nested heirarchies as evidence against darwinian evolution

His question is why don't new vertebrates evolve all over again from invertebrates, and thus form a second vertebrate branch.Corollary: how would you know it hasn't happened?Enjoy.

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In other words the depth of a taxonomic division is related to the age of the common ancestor where the divide occurs.In fact you could build an arbitrary tree based on common ancestor relationships using just certain specified ages (1 every million years?) and the species alive at those times to define the names for those levels of development.When you are done, compare it to a standard taxonomic tree.Welcome to the fray bluejay.

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This is similar to the denial of transitional fossils where - for the avid creationist - every time you find a transitional fossil you create an additional gap. The difference is that here we can use genetic data to show the nested hierarchy and then compare that to the fossil evidence to see how they fit together.One can use the hominid tree from the Smithsonian Institute: Early Human PhylogenyOr one compiled by Bruce MacEvoy: Human Evolution

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Human evolution is a puzzle made up of thousands of fossil pieces. The Chart of Human Evolution (below) shows the major pieces of that puzzle arranged in a likely solution, which is open to clarification as new fossil or DNA evidence is reviewed in the scientific literature.

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Getting back to the "nested hierarchies" of the openning post we see this from Bruce MacEvoy:

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According to The Tree of Life by Guillaume Lecointre and Hervé Le Guyader (Harvard University Press: 2006), the similarly named and easily confused categories of humans and near human apes, in order of increasing inclusiveness, are:

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” Hominini - modern humans and all previous human or australopithicine ancestors

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” Homininae - humans and chimpanzees (Panini), our closest living biological kin (so close that some scientists have suggested their genus name should be changed from Pan to Homo).

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” Hominidae - humans, chimpanzees and gorillas (Gorillinae)

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” Hominoidae - humans, chimpanzees, gorillas and orangutans (Pongidae)

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” Hominoidea - humans, chimpanzees, gorillas, orangutans and gibbons (Hylobatoidae).

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http://www.handprint.com/LS/ANC/apes.gif

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This is the nested hierarchy that is based on genetic information from existing species.Enjoy.

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So you agree that Tiktaalik is a transitional that fits within the previous gap between fossils involved in - and demonstrating - the transition from fish to quadruped?Excellent.Then we can talk about whale transitionals ...Enjoy.Added by edit:Looks like the comment I made has not been shown to be false by Randman. So much for it being a false accusation then.Edited by RAZD, : whale of an additionEdited by RAZD, : opportunity not taken
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Let me start by restating the question to see if I have it right:(1) The first known life in the fossil record is a cyanobacteria.Fossil Record of the Cyanobacteria

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The cyanobacteria have an extensive fossil record. The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old.

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(2) Cyanobacteria exist today.Life History and Ecology of Cyanobacteria

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Though cyanobacteria do not have a great diversity of form, and though they are microscopic, they are rich in chemical diversity. Cyanobacteria get their name from the bluish pigment phycocyanin, which they use to capture light for photosynthesis. They also contain chlorophyll a, the same photosynthetic pigment that plants use.

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Cyanobacteria are very important organisms for the health and growth of many plants. They are one of very few groups of organisms that can convert inert atmospheric nitrogen into an organic form, such as nitrate or ammonia.

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(3) if other forms of life (eukaryote, multicellular, etc) evolved from cyanobacteria in the past, why don't we see other forms of life (eukaryote, multicellular, etc) evolving from cyanobacteria now?Is that a fair statement of your basic question?

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If that is a fair statement, then we can move on to the next level of the question, a level that is not as explicitly clear, so I'll put up a couple of alternatives:Scenario APopulation A₁ evolves to a point where it divides into two populations, A₂ and B, where A₂ is genetically similar to A₁ (perhaps identical), while B is genetically distinct from A₁ and A₂. B goes on to evolve into some organism C before evolving into another organism D (etc).Population A₂ evolves to a point where it divides into two populations, A₃ and B', where A₃ is genetically similar to A₂ (perhaps identical), while B' is genetically distinct from A₁, A₂ and A₃.Etc. so we always have some A_n that may be genetically similar (perhaps identical) to A₁.Should (any) B' be(a) genetically similar to (every other) B or
(b) distinct from it? Perhaps as distinct as it is from A_whatever?If (a), then we should see very similar types of organisms evolving again and again as this process is repeated at each level.Historical note: before the time of Pasteur it was thought that small organisms were spontaneously generated and that they continually transformed into "higher" organisms, and each type of organism was continually replaced by new recruits, transformed into similar-or-near-identical forms, while the old guard moved on, transformed into even "higher" forms.Result (a) would produce a similar result to "spontaneous generation" in the continual appearance of similar species from uncommon ancestors.If (b), then B' could never evolve into C (D, etc). They could still continue to evolve, but the products would be different from the product of the B generation.It may (eventually) evolve into something similar to C (or D, or Z, skipping C and other intermediates entirely), however that would be a case of convergent evolution, such as we see with flying squirrels and sugar gliders (ain't they cute?).Scenario BPopulation A evolves to a point where it divides into two populations, B and C, where B is genetically distinct from A and C is genetically distinct from both A and B. C goes on to evolve into some organism D, before evolving into another organism E (etc).The results of this scenario are the same as they are for A's result (b) above because they are already distinct genetically.Nor can (as others have pointed out) A re-evolve into B or C, because there is no A left.Re-evolving the wheelThus the only way you could re-evolve a similar organism is if Scenario A result (a) can happen. How likely is this?Evolution is dependent on two basic forces:(1) random variation
(2) selectionRandom variation means that repeating a previous variation is unlikely, and the longer the DNA strand is, the more possibilities for variation there are (exponentially), however this can be offset by some mutations being more likely than others.Selection means that those better able to take advantage of the opportunities of an ecological system will do better than those less able, whether at survival or reproduction or both, and thus more likely to spread within the ecological system.Simply put, in order to evolve a B' that is genetically similar to B you would need to repeat a random variation AND have the same ecological system available for B' that existed for B.The problem is that this ecological system is necessarily different, because it is already inhabited by B (or by C, which has evolved from B due to selective advantage). B' would have to find an ecology that is not inhabited by B to have the opportunity to evolve further, so while B only needs a nonA ecology, B' needs one that is nonA and nonB.We can look at another example here: mudskippers (introduced on several other threads): What would be the obstacles for a mudskipper to move on to land at a time when there were no land animals?What are the obstacles now?The difference is that other organisms change the ecology, and this changes the opportunities available. This is most visible after extinction events when there are higher rates of evolution than there are in a fully diversified ecology.Thus, even if A_n^p is very similar to A₁, it is effectively a different organism because it is living in a different ecology, so it cannot evolve in the same way that A₁ did.

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Scenario COr possibly neither of these scenarios really addresses your question, you want to know why something really novel doesn't evolve that would make a whole different type of organism from all the others in existence now or in the past.The questions are:(1) is it possible?Yes.(2) would it be a new phyla?No.(3) does this mean evolution is finished?Not in the slightest.To answer this clearly let's look at a current taxonomic tree of different classifications of all the various organisms today (from Woese): There is no line that goes back in time. Phylogeny is not defined by the differentness of an organism, but by the (differences between) descendants of the organism.Any new type of organism is a new species, by definition, period, no matter how novel, original or new it is in any feature.Taxon levels are arbitrary distinctions that make it easy to talk about different types of organisms, and there is nothing sacred about the different levels and designations: they reflect some, but not all, common ancestors that happened in the past along the path to the diversity of life today. Others could be chosen that would be just as valid, just as descriptive.For instance, we could arbitrarily say that all the species alive on earth 10 million years ago form a taxon level, and all species alive since then are part of the taxon defined by their (whatever it happens to be) ancestor species that was alive 10x10^{^6}(10e6) years ago. We can label them "10e6ers". Then go back another 10 million years and do the same, labeling them "20e6ers" and noting which of the 10e6's are descended from which of the 20e6's. Keep doing that and you will develop a tree that has 3.5 billion / 10 million = 350 levels (instead of the current 7 or so traditional levels, but that is identical in form to the current tree of life, just with different labels at different arbitrary points along the branches. Opportunity, opportunity taken, followed by opportunity filled. Mudskippers facing land predators.Enough for me tonight. Does that help? Is it in the right direction?Enjoy.

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Welcome to the fray pumaz. Actually the original system was developed by using comparative anatomy and grouping existing organisms by their visible similarities. The basic assumption of the original system was that animals could be sorted into various "kinds" -- see Carl Linnaeus:

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Carl Linnaeus (Carl Linné, latinised as Carolus Linnaeus, also known after his ennoblement as Carl von Linné (help·info), May 13, 1707[1] - January 10, 1778) was a Swedish botanist, physician and zoologist[2] who laid the foundations for the modern scheme of nomenclature. He is known as the "father of modern taxonomy.

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... He then returned to Sweden where he became professor of botany at Uppsala. In the 1740s he was sent on several journeys through Sweden to find and classify plants and animals. In the 1750s and 60s he continued to collect and classify animals, plants and mineralia; publishing several volumes. At the time of his death, he was widely renowned throughout Europe as one of the most acclaimed scientists of the time.

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You will note that this all precedes Darwin and Wallace and the theory of evolution. Further in the article states:

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At Uppsala, in the University's botanical garden, he arranged the plants according to his system of classification; he then made three more expeditions to various parts of Sweden and inspired a generation of students. Linnaeus continued to revise his Systema Naturae, which grew from a slim pamphlet into a multivolume work, as his ideas were changing and more and more plant and animal specimens were sent to him from every corner of the globe. His pride in his work was very much evident; he thought of himself as a second Adam. He liked to say ' Deus creavit, Linnaeus disposuit, ' Latin for, "God created, Linnaeus organized". This self-perception was further shown by the artwork on the cover of his Systema Naturae, which depicts a man giving Linnaean names to new creatures as they are created in the Garden of Eden.

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When not on travels, Linnaeus worked on his classifications, extending them to the kingdom of animals and the kingdom of minerals. The last may seem somewhat odd, but the theory of evolution was still a long time away. Linnaeus was only attempting a convenient way of categorizing the elements of the natural world.

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The Linnaean system classified nature within a hierarchy, starting with three kingdoms. Kingdoms were divided into Classes and they, in turn, into Orders, which were divided into Genera (singular: genus), which were divided into Species (singular: species). Below the rank of species he sometimes recognized taxa of a lower (unnamed) rank (for plants these are now called "varieties").

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His groupings were based upon shared physical characteristics. Only his groupings for animals remain to this day, and the groupings themselves have been significantly changed since Linnaeus' conception, as have the principles behind them. Nevertheless, Linnaeus is credited with establishing the idea of a hierarchical structure of classification which is based upon observable characteristics.

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That's the nuts and bolts of it.What the theory of evolution has done is provide a reason for the physical characteristics to show nested heredity of traits, homologies, that can be traced back to common ancestors.The theory of evolution and descent from common ancestors does not necessarily predict or depend on life evolving from a single common ancestor, just that descendants from a common ancestor will share hereditary traits.The evidence - biological, genetic, fossil, etc - shows that life appears to have a single common ancestor population of simple single celled organisms. Exactly.Any newly evolved organism will de facto be descended from some previously existing organism that already belongs to a taxonomic branch, and it will never be classifies as anything other than a new species no matter how different it is.Taxonomy does not depend on the degree of difference, just on the hereditary relationships.Enjoy.ps - for you, and other new people, some format tips: type [qs]quotes are easy[/qs] and it becomes: or type [quote]quotes are easy[/quote] and it becomes:

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Exactly, and the reason is that the traditional classification system is becoming unweildy, that there aren't enough classification groups and new ones ARE being added:Cladistics - Wikipedia

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Prior to the advent of cladistics, most taxonomists used Linnaean taxonomy to organize lifeforms. That traditional approach, still in use by some researchers (especially in works intended for a more general audience[11]) uses several fixed levels of a hierarchy, such as Kingdom, Phylum, Class, Order, and Family. Cladistics does not use those terms, because one of the fundamental premises of cladistics is that the evolutionary tree is very deep and very complex, and it is not meaningful to use a fixed number of levels.

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(comparison table)Linnaean Taxonomy
Often must invent new level-names (such as superorder, suborder, infraorder, parvorder, magnorder) to accommodate new discoveries.

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That's part of the answer, the other part is how much opportunity exists for existing bacteria to evolve into multicellular life etc. With the diversity of life we know, most of those opportunities have already been taken, and the ecology includes predator prey relations that meke it difficult for a new one to evolve.Enjoy.

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