scigirl

I would say from a strict survival standpoint, we are definitely getting worse. This is not because of increased mutations, but because of decreased selection. Modern medicine, indoor plumbing, housing, clothes, etc, has shielded us somewhat from the environmental selectors that our ancestors had to face. Think about how many of us would be too blind to hunt very well.

And that's just one example.

Of course I'm making a career out of the fact that humans thumb their nose at evolution - so thumb away!

scigirl

scigirl

Well since you want a truthful answer (as opposed to all those blatant lies we all just make up to confuse creationists )

Mutations that are inherited MUST occur in a sperm or egg cell. If a mutation happens in my arm cell, so what? It won't affect my progeny.

But no they don't occur during fertilization (at least not usually) - they occur during gametogenesis - when we are making sperm and eggs (adult females don't really make eggs anymore but now we are getting too complicated.)

There are several types of mutations that can occur in DNA. Some of them happen when the DNA is just sitting there (UV light, or even worse, X rays if you weren't wearing a lead apron at the doctor's office, can permanently alter the sequence of the DNA).

Most mutations, though, happen during DNA replication, or during meiosis. You can get point mutations (DNA polymerase puts in the wrong base when it's copying the DNA), frameshift mutations (a base gets added or deleted which changes the rest of the gene downstream). You can also get large chromosomal mutations - where one sperm gets two copies of, say, chromosome 21, and the other sperm gets zero. If the first sperm actually fertilizes an egg (which has one copy of 21 of course), you get Down's syndrome - a tri somy. Also, this is where homologous recombination happens.

You know what - rather than me try to explain all this stuff, I encourage you to peruse this cool on-line biology book:

<a href="http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookhumgen.html" target="_blank">http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookhumgen.html</a>

Happy reading!

pz

So what? Think how poorly that ancestor would do on a biochem exam, or in crossing a city street. Adaptation is entirely context dependent, and we are living in a different environment from our ancestors.
Let's not confuse real ideas about evolution with teleological misconceptions. The availability of medical care is just making it possible for more people to survive and use your services -- that's not thumbing their nose at evolution, it's an example of evolution.

Besides, if we take your attitude, you seem to be thumbing your nose at evolution, too. Shouldn't you have had a half dozen babies by now, and be an expert at the career of gathering roots and berries?

scigirl

Ok I have to disagree - unless you can show me that availability of medical care is somehow encoded in our genome.
Well yes I am. My fitness is zero, right?

I think the point that I was trying to make is that we see more genetic diseases today (I use the term disease loosely) than what we would predict if we were all acting under selection like we did when we were primitive man. I'm not sure if we can even measure this, but I do know that certain diseases which have a genetic component are on the rise because of our behavior (heart disease is one, cancer is another). Or, many children survive and are able to reproduce because of technology - hemophilia is one example.

Yes it is true that our ancestors would have performed poorly in biochem (funny you should use that as an example, I just had a biochem test today). However, they didn't need biochem. We still need good hearts and blood clotting machinery. Does this make sense?

Just because we can fix hearts with pieces of plastic, doesn't mean we have evolved. Take away all our technology, and many of us would die, because the technology is not encoded in our genomes.

I'm not exactly sure what we are debating anymore - but if you give me 3 choices: is the human genome staying the same, accumulating more mutations, or accumulating less mutations, I have to go with the middle answer.

What this means in terms of evolution and this discussion? I have no idea.

scigirl

scigirl

Ok maybe what I am trying to say is that the frequency of what we would call genetic 'mutations' is increasing over time, since the mutations are still mutating along like they always have been, but our selective pressures have significantly dropped.

scigirl

pz

Right after you show me how a preference for a diet of meat and sweet foods is encoded in our genome. Or an ability to chip flint or make a fire.
Got any brothers, sisters, nephews, nieces, cousins? We could still make an argument that your inclusive fitness is non-zero. I hope that makes you feel better, and discourages you from rushing out to get pregnant right now.
You left out an option: it's not staying the same, and it's accumulating mutations at roughly the same rate per individual as it would have 10,000 years ago. That's the position I'd take, anyway. Most mutations are going to be neutral, and all of our genes are going to be mutating at a rate of about 10^-6/individual/generation, so not much has changed. Modern medicine allows some alleles that would have been lethal once upon a time to survive and increase their proportion in the population, but I'd argue that those are relatively rare and could be counterbalanced by other alleles that have become detrimental in our modern world.

The big change is in population size. We harbor much more genetic diversity in the human population now than ever before solely because there are over 6 billion of us.

pangloss

No, I am trying to pin down creationists on their views on 'inforamtion' because I have a published example that I want to then address. If you say so, but that is not what this is about. Very good. Then you must not be a creationist 'information monger.' AExcept for lethal mutations, I find those definitions arbitrary and unsatisfactory.

scigirl

Whew, what a relief! (sorry to my fan club. . . )

I agree that we are accumulating mutations at the same rate - I still think though that selection is acting on us less than it was 10,000 years ago - at least, selection is not acting on deleterious alleles as fervently as it used to be.

Not rare enough to keep me out of work though!

Also - there are a lot of diseases which have a genetic component to them, but aren't necessarily a "genetic" disorder. For instance, susceptibility to certain pathogens encoded by our MHC. At any rate, these things are tough to measure.

scigirl