Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 119 (8778 total)
Current session began: 
Page Loaded: 08-18-2017 8:44 AM
361 online now:
Faith, jar, JonF, PaulK, Percy (Admin), Phat (AdminPhat), Pressie, Tangle (8 members, 353 visitors)
Chatting now:  Chat room empty
Newest Member: BruceR.Fenton
Post Volume:
Total: 816,286 Year: 20,892/21,208 Month: 1,325/2,326 Week: 661/345 Day: 23/161 Hour: 3/5

Announcements: Reporting debate problems OR discussing moderation actions/inactions


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
RewPrev1
...
910111213
14
Author Topic:   why is the lack of "fur" positive Progression for humans?
RAZD
Member
Posts: 18855
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 196 of 202 (561743)
05-22-2010 11:12 PM
Reply to: Message 194 by Dr Adequate
05-21-2010 8:24 AM


Re: Neotony vs. paedomorphism
Hi Dr Adequate,

Not neceassarily. Consider the possibilities that (a) it was a side-effect of an adaptation for a non-neutral trait, which is what I suggested; or (b) it got fixed at some time before the human population was small and undispersed.

We also need to consider that what we are talking about is a juvenile hair pattern, rather than bareness.

It is unlikely that the juveniles were unfit.

http://en.wikipedia.org/wiki/Vellus_hair

quote:
The growth of vellus hair is of a different growth cycle than terminal hair.[3] When a person reaches puberty, androgen can cause much of the vellus hair to turn into terminal hair as well as produce new hair growth. In males this causes the changes in the vellus hair on the face and body. In both sexes it can produce the appearance of armpit and pubic hair.

While babies could be protected from cold by mom cuddling, this would be unlikely in prepubescent juveniles.

Enjoy.


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 194 by Dr Adequate, posted 05-21-2010 8:24 AM Dr Adequate has not yet responded

  
Dr Jack
Member
Posts: 3505
From: Leicester, England
Joined: 07-14-2003


Message 197 of 202 (561769)
05-23-2010 4:34 AM
Reply to: Message 195 by RAZD
05-22-2010 11:01 PM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Neoteny\paedomorphy\tomatoe quibble. Meaning is the same in the end.

No, it isn't. The two are distinctly different in the genetics behind them, the protein changes that produce them and the overall effect on the organism one should expect.

In Neotony the changes usually result at the production end of the signals producing adult features and form, whereas paedomorphy results from alterations to the response to existing signalling. Neotony means that childlike features in one area are very likely to correlate with childlike features in another because they both have the same cause; paedomorphy doesn't share this feature.


This message is a reply to:
 Message 195 by RAZD, posted 05-22-2010 11:01 PM RAZD has responded

Replies to this message:
 Message 198 by Blue Jay, posted 05-24-2010 10:49 AM Dr Jack has responded
 Message 201 by RAZD, posted 06-13-2010 3:39 PM Dr Jack has not yet responded

  
Blue Jay
Member (Idle past 193 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 198 of 202 (561914)
05-24-2010 10:49 AM
Reply to: Message 197 by Dr Jack
05-23-2010 4:34 AM


Paedomorphosis
Hi, Mr Jack.

Mr Jack writes:

In Neotony the changes usually result at the production end of the signals producing adult features and form, whereas paedomorphy results from alterations to the response to existing signalling. Neotony means that childlike features in one area are very likely to correlate with childlike features in another because they both have the same cause; paedomorphy doesn't share this feature.

Here's what I found from Encyclopedia Britannica:

quote:
paedomorphosis (in paedomorphosis (biology))

Retention by an organism of juvenile or even larval traits into later life. There are two aspects of paedomorphosis: acceleration of sexual maturation relative to the rest of development (progenesis) and retardation of bodily development with respect to the onset of reproductive activity (neoteny).

Some formatting changes made


Basically, I think it means paedomorphosis is the phenotypic result of either or both of the two concepts you described (increase in sexual development vs decrease in somatic development).


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 197 by Dr Jack, posted 05-23-2010 4:34 AM Dr Jack has responded

Replies to this message:
 Message 199 by Dr Jack, posted 05-24-2010 10:56 AM Blue Jay has responded

  
Dr Jack
Member
Posts: 3505
From: Leicester, England
Joined: 07-14-2003


Message 199 of 202 (561916)
05-24-2010 10:56 AM
Reply to: Message 198 by Blue Jay
05-24-2010 10:49 AM


Re: Paedomorphosis
Yeah, I wouldn't use the Encyclopedia Britannica as a source for biological terminology. Paedomorphosis can refer to changes in individual features or to the entire organism; neoteny refers to change in the entire organism. Humans are not neotenous; they are paedomorphic for certain traits.
This message is a reply to:
 Message 198 by Blue Jay, posted 05-24-2010 10:49 AM Blue Jay has responded

Replies to this message:
 Message 200 by Blue Jay, posted 05-24-2010 3:47 PM Dr Jack has not yet responded

  
Blue Jay
Member (Idle past 193 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 200 of 202 (561943)
05-24-2010 3:47 PM
Reply to: Message 199 by Dr Jack
05-24-2010 10:56 AM


Re: Paedomorphosis
Hi, Mr Jack.

Mr Jack writes:

Yeah, I wouldn't use the Encyclopedia Britannica as a source for biological terminology.

Encyclopedia Britannica is just the source I chose to cite because the definition was concise and straightforward. Their way of presenting it seems to be pretty pervasive, though.

For example, here is an online database associated with an evolutionary biology textbook from Blackwell Publishing.

Most of what I could find says that either neoteny is a type of paedomorphosis, or that paedomorphosis is a symptom of multiple genetic conditions, which are referred to as neoteny (slowing of somatic maturation) or progenesis (speeding up of sexual maturation).

I haven't seen anything like the production/receptor dichotomy you were talking about earlier, but I admittedly haven't put a lot of effort into it yet.

Anyway, I see the distinction you're making with your argument, and I'm really just quibbling the terminology here. It's no big deal.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 199 by Dr Jack, posted 05-24-2010 10:56 AM Dr Jack has not yet responded

  
RAZD
Member
Posts: 18855
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 201 of 202 (564886)
06-13-2010 3:39 PM
Reply to: Message 197 by Dr Jack
05-23-2010 4:34 AM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Hi Mr. Jack,

No, it isn't. The two are distinctly different in the genetics behind them, the protein changes that produce them and the overall effect on the organism one should expect.

And yet the end result is the same: juvenile features arrested in development and preserved in the adult form.

Neotony means that childlike features in one area are very likely to correlate with childlike features in another because they both have the same cause; paedomorphy doesn't share this feature.

So this would mean that the correlation of juvenile hair with other childlike features would mean that neotony is the correct term, rather than paedomorphy, yes?

Which does not surprise me given the source of the neotony comment ... this claim has been around for a while.

And it is common for further development of an organism to halt once sexual maturity has developed.

Interestingly I get a number of responses to googling "neoteny in humans" ... so there are a lot of sources that say neotony.

http://en.wikipedia.org/wiki/Pedomorphosis

quote:
In developmental biology, paedomorphosis (also spelled pedomorphosis) or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Peramorphosis is change in the reverse direction. Paedomorphosis was first proposed by Walter Garstang in 1922[1]. The underlying mechanisms for this include heterochrony.

There are several kinds of paedomorphism which may appear independently or in combination:

• Neoteny, in which somatic (or physical) development is slowed, resulting in a sexually mature juvenile or larval form. ...


Ooo, it looks like it could be both ...

And, as the process that results in the paedomorphy is neotony, then it is more accurate to refer to it as neotony.

End result: sexual selection for juvenile appearance in sexually mature females has resulted in juvenile hair being arrested in development into mature hair in women.

It doesn't matter what you call it, the result is still the same.

Enjoy.

Edited by RAZD, : no smilies

Edited by RAZD, : mre accurate

Edited by RAZD, : again with the no smilies -- I don't know why this is not the default! (or at least stay checked once checked)


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 197 by Dr Jack, posted 05-23-2010 4:34 AM Dr Jack has not yet responded

Replies to this message:
 Message 202 by Ken Fabos, posted 08-19-2010 1:15 AM RAZD has not yet responded

  
Ken Fabos
Member (Idle past 1681 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 202 of 202 (575166)
08-19-2010 1:15 AM
Reply to: Message 201 by RAZD
06-13-2010 3:39 PM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Is it even clear that this characteristic is the result of sexual selection or even developed gradually rather than rapidly as a result of a mutation? It seems unlikely to me that fur-less individuals amongst the furry would be viewed as more attractive; the trait would be more reminiscent of babies than juveniles on the verge of sexual maturity until enough fur-less juveniles had been around awhile - and they'd shown themselves to possess greater 'fitness'. Do most people think fur-less dogs look more attractive than their fully coated counterparts? Unless it's not attractiveness that the most important aspect of 'sexual selection' but the ability of (mostly) males to intimidate and dominate others in order to get the best and most females. Even so, would the earliest of them consider the fur-less to be the most attractive choice or even recognise that trait as the reason for their own success?

Maybe more importantly, did the changes to our sweat glands precede or post-date the fur-lessness; either alone may not add much advantage to heat dissipation, which may not show itself to be an obvious advantage until both are present. Advantage with respect to ecto-parasites seems likely to at least be immediate; my own hypothesis that finer, sparser hairs are more sensitive to low threshold tactile impulses would fit with this - parasites would not have the fur to hide them and individuals would have greater sensory awareness of their presence. Together this could lead to dramatic reduction of metabolic load from parasites and produce healthier individuals - who could then go on to oust the furry alpha male and get to be choosy.

I have to say that I'm beginning to think that it could have been as much pure luck as fitness or attractiveness that led to the earliest forms of this, that it began as a maladaptive trait that the cleverness of proto-humans overcame; the real advantage could have been in the way they overcame it, such as by use of built shelters, fire and clothing. Rather than a warming climate it could have been a deep cold period, that swung the advantage towards the ones who stooped to draping skins over themselves for warmth and to disguise their ugliness.


This message is a reply to:
 Message 201 by RAZD, posted 06-13-2010 3:39 PM RAZD has not yet responded

  
RewPrev1
...
910111213
14
Newer Topic | Older Topic
Jump to:


Copyright 2001-2015 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2017