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absael
2005-Sep-20, 07:59 PM
First of all, could someone more knowledgeable on the subject tell me if my assumptions regarding natural selection are correct, or if Iíve left something out? Iíve always thought that natural selection was due to two factors (if this is true, which has the greater effect? Or do they result in different types of adaptation?)

Survival of the fittest: A few individuals will develop a favorable adaptation, ensuring a higher probability of survival than the general population of the species. This adaptation becomes more prevalent, and eventually universal, as the individuals lacking this adaptation die at a higher rate.

Competition for mates: Individuals will mate with those that they instinctually feel will produce the fittest offspring. Also, in some species (and to a lesser extent humans), the biggest and strongest males will chase off other suitors for available females, ensuring that genes for vigor are passed on.

OK, here's my question: Could a strong argument be made for a more purely adaptive model, in which all members of a species adapt due to environmental pressure? What could be the biological mechanism for relatively widespread and rapid adaptation?

HenrikOlsen
2005-Sep-20, 08:35 PM
What could be the biological mechanism for relatively widespread and rapid adaptation?
Simple answer:
Sex :)

Slightly less simple answer:
No member of a species adapt to anything, they just live or die.
Whether a trait will spread is down to whether having it gives a higher chance of having surviving offspring.

BTW, Survival of the fittest was a phrase coined by Herbert Spencer when explaining to the public what Darwin's The Origin of Species was about, Darwin didn't use it himself.
It is generally not used when discussing natural selection, because it give the impression that something is desided with the help of some sort of fitness criterion.

Natural selection is down to this:
Individuals have different genes
Sometimes a gene will result in an individual surviving.
Offspring inherit these genes from their parents.
Therefore more offspring will have this gene than not.
Repeat from start.

The subtle part of this loop is that the gene that cause the individual to survive don't have to be expressed in the individual, but eg. in the parent.

As long as the expression of the gene results in an increased number of individuals with a reasonable chance of having the gene, then the gene will tend to become more common.

fossilnut2
2005-Sep-20, 09:08 PM
Henrik gives a concise and good answer. It's all a numbers game. 'Fittest' is a bit too subjective a word. All that matters is who passes on genetic material. What's 'fittest' can change. Perhaps in one scenario 'fittest' is being small: there is a shortage of food and the ability to survive depends on being small and not needing as much energy. In another scenario 'fittest' can mean simply being bigger and able to drive off the other guy and take his mate.

Individuals in a group don't adapt to anything genetically. Whether you spend your life staring at the wall or being a rocket scientist, it makes no difference to the genetic material passed on to your offspring.

worzel
2005-Sep-20, 09:47 PM
You neo-darwinists you! What about group sex?

astronomo flaquito
2005-Sep-20, 09:47 PM
absael asked:
ďCould a strong argument be made for a more purely adaptive model, in which all members of a species adapt due to environmental pressure? What could be the biological mechanism for relatively widespread and rapid adaptation?Ē

From what I understand, the answer to the first question is likely no. According to the theory of Punctuated Equilibrium, large, stable populations are very homogenous and tend to stay that way because any gene mutations that occur are diluted by the large number of individuals through which they must spread. But a population that exists in isolation (one that has no contact with the parent population), or on the periphery of the range (with little contact with the parent population), can exhibit greater and more rapid change due to the smaller population size and the fact that the periphery represents the outer limits of ecological tolerance for the ancestral adaptations. Thus new species arise in a sub-population, not as a result of a change in all members of the species.

As for the second question, Punctuated Equilibrium is the most common theory to explain relatively rapid speciation, but it is usually applied to smaller populations (living in isolation or on the periphery as explained above). It seems that widespread adaptation (speciation) in a general population, would occur very slowly, if at all.

Enzp
2005-Sep-21, 03:12 AM
And possibly when you ask if a whole group can adapt together, it sounds as though you are not making the distiction of individuals - or groups - adapting to their environment, and species adapting evolutionarily.

That is to say if a group of people started at the equator a grew bananas to eat, if they found themselves much farther north, they would have to learn to grow apples. Or if a farming area becomes flooded, they would have to adapt by learning to fish. That is people adapting.

But for a species to adapt in an evolutionary sense, it is not something any individual does in his liftime, it is instead the accumulated changes over time. NAtural selection would weed out those genetic lines less well suited for newer environs over time, leaving the gene lines better suited. Thus the population adapts, not the individuals in it.

Don't mix up the two different meanings of the word "adapt."

beskeptical
2005-Sep-25, 08:39 PM
The idea of survival of the fittest has really evolved into selection pressures.

Selection pressures can be positive, negative or neutral. The other very large intervening factor is not all traits are single.

Mate selection is not always clearly a selection of the fittest mate because the relationship is indirect. Thus you get male peacocks with tail feathers so big they no longer serve as a survival trait, but rather make it harder to outrun a predator. Yet the tail feather survives for whatever reason the female is selecting it.

Combined traits may have a selection pressure for one trait but another trait comes along with it. Thus you get sickle cell anemia being selected in areas with high rates of malaria.

We have lots of genetic variability that is passed on without any selection pressure but is already there when a need arises. A CCR5 deletion is a mutation that has been around since at least the 1400s that turns out to have some benefit in preventing HIV infection. Surprisingly, it arose in a population not exposed to HIV. Northern Europeans have the mutation in a small percentage of the population where as African's where HIV arose do not have it.

You have to remember that we have 3 billion base pairs and, I forget, but I think about 30,000 individual genes. That's a lot of genetic material to be acted on by a lot of selection pressures. It just can't be over simplified into the fittest reproducing more without losing a lot of the specifics.

diskmaster
2005-Sep-26, 12:00 AM
Would it be better to say survival of the ( through ) surviver's good or bad genetic code determines what is passed along? Most people marry for love not genes.

HenrikOlsen
2005-Sep-26, 03:51 AM
But they mate for physical attributes:)

beskeptical
2005-Sep-26, 05:23 AM
Would it be better to say survival of the ( through ) surviver's good or bad genetic code determines what is passed along? Most people marry for love not genes.How do you separate love from genes? Are you attracted to everyone? Why are you attracted to one mate over another? What about gay attraction in which more nature than nurture seems to be supported by the evidence?

Do animals love? Some make lifelong pairs some don't. Isn't that genetics? We are in the animal kingdom as far as genes go.

Anyway, mate selection among animals including humans is a combination of nature and nurture. Culture plays a big role in defining what is attractive. Yet genes also play a part in the selection. The end result is selection pressure to reproduce certain genes more than others.

But disease also selects as does circumstance of birth as does culture and religion. One just cannot oversimplify genetics.

ZaphodBeeblebrox
2005-Sep-26, 05:53 AM
What's Even Weirder ...

At Some Scales, Such as Point-Wise Mutations, Where a Single Base Pair, is Involved; Quantum Mechanics, Even Comes, Into Play!!!

In Other Words, Under Certain Circumstances, Small Mutations, SEEM to Happen, Before a Stimuli is Introduced, But, After, It has Been Measured, Not, To Have It!!!

The Implications, Are Odd, To Say, the Least!!!

:shifty:

diskmaster
2005-Sep-26, 08:08 AM
Physical appearance and attributes are often reason for procreation, but recessive portions of the genitic code can be passed on to the next generation or more that does not make one fitter only a survivor. Homosexual sex does not procreate. The use of the word love was a poor choice on my part.

HenrikOlsen
2005-Sep-27, 12:43 PM
Drop the word fitter, it's not relevant for the discussion, survival is the whole point of the game.
Remember also that there's not a one to one relationship between a gene and an expressed trait.

A simple example is sickle cell anemia, which is inherited as an autosomal recessive trait, only expressing itself as anemia when it's inherited from both parents.
If this was the only expression of the gene, it's simple math to see that it would never have spread in the population.
Fortunately for the gene, a person who only inherited it from one parent expresses the gene in a different way, namely by having a higher resistance to malaria.
This means that in areas where malaria is endemic, the carriers have a higher chance of surviving than the non carriers, so the gene survives in those populations.

Maksutov
2005-Sep-27, 12:54 PM
You neo-darwinists you! What about group sex?Man, I bet you gripe as you grope! :razz:

Monique
2005-Sep-29, 09:59 PM
You neo-darwinists you! What about group sex?
Americans do not allow!! :naughty:

:)

Maddad
2005-Sep-29, 10:30 PM
Do three people count as a group?

ZaphodBeeblebrox
2005-Sep-29, 11:09 PM
Do three people count as a group?
YES!!!

Tell us More ...

;)

worzel
2005-Sep-29, 11:55 PM
Don't you find that when planning parties, selecting individuals to invite is so much easier than weighing up the pros and cons of different groups, though? It's enough to punctuate ones equilibrium!

Maksutov
2005-Sep-30, 01:45 AM
Don't you find that when planning parties, selecting individuals to invite is so much easier than weighing up the pros and cons of different groups, though? It's enough to punctuate ones equilibrium!Please spare us the detailed description of what hangs in the balance! http://img137.imageshack.us/img137/566/iconwink6tn.gif

CalabashCorolla
2005-Sep-30, 03:17 AM
OK, here's my question: Could a strong argument be made for a more purely adaptive model, in which all members of a species adapt due to environmental pressure? What could be the biological mechanism for relatively widespread and rapid adaptation?

Widespread mutation and adaptation is unlikely within a single generation fo a species. However, if you consider rapidly re-generating species such as bacteria or some insects, then widespread adaptation appears to us to occur. For example, the hatching cycles of 13 and 17-year cicadas are staggered such that an entire brood will only hatch at a specific time...this ensures that no two broods will ever hatch in the same season, and that the competition for resources is lower on the whole population, thus creating a greater rate of survival for the whole species. It may be that whole broods died in the past because of the lack of adequate food sources, and that whole populations had to try and try again to find the most successful hatching pattern. Thus in this respect cicadas have evolved as groups, rather than as individuals.

Then there are the many communal insect species whose adaptations as a group are crucial for the group's survival and defense. A certain hive of bees may have to try several different defense strategies (at the sacrifice of many members of the hive) before they find one that is the most beneficial to the safety of the group.

Gillianren
2005-Oct-02, 06:06 AM
Americans do not allow!! :naughty:

:)

hey, according to our Supreme Court, it's none of anyone's business what we do in our own bedrooms between consenting adults.

ZaphodBeeblebrox
2005-Oct-02, 08:57 AM
hey, according to our Supreme Court, it's none of anyone's business what we do in our own bedrooms between consenting adults.
Yeah ...

Unless, they Actually, CATCH you ...

Then, It's Anybody's Guess!

:wall:

HenrikOlsen
2005-Oct-03, 11:04 AM
For example, the hatching cycles of 13 and 17-year cicadas are staggered such that an entire brood will only hatch at a specific time...this ensures that no two broods will ever hatch in the same season, and that the competition for resources is lower on the whole population, thus creating a greater rate of survival for the whole species.
The relative prime cycles of the multiple cicada species also makes it very difficult for a predator to develop with a reproductive cycle that matches them all, thus ensuring that there's simply too many for all to be eaten.