FRDB Archives

Freethought & Rationalism Archive

The archives are read only.


Go Back   FRDB Archives > Science & Skepticism > Evolution/Creation
Welcome, Peter Kirby.
You last visited: Yesterday at 03:12 PM

 
 
Thread Tools Search this Thread
Old 03-29-2007, 02:36 PM   #21
Veteran Member
 
Join Date: Nov 2000
Location: Middlesbrough, England
Posts: 3,909
Default

Quote:
Originally Posted by Revolutionary View Post
Pinquins? Is that some strange Biblical beast? :wave:
Mock away. You only hurt youself. I shouldn't have to point out that not all penguins are closely related to Pingu.

Boro Nut
Boro Nut is offline  
Old 03-29-2007, 02:42 PM   #22
Veteran Member
 
Join Date: Jun 2001
Location: Roanoke, VA, USA
Posts: 2,646
Default

Quote:
Originally Posted by Third_Choice View Post
if 2 individuals is too little, then how do we have species that reproduce with just females? 1 individual is less than 2, yet it works.
Because when one female breeds parthenogenetically, she produces an exact (except for mutations) copy of herself. This avoids the problems of sexual reproduction with low population levels, namely inbreeding, which can lead to large percentages of lethal mutations.

No bull about it!

NPM
Non-praying Mantis is offline  
Old 03-29-2007, 03:02 PM   #23
Veteran Member
 
Join Date: Oct 2006
Location: Kahaluu, Hawaii
Posts: 6,400
Default

Quote:
Originally Posted by Third_Choice View Post
if 2 individuals is too little, then how do we have species that reproduce with just females? 1 individual is less than 2, yet it works.
Reproduction isn't the issue. Its the viability of the resulting population. A single individual could clone but the offspring would be very similar to the parent. If that continues for very long, the resulting population would be very, very similar and highly susceptible to predators or diseases that evolved quicker or the occasional natural event. In other words, what kills one, if they are all similar, will likely kill them all. That's why evolution isn't just a handy modifier of life, its essential for life to persist. If you had a single species with clone like similarity, what happens if the climate suddenly changes? Whoops, the slight variability allowed by simple mutation most likely will not be sufficient to allow that single species to survive as a population. What if their food source fails? There are many possible sources of extinction for a highly homogenous, unchanging species, much more than for a highly addaptive, quickly changing species.

More initial variability means more eventual variability. A larger population spread over a larger environmental range has more probability to survive changes to that range.
RAFH is offline  
Old 03-29-2007, 03:07 PM   #24
Veteran Member
 
Join Date: Aug 2004
Location: 152° 50' 15" E by 31° 5' 17" S
Posts: 2,916
Default

Quote:
Originally Posted by pkostrze View Post
Assuming the ark myth were to be true, what would the smallest number of each species need to be to successfully re-populate the earth with the smallest number of inbreeding caused defects? I'm no geneticist but I'm pretty sure it's larger than two.
There's a species of Japanese duck that came back from a population consisting of one 'pregnant' individual in the '70s. Though of course its long term viability isn't proven yet.

Species can survive severe inbreeding. It needn't be all that bad if the founders are healthy. And rapid expansion of the population reduces the loss of diversity.

Nevertheless, the amount of genetic diversity in existing species is evidence that they didn't go through any such genetic bottleneck in the last five or six thousand years. Humans, for example, show signs that their most recent bottleneck was a population of about 15,000 about 70,000 years ago.

On the gripping hand, a god who could miraculously return the kangaroos to Australia, the kiwis and wetas to New Zealand, jaguars and tapirs to South America, and dodos to Mauritius after the Flood could easily have faked the genetic data. Just as He is supposed to have faked the fossils, faked the morphological evidence for evolution, faked the genetic evidence of common descent, and faked the light coming from distant stars.
Agemegos is offline  
Old 03-29-2007, 03:15 PM   #25
Veteran Member
 
Join Date: Oct 2006
Location: Kahaluu, Hawaii
Posts: 6,400
Default

Quote:
Originally Posted by Pisano112 View Post
I believe when I was reading an article on cloning mammoths, and how many unique individuals would need to be cloned in order to restore the species. The number was between 20 and 30, so I'd guess for most mammals that'd be about right. I know that previous studies have indicated that populations risk extinction due to demographics stochasticity when they have less than 10-100 individuals. Some species would need more than 100, some would only need less than 10, but that's the rough window.

But inbreeding wouldn't necessarily drive the population extinct - the population would just rebound to large numbers more slowly.
Or not.

There is a big difference when you are discussing a human controlled breeding program versus a herd in the wild. We will act as a 'god' of sorts and protect our little herd. We will provide it with antibiotics it might take thousands of generations to acquire and domesticate naturally. We will protect it against variations in environment, we will protect it against natural predation.

If you were to reconstitute 20 unique mammoths and let them loose on their own in a human-less environment they would very likely die out with a few generations at most. The only way to tell would be to do so with a number of equally variable herds in similar environments. But my guess is they would succumb to disease, hunger or predation very quickly. That's why they were herd animals. Bigger herds, more variability and greater protection against threats.
RAFH is offline  
Old 03-29-2007, 06:20 PM   #26
Veteran Member
 
Join Date: Nov 2003
Location: Eagle River, Alaska
Posts: 7,816
Default

Quote:
Originally Posted by Agemegos View Post
Nevertheless, the amount of genetic diversity in existing species is evidence that they didn't go through any such genetic bottleneck in the last five or six thousand years. Humans, for example, show signs that their most recent bottleneck was a population of about 15,000 about 70,000 years ago.
Not 8 about 6,000 years ago?

I think this is a stronger argument (ie lack of bottleneck), in terms of genetic evidence, than an appeal to minimal viable population.

Can you provide a specific source for your numbers?
Amaleq13 is offline  
Old 03-29-2007, 10:17 PM   #27
Veteran Member
 
Join Date: Aug 2004
Location: 152° 50' 15" E by 31° 5' 17" S
Posts: 2,916
Default

Quote:
Originally Posted by Amaleq13 View Post
Not 8 about 6,000 years ago?

I think this is a stronger argument (ie lack of bottleneck), in terms of genetic evidence, than an appeal to minimal viable population.

Can you provide a specific source for your numbers?
I think you'll find the original paper here: Stanley H. Ambrose (1998). "Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans". Journal of Human Evolution 34 (6): 623–651.

I read about it in The Economist.

A superficial Google search also throws up the following:

http://www.sciencedaily.com/releases...0908074159.htm

http://news.bbc.co.uk/2/hi/science/nature/166869.stm

http://en.wikipedia.org/wiki/Toba_catastrophe_theory
Agemegos is offline  
Old 03-29-2007, 10:29 PM   #28
Contributor
 
Join Date: Mar 2004
Location: Dallas, TX
Posts: 11,525
Default

Quote:
Originally Posted by pkostrze View Post
Assuming the ark myth were to be true, what would the smallest number of each species need to be to successfully re-populate the earth with the smallest number of inbreeding caused defects? I'm no geneticist but I'm pretty sure it's larger than two.
Well, two actually could do it, assuming they were prolific. Yes, you would end up with inbreeding issues in the short run, but that would work its way out. I guess the creationist explanation for the fall of the dinosaurs must be that they were food for all the meat eaters while things were getting going.

Lions have to eat fairly often ya' know.
spamandham is offline  
Old 03-29-2007, 10:56 PM   #29
Veteran Member
 
Join Date: Nov 2003
Location: Eagle River, Alaska
Posts: 7,816
Default

Thanks
Amaleq13 is offline  
Old 04-03-2007, 01:47 PM   #30
Veteran Member
 
Join Date: Aug 2004
Location: Mid-west (U.S.)
Posts: 1,953
Default

Quote:
Originally Posted by show_no_mercy View Post
Is this some sort of variant to the Argument from Bull?
im not sure what that is.
Third_Choice is offline  
 

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Forum Jump


All times are GMT -8. The time now is 12:59 PM.

Top

This custom BB emulates vBulletin® Version 3.8.2
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.