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Breaking News: We're All Mutants!

Started by PPI Brian, September 04, 2009, 05:54:35 PM

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PPI Brian

Scientists have come to the conclusion, after studying variations within the DNA of two people who shared a known ancestor from the common date of 1805, that we all show the influence of mutation. Surprisingly, though, the actual mutations are of a very slight number. Are mutations a normal part of biological advancement?

http://news.bbc.co.uk/2/hi/science/nature/8227442.stm
"Extraordinary claims require extraordinary evidence."--Carl Sagan

Brigham

This isn't all that surprising to me. It's known that in a normal, healthy individual, DNA replication will result in mutation with a certain statistical probability. There are mechanisms in the body that help mediate and control the effect of these mutations, so except in exceptional circumstances these don't amount to much. If, on the other hand, one of these mutated DNA strands happens to be half of your genome inside a gamete, then the mutations will proliferate throughout every cell in the offspring. I think the surprising part isn't the number of mutations they found, because they seem to fall in with the theoretical estimates, but rather that they were finally able to get a more concrete measure of what the statistical probability is by actually looking at the DNA directly.

Many mutations will turn out to be neutral or detrimental, while others will be beneficial. This drives natural selection. In that sense, I find the following a little confusing:
QuoteIt is hoped that the findings may lead to new ways to reduce mutations and provide insights into human evolution.
They want to simultaneously understand evolution and prevent one of its contributing factors? Perhaps they are referring only to specific mutations that are known to be troublesome. My thought seems to be mirrored here:
QuoteJoseph Nadeau, from the Case Western Reserve University in the US, who was not involved in this study said: "New mutations are the source of inherited variation, some of which can lead to disease and dysfunction, and some of which determine the nature and pace of evolutionary change.

I think a critical thing to point out, though, that there's not really a dichotomy here. It's not "these mutations are bad, while these ones drive evolution." In reality, both good and bad mutations will have an effect on evolution. If the only remaining individual with a particular gene falls victim to a some other cancer-causing mutation and dies, then that gene will simply disappear from the genepool forever, which would certainly have a significant effect on evolution.
Anybody wanna peanut?

PPI Jason

Quote from: PPI Brigham on September 05, 2009, 03:34:20 AM
I think a critical thing to point out, though, that there's not really a dichotomy here. It's not "these mutations are bad, while these ones drive evolution." In reality, both good and bad mutations will have an effect on evolution. If the only remaining individual with a particular gene falls victim to a some other cancer-causing mutation and dies, then that gene will simply disappear from the genepool forever, which would certainly have a significant effect on evolution.

Very interesting point Brigham.

I have a question. What do you mean by, "if the only remaining individual with a particular gene falls victim to a[sic] some other cancer-causing mutation and dies, then that gene will simply disappear from the gene pool forever"? Don't some cancer causing genes get passed on before the person dies, thus continuing to live on?

Here's another question that comes to my mind when I read this: "What mutations are beneficial?" or "How do we go about determining what constitutes a beneficial mutation?" It's easy to define a "harmful" mutation. And a neutral mutation is similarly easy as it could be considered any mutation that isn't harmful or which doesn't cause the person to suffer significant health problems. But what is "beneficial"?
Probably the earliest flyswatters were nothing more than some sort of striking surface attached to the end of a long stick.
-Jack Handey

PPI Tim

In some cases certain genetic defects are good. People who have sickle cell anemia can't get malaria due to the way the blood cell is shaped. I know it is a double edged sword but I bet there dozens of things like that in the world. If you have this then you can't get that.
I also believe that genes we have were never own to begin with. There is no pure race of human.
Now
If I had a choice of gene mutation, give the one where I can fly. ;D
Sounds interesting...Go on.

Brigham

Of course, you're right, Jason. Cancer-causing genes could easily be passed on before causing death. But in my example, I am talking about some other particular genetic trait that for whatever other reasons was reduced to a single remaining individual. If a unique mutation in their genome caused them to be predisposed to childhood leukemia, for example, they might never reproduce. One person is enough to pass on a gene to a whole species, but not if they die first.

Example of a good mutation: light skin. White folk evolved because in cold, European climates during recent glacial advances, less skin was exposed due to heavy clothing, and less sun is available at those latitudes. Thus, lighter skin lets more sunlight through, increasing our ability to produce vitamin D. Once again, it's a double edged sword, because it means we burn more easily and are more vulnerable to skin cancers.
Anybody wanna peanut?

PPI Jason

A point I'd like to make about "beneficial" mutations is that what is determined to be "beneficial" seems to depend a lot on the environment. Take the light skin example Brigham mentioned. That mutation is beneficial in northern climates, not so much on the equator. Another classic example is the English Peppered Moths. The dark colored variety were rare before the industrial revolution. When England revved up it's machine-making industries then the heavy pollution made it easier for the moths natural predators to see and eat the white variety (making them the rare type). Now that we're "green" again it seems the environment doesn't favor the poor dark variety peppered moths anymore.

It just seems to me that what is considered a "beneficial" mutation may be helpful under one set of circumstances, and then harmful down the road. Sickle cell anemia may be great to prevent malaria. So, in theory, parts of the world dominated by malaria should eventually be mostly inhabited by people who have sickel cell anemia (since the environment favors them). But then malaria eventually would develop a strain that works well on people with sickel cell anemia (or some completely new disease developes) and then we come full circle where the environment favors people that don't have sickel cell anemia (or at least some other trait).

My point is this. Genetic mutations don't seem to be making us better (like superman). They just seem to allow the species to adapt to circumstances which are constantly changing. What's good one day may not be good the next. So when we start screwing too much with our genes to try and make us "better" we may end up screwing ourselves down the road.
Probably the earliest flyswatters were nothing more than some sort of striking surface attached to the end of a long stick.
-Jack Handey

Brigham

You seem to have stumbled upon a fairly deep insight from what seems to me to be a somewhat fuzzy picture of natural selection and evolution. Darwinian selection absolutely actus solely upon those genes which are beneficial to reproduction at that time. Sickle cell anemia is in fact a detrimental mutation, in isolation. It's only when it prevents the spread of a blood-borne illness that it actually increases your chances of survival. Just like light skin is detrimental in our species' home territories in Africa, but allows survival in cold, northern areas.

Clearly, some series of mutations and combinations of extant genes are "good" in most any context, such as larger brains, stereo color vision, or a highly efficient, upright gait. Those ones have survived for millions of years.

Selective breeding in the mechanistic, Mendelian sense wouldn't allow for all the changes we see between ourselves and our distant ancestors. Many minor mutations must have occurred along the way, some beneficial, some detrimental, some neutral. And of course, as humans migrated and the world environment changed, various genes in the pool switched between those categories. This is why Homo habilis was able to come along as an evolutionary upgrade, for example, and now there's not a single one left alive.
Anybody wanna peanut?

PPI Jason

Quote from: PPI Brigham on September 18, 2009, 06:50:08 PM
This is why Homo habilis was able to come along as an evolutionary upgrade, for example, and now there's not a single one left alive.

Hey, I just saw one the other day. He was selling car insurance for Geico. Or was he Austalopethicus Anamensis or Neanderthal? I always get those mixed up and they tend to get really offended when you ask, apparently.
Probably the earliest flyswatters were nothing more than some sort of striking surface attached to the end of a long stick.
-Jack Handey