Evolutionary Origins of Flight
Threads - Evolutionary Origins of
Flight, Flights - of Fancy
On
23/1/2003, Paul Williams posted:
Recently we talked about dino/bird flight origins.
The evolutionary process is often educated guess work.
Without dinosaur DNA this appears to be an unchanging difficulty.
Nevertheless, new fossil evidence, particularly from China*, is
delightfully muddying 'the waters':
Chinese Fossils*
http://www.abc.net.au/science/news/stories/s767860.htm
There may be some thoughts that all (now 3) theories regarding
dino/bird flight origins are 'correct'.
i.e: - Different species may have found different pathways to fill this
important environmental niche.
The DNA differences between extanct birds may indicate that only one
line survived though.
I do not know whether we know enough to judge?
Examples of different 'lines' becoming adapted through different
pathways to a 'new' environment may be manatees, dugongs, seals,
penguins and dolphins/whales?
The insect world is full of flight adaptions. One arguement for
multiple wing evolution amongst stick insects is just that - arguable:
http://www.abc.net.au/science/news/stories/s764855.htm
This one I doubt. Usually once an adaption is lost, it appears to be
lost forever.
Gills for example.
Different pathways may be used though.
Also, maybe 'junk DNA' is not junk at all?
Bats appear to have 'invented' flight twice...
Any thoughts?
Peter Macinnis
replied:
>This one I
doubt. Usually once an adaption is lost, it appears to be lost
>forever.
>Gills for example.
>Different pathways may be used though.
Not necessarily -- it may be that
the key gene is merely repressed -- so if the repressor is repressed, it
may spring back. A key refutation is found in paedomorphism,
where a "juvenile" form in the ancestor becomes the norm in a descendant.
You never know what might come
back :-)
Ray added:
Paul, the more I
learn about DNA and additional suspicion developing for the view that
transmission of phenotype information can be sequenced through the
histone and nucleosome of the chromosomes as well as DNA-RNA, the more
it looks like only very minor differentiations are required for big
changes.
Growing
understanding of genetics tends to confirm the theory of Evolution, I
think, when as little as 0.25% of the genome is all which separates two
people as different as pigmy and sumo wrestler.
I believe wings
are virtually just extra long fingers and webbing, and an extra long
developing period for humans than lemur gives us a larger brain than
them.
We may discover
gene medication is working on something so subtle and yet precise, that
an ion out of place spells mutation, be it advantage or disaster.
Podargus
responded to Ray:
>
I believe wings are virtually just extra long fingers and webbing,
In
bats yes, but you must have seen a bird, or an insect?
and
to Paul:
>
The insect world is full of flight adaptions. One arguement for multiple
> wing evolution amongst stick insects is just that - arguable:
> http://www.abc.net.au/science/news/stories/s764855.htm
>
> This one I doubt. Usually once an adaption is lost, it appears to
be lost
> forever.
The
idea here is not that the genes for the adaptation are lost, rather the
genetic switch is off. If this is only one gene then it may be
'easy' to switch it back on.
Paul replied to
Podargus, and Zero Sum:
A better example
- plainly seen is the (giant) "panda's 'thumb' " - made famous by S. J.
Gould in his essay of the same name.
Briefly - the
true thumb is lost - the ability to resurrect it is lost. New niche
produces need for a thumb. - A different pathway is used - hence a bony
projection is used in lieu.
> > Different pathways may be
used though.
> >
> > Also, maybe 'junk DNA' is not junk at all?
> >
> That is not junk it is an unused, unindexed (and probably
unmaintained)
> library,
I believe that
this may well be correct.
> > Bats appear to have
'invented' flight twice...
> >
> That I hadn't heard. Any URL?
Yes.... This
hypothesis is arguable - of course :-)
http://tolweb.org/tree/eukaryotes/animals/chordata/mammalia/chiroptera/chiroptera.html
Relevent quote:
-------
"The bat
monophyly hypothesis states the Megachiroptera and Microchiroptera are
each others closest relatives in an evolutionary sense (i.e., they form
a clade). If this is true, then their shared characteristics, including
the ability to fly, would have been present in their most recent common
ancestor (Simmons, 1994; 1995). It follows from this that there was only
one origin of powered flight in
mammals.
In contrast, the
diphyly hypothesis states that megachiropteran and microchiropteran bats
do not form a monophyletic group, instead having evolved independently
from two different groups of non-flying mammals. It has been suggested
that Megachiroptera is more closely related to Dermoptera and Primates
than to Microchiroptera (Smith and Madkour, 1980; Pettigrew, 1986,
1991a, b, 1995; Pettigrew and Jamieson, 1987; Pettigrew et. al., 1989).
In this case, the characteristics common to both groups of bats either
evolved as a result of convergent evolution or are simply the result of
retention of primitive features. If bats are diphyletic, the ability to
fly must have evolved once in Megachiroptera and again in
Microchiroptera."
-----
More recently
this possible close relationship of Megachiroptera with primates has
been called into question....:-)
Ray
commented:
>
I believe wings are virtually just extra long fingers and webbing
>>In bats yes, but you must have
seen a bird, or an insect?
In
pterosaurs too, I think Podargus.
>From
there I'd guess birds too. ?? not sure, but don't birds have vestigial
phalanges?
Insects
use other systems than muscles for motion, I believe (kind of a
biochemical explosion), so for them flight, like walking, is a totally
different mechanism.
Which
would figure since their skeletal support is external.
Paul Williams
replied:
>
<snip>
> > The insect world is full of
flight adaptions. One arguement for multiple
> > wing evolution amongst stick insects is just that - arguable:
> >
http://www.abc.net.au/science/news/stories/s764855.htm
> >
> > This one I doubt. Usually once an adaption is lost, it
appears to be lost
> > forever.
>
> The idea here is not that the genes for the adaptation are lost,
rather the
> genetic switch is off. If this is only one gene then it may
be 'easy' to
> switch it back on.
This certainly
sounds credible.
My difficulty in
accepting this is not knowing any examples demonstrating this mechanism.
(Not to mention
my poor grasp of genetics in the first place)
Why do sea going
mammals not have gills? (They would be extremely advantageous I believe)
My thoughts are
that the information to make same is lost - or perhaps irretrievable.
To retrieve
information requires a search 'programme' - perhaps this programme
itself is lost or corrupted. (RNA appears to be the likely programme
vehicle).
Perhaps the
information can no longer be inplemented into the new complexity of the
animal.
I don't know.
Ian
Musgrave posted:
>Ray
wrote
> >>> I believe wings are
virtually just extra long fingers and webbing
>Podgardus wrote
> >>In bats yes, but you must
have seen a bird, or an insect?
>
>In pterosaurs too, I think Podargus.
Yes,
Pterosaurs and Bats use both long fingers and webbing (but in different
ways) AND arms, but birds and insects do not
>
From there I'd guess birds too. ??
Ever
seen a plucked chicken in a butcher or supermarket? Note the lack of
webbing. (or a living bird, such as pigeons and sparrows or magpies,
note again the lack of webbing)
>not
sure, but don't birds have vestigial phalanges?
Vestigial
phalanges wouldn't be very useful for supporting webbing or flight, as
the surface area would be too small.
Again,
look at a plucked chicken in a butchers shop, or inspect the bones of a
cooked chicken wing after you have munched on it. Birds have only three
of the "standard" five vertebrate digits, two of these three fuse at an
early embryonic stage, forming effectively a largish bony strut
projecting from the wrist (how large depends to the birds mode of
flight, gliders tend to have longer digits that rapid flyers).
In
Bats and Pterosaurs, the flight surface is membrane stretched between
the body and the arm (and between the fingers in the bat). In birds, the
flight surface is made up of feathers attached to the trailing edge of
the arms and finger (the feathers on the leading edge play a role too,
but in a more complicated way). In insects, the wings are probably
modified gill covers.
For
a good (if now dated, due to the amazing Chinese feathered dinosaur
finds, including our new 4 "winged" friend) overview of how flight works
in birds and bats and so on, and ideas on the evolution of flight, I
can heartily recommend "Taking Wing" by Pat Shipman. This deals
comprehensively with things that are too detailed to go into here.
>Insects
use other systems than muscles for motion, I believe (kind of a
>biochemical explosion),
What
utter rubbish, insects use muscles just as vertebrates do.
>so
for them flight, like walking, is a totally different mechanism.
Insect
flight _is_ very different to vertebrate flight, if only due to the
scale involved, airfoil like systems for generating upward thrust don't
work. Nonetheless insects still flap their wings via muscular activity
as do vertebrates (even if it is weird vortex effects that provide lift).
>Which
would figure since their skeletal support is external.
Just
means that the muscles are attached on the inside.
and in response to Zero Sum:
re
loss and gain of insect wings in mantids]
>
> This one I doubt. Usually once an adaption is lost, it appears to
be lost
> > forever.
Usually
being the word. Because in the absence of selection the many genes that
make a complex structure get mutated to uselessness relatively rapidly
(as there are so many genes to hit, mutations occur in more than one,
and multiple mutations are less likely to reverse).
But
in this case there are two circumstances that make it more likely.
1)
"wing loss" in many of the mantid lineages means only that the wing
doesn't function, and is still present (or is present, functionally, at
an early stage of development). In many cases total, complete wing loss
is rare. So there are structures that can be rescued by simple mutations
in most lineages.
2)
The regulatory genes involved in "making" mantid wings have other
important roles in Mantid development. The genes are not broken so much
as turned off when wings should develop. It's relativelyeasy
to reverse this kind of mutation.
> > Gills for example.
>
>Uhmm,,, Axolotls? Don't quite fit, but...
>
> > Different pathways may be
used though.
> >
> > Also, maybe 'junk DNA' is not junk at all?
> >
>That is not junk it is an unused, unindexed (and probably
unmaintained)
>library.
Sorry,
but junk DNA is just that, junk. The largest percentage of non-coding
DNA is mostly things like huge numbers of copies of ALU repeats and
other short pieces of highly repetitive DNA, LINES and SINES and so-on
(If it's a library, it's a library crammed with books whose pages
are filled with the DNA equivalent of "UmmErrr"). This is followed by
broken bits of viral genes, then by broken bits of the organisms genes.
Real, quiescent genes are a minute fraction of the total non-coding DNA.
Some
non-coding DNA that functions as control sites and so on (and there is
also the introns, bits of code in the middle of the gene that gets cut
out and thrown away, most of this has no function, but some introns
function as binding sites for regulatory genes, and some of the thrown
away code functions as small nucleolar RNA.), but well over 95% of
non-coding DNA is just junk.
Podargus added:
> > I believe wings are virtually
just extra long fingers and webbing
> >>In bats yes, but you must
have seen a bird, or an insect?
>
> In pterosaurs too, I think Podargus.
> From there I'd guess birds too. ?? not sure, but don't birds have
vestigial
> phalanges?
Yes they do, but
no membrane. Birds use feathers to give an airfoil section that is
very efficient. Membranes are commonly used to give gliding
flight. This however means some height is required to 'take off'.
Even bats have this limitation, they need to flap first so as to be more
or less horizontal before they can fly. They need to get air
under the wing to achieve a airfoil shape in much the same way a fore
and aft sailing boat does to move into or across the wind.
> Insects use other systems than muscles for motion, I believe (kind
of a
> biochemical explosion), so for them flight, like walking, is a
totally
> different mechanism.
I am not sure
what you are getting at here. They still use muscles.
>
Which would figure since their skeletal support is external.
To which the
muscles are attached.
and to a post
from Kevin Phyland
>
Sorry to drag this fascinating convo slightly off-course but
> your comment about vortex effects being important for insect
> flight rang some distant bells...
>
> I vaguely recall watching a doco sometime ago where they
> likened air to a viscous liquid as far as insect scale or
> smaller organisms were concerned and wonder whether the old
> (possibly apocryphal) tale of engineers "proving" that a
> bumblebee couldn't possibly fly was based on macro-scale
> application of aerodynamics rather than turbulence??
>
> Any ideas one way or another?
There is a
reasonable answer to the above here
http://www.iop.org/Physics/News/Archive/0012i.1
Paul
Williams posted:
>
[re loss and gain of insect wings in mantids]
<snip>.
Thanks
Ian,
I've
just studied the Nature 'letter' (pdf) and have lifted the following
paragraphs.
I
no longer doubt (much) this turning on of this ancestral state.
"Entomologists
have long assumed that re-evolution of wings in apterous lineages was
impossible, because functional wings require complex interactions among
multiple structures, and the associated genes would be free to
accumulate mutations in wingless lineages, effectively blocking the path
for any future wing reacquisition.
However,
this assumption requires that developmental pathways for wing formation
are largely independent of pathways required for development of other
structures. For instance, in Drosophila and other insects, leg and wing
imaginal discs have a common origin from a single group of cells and the
developmental pathway for wing determination has been largely co-opted
(recruited) from the pathway required for limb formation
Therefore
it is not surprising that the basic genetic instructions for wing
formation are conserved in wingless insects, because similar
instructions are required to form legs, and probably other critical
structures.
Studies
of flight motor patterns in flying and non-flying phasmids indicate
that the non-flying phasmids have retained the neural
structures
and basic functional circuitry required for flight, as indicated by
flight-specific neural activity in thoracic muscles
demonstrating
that the loss of wings does not correlate with the loss of flight
musculature and innervation."
Click
on - "Wing evolution in stick insects" then the pdf file.
http://www.nature.com/evoeco/
> > > Gills for example.
> >
> >Uhmm,,, Axolotls? Don't quite fot, but...
> >
> > > Different pathways may
be used though.
> > >
> > > Also, maybe 'junk DNA' is not junk at all?
> > >
> >That is not junk it is an unused, unindexed (and probably
unmaintained)
> >library.
> Sorry, but junk DNA is just that, junk. The largest percentage of
> non-coding DNA is mostly things like huge numbers of copies of ALU
repeats
> and other short pieces of highly repetitive DNA, LINES and SINES
and so-on
> (If it's a library, it's a library crammed with books whose pages
are
> filled with the DNA equivalent of "UmmErrr"). This is followed by
broken
> bits of viral genes, then by broken bits of the organisms genes.
Real,
> quiescent genes are a minute fraction of the total non-coding DNA.
>
> Some non-coding DNA that functions as control sites and so on (and
there
is
> also the introns, bits of code in the middle of the gene that gets
cut out
> and thrown away, most of this has no function, but some introns
function
as
> binding sites for regulatory genes, and some of the thrown away
code
> functions as small nucleolar RNA.), but well over 95% of
non-coding DNA is
> just junk.
Not
that I wish to argue for or against this...but :-) There are hypotheses
around which may lead one to feel that not all is junk - or if it is all
gobblygook it still functions as a buffer to separate coding sequences.
One problem is the size of genomes does not indicate complexity.
For instance (as recouted in the Harvard site below) an onion has 12
times the DNA of humans. The reason appears to be that some
species delete non coding sequences often. Others faithfully copy
everything and the non coding sequences build up over time.
This
leads one toward the conclusion that non coding sequences really are
just junk.
I
guess the jury is still out, but a 'philosophy of efficiency' appears
to be driving the 'not junk' believers.
Although...
James
A. Shapiro has some interesting ideas on genome system architecture and
natural genetic engineering. Unfortunately my background knowledge is
still too weak to fully understand much of his writings.
Very
brief comments by the genome sequencers on junk DNA:
http://www.wired.com/news/technology/0,1282,41750,00.html
A
fairly light-hearted look at non coding DNA by Dr. Karl:
http://www.abc.net.au/science/k2/moments/s133634.htm
Harvard
biologists say probably junk:
http://www.news.harvard.edu/gazette/2000/02.10/onion.html
I
do not pretend to fully understand Shapiro's papers but he has some
interesting
thoughts on DNA and natural genetic engineering:
http://shapiro.bsd.uchicago.edu/index3.html?content=publications.html
"The
genome is the long-term storage medium for each species (much like a
computer hard disk) and consists of the total information content of the
DNA molecules in the cells of that species. Although most genomics
researchers focus on the "coding" regions of the genome that determine
the proteins a species can synthesize, genomes are built up of
protein-coding and other classes of DNA sequences that are
combinatorially formatted to carry out the multiple tasks necessary for
overall genome function (Table II). While textbooks call the triplet
code for amino acids in proteins "the genetic code," there are in fact
many genetic codes for the different aspects of genome coding,
packaging, replication, distribution, repair and evolution."
Chris Lawson
responded:
>Why
do sea going mammals not have gills? (They would be extremely
>advantageous I believe)
>My thoughts are that the information to make same is lost - or
perhaps
>irretrievable.
>To retrieve information requires a search 'programme' - perhaps this
>programme itself is lost or corrupted. (RNA appears to be the likely
>programme vehicle).
>
>Perhaps the information can no longer be inplemented into the new
complexity
>of the animal.
>
>I don't know.
There is a
*very* large evolutionary gap between the sea-going mammals and the
fishes. So long, in fact, that one would not expect the old genes for
gill development and function to be even close to functional. The only
ones still in use would be ones that had adapted over time to other
functions, and therefore not easily turned back into gills. The idea
behind junk DNA
being a library
of disused genes has some appeal, but genes that are never critical to
the organism's life success will decay over time, and the longer the
decay process, the more degraded the gene, with an endpoint of being
essentially noise or having been lost to the organism altogether.
and replying to
Kevin:
>(possibly
apocryphal) tale of engineers "proving" that a
>bumblebee couldn't possibly fly was based on macro-scale
>application of aerodynamics rather than turbulence??
>
>Any ideas one way or another?
I don't know if
there ever was an engineer who said bumblebees couldn't fly, but there
are several things that may not have been accounted for. The first is
the viscosity of air on the insect scale, as you point out. Another is
that insects, unlike aircraft, don't have rigid wings, and the wing
changes shape as well as angle of upstroke vs. downstroke. This means it
gets a lot more oomph out of the downstroke than it gets drag out of
the upstroke. Mind you, this ought to be bleeding obvious and applies to
all
flying
creatures. If you have a rigid wing with a fixed angle of attack, then
you can only glide, you can't fly, because by definition the lift
generated by flapping down will be undone by the upstroke.
Steve Van Z queried:
Is this the
reason that there is so much "junk" in our genetic code? Genes that have
done their duty and are now switched off? If this is true, what would
happen if scientists were successful in switching genes on again?
Or am I talking
a lot of nonsense? Like sprouting wings?
Ray added:
>>If
you have a rigid wing with a fixed angle of attack,
then you can only glide, you can't fly, because by definition the lift
generated by flapping down will be undone by the upstroke.
Isn't insect
flight to the helicopter as bird flight is to the aeroplane?
At least I
recall hearing somewhere that the helicopter was modelled on the flight
of dragonflies.
PS ..and
aren't gills, if non-functional, evident in the early embryo of all
vetebrates including humans?
and:
Actually Stevan,
it is the junk DNA which provides for the forensic distinction between
individual DNA samples. The functional DNA which templates for the
RNA to synthesise a particular protein (like amylase or haemoglobin) is
pretty much the same sequentially from one human individual to another,
and it is the stuff which appears to do nothing which differentiates.
Were it not for
Junk DNA, it would be considerably more difficult to distinguish one
person from another through bands of DNA segments in an electrophoresis
gel.
Just for the
record. The above information surprised me when I first learned of
it a few months ago too.
Ian
Musgrave responded:
No.
In the human genome, something like 95% of the DNA is non-coding (ie it
doesn't code for an expressed or potentially expressable gene, whether
protein of things like small RNA subunits of ribosomes). Of that,something
like 95% represents multiple copies of veryshort
to short DNA segments (for example the ALU repeat sequence). Most of
these short sequences seem to be a kind of "parasite" DNA. Broken genes,
that can potentially be turned on again, represents a small fraction of
the junk DNA (but is a surprisingly large faction of working coding
genes). Seriously broken genes that can't be turned on again, like the
stub of the gene that synthesises ascorbic acid in other animals,
represent a larger fraction of the junk DNA, broken viral genes are
also abundant.
Certain
amoeba have around 5 times as much junk DNA as humans, most of this
represents these short repeats.
>Genes
that have
>done their duty and are now switched off? If this is true, what
would
>happen if
>scientists were successful in switching genes on again?
Depends
on what the genes were and how long they had been turned off. Other
dependent pathways may have been mutated to uselessness.
>Or
am I talking a lot of nonsense? Like sprouting wings?
Could
happen, depends on the pathway. Researchers have managed to get chicks
to grow tooth buds again.
and:
A
very elderly follow-up, but it may be worth it for bird evolution
afficionadoes.
At
07:28 23/01/03 +1000, you wrote:
>Recently we talked about dino/bird flight origins.
>The evolutionary process is often educated guess work.
>Without dinosaur DNA this appears to be an unchanging difficulty.
>Nevertheless, new fossil evidence, particularly from China*, is
delightfully
>muddying 'the waters':
>Chinese Fossils*
>
http://www.abc.net.au/science/news/stories/s767860.htm
>There
may be some thoughts that all (now 3) theories regarding dino/bird
>flight origins are 'correct'.
>i.e: - Different species may have found different pathways to fill
this
>important environmental niche.
Or
that different mechanisms may have been involved in different stages.
The
question that has been debated for may years is how did bird flight
evolve.
Did
they start as arboreal gliders and move to flapping flight or did they
start as runners and evolve flight as an adjunct to running?
Gliding
to flying is an obvious path, and bats have taken this path (with
obvious intermediates seen in various flying squirrels and possums
etc.). However, if birds evolved from dinosaurs such as the
coeleosaurians (from skeletal evidence and the discovery of
coeleosaurian dinosaurs with true feathers), these are predominantly
runners and until a year ago there was no evidence that any were
climbers. To glide, one has to get into the trees (or other high
objects) to do so. How did bird ancestors do it? Especially since the
nascent wings of birds prevent the kind of climbing flying
squirrels/possums
use. Also, Archaeopteryx doesn't seem to have specific arboreal
adaptions. If they started as runners, how did proto-wings evolve to the
point that they could be used in flapping flight? We have no existing
plausible intermediates like flying possums in this instance.
The
Wing Assisted Incline Running solves this problem. It shows that
proto-wing could be used for things other than flight, and specifically
to get running birds up near vertical trees. Once in the trees the
proto-wing could be then used for gliding. Mircoraptor gui (represented
by six fossils) is just such a gliding beast (and there is at least one
other feathered
dinosaur that was arboreal see
http://www.luisrey.ndtilda.co.uk/html/chinesenov.htm
for a reconstruction).
Microraptor
gui is probably not representative of the final common ancestor of
birds, but it shows that gliding is a viable option for the origins of
bird flight.
So
it looks as if our theories are all correct. Birds started as runners,
using their proto-wings for things like balance and stability while
running, this allowed them to run up steep tree trunks into high
positions where they could become gliders, then flappers.
Of
course, this model will have to be firmed up with more evidence, but
with the rate spectacular feathered dinosaurs, early birds and
proto-birds have been coming out of the Chinese fields, I'm sure we
won't have to wait long.
and:
At
12:42 24/01/03 +1000, Paul wrote:
>[snip loss and return of working genes]
>To retrieve information requires a search 'programme' - perhaps this
>programme itself is lost or corrupted. (RNA appears to be the likely
>programme vehicle).
Warning,
biology is not like engineering or computer programming, although
computer programming analogies are often used to illustrate ideas about
DNA replication and coding, it is a very limited anaology.
There
is no equivalent of a "search program" for activating working genes.
Transcription enzymes are made, bind to anything with an
appropriate "start" codon, and transcribe the gene. If the start codon
is mutated, no protein is made, if there is a mutation that makes the
protein non-functional, the protein is still made (if just doesn't do
anything). There is no indexing or table of contents in the
genome, and RNA is not a program vehicle.
and:
At
11:33 24/01/03 +1000, Kevin wrote:
>Hi Ian,
>[snip]
>I vaguely recall watching a doco sometime ago where they
>likened air to a viscous liquid as far as insect scale or
>smaller organisms were concerned and wonder whether the old
>(possibly apocryphal) tale of engineers "proving" that a
>bumblebee couldn't possibly fly was based on macro-scale
>application of aerodynamics rather than turbulence??
You
have already had a link to a good answer to this from Podargus. But the
short answer is that engineers and physicists knew that the equations
used for fixed wing aircraft wouldn't work for insects such as
bumblebees, but hadn't worked out what the appropriate factors were.
This mutated into the urban myth that scientists had proved that
bumblebee couldn't fly.
The
bumblebee is oddly wrought
aerodynamically
it ought
to
find it quite impossible to rise
but
bumblebees don't know the rules
bumblebees
don't go to schools
they
flies.
Paul Williams
replied:
>
There is no equivalent of a "search program" for activating working
genes.
> Transcription enzymes are made, bind to anything with an
appropriate
> "start" codon, and transcribe the gene. If the start codon is
mutated, no
> protein is made, if there is a mutation that makes the protein
> non-functional, the protein is still made (if just doesn't do
anything).
> There is no indexing or table of contents in the genome, and RNA
is not a
> program vehicle.
Thanks Ian.
Because my
knowledge is shot full of gaping holes - some may say 'yawning' chasms
:-) - I sometimes use inappropriate analogies.
I was thinking
about the fairly recent discovery of "microRNA genes".
'Newfound RNA
suggests a hidden complexity inside cells':
http://www.sciencenews.org/20020112/bob9.asp
"They developed
techniques to pick out RNAs about 24 nucleotides long, ones that
normally would get discarded in experiments because of their small size.
Tuschl's team identified 16 novel microRNAs in fruit fly embryos and 21
in human cancer cells."
" In the Oct.
26, 2001 'Science', Ruvkun speculates that "the number of genes in the
tiny RNA world may turn out to be very large, numbering in the hundreds
or even thousands in each genome. Tiny RNA genes may be the biological
equivalent of dark matter-all around us but almost escaping detection." "
---------------------
Reading and
attempting to understand James A. Shapiro's papers and then adding in
the possible roles of these short RNA strands into Shapiro's 'cellular
information processing', I'm probably developing erroneous hypotheses.
I should
probably take "J"'s doctor's advice in "Three Men in a Boat':
"1
lb. beefsteak, with
1 pt. bitter beer every 6 hours.
1 ten-mile walk every morning.
In bed at 11 sharp every night.
And don't stuff up your head with things you don't understand."
and :
>
So it looks as if our theories are all correct. Birds started as
runners,
> using their proto-wings for things like balance and stability while
> running, this allowed them to run up steep tree trunks into high
positions
> where they could become gliders, then flappers.
>
> Of course, this model will have to be firmed up with more
evidence, but
> with the rate spectacular feathered dinosaurs, early birds and
proto-birds
> have been coming out of the Chinese fields, I'm sure we won't have
to wait
> long.
Some years ago
now, we were breeding muscovy 'ducks'.
Haybales were
used as separators to the individual clutches and mothers.
Some chicks
burrowed*out between the intertices or the joining points of the bales.
Others would run
up the faces of the bales and escape as they (the ducks) matured.
Not all would do
this.
(The faces of
the bales were often not at right angles to the ground).
I've seen the
possible evidence but was too dense to understand the significance.
Something to be
said for video cameras...
No excuses - one
can look at things in almost infinitely variable ways.
Lack of
competition can lead to (at first) poorly adapted but often (as we can
now see) well adapted creatures to their environment. One modern example
is the tree kangaroo which one may easily describe as 'pathetic' and
due for extinction. :-)
We are biased
after seeing well adapted creatures.
When there is no
competition, tiny genetic changes can eventuallyend in 'brilliant'
adaptions.
Regarding
flight, it can be argued that merely the ability to perch at night may
have saved a (now changed) line from extinction.
It seems
reasonable to believe that predatory snakes (for example) took some time
to follow these food sources into a new environment - which would have
been dominated by insecta/food then. (There may, of course, have
been existing insectivorous snakes - or other predators - but they
would have still have had to adapt to this new food source)
So just a
controlled 'run up/flap and perch' may have been a wonderful start.
Ian
replied:
>[snip
interesting info on Musovy ducks running up bales]
>Lack of competition can lead to (at first) poorly adapted but often
(as we
>can now see) well adapted creatures to their environment.
>One modern example is the tree kangaroo which one may easily
describe as
>'pathetic' and due for extinction. :-)
Only
if you don't understand the biology. Tree kangaroos are very well
adapted for arboreal life in rainforest environments. We might thinkthey
are pathetic because they seem a bit slow to us, but they have survived
nicely for tens of millions of years, against backgrounds of massive
climate change. They are currently under pressure from habitat loss and
human incursion, but its hard to find a creature that isn't so
threatened (apart from standard possums and red and grey kangaroos).
>We
are biased after seeing well adapted creatures.
>
>When there is no competition, tiny genetic changes can _eventually_
end in
>'brilliant' adaptions.
Even
with competition, as competition can and does drive adaption. Tiny
changes can be the difference between life and death, in the case of
finch beaks a mere 1 mm is all that it takes.
Ian responded:
Yes, this is an
exciting finding that adds to our knowledge of the control of gene
transcription, the expanding role of RNA in the cell (did you know that
it is the RNA in the ribosome that splices together the amino acids, not
the protein component) and is additional evidence for an RNA world
being a step in the origin of life.
But the
mircoRNA's act in the same way as protein transcription factors.
Chris
Lawson added:
Only
if you don't understand the biology. Tree kangaroos are very well
>adapted for arboreal life in rainforest environments. We might
_think_ they
>are pathetic because they seem a bit slow to us, but they have
survived
>nicely for tens of millions of years, against backgrounds of massive
>climate change. They are currently under pressure from habitat loss
and
>human incursion, but its hard to find a creature that isn't so
threatened
>(apart from standard possums and red and grey kangaroos).
I
second that. We humans have a tendency to misunderstand many aspects of
evolutionary theory. One of the most common misunderstandings is
about "fitness", where we tend to impose our values on the term, rather
than the evolutionary meaning. As Ian says, tree kangaroos are *very*
well adapted to their ecological role. Slowness is only a problem if you
have fast predators or fast prey. Since tree kangaroos eat plants
(which are not noted for their speed) and have no large tree-hunting
predators, then it would be *wasteful* to run around as fast as they
could. Much like the sloth, they have evolved a slower way of life
because it suits their situation.
The
problem comes when the environment changes. Suppose a new predator
evolved in Australia (or was introduced) that hunted in trees. Then tree
kangaroos would be in trouble. But this sensitivity to environmental
change applies to almost all closely-adapted creatures.
The
classic example of people applying value terms to "fitness" is when you
see people complaining about how modern medicine is keeping alive people
who would have died in times past, thus "reducing the fitness of the
gene pool." But the Darwinian definition of fitness is that it
increases an organism's chances of passing genes onto the next
generation. So the Darwinian perspective is NOT that "unfit" genes are
sweeping into the gene pool, but that the environment has changed so
that these genes are no longer as deleterious. What's really happening
when people complain about "unfit genes" in the gene pool is they're
saying "I don't like seeing people with <insert condition>; it
makes me feel uneasy and I wish they wouldn't keep breeding; I can't say
that because I would be pilloried for being a bigot; so instead I will
(mis)use Darwinism and put it all in distant abstract terms to defend
my personal revulsion."
Paul Williams
replied:
I agree totally.
The tree
kangaroo is obviously well enough adapted to it's environment (because
it is extant).
When competition
comes (as Chris mentions below) a comparatively slower or less agile or
more 'stupid' creature (than the potential predator) may be in trouble.
A more
specialised tree dweller may outcompete the tree kangaroo(s) for food
resources.
_This of course
bears no relation to a creature's current fitness to it's
existing niche._
I withdraw my
above (quoted) loose comments - was trying to simplify things and this
was silly.
Now this is what
I was thinking:
When there is no
or little competition for an unfilled ecological niche, small adaptive
differences can make survival possible.
When competition
comes - as it almost always has done, comparative advantages will be
selected for.
We now see
incredibly well adapted (specialised) creatures and marvel at this.
One modern
example which appears (comparitively to other aboreal mammals) to be
only partially specialised is the tree kangaroo (2 species)
Some may see
this animal as poorly adapted. It has in fact become well adapted enough
to survive.
It is not as
specialised as some other aboreal mammals in climbing dexterity and
agility.
Arguably,
speciation often appears to occur in isolated populations. (Galapogas
finches for example)
Where there is
no competition, potentially rich unfilled niches will be filled over
time.
More specialised
animals would already occupy these niches in some other environments.
Competition
drives speciation and specialisation but lack of competitition drives
speciation as well.
Without
competition, an animal may well appear to us to be 'frozen' in it's
current form.
After speciation
environmental pressures - including predators or competitors for the
food resource or nesting site, or cave, or any number of things - can
and does drive specialisation.
In the case of
flight, a plethora of unfilled niches beckoned.
The early
adaptions did not have the impossible pressure of needing to be
instantly specialised.
Once a niche is
almost perfectly filled it is unlikely for a non specialised newcomer to
surplant the 'holder' of this niche.
We can be misled
in thinking that placentals are invariably 'better' than masupials or
ground dwelling birds.
South America wasarguably a good
example of ground dwelling birds outcompeting marsupials for various
niches.
Placentals
stuffed things up eventually.
In Australia
there is some evidence to show that marsupials outcompeted placentals a
long time ago.
Birds still
'ruled' the skies though - as they still do.
There is
something to be said for generalists.
There is
something to be said for the specialists.
Birds are
everywhere.
Viva the
generalists.
Birds are
everywhere.
Viva the
specialists.
Chris
Lawson posted:
Paul,
I think you missed my point.
I
was arguing that tree kangaroos *are* well adapted to their niche. Not
just a little bit. And the arrival of a more effective predator is not a
sign of the tree kangaroo's poor adaptation, it's a sign of an
environmental change that could be catastrophic.
This
may sound counter-intuitive, but what tends to happen is the opposite
of what you describe. When a new predator (or climate change, or
elevation of a new mountain range, whatever) comes along, it is the
finely-adapted species who fare worse. The more adapted you are to your
niche, the more difficult it is to adapt to the new conditions. This is
why "generalist"
species
do best after environmental upheavals. Cockroaches, sharks,
crocodilians. These are all species widely distributed across the globe
in a number of different ecosystems. These are the sort of species who
do well, not the ultra-specialists confined to small regions like that
weird Madagascan possum or the dodo.
So
in fact, if a new predator comes along, the tree kangaroo is NOT in
much danger from other specialised tree dwellers. It is mostly
endangered by its own specialisation and the change in conditions.
At
least, that's MHO.
Paul Williams
answered:
I agree - my
next *highlighted* line directly after the above quote was:
"This
of course bears no relation to a creature's current fitness to its
existing
niche."
Sorry if I
accidently misrepresened your clear views.
There are
comparisons we make regarding different animals living in similar
ecosystems.
The Australian
species of tree kangaroo are probably as well adapted as they perhaps
can be.
This does not
mean that they have optimal adaptions. Tree kangaroos are specialised,
it is just that because we can see other creatures in similar habitats
with optimal adaptions we compare species; -*often
erroneously*
Tree kangaroos
are constrained by their historic ancestors and the gene pool they
inherited.
It appears that
they are doing the best with what they've had to work with.
It also appears
that some of this genetic heritage has also advantaged them - for
example their digestive system - they also jump pretty well too :-)
They are
nevertheless constrained by their heritage.
I really truly
have nothing against tree kangaroos at all.
If the horror
happens and even one species of tree kangaroo becomes extinct, the
finger will point invariably to us.
>
This may sound counter-intuitive, but what tends to happen is the
opposite
> of what you describe. When a new predator (or climate change, or
elevation
> of a new mountain range, whatever) comes along, it is the
finely-adapted
> species who fare worse. The more adapted you are to your niche,
the more
> difficult it is to adapt to the new conditions. This is why
"generalist"
> species do best after environmental upheavals. Cockroaches, sharks,
> crocodilians. These are all species widely distributed across the
globe in
> a number of different ecosystems. These are the sort of species
who do
> well, not the ultra-specialists confined to small regions like
that weird
> Madagascan possum or the dodo.
I don't disagree
that tree kagaroos are probably as well adapted to their niche as they
can be.
"Tree kangaroos
have secondarily adapted to life in the trees (and a pretty ungainly one
at that). The current wisdom is that the bounding gait of
kangaroos comes from a rat-kangaroo-like heritage of small,
ground-dwelling animals."
- Dr Paul M.A.
Willis (Consulting Vertebrate Palaeontologist.)
(I am led to
believe that some New Guinea species are not "ungainly" at all).
Finely
specialised species are of course dependent on the status quo.
A specialised
niche is great until this niche disappears.
Australian tree
kangaroos are specialised, yes, but appear to have a heritage phylogeny
- or phylogenetic constraints which restrict the fine tuning of their
adaption to aboreal life.
I think it
unlikely that another comparitively more acrobatic aboreal creature
could outcompete the tree kangaroo for it's (low energy) food resources.
You mentioned
the sloth in a previous post.
The koala also
is no brilliant acrobat.
I realise that
we can be fooled by a creature's appearance.
This was the
intention of my original (poorly stated) and now withdrawn point:
"One modern
example is the tree kangaroo which one may easily describe as 'pathetic'
and due for extinction. :-)
We are biased
after seeing well adapted creatures."
I was attempting
to demonstrate that flight did not have to appear de novo.
Perhaps a bad
example.
My thought was
to demonstrate that even a poor flier may have had great advantages.
*Arguably* a
niche was open for the tree kangaroo's ancestors. If say, a rainforest
koala already occupied this niche, a new-to-the-trees creature would
have found it virtually impossible to surplant them. - Breeding rates
etc compound this simplicity.
In the case of
flying animals, myriad niches were available.
Available niches
are filled - eventually.
>
So in fact, if a new predator comes along, the tree kangaroo is NOT in
much
> danger from other specialised tree dwellers. It is mostly
endangered by its
> own specialisation and the change in conditions.
>
> At least, that's MHO.
This certainly
does appear to be the case.
My writings are
oft (unfortunately) obtuse and more often than I like, ocassionally
riddled with errors.
In attempting to
put ideas/thoughts - definitely not universal truths - in writing I
stuff up ocassionally.
I'm learning.
This current
subject and most/all others is so complex - it has so many 'what if's'
involved that I'm humbled - am still bloody interested though.
:-)
Gerald
Cairnes added:
Just
a brief observation on the four winged dino. Judging by the
illustration it would seem that this is a gliding animal rather than a
flying one. For the hind legs to provide efficient flight such as is
achieved with normal wings as in birds there would have to be a large
development in the pelvic girdle musculature. This illustration appears
to show a pretty stock standard pelvic arrangement which would appear to
lack the necessary muscular development for active flight such as is
seen in the pectoral muscles of birds.
I
assume that gliding was a precursor to active flight. The use of the
the hind legs for gliding or flight would have involved the loss of
bipedalism and inhibited the development of the front legs as wings. My
guess is that the tail became more important in directional stability
and the hind legs became more useful in locomotion. Active flight would
have given a large advantage in available territory and resources.
Zero Sum posted:
Looking at the
picture of that four (five?) winged thingy, it looks to me as though the
feathered tail could have been used as the driving force and the
remaing four used to provide lift and co-ordination. You could see
the tail becoming weaker and just for balance as the forewngs develop
true flight capabilities - but they could start as just an assist.
On
12/7/2003, Donald Lang, in a new thread, Flights - of Fancy, posted:
In
Fridays SMH there is a story:
http://www.smh.com.au/text/articles/2003/07/10/1057783286455.htm
The
text, see below my signature, asserts that certain fossil birds are
known to have been capable of flight. It is not obvious to me. If it
should be, please will somebody try to make it so?
ttfn.
DEE
Flight
theory has legs
Date:
July 11 2003
By
Greg Roberts
The
question of how birds learned to fly has long puzzled the experts.
Anatomists and palaeontologists have generally favoured the "top
down" theory - that some time during the Jurassic period before about
150 million years ago, dinosaurs clambered up trees and eventually,
after developing feathers and bristles and learning to glide to the
ground, the art of flying somehow evolved. Now,
it seems, the "bottom up" theory has more feathers to fly with.
A
study on the claws of birds suggests their forebears were much more
terrestrial, or ground-dwelling, than had been thought, and that they
had their feet very much on the ground before taking off. In the first
major study of its kind, Chris Glen, for his doctoral thesis at the
University of Queensland, has studied the claws of 1500 modern-day birds
from 500 species and compared them with the fossils of long-extinct
"dino-birds".
In
a paper delivered to a national conference of palaeontologists at the
Queensland Museum in Brisbane this week, Mr Glen explained that the
curvature of the modern birds' claws varies radically and relates
directly to the extent to which birds spend time on the ground. At one
end of the spectrum, the claws of woodpeckers, which vigorously climb
tree trunks, curve 170 degrees. At the other end, the claw of the
flat-footed jacana, a lily-trotting waterbird, curves barely at all.
"In
between, and including all the perching birds we're so familiar with,
you have the full range," Mr Glen said outside the conference.
When he checked the fossil records of the ancestors of birds that
lived between 120 million and 150 million years ago, he was surprised
by the extent to which they matched the claws of the flat-footed birds.
For instance, the sinornithosaurus was a two-legged beast - there has
long been debate about whether many dinosaurs were reptiles, birds or
something in between - about 1.5 metres tall that hunted in packs.
(They are the mean-looking critters continually trying to make a meal
out of Sam Neill in Jurassic Park.) The sinornithosaurus had
been suspected of having tree-climbing capabilities but Mr Glen said
its claws indicate this is not so.
Other
dino-birds known to be capable of flight, such as the starling-sized
confuciusornis of China and Europe's magpie-sized archaeopteryx, were
thought to be arboreal. But Mr Glen said the claws of most suggest they
were more likely to be terrestrial,
probably behaving similarly to modern-day chickens or ground pigeons,
which fly reluctantly.Only one of the flight-capable dino-birds he
examined, the sinornis of China, appears to have been primarily arboreal.
"The
evidence is quite clear that most of these bird ancestors were
ground-dwellers," Mr Glen said. He said the tree theory - that birds
"used the height of the tree and so on to advantage to gradually develop
a flying capability" - had made a lot of sense. "However, it appears
more likely now that it was a case of from the ground up."
David Maddern
replied:
I dont know it
is particularly asserting that. They became fossils after they
flew.
Except for this:
>Other
dino-birds known to be capable of flight, such as the starling-sized
> confuciusornis of China and Europe's magpie-sized archaeopteryx,
were
> thought to be arboreal.
There are
pictures here:
http://www.peabody.yale.edu/exhibits/cfd/CFDconfu.html
There they
describe flight feathers.
Overall the
article looks at the top down theory and bottom up theory It then
overlays foot shape of fossils thought to be bird ancestors to assert
that flat footed were from the ground, perhaps flying like chooks.
I suppose there
is a point of contention about definition; where flight starts and
jumping stops.
Paul
Williams added:
For
those who may have missed this, below my signature is an
excellent post from Ian Musgrave:
"Evolutionary origins of flight?" (Jan 26th. 2003). There are quite a
few good URLs (some broken) included to rummage through.
The
last link has some lovely reconstructions (paintings) of some of
the Chinese
feathered Dinosaurs
- slow to load but worth the wait, I believe.
