2xhelix

This question focuses on the validity of Macro-Evolution applied to humans.

I will first say, that I am not an expert in this area, but I do understand the basics of the theory of evolution ( at least I hope I do).

A mutation is something that occurs at the gentic level, which produces a physical mutation. Are there any examples where a 'positive' mutation is wide spread?

For example, we know that Down Syndrome is caused by a certain gene. To me, this would suggest that there was some type of mutation, and it was passed down over many generations.

So are there any examples of a mutation that is positive?

nogods4me

depends on the situation. many past mutations have quite obviously turned out to be positive, we are here and doing well after all.

as a further example: people who have sickle cell disease also seem to have an increased resistence to malaria. In this situation depending on where the person happens to live it could be either a positive or a negative.

Coragyps

Two other mutations in humans that have been mentioned here recently are the one, primarily in North Europeans, that allows adults to continue to digest lactose (lactose intolerance is apparently the "standard issue" in adults), and Hemoglobin C. The latter is similar to sickle-cell anemia, except that the ill effects are usually minor or even unnoticed. It confers malaria resistance like sickle-cell, and is distributed in a target-like area among West African populations. It is thought to have spread from a single mutation there within the last millenium or so.

DonaldW112

This is not a clear example of a positive mutation but gorillas, chimps and humans have a mutation in the gene that produces the protein that manufactures vitamin C. We still have the gene but unlike most mammals we can not produce vitamin C and must eat fruits and veggies to get it. While this may seem like a bad thing it might have had positive benefits since we began eating a much wide ranging diet with a larger variety of vitamins, minerals, proteins, etc. Sometimes it is hard to tell if a mutation is good or bad in the short run.

lpetrich

That reminds me of some interesting research I had once done. I checked out the nutritional needs of various species across the animal kingdom commonly kept in captivity, such as common pet and laboratory species. I checked out, IIRC, dogs and cats, birds, fish, and insects. I found that they were all very much the same -- the same essential amino acids, the same vitamins, the same minerals, though sometimes with a few differences here and there.

This suggests that the animal kingdom's common ancestor had had similar biosynthesis deficiencies, which would come about as a result of eating the flesh of other organisms and DonaldW112's spoilage mechanism. The essential amino acids are generally the more complicated ones, meaning that they are more difficult to manufacture -- and if there is a good supply of them from one's food, the manufacture of them can atrophy the way that vitamin-C manufacture has atrophied in the ancestors of the great apes.

However, it has to be fresh flesh or else other organisms will get to it and consume these substances. And many organisms of decay, like many fungi and bacteria, are much less finicky, being able to subsist on any one of a variety of biomolecules. Beggars can't be choosers, as the old saying goes.

One further indication that these animal-kingdom nutritional deficiencies are ancestral comes from adaptations for eating land plants, whose biomolecule output is slanted rather heavily toward producing cellulose, an essential structural material. This has side effects like their sap containing big concentrations of simple sugars. Which makes land plants a sort of "junk food".

If one has beggars-can't-be-choosers biosynthesis, one would have no trouble with land plants, at least if one can digest cellulose. But if one has half-crippled biosynthesis, one has to

1. Do a lot of re-evolution
2. Have a voracious appetite
3. Eat the least cellulosified parts
4. Grow colonies of microbes inside of oneself that do the digestion of plant material for you

Solution 1 does not seem to have happened in the animal kingdom -- too difficult?

Solution 2 is feasible for caterpillars and the the like, but not for big animals.

Solution 3 is common -- many animals have a preference for fruit or seeds. For exmaple, rodents' front teeth are an adaptation for getting past the hard shells of many seeds, such as the shells of nuts.

Solution 4 is somewhat common, and has evolved several times. Aphids live off of plant sap, and special bacteria live inside of them and produce extra nutrients for them. Termites eat wood, and maintain a zoo of microbes to digest it. Maintaining colonies of microbes to assist in plant digestion is also common among mammals, notably the ruminants.

DonaldW112

Quote:
_________________________
This suggests that the animal kingdom's common ancestor had had similar biosynthesis deficiencies, which would come about as a result of eating the flesh of other organisms and DonaldW112's spoilage mechanism. The essential amino acids are generally the more complicated ones, meaning that they are more difficult to manufacture -- and if there is a good supply of them from one's food, the manufacture of them can atrophy the way that vitamin-C manufacture has atrophied in the ancestors of the great apes.
__________________________________

This brings up an interesting point. I wonder if vitamin-C manufacture atropied (ie when the mutation occured it was no big deal) or it occured and caused a radical but positive change in diet. It would be interesting to know if your fruits and veggies are "brain" foods (ie the reason we and great apes are so "smart" is because we had to change our diet). I wonder if this is known? Not my field of expertise at all.

Donald

Coragyps

Donald - Not my field, either, but I think the primary primate hypothesis (I couldn't help myself!) is that some ancestor was already eating fruit for the high sugar = quick energy content, and the loss of Vitamin C synthesis abilities just wasn't much of a loss with fruit already in the diet. Many monkeys eat lots of fruit, and they, AFAIK, all can make vitamin C.

As for "brain food," there's a news article in the May 3 issue of Science (p 835) describing a recent paper which suggests: The authors suggest, too, that the paleo folks need to look for seafood remnants way back in the days of H. erectus brain expansion, as seen in fossils. They admit that this may be tricky, as sea levels have risen since then - maybe the rift lakes where so many hominids have been found can be persuaded to give us some clamshell middens, too.

MortalWombat

Nope. It is caused (in the vast majority of cases) by having an extra copy of chromosome 21, due to an error in partitioning of chromosomes during meiotic cell division during gamete formation. In a small minority of Down cases, a portion of chromosome 21 is fused to another chromosome. Using this data, geneticists have narrowed the list of genes down to a few dozen, but certainly not a single gene.

MortalWombat

Nope. All primates (including humans) need vitamin C in their diet. In fact, in all primates studied, there is the same crippling single base deletion in the GLO gene, which codes for a protein needed in vitamin C synthesis.

DonaldW112

I have that issue in my backpack I will read it this morning. Thanks!

(Edited to fix quote tag)

[ May 16, 2002: Message edited by: DonaldW112 ]</p>