Not wanting to hijack beatle's thread...

General Questions
#1

But what I want to ask fits nicely with the other thread on evolution.

BorisB alluded to an idea of his he calls “giraffe neck stretching”. My question is this: is there a mechanism which transfers physical characteristics acquired or modified after birth to the genes in the sex cells of the individual (or any cells for that matter)? In other words, take the precursor to a giraffe. Looks like a horse, kinda long neck-maybe a yard. Now, over this animal’s lifetime, through craning and stretching its neck, the neck grows to 4.5 feet. Now, if my understanding is correct, the animal’s genes were programmed to grow a neck of 3 feet. Through physical conditioning, the neck muscles/tissue/skin have grown another 1.5 ft. Will the genes this animal pass on be programmed to grow a neck of, say, 4 ft.? And if so, how are the original genes modified by the physical conditioning?

And the problem with small furry animals
in corners is that, just occasionally,
one of them’s a mongoose.
Terry Pratchett, Witches Abroad

#2

Flypside, nope, the genes are as they stand for the 3 foot neck and the 1.5 extension the animal makes doesn’t transfer in.

Basically, evolution happens through a series of random events. The mean length of neck of the horse’s offspring may be 3 feet, but some will be slightly shorter and slightly longer by random chance.

Now, isolate a portion of the population in say, a part of Africa, where the land is barren and all the low-lying plants are eaten quickly by the population. Those animals with a slightly longer neck can get the high leaves too, so they can still eat while their stumpy necked brothers and sisters croak. Now only the long neck ones are alive, and the mean neck length gets slightly higher, and the process repeats itself.

Of course, this process is governed entirely by the conditions AT THE TIME, so it could easily reverse itself if say, the animal found a new food source or a new one evolved. Remember, natural selection is the ‘survival of the fittest’ which means ‘fittest at that moment in time to match the conditions’. It does NOT mean the strongest, and it does not imply that an animal that was fit 1000 years ago can survive today. (look at the chettah, which is quickly dying off, and all kinds of species of Whale that humans have overhunted)

#3

No. There was a Stalin-era Russian biologist (I forget the name) who theorized that this would take place, and his theory was adopted by the Soviet communist party as fact, but he’s been discredited.

#4

Classic example–various groups have been circumcising boys for millinia, but they’re still born the same.

#5

Actually a recent Nature article describes biological phenomenon that on the surface, seem Lamarckian.

Here’s the situation:

Waterfleas (little microscopic buggy things), when exposed to a chemical made by predators will grow long “helmets” that protect them better from the predators.

Now, the offspring of these helmeted waterfleas will have long helmets regardless of the environment they are born in. The offspring will have helmets even if the water they are born in does not have this inducing chemical.

Simply stated, the offspring are born with a characteristic that the parents obtained later in life. This appears to be Lamarckian inheritance. But as was explained earlier, our understanding of genetics forbids that.

The explanation provided by the article is “the parent’s environment affects how the genetic code in the offspring is translated, then certain acquired traits can be delivered to the offspring.”

The article can be found in the 2 Sept. 1999 issue of Nature p.22-23.

Back off, man. I’m a scientist.

#6

Random,

The guy you’re thinking of did indeed shape the Soviet view on evolution, but I don’t believe he himself was Russian. His name was Jeane Baptiste Pierre Antoine de Monet, the Chevalier de Lamarck.

His discredited evolutionary theory is now referred to as Lamarckian biology.
http://landow.stg.brown.edu/victorian/darwin/darwin2.html has more info, if you’re interested.

~ Complacency is far more dangerous than outrage ~

#7

Alphagene,

I posted without first reloading the page to see if there were any new comments, so I ended up repeating your bit about Lamarckian biology. Sorry.

Hmmmm, I’ll have to read the Nature article in question. That situation does seem earily Lamarkian.

Is Nature online, do you know?

~ Complacency is far more dangerous than outrage ~

#8

I believe Random was referencing Lysenko, who was placed in charge of Soviet argiculture by Stalin himself. Lysenko successfully argued that Darwinian theory was in conflict with Marxist/Leninist doctrine. Therefore, Lamarckism, being in agreement with the dialectic, was to be the basis for the Glorious Revolution in Soviet Food Production and a means to discredit the capitalist Darwinist swine.

Lysenko’s policies are one of the reasons I no longer have any cousins in Europe. The Ukranian famine was a direct result of the suppression of science by ideology.

#9

STARK:

Nature is online ( www.nature.com ), but a subscription is needed to access the article.

Back off, man. I’m a scientist.

#10

If I understand your question correctly, you’re asking how adaptations take place on a genetic level. From what I understand of evolution, (I’m no expert) you’ve got it backwards. Here’s an extremely simplified explanation. Other’s may feel free to add/correct/modify/shoot it down.

There is no mechanism for transferring physical characteristics aquired or modified after birth. The way it works is that your hypothetical first giraffe is born with a genetic mutation which results in its neck being longer then the rest of its kind. This trait can be either positive or negative, if its negative the chances are that it won’t live long enough to reproduce. If it’s positive, it will have an advantage over others of its kind, and will do exceedingly well. In the case of the giraffe, its longer neck allowed it to feed freely without much competition from other animals. This allowed it to thrive and produce offspring which had the same genetic trait for long necks.