Molecular phylogeny

Note also that the number of trees rapidly reaches very large numbers: for 10 sequences there are over 34 million possible rooted trees. For a relatively modest 20 sequences there are 8,200,794,532, 891,637,559,000 possible trees, whereas the number of different trees for 135 human mitochondrial DNA sequences used in the study of the evolution of modern humans (see Chapter 4), 2.113 10^267, exceeds the number of particles in the known universe! This explosion in number of trees is a fundamental problem for phylogeny reconstruction, where the goal is to identify which tree of all the possible trees is the best estimate of the actual phylogeny. pg. 18Page and Holmes 1998. Molecular Evolution: A Phylogenetic ApproachI am trying to better understand the scientific evidence for common descent but am a layman.
Can anyone "dumb this down" for me?Thanks

Do you have more context? That bit is chopped off a bit too small for the likes of me. The preceeding couple of paragraphs would help.A wild assed guess it that they are looking at variances in gene sequences and trying to reconstruct what a base was from which the extant sequences evolved. But there are a lot of different possible combinations to consider. (LOL, "a lot" being something of an understatement).

Thanks for the reply Ned. I don't have any more unfortunately.
But prhaps I could explain some more. The quote was given to me in an attempt to illustrate something in regard to nested heirarchies and evidence for men and chimps sharing a common anscestor.
I really am a layman and am not even sure I understand the terms but would like to understand the science , and why this shows that "evilutionists" are being reasonable in their conclusions.p.s. I am a cretinist at the moment but want to try to understand the evidence for common descent.

Hi Judge,Imagine you have gene sequences from ten different species, & are attempting to infer a phylogeny from the nucleotide sequences. There are 34,459,425 different ways you could connect these 10 species into a tree, but there is only one true reconstruction. This is why cladistic/phylogenetic analyses are such good evidences of evolution; they consistently return similar results which are highly unlikely (/understatement) if evolution hadn't occurred.The computing power required to search all 34,459,425 trees & tell you the most parsimonious one(s) is considerable. The larger the number of taxa the greater the problem. There comes a point where it just takes too long to find the most parsimonious tree, even on the most powerful computers it can take more time than the universe has existed for larger trees! In cases like these tree builders turn to heuristic methods to infer phylogenies. Basically this greatly speeds up the process at the potential expense of precision. It works by looking at a small subset of the tree & finding optimal solutions from that, in the hope that the subset is indicative of the tree as a whole. It then finds the most parsimonious tree from the shortlist.Hope that helped.Mark[This message has been edited by mark24, 04-04-2004]

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"Physical Reality of Matchette’s EVOLUTIONARY zero-atom-unit in a transcendental c/e illusion" - Brad McFall

Judge,Hope this isn't too late. I just found this site today. I wouldn't worry about the math too much. Like Mark24 said, there are millions of combinations in how you could potentially group the species. Just like the lottery that has only 6 two digit numbers can produce tens of millions of different combinations.But I would point out that you don't need to worry about the details. We know that humans and chimpanzees had a recent common ancestor because of all the animals on earth, chimpanzees are the most similar to humans both anatomically and genetically. Note also that the goal of phylogenetics is not to prove that evolution is true, or even likely. It is a tool that evolutionary biologists use. Phylogenetics assumes, quite rightly, that all of the species you are examining originated by descent from a common ancestor.Good luck. Page and Holmes' book is not really geared toward the layman.Mike

Oh Fudge!Now, we have 2 Mike's.

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The Laminator

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Crap. I thought when I registered if there was another Mike it wouldn't let me.

There's this guy Mike The Wiz, but we called him Mike because he was the only Mike.Don't worry, I doubt we'll be confused. You can be Mike now and I guess we'll call the other one "Wiz." Welcome aboard, btw.