"If men with ApoE4 have 0.1 percent less fewer children that would be enough to rapidly remove the gene from a population." Does that make any sense to you? Maybe in geological time but not in a few thousand years. Furthermore they have no way of knowing the prevalence of dementia a thousand years ago so to draw any conclusions about it disappearing seems a stretch.

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They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

This is going to sound nutty but it's true, I can "see" cancer on/in people long before the cancer ever developes. I can't always see it been when I do I'm never wrong.

I have left two past girlfriends because I saw cancer on them. They are both now dead from cancer.

I have had numerous encounters where I've seen cancer on people and so far they have all got it (there are three people I know who I see it on but have not got it yet but my confidence is high).

The only way I can explain what it is exactly that I see is to say this...

...it is literally written on their faces but in a script that cannot be described.

I hate sharing this because it makes people think I'm crazy.

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Civilize the mind, but make savage the body.

- Chinese proverb

That was one of the surprising findings when evolutionary biologists started applying mathematics to evolutionary theory. Small advantages or disadvantages in selection "add up" quickly over the generations. Of course this assumes the same advantage/disadvantage year after year, which probably never occurs.

I'm surprised that something that doesn't show up until the vast majority of men are done having kids is affecting their fertility.

Okay help me out with this one. 0.1 percent is one in a thousand. So in one generation if 1000 men have this gene they will have on average have one less children than a population without this gene. In this case a generation should be pretty long at least 50 years because the effect is felt at the end of life because as they state it would be less men at quite an older age having children. So every 50 years you lose one person compared to the normal group. At least for the first ten or so generations. As you get further along you lose less than one person because 0.1 percent of 900 hundred for instance is 0.9 persons. So it would take at least 5000 years to lose 100 persons from you original 1000 people. You still have 900 people with the gene. Is my reasoning faulty? Secondly I think Alzheimers is not linked to just one gene. Third if this is the way things work why have not all cancers and other inheritable diseases been bred out of human populations? Most cancers present at relatively advanced ages but most cancers also present at younger ages at more frequent intervals than the youngest alzheimer patients. Yes you can get new mutations causing cancers but similarly you would get new mutations causing dementias. I don't think dementia or Alzheimers is going away from natural selection.

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They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

Interesting.
My wife was diagnosed with metastatic melanoma a bit over 6 years ago.
She's pretty damn tough, and so far so good (remission), but before she was diagnosed, our dog would bury his nose in the crease of her left thigh/hip and we thought he was just a dirty little fucker getting a sniff of you know what, but turns out he could smell the cancer and he was trying to get at it (was right where he was going for)

Same sort of thing when the dog refused to leave my son's side (and was whining and trying to wake my son) one evening as he was asleep on the lounge. My son is a type 1 diabetic and his BGL was dropping dangerously low and the dog could smell that too.

Wouldn't trade that dog in for anything....

Can't help you with the mathematics, I assume it's in the paper, and I'm sure beyond me anyway.

The vast, vast majority of cancers are not heritable so natural selection will have are hard time eliminating it. There are certainly genes that make people susceptible to certain cancers, so natural selection could help there, but for all we know these genes are advantageous for other reasons. The problem with cancer is that it is caused by a number of novel mutations that arise during a person's lifetime, somewhere around a dozen or so in a given cell line for it to become cancerous.

The basic problem is that when multi-cellular life arose evolution had to come up with some way for cells to not make endless copies of themselves in order to out compete the other cells in the organism. It did that such that the production of new cells is usually well regulated. But natural selection will favor whatever cell or organism leaves more copies of itself in future generations. So if a cell escapes an organisms limits on its own reproduction it will be favored, and that is what cancer is. Now because it's a "blind" process the cancer cells don't know that if they are too good at making descendants they will ultimately kill themselves by killing the host organism. Cancer can be thought of as the evolution of new species within an organism but ultimately one that is doomed to extinction (except for very, very few incidences where contagious cancers have evolved).

So as long as cells are making copies of themselves and mutations occur, cancer isn't going away.

Humans have a really poor sense of smell. We've lost all kind of olfactory receptors even since our split from the last common ancestor with chimpanzees (last time I read anything about it, most of the genetic differences between us and chimps that had been identified were these lost olfactory genes in humans). Compared to a dog or bear we must be just horrendous at smelling.

Alot of the really lethal genes are recessive so they keep getting passed on because they only cause major problems when you have two copies. Cystic fibrosis for instance one in 25 people is a carrier. Up until the last 30-40 years the chance of reproducing with CF would be zero. A dominant lethal gene disappears fairly fast unless it asserts itself later in life. There are a few I really wish would go away Huntington's comes to mind.

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They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

Yeah and a number of those are thought to be advantageous when you only have one copy of the gene. The classic example being the protection one copy of the sickle cell gene provides against malaria.

what difference does it make?

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sometimes

If it makes you feel any better, we were all convinced long before this latest revelation... :)

Compared to a dog or bear we must be just horrendous at smelling.

That may be true...we certainly don't have drug sniffing humans at the airports...but recent research shows we have similar physical capability...number of olfactory neurons...as most animals and can outperform dogs with certain scents. So it may be largely a matter of what we train ourselves to pay attention to rather than a genetic modification.