Natural Selection

[Digit]

I suggested in an earlier thread that a mutatation in one individual should be sufficient, under the right cirumstances, to start the development of a new species. From todays Daily Express.
Harvard University scientests claimed yesterday that Anolis lizards on the Bahamas changed body shape within a year of a new predator being introduced, Science Magazine reports. First they developed longer legs to help the outpace the newcomer, the larger curly tailed lizard. But then they found that climbing trees was a better escape route- and developed shorter legs, all within twelve months.

[War Arrow]

I suggested in an earlier thread that a mutatation in one individual should be sufficient, under the right cirumstances, to start the development of a new species.

Hello again Digit. Hopefully I haven't misread your point, but in any case I'm agreeing with you. Not only would a mutation in one individual be sufficient but er... well, so far as I can see, that's the only way it would happen (at least regarding the very first instance of said mutation). After all, what's the alternative? A million to one mutation occuring at the same time in more than one individual - sounds a bit to much like intelligent design.
I'd still be interested in the nitty gritty theoretical details. I've read both Stephen Jay Gould and Richard Dawkins at reasonable length, and the punctuated equilibrium idea (Gould and Etheridge) seems to make sense, although I wonder if I got it properly because try as I might I still cannot see what Dawkins' objections might be.

[Digit]

I haven't read Dawkins WA, my local library and book shops don't run to that sort of thing, but punctuated equilbrium seems to me to be the only logical view. With those lizards the mutation must have already existed within the poplation to achieve such rapid progress through the species, all that would be needed then, I would think, would be a very effective predator and a high reproduction rate.
Personally, I still adhere to Darwins idea that there should be intermediate forms between one species and the one that it is suceeded by. I can't see a major, and outwardly obvious, change in one individual being acceptable as a mate.

[Minimalist]

Suppose you had a species of crab. Half of them tended to be all black and half tended to have a white streak running down the back of the shell.

One day a seagull shows up and finds it easier to target the white streak crabs. He sends an e-mail to his seagull pals and pretty soon it is open season on white streaked crabs while the black shelled crabs just keep on doing their thing.

Pretty soon, the white streaked crabs are gone and the seagulls move on.

There has been 'no mutation'...no evolutionary change...but the genetic code for the white streak has been blasted out of the gene pool simply because an existing trait present in half of a population made them targets while the other half remained concealed.

This is natural selection, too.

[stan]

Yeah, Bob. I think your example might be called "deselection" or
being "selected out."

What I don't understand is what Digit alluded to above...say a lone individual is born with all the right genes to improve or change the species. He or she has got to mate with one of those similar to his mom and dad, so his great new traits may or may not appear among his or her offspring. Likewise any of the children born would have to mate with
one of those old- fashioned dudes or dudettes, or else a sibling.....
So the splitting off of HS and HSN couldn't have happened in a clean break. HS children for at least two generations would have had to interbreed with the previously existing type.
How a new species gets generated out of this pattern is confusing to me....
Can anyone point to an explanation for this that a novice can understand?

[Cognito]

I can't see a major, and outwardly obvious, change in one individual being acceptable as a mate.

That is ... until the hormones start raging or the beer flows!

[stan]

or on a dark night....

[Cognito]

What I don't understand is what Digit alluded to above...say a lone individual is born with all the right genes to improve or change the species.

Alright, here we go. The genetics process in humans (as well as other animals ... sorry Arch) is subject to random recombination of genes every time a sperm successfuly hooks up with an egg. Not only do mutations occur at this level but they occur constantly in the background during the lifetime of the subject. Cells grow, divide and die over and over. During the replication and subsistence phase mutations occur. Some mutations kill off the cell outright while others linger into following generations.

Everything mentioned above is continuously occurring in every one of us. Mutations and variations are common. What propels something radically different is rapid and radical environmental change. In the above example a new predator was added to the environment. That mutation for short legs was occurring all along but had no environmental benefit until it became necessary to climb trees to escape the predator and thereby survive. If only one mutant survives who can find a mate, their union will create additional offspring who will also survive (theoretically 50%) since they, too, can now climb quickly. The environment prompted the change, not the mutation.

Look for times of greatest stress in the environment and you will find the greatest genetic transformations. Europe in the late pleistocene was undergoing remarkable and swift changes from cold to warm and back again. HSN's cold-adapted abilities were not always needed after HSS arrived on the European scene about 40,000bce. The years leading up to the Last Glacial Maximum (LGM) were typified by rapidly shifting warm to cold conditions and back again. Yes, the LGM was a whopper, but HSNs had already disappeared by 23,000bce. HSS could compete better in warm environments while HSN was better suited to cold conditions. Since the environment flip-flopped multiple times during co-existence, it see-sawed advantage between the two groups. Was a hybrid produced with something different that allowed it to thrive no matter what the climate was doing? Hint: look to the organization of the brain. News at 11.

[Digit]

Thanks Cog. Very nice explanation.

[War Arrow]

Thanks also from me.
There's an excellent real-life version of Min's illustration given by Carl Sagan in the Cosmos series (God! Those were the days! I still miss that guy!) and in the accompanying book (page 25) which describes Japanese Heike crabs of which the carapace is contoured to bear a passing resemblance to the face of a samurai. Natural selection would have been applied in so much as fishermen would have been reluctant to keep those crabs whose shells appeared to carry the face of an ancestor. I'll see if I can find anything on the internet.

Oh... here we go. Hopefully...

[stan]

Thanks Cog. Very nice explanation.

Thanks for the try, Cognito, but I don't think your response answered
my question. Can you walk me through what happened in the first few generations after
the first HNS was born and how his or her species/type became so numerous?

Thanks.

[Cognito]

Thanks for the try, Cognito, but I don't think your response answered my question. Can you walk me through what happened in the first few generations after the first HNS was born and how his or her species/type became so numerous? Thanks.

Ha! My wife says the same thing: "Well, that was a great explanation, but it isn't what I asked you about!" Then she goes into something about my gender. For a quick answer to your question take a look at:

http://cogweb.ucla.edu/ep/Paleoanthropo ... anderthals



Notice where the HSN range is located. They were not successful enough to fan out across Asia and into Africa since they were a cold-adapted species. Is that where you are headed with the question? That is, why was HSN selected as a species in the first place, and what were its advantages over its predecessor?

[Digit]

Hi Stan. See if this helps. Assume the population is A, a mutation occurs, we'll call it B. Let us assume. for example that the mutation is a change in dentition, not even visible without examination. As you correctly say B has to mate with As as he is the only B. Now, according to Mendel's work the offspring will be as follows. A-AB-BA-B, if B now breeds with B all offspring will be Bs, if B breeds with A, AB or BA you will have mixtures of A and B in accordance with the Mendel's ratio. I suggest you look that up or I could be here all day!
If the circumstances into which B was born permitted him (or her) to thrive, then As Bs ABs and BAs will co-exist, maybe for many generations till something changes, climate, living conditions etc, so as to favour one or other group. Using dentition again, they have to change to a tougher form of food, the group with the best dention for the new circumstance will thrive at the expense of the other. Okay?