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Author | Topic: How do we define a "new" species. | |||||||||||||||||||||||||||
pink sasquatch Member (Idle past 6049 days) Posts: 1567 Joined: |
Yeah, what I am trying to figure out is if there is some physical reason why two species can't breed--like a chemical reason or something. Generally it is a DNA-level issue. Offspring need to have a complete complement of all genes necessary for life; however, if you have two species where the genes are differently distributed across the chromosomes, or a different number of chromosomes, the necessary complement of genes is not going to make it into the offspring even if the mismatched parents manage to produce a fertilized egg, and it will likely die in utero. (Please let me know if that makes sense.) In many cases protein-level incompatibilities between sperm and egg also prevent fertilization.
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robinrohan Inactive Member |
I got it.
Can we then say the following?: A "species" can be defined as an isolated gene pool---not isolated by some external factor, such as locale, but isolated because its DNA is not compatible with any other DNA. There are a few cases--such as wolves and dogs--which are accorded separate species-status more for traditional, cultural reasons rather than DNA incompatibility.
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crashfrog Member (Idle past 1493 days) Posts: 19762 From: Silver Spring, MD Joined: |
A "species" can be defined as an isolated gene pool---not isolated by some external factor, such as locale, but isolated because its DNA is not compatible with any other DNA. There are a few cases--such as wolves and dogs--which are accorded separate species-status more for traditional, cultural reasons rather than DNA incompatibility. That's good but it seems to me that DNA incompatibility is usually the last step on the road of speciation, and it's the step that takes the longest. But I think you're on the right track in referring to the isolation of the gene pool. In practice I think "species" tends to refer to a gene pool that is isolated now, for whatever reason, and in all likelyhood will continue to be isolated. To the degree that this relies on our ability to prognosticate about the future of a gene pool it might not be pretty, but I certainly think its the most practical, and provides the results closest to the traditional "folk" concept of species.
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nator Member (Idle past 2196 days) Posts: 12961 From: Ann Arbor Joined: |
It should be mentioned here that there have been a few cases of mules which have been able to reproduce.
Extremely rare, but there it is. Found this: http://freespace.virgin.net/gwyneth.wright/fertile.html
ARE MULES EVER FERTILE?
Mules are generally infertile, but there does appear to be evidence that a very few female mules are fertile. Such fertility is very rare. The Romans had a saying: Cum mula peperit - meaning "when a mule foals", roughly equivalent to "once in a blue moon". HOW MANY MULES HAVE PRODUCED FOALS? In 1990, Lorraine wrote: "Since 1527 approximately 60 live births of foals to mules have been reported, in Europe, the USA, South America, North Africa and China." One of the best documented earlier cases was Old Beck, investigated by Texas A&M (USA) in the 1920s. In the 1980s, there were cases of a fertile mule and a fertile hinny in China and mules in the USA and Brazil who produced more than one foal! More recently we have had reports of a fertile mule in Morocco and a fertile hinny in China. And in 1994, there were reports in the press about a mule in Albania having a miscarriage. WHY ARE MULES USUALLY INFERTILE? Basically, because the chromosomes of horses and donkeys are different: "The donkey has 62 chromosomes (31 pairs), the horse 64 (32 pairs) and the mule and hinny each have 63 chromosomes - of which many pairs are unevenly matched. It is not just the number of chromosomes which is different in donkeys and horses, but their structure: they have developed slightly differently over evolutionary time....The donkey and horse chromosomes are almost completely unable to pair up."
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Loudmouth Inactive Member |
quote: It is still quite simple. Species are separate gene pools. Separate species do not interbreed in the wild, or very rarely interbreed. They may produce a viable offspring through artificial insemination, but this matters very little for the process of evolution. Gene isolation is gene isolation, no matter the reason. It is not a question of "if they can" but "do they". There are many reasons that separate species may not interbreed, one of which is DNA incompatibilities. Others may include sexual selection, physical incompatibility, egg/sperm recognition, and hybrid sterility. One example that is pseudo-famous is Darwin's finches. These finches are isolated in the Galapagos Islands made famous by Darwin (hence the name). A research group captured and measured the characteristics of every bird on one of the islands. They also recorded the feeding habits. During their research a drought occured on the island. As a consequence, there were two main food sources, softer seeds and tougher seeds. As a result, the finches split into two main groups. One group had larger beaks and ate the tougher seeds and the other group had smaller beaks and ate the smaller, softer seeds. Interbreeding between the groups was common place before the drought, but was rare during the drought. For this reason this was considered the start of a speciation event, the isolation of gene pools as a function of beak size and natural selection. (To all: it's been a while since I read up on this so feel free to make corrections). A more difficult scenario is geographic isolation. It is very rare for a species to be totally split into two geographic areas. There is usually a small corridor that connects the two. It is in this corridor that one can observe whether or not interbreeding occurs. Then the question of ring species comes into play, which we can get into later after we all have a firm understanding of the scientific definition of species.
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robinrohan Inactive Member |
Loudmouth writes: Gene isolation is gene isolation, no matter the reason. It is not a question of "if they can" but "do they". There are many reasons that separate species may not interbreed, one of which is DNA incompatibilities. Others may include sexual selection, physical incompatibility, egg/sperm recognition, and hybrid sterility. I was thinking that geographical isolation has nothing to do with it. You got a bunch of deer over here in the Northwest and another bunch of the same deer in the Northeast, and they never get together. Nonetheless they are the same species. (later, of course, much later, this situation might change--they evolve differently). As regards physical compatibility, I suppose you mean something like big dog/little dog. But they are the same species. There seem to be some exceptions. Hard to pin it down. I don't understand why DNA incompatibility would not be the deciding factor. Surely there are no cases where you have creatures that don't look alike having DNA compatibilities.
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robinrohan Inactive Member |
Robin writes: Surely there are no cases where you have creatures that don't look alike having DNA compatibilities. You're such an idiot. You just mentioned big dogs/little dogs.
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MangyTiger Member (Idle past 6380 days) Posts: 989 From: Leicester, UK Joined: |
Gene isolation is gene isolation, no matter the reason. This raises the (to me at least) slightly odd possibility that what had been two species could suddenly become one. If you have two groups that can breed together in the wild but don't only because of some physical barrier they are two species by this definition. If however the physical barrier is removed these two groups/species will be able to mix and breed and so become one species. Is this just so unlikely/insignificant that it isn't worth bothering about ? Confused ? You will be...
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MangyTiger Member (Idle past 6380 days) Posts: 989 From: Leicester, UK Joined: |
LDS - I don't know if it will help you get your topic about perfection advanced but I think the link you want is :
http://www.kiawahturtles.com/...Evolution%20of%20Turtles.htm See - even on this site the non-creationists can be helpful On the other hand I don't have a clue what your topic is about - maybe if Ned helps you advance it everything will become clear. Confused ? You will be...
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pink sasquatch Member (Idle past 6049 days) Posts: 1567 Joined: |
Surely there are no cases where you have creatures that don't look alike having DNA compatibilities. As you state later, this is quite incorrect. There have been some cases where males and females of the same species were once identified as separate species because they looked so entirely different from one another - that's differences within a single species - until they were seen successfully mating. Here is one of my favorite examples of "don't judge a species by its cover":
These are eight different cichlid fish species from the rift lakes of Africa. Using a morphology-based model to predict relatedness and reproductive success, you would likely guess that related/compatible species were organized by rows. However, the opposite is the case - the columns represent closely related species, even though they look different and have different modes of feeding. In captivity, species within the same column can mate with one another, even though they look quite different. However, the species are incapable of mating between columns, even with species that share their morphology (facing one another in rows in the figure). The image was taken from a nice paper on jaw evolution in these cichlids - the full text is free here.
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jar Member (Idle past 420 days) Posts: 34026 From: Texas!! Joined: |
I used to work for the GaDNR. One of our programs was sea turtles and every season we'd sit on the beaches at night watching for turtles coming ashore to lay their eggs. Then we'd gather our information, check or tag, and when she struggled back down to the sea we'd wire off the nest to protect the eggs from dogs, raccoons and hogs.
We'd also get several sea turtles each year that had been trapped in nets or tangled up in fishing lines. The Loggerheads were enormous. Their heads were so broad and they were downright threatening. One of our biggest projects was developing a turtle excluder device that would keep them from getting caught in the shrimp nets and still not cut down on the shrimp harvest. They are neat critters. Aslan is not a Tame Lion
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MangyTiger Member (Idle past 6380 days) Posts: 989 From: Leicester, UK Joined: |
Cool - once I'd worked out what GaDNR meant (fortunately my twelve year old memory of living in the US came back to save me having to look it up ).
Confused ? You will be...
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robinrohan Inactive Member |
Robin writes: You're such an idiot. I beg your pardon? If you meant that as a joke, you should have put a little smily face. If you did not mean it as a joke, well then you--you of all people--should not be making a comment like that. Talk about the pot calling the kettle black . . . This message has been edited by robinrohan, 01-26-2005 19:08 AM
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robinrohan Inactive Member |
Robin writes: If you meant that as a joke, you should have put a little smily face. You literal-minded jackass! Were you raised in a barn? Don't you understand that it is possible for a comment to be both serious and comic at the same time? It is possible to be serious without being solemn. If I put that smily face down, it would destroy any ironic comment I make. I will try to make it easy for you, duncehead. I will make the irony VERY OBVIOUS--okay? I know, there is a difference between the Internet and talking to someone face to face. I understand that you cannot detect the tenor of the person's voice on the Internet. But neither can you with a book! God, you make me sick!
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AdminJar Inactive Member |
both of you.
Back on topic or you both get to sit in time out! New Members should start HERE to get an understanding of what makes great posts.
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