Re: News: Darwin's Tree of Life May Be More Like a Thicket

On Jan 29, 3:04=A0pm, "Robert Karl Stonjek" <rston...@xxxxxxxxxxxxxx>
wrote:
Darwin's Tree of Life May Be More Like a Thicket
January 27th, 2009 in General Science / Biology

(PhysOrg.com) -- In On The Origin of Species, Darwin used the image of a
tree of life to illustrate how species evolve, one from another. Even tod=
ay,
branches sprouting from lower branches (representing ancestors) is how ma=
ny
people view the evolution of species.

However, for some time, evolutionary biologists have known that the pictu=
re
is not quite so clear. A recent feature article in New Scientist
investigates the current views of biologists - that organisms may pass
traits not just to their offspring, but to other living organisms - and
suggests that uprooting the tree of life may be the start of a revolution=
ary
change in biology.

The possibility that evolution isn't as clear as the tree of life is not =
a
brand new idea to biologists, but it has slowly risen from various studie=
s.
In the 1950s and following decades, the discovery of DNA, RNA, and protei=
n
sequences revealed that species once thought to be near each other on the
tree are in fact quite different, molecularly speaking. In the early '90s=
,
scientists had hoped that gene sequencing would help them piece together =
the
tree of life, but instead it showed conflicting results. For instance, so=
me
species that are closely related based on their DNA are not closely relat=
ed
at all based on their RNA.

In order to make sense of the conflicts, biologists had to reconstruct
Darwin's tree, which assumed that organisms primarily pass their traits d=
own
to their offspring. Besides this "vertical" gene transfer, organisms may
also share traits through "horizontal" gene transfer with other species, =
or
even by reproducing with other species to produce genetic hybrids.
Horizontal transfer and hybridization would result in a web of life, with
species sharing some traits but not others, as the molecular evidence sho=
ws.
Perhaps, the tree of life is just a way for humans to classify nature, as
biologist W. Ford Doolittle has suggested.

Today, biologists disagree on whether horizontal gene transfer plays the
prominent role in evolution, or if it just adds noise and makes it diffic=
ult
to pinpoint the complex branching of the tree of life. Some scientists th=
ink
that horizontal gene transfer may accurately explain the evolution of the
simple organisms such as bacteria, archaea and prokaryotes such as amoeba=
,
but that complex animals evolve vertically. But considering that these
simple organisms make up 90% of all species, and have been around for 3.8
billion years whereas multi-cellular organisms appeared just 630 million
years ago, a linear tree of complex creatures would be more like a small
offshoot of the overall web.

But more recently, evidence suggests that complex organisms also have an
evolutionary history of horizontal gene transfer and hybridization. It se=
ems
that viruses are constantly cutting and pasting DNA from one genome to
another; in humans, up to half of our DNA may have been imported
horizontally by viruses. In addition, hybridization occurs more commonly
than previously thought. Evidence even shows that early Homo sapiens may
have hybridized with some extinct related species, such as Homo erectus a=
nd
the Neanderthals.

While this interrelatedness makes evolution more complex than originally
thought, vertical processes still explain how multi-cellular organisms ar=
e
related to each other pretty well - so the tree is still useful, but just
for parts, not the whole. More significantly, understanding the complexit=
y
of evolution's branches may reveal that biology overall is more complex t=
han
it seems. As New Scientist points out, the field of biology is looking
remarkably similar to that of physics around 1900 - just before
groundbreaking discoveries in relativity and quantum mechanics
revolutionized the field and the way we view the physical world.

via: New Scientisthttp://www.physorg.com/news152274071.html

Posted by
Robert Karl Stonjek

Very interesting. I still think my analogy of water down a mountain is
better than a tree.
It suggests first an outside source - the cyclical sun that pumps in
energy (water coming down)
then the paths down the mountain can run out, or merge, much like
life. I like it better.

.

Relevant Pages

  • Darwin Was Wrong (Apparently)
    ... Why Darwin was wrong about the tree of life ... Read our related editorial: Uprooting Darwin's tree ... time he published On The Origin of Species 22 years later, ... Without it the theory of evolution would never have happened. ...
    (talk.origins)
  • Re: Darwin IS Wrong (OBVIOUSLY)
    ... Why Darwin was wrong about the tree of life ... Read our related editorial: Uprooting Darwin's tree ... time he published On The Origin of Species 22 years later, ... Without it the theory of evolution would never have happened. ...
    (talk.origins)
  • Re: Darwin Was Wrong (Apparently)
    ... Why Darwin was wrong about the tree of life ... Read our related editorial: Uprooting Darwin's tree ... time he published On The Origin of Species 22 years later, ... Without it the theory of evolution would never have happened. ...
    (talk.origins)
  • News: Darwins Tree of Life May Be More Like a Thicket
    ... Darwin's Tree of Life May Be More Like a Thicket ... tree of life to illustrate how species evolve, ... However, for some time, evolutionary biologists have known that the picture ...
    (sci.bio.evolution)
  • Re: Part 1 (of 3): What are major aspects of evolutionary theory?
    ... But if I have an unrooted tree, ... > branching node adjacent to Harrietphyta is only around 65-70 million ... > extremely long-lived species which is ancestral to the branch point ...
    (talk.origins)