Here is an Electronic Telegraph story based on a forthcoming NATURE
article that claims that the tree of life has just had to have a drastic pruning
(more like chain-sawing!), based on genetic data.
Basically its gone from this 5-branched tree (view with monospaced font):
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MORPHOLOGY-BASED TREE OF ANIMAL RELATIONSHIPS
Verteb- Lamp Insects Seg- Moll- Unseg- Jelly
rates shells | mented uscs mented fish
| | | worms | worms |
| | | | | | |
------- ------- | | |
| | | | |
1 2 3 4 5
| | | | |
--------------------------- | |
| | |
|-------------------- |
| |
|---------------------------
|
----------------------------------------------------------
to this 3-branched tree:
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MOLECULAR-BASED TREE OF ANIMAL RELATIONSHIPS
Verteb- Insects Unseg- Seg- Moll- Lamp Jelly
rates | mented mented uscs shells fish
| | worms worms | | |
| | | | | | |
| -------- ------ | |
| | | | |
| ----------------------- |
| | |
1 2 3
|---------------| |
|--------------------------
|
Three major lineages:
Deuterostome
Ecdysozoan
Lophotrochozoan
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One big change is that vertebrates are much deeper in the tree of life than
first thought (presumably well before the Cambrian Explosion?).
If relationships can change so much, one wonders how much
paleontologists can really tell from fossils which is ancestral to which
without the soft parts? It will be interesting if paleontologists take this lying
down. I wonder what spin the good doctor Spin Jay Gould will put on it? :-)
Also, it would seem not take much to have three separate trees with no
actual universal common ancestor as origin-of-life specialist Carl Woese
(Proceedings of the National Academy of Sciences USA, Vol. 95, June
1998:6854-6859), has maintained:
Vertebrates Invertebrates Jellyfish
| | |
| | |
| | |
| | |
| | |
? ? ?
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Genetic blueprints of animals help to prune the tree of life
By RogerHighfield
THE century-old family tree of the animal kingdom has been felled by
scientists who have worked out the relationships between creatures by
studying their genes.
For more than 100 years, scientist have depended on animal morphology
form and structure - to determine their place on the tree. But over the past
few years, a new tree has been proposed based on comparisons of genetic
blueprints.
Click to enlarge
Writing in the journal Nature, scientists from the University of
Wisconsin-Madison, the University of Paris, Cambridge University and St
Petersburg University, Russia, report the discovery of a common genetic
theme that provides powerful new evidence to firmly place nearly all
animals - from molluscs to humans - on a three-limbed tree of life. It
simplifies the previous animal kingdom family tree by substituting one
branch in place of many offshoots first suggested through anatomical
comparison.
Their work substantiates earlier genetic investigations suggesting that the
vast majority of animals belong to one of three primary evolutionary lines,
rather than the multiple branches suggested by earlier studies. And it
suggests that genetic analysis could reveal something about the genes of
the common ancestor of all animals that lived more than 600 million years
ago.
The animal fossil record stretches back to 540 million years ago, so
scientists have no clue as to what this ancestor looked like. The new
genetic evidence suggests that in the animal kingdom three primary lines of
descent first diverged from a common ancestor and that gave rise to most
animals (with the exception of jellyfish and sponges) living today, said
Jennifer Grenier, the lead author.
The study was based on exploration of so-called c which comprise part of a
toolbox that is central to animal development. They help organise cells into
the different body parts and determine such things as number and
placement of legs, wings and other appendages.
The team studied the genes in three distinct kinds of animals: the
Americans decoded the Hox genes of a priapulid, a little-known marine
worm of enigmatic evolutionary heritage, which looks like a small, squishy
feather duster. Researchers at the University of Paris studied the Hox genes
of a brachiopod (lamp shell), an ancient marine animal that looks like a
clam. Scientists at Cambridge University worked on a polychaete, a marine
relative of earthworms and leeches.
By looking for, and finding, essentially the same critical organising genes in
seemingly unrelated animals, the groups could, in essence, look far back in
time and infer what critical body-organising genes were present in a
common ancestor. Closely related animals should share a similar
assortment of Hox genes, while more distant relations have fewer in
common.
By comparing the assortments of Hox genes found in the three species to
those found in previously studied animals - including mice, fruit flies,
leeches, and sea urchins - the team confirmed the division of the animal
kingdom into three primary evolutionary lines. On the new, gene-based
tree, animals with backbones are on the same branch as starfish and their
relatives - a longstanding classification.
But the new tree reorganises almost all of the remaining groups of animals.
Animals that moult, such as crustaceans, insects, roundworms and
priapulids, now sit together on a second branch.
[...]
http://www.telegraph.co.uk/et?ac=000113078204876&rtmo=kJJ7YA7p&a
tmo =YYYYYYkp&pg=/et/99/7/1/ecngene01.html
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"The gaps in the record are real, however. The absence of a record of
any important branching is quite phenomenal. Species are usually
static, or nearly so, for long periods, species seldom and genera never
show evolution into new species or genera but replacement of one by
another, and change is more or less abrupt..." (Wesson R.G., "Beyond
Natural Selection," [1991], MIT Press: Cambridge MA, 1994, reprint, p45)
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