Evolution through 21-year E. coli experiment

Notedstrangeperson · #31 23rd October 2009, 10:09 PM

Originally Posted by Cabal

And just because there was a controlled environment, doesn't mean there weren't conditions there the E.Coli could adapt to - citrate feed being one of them, as the initial line couldn't digest that, but some lines eventually evolved the ability to do so.

So I was wrong.

I had heard of a roughly similar report in New Scientist a year or two ago: evolution consists of long periods of slow change punctuated by short periods of rapid change, as seen in this E. Coli experiment.

Wiccan_Child · #32 24th October 2009, 09:02 AM

Originally Posted by Notedstrangeperson

The E. coli were grown in a controlled environment, which is quite the opposite to natural selection.

Natural selection doesn't require a 'wild' environment. It's an emergent phenomenon that crops up wherever replicators are allowed to reproduce under their own violation. They may be put in artificial environments, but the selection process is wholly natural.

It wouldn't be natural selection is the experimenters determined which organisms reproduced and continued the germ line, but they didn't do that. They let them breed naturally.

random325nicaea · #33 24th October 2009, 02:39 PM

"there was time for 653 mutations by generation 40,000, the later ones being mostly not helpful to the bacteria"

noo, new metabolic pathways are extremely beneficial.
but you seem to forget something, eukaryote have WAY much more DNA to replicate and mutate, not to forget the room that leaves for non or homologous recombination....introns, ext.

"surely at a minimum to go from ape ancestor to human would take some 30 million minor changes"

emh...1 insertion= an entirely new reading frame= new protein sequence/no protein
not to mention that you have no idea how little changes in the right places can create large morphological differences. ever hears of hetero chromatin or the vast regulatory systems in eucaryote genome replication or transcription?

the gentics say that most of the difference in humans and chimps lies in regulatory sequences. sequences where few mutations can make "huge" differences

really...buff up on the science...your ignorance is showing.

random325nicaea · #34 24th October 2009, 02:43 PM

"Has anyone ever actually done an equation to work out human evolution?"

yes, how the hell do you think we figured our mitochonrial eve and Y adam...not to mention the estimates we have about the divergence period.

"

Why don't humans really evolve that much any longer?

We are continually evolving. It's just the level of change we can witness directly over our lives (3-4 generations max) isn't going to be as readily apparent as something like a 40,000 generation experiment with E.coli."

that and farming pretty much removed almost all natural selection.
in the plus side tho....lots of gene diversity for all those pesky viruses...

random325nicaea · #35 24th October 2009, 02:44 PM

"Why don't humans really evolve that much any longer?"

you seem to fail what the term "evolve" encompasses.
EVERY GENERATION evolves.
life cannot do anything but evolve, it is an innate property of all life on earth, due to the process of it's replication. we are no exception.

random325nicaea · #36 24th October 2009, 02:52 PM

"The E. coli were grown in a controlled environment, which is quite the opposite to natural selection."

face->>palm
you seem to fail to understand that BECAUSE it was a controlled experiment, we where able to observe such precise natural selection, because we knew exacly what the selecting criteria were.
and before you start arguing semantics here. we don't replicate the E coli, we don't tell them to evolve the capacity to metabolize citrate. the e coli replicate themselves and natural selection favors those individuals that are best suited to the enviroment, like when they have a new metabolic feature.

Jazmyn · #37 24th October 2009, 09:28 PM

Originally Posted by Wiccan_Child

We do. Large, morphological change requires many thousands of years, something most humans don't live long enough to see .

But we have evolved. For example, most humans are lactose intolerant, simply because we never used to drink milk beyond our infancy. But in Europe, only 10% of people are lactose intolerant: the European population has evolved and diminished the number of people who can't drink milk. But, in Native American tribes, lactose intolerance is universal: 100% of people can't drink milk. This is because they never really drank milk, so they never experienced the same selection pressures as humans.

But that can also be determined by what we are exposed to in infancy and in the womb too.
Also, UHT and skimmed/semi-skimmed milk may exacerbate the problem because it's too easy to digest and breaks down too quickly in the intestines. Just a hypothesis, but processed food and stress may be a large cause of IBS.

Mike Elphick · #38 25th October 2009, 05:09 AM

Originally Posted by Jazmyn

But that [lactose intolerance] can also be determined by what we are exposed to in infancy and in the womb too.

You are quite right in thinking that what one is exposed to in early life certainly can have a profound effect later on. For any given inherited genotype (the organism's fixed genetic makeup), it's interesting to note how much its phenotype (the eventual expression of the genes in terms of an organism's physiology and morphology) can vary. This so-called phenotypic plasticity is important because it's the phenotype that gets exposed to natural selection, and the genotype therefore only indirectly. In the case of digesting lactose, however, since we are all exposed to lactose in our mother's milk, lactose intolerance is unlikely to be caused by this effect.

Also, UHT and skimmed/semi-skimmed milk may exacerbate the problem because it's too easy to digest and breaks down too quickly in the intestines. Just a hypothesis, but processed food and stress may be a large cause of IBS.

That's a good idea, but it doesn't actually fit the facts.

First of all, adult lactose tolerance is directly linked to one or more recently occurring genetic variations. These have been associated with gene regulators, rather than with the actual gene that produces lactase. Having multiple gene regulatory pathways like this gives a wider base for mutations to occur and thus the opportunity for many more subtle variations in gene expression compared with 'simpler' organisms like E. coli.

Secondly, it can be linked to man's early agricultural practices, which differed from one region to the next:-

[M]ost modern Northern Europeans and people of India, as well as people of European or Indian ancestry, show the effects of this mutation (that is, they are able to safely consume milk products all their lives), while most modern East Asians, sub-Saharan Africans and native peoples of America and the Pacific Islands do not (making them lactose intolerant as adults).
ht*p://en.wikipedia.org/wiki/Lactose_intolerance

BTW don't let those creo guys tell you that lactose intolerance is the 'normal' condition. Lactose tolerance and intolerance are both normal. And certainly don't fall for that 'more evolved/less evolved' claptrap we get from Creation Ministries International (ht*p://creation.com/lactose-intolerance).

catzrfluffy · #39 25th October 2009, 05:43 AM

Why would not being able to digest milk subject someone to natural selection? Or was it more of an ongoing process of exposure resulted in this mutation?

Wiccan_Child · #40 25th October 2009, 08:22 AM

Originally Posted by Jazmyn

But that can also be determined by what we are exposed to in infancy and in the womb too.
Also, UHT and skimmed/semi-skimmed milk may exacerbate the problem because it's too easy to digest and breaks down too quickly in the intestines. Just a hypothesis, but processed food and stress may be a large cause of IBS.

That it may. Interestingly, baby poop is made much smellier by giving them non-human milk: it contains many fats and proteins the baby doesn't recognise, so they're expelled out the other end. Human milk, on the other hand, is almost all absorbed by the baby, so what little comes out doesn't have that awful smell.

But anyway, the evolutionary link is clear: the probability of lactose intolerance is linked to ancestry, not what you were raised on.