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Author Topic:   hormones and receptors - what came first?
caligola2
Inactive Member


Message 1 of 13 (182158)
01-31-2005 9:15 PM


first, i will start and say that i am evolutionist.
How does evolution could explain the emergence of new hormones and their receptors?
hormone by definition is : Chemical messenger from one cell (or group of cells) to another.
receptor by definition is: Protein molecule that receives and responds to a specific neurotransmitter, hormone, or other substance.
both receptors and hormones are coded in the DNA.
The function of many proteins is to interact specifically with other molecules in tightly integrated regulatory systems. When the function of each part depends on the prior existence of all the other parts, the Darwinian model seems to breaks down.
What's the selective pressure that drives the evolution of a new hormone if there's not already a receptor to give it a function? Conversely, how does a new receptor evolve unless there's a hormone present?

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AdminAsgara
Administrator (Idle past 2302 days)
Posts: 2073
From: The Universe
Joined: 10-11-2003


Message 2 of 13 (182160)
01-31-2005 9:19 PM


Thread moved here from the Proposed New Topics forum.

  
crashfrog
Member (Idle past 1466 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 3 of 13 (182163)
01-31-2005 9:30 PM
Reply to: Message 1 by caligola2
01-31-2005 9:15 PM


The early "hormones" might simply have been the actual catalysts of the cellular function they signaled; they might have been both signal and agent, themselves.
The early receptors might have evolved, then, as helpers to those catalysts. As their effecacy improved via evolution, the effecacy of the hormone might have decreased, until the hormone itself had no purpose but to trigger the receptor.
When the function of each part depends on the prior existence of all the other parts, the Darwinian model seems to breaks down.
It doesn't, actually, because evolution works often by co-opting what is already present, not by creation ex nihilo. An analagous example is the construction of a stone arch - remove one piece and the whole thing fails. Yet, arches are constructed one piece at a time. How? Via scaffolds - simpler, less effective structures that are themselves able to be built piece by piece. You build the scaffold, it supports the arch; when the arch is completed the scaffold has no purpose and is removed.

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PerfectDeath
Inactive Member


Message 4 of 13 (182171)
01-31-2005 10:16 PM
Reply to: Message 3 by crashfrog
01-31-2005 9:30 PM


replacement.
when i read this i wondered the same thing. "which did come first?"
but as you explained now i can understand it.
it's like enzymes: how did the first enzyme form. because enzymes are catalysts heat and time were the only things to help break things down so a structure that could take the place of that catalyst would be very usefull. so early receptors would have reacted to something in the environment and eventually a replacement was produced.
but so a glucose molecule, heat, or sumthing like that might wave been the catalysts?
and nice neji avatar caligola2

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caligola2
Inactive Member


Message 5 of 13 (182519)
02-02-2005 8:28 AM


Irreducible Complexity
as i mentioned in the first post i am an evolutionist..
As i read creationists claims about Irreducible Complexity i got puzzled.
let's look on the following Irreducible system:
The problem only gets complicated to explain,
if we look on the suckle reflex in mammals, a friction sensors on the mother nipples sense the infant sucking, as a result a signal is being sent via neurons from the nipples to the hypothalamus in the brain. after the signal has been processed a signal is being sent to the hypophyses gland.
as a result the hypophyses gland releases two hormones to the blood stream.
the two hormones travels in the blood stream until they reach a specific receptors in a specific cells membranae in the milk glands.
this results two things:
1. the milk is being squeezed.
2. the milk reproduction process is being accelerated.
the process could be read here:
Human Milk and Lactation: Background, Physiology, Human Milk and Preterm Infant
how could this 'irreducible complexity' system be reduced?
each factor is important for this system evolution, the friction sensors is important, the neurons connection to the hypothalamus, the process in the hypothalamus, the signals which is sent from the hypothalamus to the hypophyses gland, the metabolic process which results the manufacture of the two hormones, the proteins in the receptors in the milk glands. and the special processes which accurs after the hormones reach to this receptors.
and all the parts of the system is a result of many genes working together, why would each part develop if another part didn't existed?
why would a friction sensors develop in the nipples if the link between the hypothalamus and the hypophyses didn't existed?
and if the receptors didn't existed? and if the hormones didn't existed?
if the whole course didn't existed why would any of the parts develop separately?
This message has been edited by caligola2, 02-02-2005 16:14 AM

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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 6 of 13 (182535)
02-02-2005 9:43 AM
Reply to: Message 5 by caligola2
02-02-2005 8:28 AM


Re: Irreducible Complexity
I think that you are seeing the processes as considerably more restricted and linear than they actually are.
There are touch receptors all thorugh the body, therefore it is not surprising that they occur in the nipples.
Secondly only one of the hormones, Oxytocin, is actually released in response to the suckling.
Finally the fact that the article says that all these elements are required for 'successful lactation' leaves a lot of room for questioning what they consider 'successful' and allows a lot of space for many rudimentary mechanisms forming a basis for mammalian lactation which would not have satisfied the aticles criteria of 'successful'.
TTFN,
WK

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crashfrog
Member (Idle past 1466 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 7 of 13 (182558)
02-02-2005 12:10 PM
Reply to: Message 5 by caligola2
02-02-2005 8:28 AM


how could this 'irreducible complexity' system be reduced?
What's irreducable about it? The "friction sensor" is just the same kind of tactile nerves our whole skin possesses. The hypothalamus does more than just regulate milk production. It sends and recieves signals of every kind, all over the body.
and all the parts of the system is a result of many genes working together, why would each part develop if another part didn't existed?
Because every part you've mentioned either serves multiple purposes in the body, or is a part easily gained by simple modification of other existing parts.
It's like trying to say that sight is irreducably complex because you need not only eyes to see, but a brain as well. The reason that argument is stupid is because we use our brains for much, much more than seeing.
Do you see how it works, yet?

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mick
Member (Idle past 4985 days)
Posts: 913
Joined: 02-17-2005


Message 8 of 13 (186432)
02-17-2005 11:46 PM
Reply to: Message 6 by Wounded King
02-02-2005 9:43 AM


Re: Irreducible Complexity
Yes, there are many ways to lactate, monotremes do it without any nipples, for example. They just have a patch of wet hair. Evidence suggests that the nipple evolved as a coopted gland from the base of a hair, so many of the apparent adaptations of lactation are actually coopted adaptations to being furry. Nothing irreducably complex about it.
mick

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caligola2
Inactive Member


Message 9 of 13 (186463)
02-18-2005 8:26 AM
Reply to: Message 8 by mick
02-17-2005 11:46 PM


Re: Irreducible Complexity
thank you for the replay,
I accept what you wrote about the mammary glands.
Do you an easy way to recognize whether a system is Irreducible Complexity or not?
This message has been edited by caligola2, 02-18-2005 15:28 AM

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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 10 of 13 (186464)
02-18-2005 8:35 AM
Reply to: Message 9 by caligola2
02-18-2005 8:26 AM


Re: Irreducible Complexity
Do you an easy way to recognize whether a system is Irreducible Complexity or not?
Now there is a very good question, but one more suited for the ID proponents to answer perhaps. One key issue is that it depends very much on the definition of IC you choose to use.
TTFN,
WK

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caligola2
Inactive Member


Message 11 of 13 (186483)
02-18-2005 9:37 AM
Reply to: Message 10 by Wounded King
02-18-2005 8:35 AM


Re: Irreducible Complexity
The definition from EvoWiki is:
1. An irreducibly complex system has multiple required parts.
2. An irreducibly complex system is one which natural evolutionary processes cannot produce.
the definition is easy to understand.
But, if i take a system such as the mammary glands as i described. how can i determine whether she is IC or not?
will a genetic mapping of the system will give the result?
[if we know that the system needs 7 genes to make her work - could this be a way to determine?]
or should i try to find info. on how the system work in other organisms?
[in order to see if variation of the system is possible]
This message has been edited by caligola2, 02-18-2005 16:51 AM

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jar
Member (Idle past 393 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 12 of 13 (186494)
02-18-2005 10:17 AM
Reply to: Message 11 by caligola2
02-18-2005 9:37 AM


Re: Irreducible Complexity
Good questions all. But is it a complete list? One problem I've had with IC is that often when we look at a system we find that many of the parts first evolved to serve some other function, one that is definitely not IC, and were then co-opted for that later function.
The world we live in is marvelously complex. And there are multiple solutions to nearly every function you can imagine. Plants see with no eyes. They eat with no mouths. They move without legs and fly without wings. They colonize without cities and attack others without armies.
The big question for me in all of the ID/IC questions is "Why ask?" If we can simply look at the system and first understand it, can we then just look beyond to find similarities either in function or detail in other systems that may or may not serve the same function? If we find the pieces parts all ready available, or if we find the function being acomplished with other pieces parts, can we eliminate both ID and IC.

Aslan is not a Tame Lion

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mick
Member (Idle past 4985 days)
Posts: 913
Joined: 02-17-2005


Message 13 of 13 (186794)
02-19-2005 3:04 PM
Reply to: Message 12 by jar
02-18-2005 10:17 AM


Re: Irreducible Complexity
Jar,
I found an article on pubmed that shows (as you suggested) that coopting previously-existing phenotypes is a realistic process for the evolution of these complex systems. It also goes some way to answering the original question on evolution of hormone receptor systems.
Here's the abstract of the article:
Immune function requires intercellular communication. The vocabulary includes messenger molecules closely linked to the immune system as well as more widely acting messengers such as hormones and neuroactive substances. To try to bring these together, we have used an evolutionary approach. Materials that resemble hormonal peptides and neuropeptides, previously thought to be restricted to multicellular animals, are present in protozoa, bacteria, and higher plants. There is also evidence for substances in microbes that bind hormones and other messengers, which resemble receptors of vertebrates. Therefore, we suggest that the molecules of intercellular communication probably arose much earlier in evolution than the endocrine, nervous, and immune systems. This insight provides new understanding of messenger systems in vertebrates, as applied to the immune system, as well as new insights into possible disease mechanisms, including those that involve autoimmunity.
The article is available at http://www.jimmunol.org/cgi/reprint/135/2/816S

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