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Steve O
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 Posted: Sat Jun 28, 2008 6:32 am Post subject: Help, please - I'm having problems with the life cycle of th |
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Hey look, I'm not one of those bat shit crazy I.D. fellers, but I'm really
having problems with reconciling the life cycle of the lancet fluke with the
theory of evolution.
Could someone please explain to me exactly how a crazy and complicated life
cycle like that could evolve in separate and distinct stages?
Preferably, in simple layman's terms for the terminally uneducated..;-)
I mean, I have no problems at all with the development of a complicated
organ such as the eye, but this life cycle has me really stumped as to how
it came about. |
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DougC
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| Posted: Sat Jun 28, 2008 6:32 am Post subject: Re: Help, please - I'm having problems with the life cycle o |
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Steve O bemoans:
| Quote: |
Hey look, I'm not one of those bat shit crazy I.D. fellers, but I'm really
having problems with reconciling the life cycle of the lancet fluke with the
theory of evolution.
|
Why do you think they call it a fluke?
Doug Chandler |
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hersheyh
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| Posted: Sat Jun 28, 2008 6:32 am Post subject: Re: Help, please - I'm having problems with the life cycle o |
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On Jun 27, 9:32 pm, "Steve O" <nospamh...@thanks.com> wrote:
| Quote: |
Hey look, I'm not one of those bat shit crazy I.D. fellers, but I'm really
having problems with reconciling the life cycle of the lancet fluke with the
theory of evolution.
Could someone please explain to me exactly how a crazy and complicated life
cycle like that could evolve in separate and distinct stages?
Preferably, in simple layman's terms for the terminally uneducated..;-)
I mean, I have no problems at all with the development of a complicated
organ such as the eye, but this life cycle has me really stumped as to how
it came about.
|
http://www.answers.com/topic/trematoda
Note that three hosts is, to some extent, the more primitive condition
and some blood flukes do have life cycles that eliminate one of the
hosts.
Keeping in mind that the fossil record of soft-bodied invertebrates,
like flukes, especially parasitic ones, is damn near non-existent, one
still has room for speculation. And the following is a fairly
reasonable speculation.
The problem of a parasite is always how to get from host A back to
host A. In the case of many flukes there is frequently a snail or
other mollusk intermediate that ingests the feces containing eggs
spewed out by the thousands by the adult parasite. The reason the
snails eat feces is not for the purpose of providing a home for the
fluke eggs, it is to get nutrition. That it *incidently* allowed some
ancestral fluke to more efficiently get back to the feces depositing
host (relative to the rate in the absence of the snail) is not done
"by design". But *because* this allowed more fluke eggs to get back
to host A, any variation in the fluke's genome that increased such
more efficient completion of the cycle would certainly be strongly
favored, even if it only did so by a small fractional percentage. In
fish (where this type of life cycle probably evolved), the eggs
develop only to a limited extent in the snail and then make their way
to a tertiary host. One can imagine this as a kind of "arms race" for
more efficient transfer back to host A, particularly if host A
undergoes selection for avoiding the snail.
Selection for a quantitative trait, one in which any change that even
modestly increases the efficiency of transfer to the next stage of the
cycle and increases the likelihood of completion of the cycle would be
favored. Evolution by selection is particularly good at optimizing
quantitative features by modifying previous systems.
In short, the cycle probably started out as an inadvertant consequence
of the fact that some organisms eat the shit out of other organisms,
thus providing the opportunity for more efficient transfer relative to
relying on an organism accidentally or unintentionally eating his or
her own shit. Those flukes better able to exploit that opportunity
would be the ones that cause all the suffering today.
I wonder, though, would a creationist really want to attribute such a
complex life cycle to God? I guess I know the answer to that: the
eubacterial flagella and its close cousin that makes some strains of
bacteria so nasty. God must really love his parasites and disease-
causing bacteria to give them such complex systems that they would
like to use as evidence of divine design. |
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John Vreeland
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| Posted: Sun Jun 29, 2008 2:20 am Post subject: Re: Help, please - I'm having problems with the life cycle o |
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On Jun 28, 4:47 pm, Friar Broccoli <Elia...@gmail.com> wrote:
| Quote: |
On Jun 28, 12:26 am, hersheyh <hershe...@yahoo.com> wrote:
On Jun 27, 9:32 pm, "Steve O" <nospamh...@thanks.com> wrote:
Hey look, I'm not one of those bat shit crazy I.D. fellers, but I'm really
having problems with reconciling the life cycle of the lancet fluke with the
theory of evolution.
Could someone please explain to me exactly how a crazy and complicated life
cycle like that could evolve in separate and distinct stages?
Preferably, in simple layman's terms for the terminally uneducated..;-)
I mean, I have no problems at all with the development of a complicated
organ such as the eye, but this life cycle has me really stumped as to how
it came about.
http://www.answers.com/topic/trematoda
Note that three hosts is, to some extent, the more primitive condition
and some blood flukes do have life cycles that eliminate one of the
hosts.
Keeping in mind that the fossil record of soft-bodied invertebrates,
like flukes, especially parasitic ones, is damn near non-existent, one
still has room for speculation. And the following is a fairly
reasonable speculation.
The problem of a parasite is always how to get from host A back to
host A. In the case of many flukes there is frequently a snail or
other mollusk intermediate that ingests the feces containing eggs
spewed out by the thousands by the adult parasite. The reason the
snails eat feces is not for the purpose of providing a home for the
fluke eggs, it is to get nutrition. That it *incidently* allowed some
ancestral fluke to more efficiently get back to the feces depositing
host (relative to the rate in the absence of the snail) is not done
"by design". But *because* this allowed more fluke eggs to get back
to host A, any variation in the fluke's genome that increased such
more efficient completion of the cycle would certainly be strongly
favored, even if it only did so by a small fractional percentage. In
fish (where this type of life cycle probably evolved), the eggs
develop only to a limited extent in the snail and then make their way
to a tertiary host. One can imagine this as a kind of "arms race" for
more efficient transfer back to host A, particularly if host A
undergoes selection for avoiding the snail.
Selection for a quantitative trait, one in which any change that even
modestly increases the efficiency of transfer to the next stage of the
cycle and increases the likelihood of completion of the cycle would be
favored. Evolution by selection is particularly good at optimizing
quantitative features by modifying previous systems.
In short, the cycle probably started out as an inadvertant consequence
of the fact that some organisms eat the shit out of other organisms,
thus providing the opportunity for more efficient transfer relative to
relying on an organism accidentally or unintentionally eating his or
her own shit. Those flukes better able to exploit that opportunity
would be the ones that cause all the suffering today.
I was wondering if there is such a thing as a generalist parasite;
something that can live in a wide range of hosts, possibly killing
most of them?
The reason I ask is that I am trying to imagine how this process
got started, and a generalist parasite that gradually evolved into
many specialized forms that didn't always kill its hosts seems like
a good starting point.
Is that sensible or is/are there (a) more probable scenario(s)?
|
To an extent, a carnivore can be considered a paasite that kills its
host, albeit very quickly and thus requiring it to seek out other
hosts. Could flukes be descended from a creature that began by
scavenging dead bodies and evolved into a creature that scavenges live
ones? |
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John Vreeland
Guest
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| Posted: Sun Jun 29, 2008 7:25 am Post subject: Re: Help, please - I'm having problems with the life cycle o |
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On Sat, 28 Jun 2008 13:47:01 -0700 (PDT), Friar Broccoli
<EliasRK@gmail.com> wrote:
| Quote: |
On Jun 28, 12:26 am, hersheyh <hershe...@yahoo.com> wrote:
On Jun 27, 9:32 pm, "Steve O" <nospamh...@thanks.com> wrote:
Hey look, I'm not one of those bat shit crazy I.D. fellers, but I'm really
having problems with reconciling the life cycle of the lancet fluke with the
theory of evolution.
Could someone please explain to me exactly how a crazy and complicated life
cycle like that could evolve in separate and distinct stages?
Preferably, in simple layman's terms for the terminally uneducated..;-)
I mean, I have no problems at all with the development of a complicated
organ such as the eye, but this life cycle has me really stumped as to how
it came about.
http://www.answers.com/topic/trematoda
Note that three hosts is, to some extent, the more primitive condition
and some blood flukes do have life cycles that eliminate one of the
hosts.
Keeping in mind that the fossil record of soft-bodied invertebrates,
like flukes, especially parasitic ones, is damn near non-existent, one
still has room for speculation. And the following is a fairly
reasonable speculation.
The problem of a parasite is always how to get from host A back to
host A. In the case of many flukes there is frequently a snail or
other mollusk intermediate that ingests the feces containing eggs
spewed out by the thousands by the adult parasite. The reason the
snails eat feces is not for the purpose of providing a home for the
fluke eggs, it is to get nutrition. That it *incidently* allowed some
ancestral fluke to more efficiently get back to the feces depositing
host (relative to the rate in the absence of the snail) is not done
"by design". But *because* this allowed more fluke eggs to get back
to host A, any variation in the fluke's genome that increased such
more efficient completion of the cycle would certainly be strongly
favored, even if it only did so by a small fractional percentage. In
fish (where this type of life cycle probably evolved), the eggs
develop only to a limited extent in the snail and then make their way
to a tertiary host. One can imagine this as a kind of "arms race" for
more efficient transfer back to host A, particularly if host A
undergoes selection for avoiding the snail.
Selection for a quantitative trait, one in which any change that even
modestly increases the efficiency of transfer to the next stage of the
cycle and increases the likelihood of completion of the cycle would be
favored. Evolution by selection is particularly good at optimizing
quantitative features by modifying previous systems.
In short, the cycle probably started out as an inadvertant consequence
of the fact that some organisms eat the shit out of other organisms,
thus providing the opportunity for more efficient transfer relative to
relying on an organism accidentally or unintentionally eating his or
her own shit. Those flukes better able to exploit that opportunity
would be the ones that cause all the suffering today.
I was wondering if there is such a thing as a generalist parasite;
something that can live in a wide range of hosts, possibly killing
most of them?
The reason I ask is that I am trying to imagine how this process
got started, and a generalist parasite that gradually evolved into
many specialized forms that didn't always kill its hosts seems like
a good starting point.
Is that sensible or is/are there (a) more probable scenario(s)?
|
I replied on Google. That was probably a mistake so I'll repeat it
here.
I suspect that creatures like flukes began as scavengers and evolved
into creatures that scavenged living animals. Certainly a scavenger
can afford to be---indeed must be---a generalist. Boring holes in
living animals requires a bit more specialization, especially if you
want to avoid killing them. |
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