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Author Topic:   Question about evolution, genetic bottlenecks, and inbreeding
harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 1 of 123 (503046)
03-15-2009 5:30 PM


Hi
I am a evolution enthusiast but I am struggling with one of the concepts.
When a species is isolated, goes through a bottle neck, or a small amount of one species is divided from the rest and branches into a new species, what prevents inbreeding having to much of a negative impact to the species survival?
Surely the time it takes variety in the smaller gene pool takes longer than it would for inbreeding to have an effect.
Educated researched answers please! No nonsense about this is a disproof of evolution, or half baked answers please!!
Edited by Adminnemooseus, : Added the ", genetic bottlenecks, " to topic title

Replies to this message:
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Adminnemooseus
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Message 2 of 123 (503050)
03-15-2009 5:57 PM


Thread moved here from the Proposed New Topics forum.

  
lyx2no
Member (Idle past 4717 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 3 of 123 (503055)
03-15-2009 6:43 PM
Reply to: Message 1 by harry
03-15-2009 5:30 PM


A Unwell Researched Opinion
When a species is isolated, goes through a bottle neck, or a small amount of one species is divided from the rest and branches into a new species, what prevents inbreeding having to much of a negative impact to the species survival?
Nothing. The subgroups risk of extinction is inversely proportional to it size, though this is mitigated to some degree by an increase in genetic drift.
The total research involved in this statement is a memory from something I read rar, rar, rar somewhere, rar, rar dealing with cheetahs, rar, rar
Welcome, Harry.
Edited by lyx2no, : Add some rars.

Genesis 2
17 But of the ponderosa pine, thou shalt not eat of it; for in the day that thou shinniest thereof thou shalt sorely learn of thy nakedness.
18 And we all live happily ever after.

This message is a reply to:
 Message 1 by harry, posted 03-15-2009 5:30 PM harry has replied

Replies to this message:
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harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 4 of 123 (503056)
03-15-2009 7:04 PM
Reply to: Message 3 by lyx2no
03-15-2009 6:43 PM


Re: A Unwell Researched Opinion
Ok, so I kinda knew that.
So, I am struggling to wrap my head fully around common ancestor and how that ties in with inbreeding.
So one little monkey, has fun time with another monkey, and they have 2 baby monkies, monkey one goes on to become humans, the other goes onto become chimpanzees.
So monkey 1 is our concestor with chimps. however, even if monkey 1, were to mate with 5 females, the grandchildren would all be very inbred.
Can somebody draw me a tree of how 1 ancestor gets enough genetic material to mix it up? Because surely it can't get that many from the species it split with, or it would not be the common ancestor, and the whole process would start again.
Thanks for the welcome!

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 Message 3 by lyx2no, posted 03-15-2009 6:43 PM lyx2no has not replied

Replies to this message:
 Message 5 by Rahvin, posted 03-15-2009 7:20 PM harry has replied

  
Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 5 of 123 (503058)
03-15-2009 7:20 PM
Reply to: Message 4 by harry
03-15-2009 7:04 PM


Re: A Unwell Researched Opinion
Ok, so I kinda knew that.
So, I am struggling to wrap my head fully around common ancestor and how that ties in with inbreeding.
So one little monkey, has fun time with another monkey, and they have 2 baby monkies, monkey one goes on to become humans, the other goes onto become chimpanzees.
So monkey 1 is our concestor with chimps. however, even if monkey 1, were to mate with 5 females, the grandchildren would all be very inbred.
Can somebody draw me a tree of how 1 ancestor gets enough genetic material to mix it up? Because surely it can't get that many from the species it split with, or it would not be the common ancestor, and the whole process would start again.
You're confused because that's not the way evolution works. You're close, but "common ancestor" does not imply individual.
Evolution occurs over populations.
So, Population A is comprised of 20,000 individuals. Something happens, and that population splits into two daughter populations - Pop. B and C, each with around 10,000 individuals. These two populations, if they do not interbreed, will continue to evolve in divergent pathways. Population B could be the ancestors of humanity, while Population C could be the ancestors of chimpanzees.
No inbreeding required.
The separation of populations can happen for any number of reasons - natural disasters, migration due to overpopulation, what have you.
Edited by Rahvin, : No reason given.

This message is a reply to:
 Message 4 by harry, posted 03-15-2009 7:04 PM harry has replied

Replies to this message:
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harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 6 of 123 (503059)
03-15-2009 7:26 PM
Reply to: Message 5 by Rahvin
03-15-2009 7:20 PM


Re: A Unwell Researched Opinion
I got the impression from the text books that a common ancestor was an individual.

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 Message 5 by Rahvin, posted 03-15-2009 7:20 PM Rahvin has replied

Replies to this message:
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 Message 8 by Rahvin, posted 03-15-2009 7:53 PM harry has replied

  
harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 7 of 123 (503060)
03-15-2009 7:41 PM
Reply to: Message 6 by harry
03-15-2009 7:26 PM


Re: A Unwell Researched Opinion
I see, I have been getting common ancestor confused with Most recent common ancestor.
Thanks for the help guys!

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Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 8 of 123 (503062)
03-15-2009 7:53 PM
Reply to: Message 6 by harry
03-15-2009 7:26 PM


Re: A Unwell Researched Opinion
I got the impression from the text books that a common ancestor was an individual.
That's a mistaken impression. As I said, evolution happens over populations, not individuals. It's an incredibly slow process that happens by increments of mutations - Species X does not give birth to Species Y. Species Y is a descendant of Species X only after many generations of mutations sufficient to disallow interbreeding between the two.
In each generation, the given population is able to interbreed with itself. No familial inbreeding, and no "single individual" common ancestors (Not to say that single individual common ancestors are impossible, simply that this is not typically what happens).

This message is a reply to:
 Message 6 by harry, posted 03-15-2009 7:26 PM harry has replied

Replies to this message:
 Message 9 by harry, posted 03-15-2009 8:02 PM Rahvin has replied

  
harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 9 of 123 (503063)
03-15-2009 8:02 PM
Reply to: Message 8 by Rahvin
03-15-2009 7:53 PM


Re: A Unwell Researched Opinion
quote:
That's a mistaken impression. As I said, evolution happens over populations, not individuals. It's an incredibly slow process that happens by increments of mutations - Species X does not give birth to Species Y. Species Y is a descendant of Species X only after many generations of mutations sufficient to disallow interbreeding between the two.
Yeah I am way beyond that level
So there is a difference between most recent common ancestor, which is an individual, and a common ancestor?

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Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 10 of 123 (503064)
03-15-2009 8:05 PM
Reply to: Message 9 by harry
03-15-2009 8:02 PM


Re: A Unwell Researched Opinion
So there is a difference between most recent common ancestor, which is an individual, and a common ancestor?
Incorrect. The most recent common ancestor is still the most recent common ancestor species, which is a population. Individuals don't even enter the picture. All of Species Y is not descended from an individual of Species X; Species Y is descended from a population from Species X.

This message is a reply to:
 Message 9 by harry, posted 03-15-2009 8:02 PM harry has replied

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harry
Member (Idle past 5468 days)
Posts: 59
Joined: 03-15-2009


Message 11 of 123 (503066)
03-15-2009 8:09 PM
Reply to: Message 10 by Rahvin
03-15-2009 8:05 PM


Re: A Unwell Researched Opinion
No that is wrong, the MRCA is not a species, I know that for sure.
Unless there is any confusion.
All humans have a MRCA, we all related through one individual.
So therefore there must be an individual from which all humans and chimpanzees are descended, regardless of whether that individual bred with with how ever many other monkeys.
Edited by harry, : No reason given.

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 Message 14 by Stagamancer, posted 03-15-2009 8:32 PM harry has replied
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bluescat48
Member (Idle past 4190 days)
Posts: 2347
From: United States
Joined: 10-06-2007


Message 12 of 123 (503068)
03-15-2009 8:24 PM
Reply to: Message 11 by harry
03-15-2009 8:09 PM


Re: A Unwell Researched Opinion
No that is wrong, the MRCA is not a species, I know that for sure.
Unless there is any confusion.
All humans have a MRCA, we all related through one individual.
No you are confused. The MRCA is a term for the most recent common ancestor of 2 species no matter how far they are from each other. It is not a single individual but a population. The MRCA between a Homo sapiens & a Homo erectus is different that the MRCA between a homo sapiens and Pan troglodytes, and different than the MRCA between Homo sapiens and Gorilla gorilla. Similarly the MRCA of Pan & Homo has a MRCA with Gorilla. One can back and find a MRCA between Humans & Grasshoppers if one wants to go back that far. In all cases these MRCA's are a species not an individual

There is no better love between 2 people than mutual respect for each other WT Young, 2002
Who gave anyone the authority to call me an authority on anything. WT Young, 1969
Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008

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lyx2no
Member (Idle past 4717 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 13 of 123 (503069)
03-15-2009 8:27 PM
Reply to: Message 10 by Rahvin
03-15-2009 8:05 PM


Thank you, Rahvin (and harry)
When harry introduced his second idea there was something uncomfortable in the back of my mind, as if something I intuited was questionable but I couldn't quite put my finger on it. Still you cleared it up; I held harry's idea in my head without even knowing it. Thank you both for shaking it out. It's nice to be rid of a misconception even when you didn't know it was there.
AbE: harry, are you referring to Y-Adam and Mitochondrial Eve?
Edited by lyx2no, : No reason given.
Edited by lyx2no, : Typo in first edit.

Genesis 2
17 But of the ponderosa pine, thou shalt not eat of it; for in the day that thou shinniest thereof thou shalt sorely learn of thy nakedness.
18 And we all live happily ever after.

This message is a reply to:
 Message 10 by Rahvin, posted 03-15-2009 8:05 PM Rahvin has not replied

  
Stagamancer
Member (Idle past 4916 days)
Posts: 174
From: Oregon
Joined: 12-28-2008


Message 14 of 123 (503070)
03-15-2009 8:32 PM
Reply to: Message 11 by harry
03-15-2009 8:09 PM


Re: A Unwell Researched Opinion
No that is wrong, the MRCA is not a species, I know that for sure.
This is true. Here's an explanation from Wikipedia:
quote:
The existence of an MRCA does not imply existence of a population bottleneck or first couple. The MRCA of everyone alive today could have co-existed with a large human population, most of whom either have no living descendants today or else are ancestors of a subset of people alive today. This seemingly paradoxical phenomenon can be easily explained, if the effect of pedigree collapse is taken into account.
When tracing human lineage back in time, most people look at parents, grandparents, great-grandparents and so on. The same approach is often taken when tracing descendants via children and grandchildren. This naive approach calculates a number of ancestors and descendants that grows exponentially. Thus, over 30 generations, or in the time since about the High Middle Ages, a single individual alive today would have 230 or roughly a billion ancestors, more than the total world population at the time.
This simple calculation does not take into account the fact that every fertilisation is really a fertilisation between distant cousins, which leads to the effect of "pruning" or collapsing the individual's family tree. The ancestry tree is thus not strictly a tree, but a directed, mostly-acyclic graph. People with no descendants are placed at the bottom of the graph and ancestors are placed above their descendants. Starting with the people with no descendants one can connect their parents above. (Half-)siblings thus become connected via one or two common ancestors, their parent(s). As each generation of ancestors is added at the top of the graph, more and more people become related to one another (first cousins, second cousin, third cousins and so on). Eventually a generation is reached where one or more of the many top-level ancestors is an MRCA from whom it is possible to trace a path of direct descendants all the way down to every living person at the bottom generations of the graph.
It is incorrect to assume that the MRCA passed all of his or her genes (or indeed any single gene) down to every person alive today. Because of sexual reproduction, at every generation, an ancestor only passes half of his or her genes to the next generation. The percentage of genes inherited from the MRCA becomes smaller and smaller at every successive generation, eventually decreasing to zero (at which point the Ship of Theseus paradox arises), as genes inherited from contemporaries of MRCA are interchanged via sexual reproduction.
What this is saying is that if you trace a family tree back far enough, you can find an individual who everybody is related to in some way. This does NOT mean that this individual is responsible for "creating" the whole human species. So, yes, there is probably an individual to which all humans and chimpanzees can trace back to. However, this does not mean that this individual had offspring that were either human or chimpanzee. The evolution still occurred at the population level.
Edited by Stagamancer, : No reason given.

"There are three kinds of lies: lies, damned lies, and statistics."

This message is a reply to:
 Message 11 by harry, posted 03-15-2009 8:09 PM harry has replied

Replies to this message:
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Taz
Member (Idle past 3292 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 15 of 123 (503071)
03-15-2009 8:36 PM


This thread reminds me of high school biology. Back then, I was a hardcore creationist who would argue for hours with the biology teacher. I remember one of the things I and many other students struggled with was this very thing you guys are talking about, that the common ancestor is a species and not an individual and that individuals don't evolve. I think part of the problem for me was I had this preconceived notion about evolution that stuff evolve by morphing. This preconceived notion of evolution is closer to what happens to Marcus Corvinus in Underworld Evolution than reality.
I think at this point I'm suppose to say god rules evolution sux.

  
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