Primary Mechanism of Evolution

[Guest ccame001]

I have a question about Darwin's theory of natural selection and Lamarck's theory of acquired characteristics. I am not an evolutionist, but one professor of Biology of mine said something that I think was significant: he said that he did not want to change my mind about evolution, but that it was still important to know it because it is an imoportant theory today. I think that is fair, and I would like to know it well.

 

Lamarck's outdated theory of acquired characteristics states that traits acquired during an animal's lifetime can be passed on to the next generation. Lamarck's theory was replaced by Darwin's theory of natural selection, which states that, within a population, certain traits and characteristics are favored, and thus get passed on to the next generation. The traits that are not favored tend to disappear. This makes perfect sense. However, it does not seem to explain how a species can evolve new characteristics, as Lamarck's theory does. It merely seems to eliminate variety within a population, or, as in the case of disruptive selection, at least reduce variety. It seems to me that the theory of natural selection does not quite account for everything that Lamarck's theory does. Yet it is still said that natural selection is the primary mechanism of evolution.

 

What am I missing? Unless I am mistaken, it seems to me more accurate to say that genetic mutation is the primary mechanism of macro-evolution, and that natural selection is an important facor in determing what evolutionary path a species will take.

 

Any help from a knowledgable person would be appreciated. Thanks.

 

Christian

[Mokele]

Mutation and natural selection go hand in hand. Mutation produces the variation, but evolution via natural selection (and sexual selection) acts on it to reduce diversity and weed out the unfit. The two processes and completely separate: Mutation can occur without natural selection (just irradiate some fruit flies to see this), and natural selection can occur without mutation (though it quickly runs out of diversity without them).

 

Think of it like a car. Evolution is the car, natural selection is the motor, and mutation is the fuel. If you don't keep filling the gas tank, the car stops. But, even if it's stopped, the engine still exists, even if it's not running.

 

Mokele

[simple]

I am questioning this myself so I am not completely sure, but when a population is separated, which can happen over great periods of time, such as a population of bison growing too large, separating into two groups, and a geographic feature forming inbetween them, isolating each, or by any other way, they will have different environments and different genetic shuffling, this will keep the separate populations similar within themselves but not to eachother... such as different races of people... these were changes overa few thousand years... if we could not travel so easily as we can and we evolved separately over many more generations we would all look very different from one another... and probably become completely different species.

 

EDIT: this has nothing to do with anything... but mokele... i am guessing malleus means something scientific... and it is a scientific pun... but i don't get those kind of jokes... could you explain?

[Sayonara]

Can I just point out that Lamarckism is not outdated; it was falsified.

[Radical Edward]

What am I missing? Unless I am mistaken' date=' it seems to me more accurate to say that genetic mutation is the primary mechanism of macro-evolution, and that natural selection is an important facor in determing what evolutionary path a species will take.

[/quote']

 

both mutation and differential reproductive success are critical to the evolution of species, and this is principally what Darwin recognised. The mutations create the variety within the population, forming new genes and changing extant ones and altering their production and so on, and then differential reproductive success (aka natural selection if you like) preserves those that are beneficial and eliminates those that are detrimental. Most mutations however are neutral, and are not selected for either way, and so these spread through the population or are eliminated through genetic drift. In sexually reproducing organisms, traits are also modified through the mixing of different alleles within the population.

 

You raise an important point though that Natural Selection does indeed "burn up" variation. but fortunately there are the two counter-forces at work here. If you allow me to personify, mutation is essentially attempting to wreck life by randomizing the genetic code, but Natural Selection is preserving the order by only allowing the functional code to proceed to the next generations. sometimes however the randomization results in something good, and so that ends up getting preserved.

 

sayonara is indeed correct that Lamarckian evolution was falsified, and falsified even further by genetics, which simply cannot work in a Lamarckian fashion. Another issue is that Lamarckian evolution could not result in new features as Darwinian can. Take for example the evolution of the feather or the mammalian ear. how would use of reptillian or theropod appendages result in some kind of inherited characteristic that would finally result in these features? Genetic mutations however can randomly vary things such as the position of the jawbone or the properties of scales, and natural selection does the rest.

[Auburngirl05]

this has nothing to do with anything... but mokele... i am guessing malleus means something scientific... and it is a scientific pun... but i don't get those kind of jokes... could you explain?

 

The malleus is one of the bones in mammalian inner ears, I'll leave the lesson on jawbone/ear evolution to Mokele because I know he'll explain it better, but I wanted to add another question about the quote. I recognized it as a revision of "With malice aforethought", but do you know wrote the original lines? I have come across it in lit class before but couldn't remember.

[Mokele]

but mokele... i am guessing malleus means something scientific... and it is a scientific pun... but i don't get those kind of jokes... could you explain?

 

There are 3 bones in the mammal ear (plus the tympanic bone, supporting the eardrum), versus 1 in every other land vertebrate. Everyone has a stapes, but mammals have 2 more bones, the malleus and incus. Mammals also have differnt jaw-bones: Our lower jaw is just one bone, the dentary, while reptiles have a dentary, splenial, angular, surangular and articular. Also, mammals lack the quadrate, a bone present in reptile jaws.

 

Basically, in reptiles, the quadrate (part of the skull) joins the articular at the jaw-joint, and the articular joins the angular, which attaches to the rest of the jaw bones. As mammals evolved, the joint moved forwards to enhance crushing power of the jaws, leaving these bones free to evolve a new function. The quadrate became the mammal incus, the articular became the mammal malleus, and the angular became the tympanic bone. These relations can still be seen in modern embryological studies of mammals; we've known for more than a century that these ear-bones were homologous to reptile jaw-bones.

 

Hence, the pun is many-layered: "Malleus" in "with malice aforethought", "getting an earful" about something, in this case the ancestral jawbones.

 

Mokele

[Kleptin]

that was waaaaay offtopic

 

Back on the comment Space Ghost made about geographic isolation, You said it yourself, if humans could not travel as freely, I don't think technology would be so relenting. Even so, How many generations do you think it takes for a complete change of species to occur? There's a good chance the human race would be extinct before that happens.

[Dr_666]

However, it does not seem to explain how a species can evolve new characteristics, as Lamarck's theory does.

 

The problem with Lamarck's theory is that it DOES NOT account for the facts. Acquired characteristics are not inherited. You may have pale skin and have tanning sessions everyday, but that will not influence the skin color of your kids.

 

As you perfectly notice, Darwin was not able to explain the origin of the variation that he appreciated in living beings. However, Darwin succesfully noticed that such variation had to be HERITABLE (so not like your tanning sessions). Unfortunately, the mechanisms of inheritance and mutation were still unknown when Darwin wrote his theory.

 

Today, Genetics provides several mechanisms to generate the above-mentioned heritable variation.Two of these mechanisms are mutation (chemical changes in the genes, for instance) and recombination (new combination of genes from the parents).

 

Hope this helps!