Macro evolution: Natural Selection: Define a species and the process of speciation?
- secretsauceLv 78 years agoFavorite Answer
A 'species' is a *biological* gene pool. A collection of organisms that are *biologically* able to interbreed and produce fertile offspring if they come into contact with each other.
But there are many things that can cause reproductive isolation between *populations* within the species. For example, if a lizard species is very rare and isolated to a valley, then if a creek running through the valley widens to become a substantial river, then the lizard species would get separated into two populations now unable to cross-breed with each other.
If that separation between two populations lasts for enough generations, then the genetic changes (evolution) within the two populations may be sufficient to cause *PERMANENT* reproductive isolation. In other words, even if the two populations come back into contact again, they are biologically unable to interbreed and produce fertile offspring.
At that point we consider them two separate *species*. They are now *permanently* unable to cross-breed, so any further genetic changes in one species has no way to cross-over into the other ... so the two species can only continue to get more and more different.
That is 'speciation'.
This is a key part of 'macroevolution', which is the study of evolutionary trends at or above the level of the species.
---- @CRR ----
I have to comment on creationist CRR's post because I find it *incredibly* dishonest!
At first I was surprised that a creationist could write such unusually coherent and well-written definitions ...
... Until I realized that he was copy-pasting from Scientific American ... without saying so.
And worse ... he was quoting from Scientific American, but then linking to "creation.com" ... and an article called "Refuting Evolution." It would quote from Scientific American ... and then completely mangle the concepts just quoted in order to turn the whole thing into complete mush.
Talk about a bait-and-switch!
1. CRR fails to put words in quotes that he is actually quoting.
2. If you follow his link, it turns out that 2 out of his 4 paragraphs are copy-pasted from different parts of the article. (His first and last paragraphs.)
3. And those two paragraphs are in turn quotes from Scientific American.
So CRR is offering creation.com as a "source" for legitimate information about evolution ... by selectively quoting (without saying so) from the only parts of that article that ARE legitimate ... the quotes from Scientific American. But if you go to that creation.com article to get get more information, you discover that they quote from Scientific American, but then completely MANGLE the conclusions drawn from them!
For example, immediately following the second quote of the SA article ("In the model called allopatry ..."), the creation.com article goes on to say:
>"Indeed, creationists point out that Mayr’s allopatric model would explain the origin of the different people groups (‘races’) after the confusion of languages at Babel induced small population groups to spread out all over the earth. Of course, the modern people groups are not reproductively isolated and are still a single biological species."
Notice the nonsense compounded on nonsense.
First, making the unfounded leap that the separation of languages is what *caused* the geographical separation, rather than the other way around. (Never occurring to creationists that this implies that the dispersal of humans to the far corners of the earth did not occur until Babel ... long AFTER Noah.)
Second, trying to give this idea legitimacy by linking it to legitimate models like Ernst Mayr's allopatric model.
Third, adding as almost an afterthought "Of course, the modern people groups are not reproductively isolated and are still a single biological species." ... which then undermines the very link to allopatric speciation that they're trying to establish!
Bottom line: I can think of no better way to leave people utterly *CONFUSED* by these basic biological concepts, than to link to a creationist article that simultaneously tries to give itself legitimacy by referring to these concepts, while at the same time trying to either "refute" those concepts, or draw incoherent conclusions from them!
All this does is illustrate how creationism is a MANGLED *MESS* of incoherent thinking.
">What? I provided a link to my source and you call me dishonest!"
I called your *answer* dishonest ... a bait-and-switch. The 'bait' is a very reasonable-sounding answer consisting of (unidentified) quotes from Scientific American ... and the 'switch' is a link to an anti-evolution site that only uses those SA quotes for purposes of undermining them!
----Source(s): The creation.com website quotes that SA article right and left ... but they give no actual citation! Only "the Scientific American article by John Rennie". (Since Rennie is the Editor-in-Chief at SA, he has written a lot more than one article.) Seriously, CRR ... how many times have I demonstrated to you that the only thing you will learn from creation.com as a "source", is how to use "quotes" the way a sidewalk con man uses cups and a ball?
- susannaLv 44 years ago
The formation of recent species can't be proved because of this scientists have now broken evolution into two phrases. Micro-evolution is nothing greater than adaptation inside a species, which everybody knew to be an actual occurrence. Macro-evolution is used on the grounds that "speciation" cannot and will not ever be proved genuine. It is no longer even a concept, it can be a speculation. No proof whatsover. God created existence to continue. We adapt to our environment. It's smart design. Could God Bless you.
- CRRLv 78 years ago
The most widely used definition, Mayr’s Biological Species Concept, recognizes a species as a distinct community of reproductively isolated populations—sets of organisms that normally do not or cannot breed outside their community.
A horse and a donkey are considered separate species even though they can breed to give a mule.
Natural selection can, but need not, lead to speciation.
In the model called allopatry, developed by Ernst Mayr of Harvard University, if a population of organisms were isolated from the rest of its species by geographical boundaries, it might be subjected to different selective pressures. Changes would accumulate in the isolated population. If those changes became so significant that the splinter group could not or routinely would not breed with the original stock, then the splinter group would be reproductively isolated and on its way toward becoming a new species.
"If you follow his link, it turns out ...". What? I provided a link to my source and you call me dishonest!
If not all the words are my own it is because I often find others are more articulate than I am.