertilized chicken egg a single cell?
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I'm working on that one!!!




Hello Jobar, I have read parts of your link with interest and the point that seems to come across from the strong willed people on that thread reminds me of an old saying which always makes me chuckle.


When I want your opinion, I will give it to you.


Anyway I will keep your closing comments in mind from that thread, and I will do my best not to mention the G. word again

Peace

Eric

Godless Dave

Most likely it would, for exactly the reasons you listed. If slow or restricted movement, added weight, and/or illness inhibited reproduction (or inhibited the ability to survive long enough to reproduce) then the trait would be unlikely to be passed on.

As to your specific example, cartilage is itself made up of cells, so a single-cell (or smaller) organism probably couldn't grow cartilage. But your example works for any new trait that hinders reproduction.

Eric H

Quote pz You also can't quantify complexity by simply counting the number of elements, like legs. Is a centipede more complex than a fruit fly? I'd say it is not.
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Hello pz, I don’t know how you could Compare a fly and a centipede in a fair way.

But look at the complexity of a centipede, the amount of detail that is required to make it work in a reasonable way,

If a quarter of the legs were moving forward while the others were going back, If some of the legs moved side to side, or didn’t move at all. If there was a fifty percent variation in the length of the largest and smallest leg, if no two legs were the same size. If ninety five percent of the legs were on one side of the body.

I can guess what you are going to say maybe it started of with four legs then the body got longer so it added a couple more legs and so on.

But if any of these increases did not work out, wouldn’t it revert back to a smaller and more efficient unit by selection?

Were is the incentive to gain more length, more legs and more complexity if it is not more efficient each time?

Peace

Eric

pz

The legs of centipedes are meristic characters -- that is, they are repeated elements generated by the same rules and processes. They are also bilaterally symmetric, generated by processes that operate identically on both sides of the body.

Generating many copies of the same structure along the longitudinal axis of the body is simple, and requires little additional information. Primitively, it is thought that this repetition was a strategy to easily increase body size, or because length was a useful advantage in swimming or tunneling.

It requires additional, special information (or an increase in complexity) to specialize segments, or to break symmetry. A fly has an underlying simple meristic body plan that is secondarily modified by suppressing limbs in some segments, modifying limbs in others to be mouthparts, and specializing others for locomotion.

Your scheme of measuring specialization by counting parts is silly. Arthropods have a molecular program for building a limb. They have a general program for specifying where to put limbs. When it makes 6 or 10 legs, it is using the same module for each one. The complexity lies in the 'limb module', and in the array of elaborations on that module that allow for specialization by segments.

I suspect that we are talking past each other. You don't seem to be aware of the basics of developmental patterning in organisms. Where are you getting these peculiar notions about what is and isn't difficult in generating morphology?

lpetrich

Eric H seems to subscribe to a view that is often called "beanbag genetics" -- a separate gene for every little feature. But although beanbag genetics works fine for proteins, it does not work well for macroscopic features.

Most bilaterally-symmetric animals have front-to-rear identity specified with homeobox or Hox genes. These genes are expressed in different regions of the body, often overlapping ones, and their order in the genome almost always parallels their body-position order. Hox genes make regions develop in a more rearward fashion; here is a simplified version of how Hox genes work:

Imagine two of them, Th, and Ab, that can be expressed in an insect's head, thorax, and abdomen.

Th in the thorax and abdomen
Ab only in the abdomen

Thus their names. If Ab is absent, then the abdomen will develop like an extra thorax. If Ab is expressed in the thorax, it will make the thorax develop like an extra abdomen. If Th is absent, then the thorax will develop like an extra head, but the abdomen will still develop like an abdomen. If Th is expressed everywhere, then the head will become a second thorax, but the abdomen will be unaffected, as in the previous case. Etc.

A fancier version of that is exactly what we see in "real life". Hox-gene mutations can cause a fruit fly to have its halteres turned into wings, its antennae turned into legs (Antennapedia), its mouthparts turned into legs (Proboscipedia), and even for it to try to grow abdominal legs.

The same thing happens in land vertebrates; their vertebrae are divided into cervical (neck), thoracic (forward trunk), lumbar (middle trunk), sacral (rearward trunk), and caudal (tail) ones -- and these divisions correlate well with Hox-gene expression. Here is a chicken and mouse comparison (page 3, lower left. Chickens have 14 neck vertebrae and mice have only 7 -- the usual mammalian number (giraffes have 7 long ones) -- and the other regions also vary in number of vertebrae.

Snakes, interestingly, have no Hox-expression zone for front limbs; some of the rearward Hox genes have their expression regions moved up to eliminate this zone.

And in general, vertebrates vary enormously in numbers of vertebrae -- frogs have 6 to 10, while snakes have 100 to 500, with individual snakes of a species sometimes varying in number. This means that vertebra development is not rigidly tied to Hox-gene expression zones.

lpetrich

Eric H has some additional questions about centipede gaits, but here again, one must think outside of the beanbag-genetics box.

There is a simple way for a centipede to walk without tripping over itself. It is to send a wave of walk instructions down the length of its body. That way, neighboring pairs of legs will be nearly in phase.

Eric H

Quote pz, I suspect that we are talking past each other. You don't seem to be aware of the basics of developmental patterning in organisms. Where are you getting these peculiar notions about what is and isn't difficult in generating morphology?
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I guess it shows that I shouldn’t have answered you on the centipede question; I sense I have been had, and it shows my lack of knowledge.

I sense that I should not attempt to try and answer your chicken question.

Anyway my questions are asked through ignorance, and so some of my questions are daft; apparently not all of them. My intentions are just to try and push the boundaries a bit, it seems if you keep asking the same questions you get the same answers.

So in a way maybe the answer is to find greater questions, like natural selection not all questions will be a success.
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If evolution was to produce a centipede; then I feel that your description coupled with the additions from lpetrich sounds an acceptable explanation.



Anyway getting back to the bony question

Start of with an earliest life form floating around in the sea any shape or size but without anything that science would describe as the earliest stages of bone.

Introduce two or three of these earliest cartilages or whatever you would call the predecessors of bone to this life form.

If these bone like growths did nod help the life adapt to its surroundings, it could be a hindrance, in the same way as an unwanted tumour or growth might be to us today. It could slow or restrict movement, add weight, or even be an unwanted biological intrusion, and it could cause illness.

My point is would natural selection prevent it passing this growth on to the next generation?

I am finding trouble in the way that evolution could introduce bone like substances in the first instances, and at the same time remain true to the selection process.

Peace

Eric