Please forgive my ignorance, but I am stumped.
1) How do we evolve if a negative trait does not kill us before we reproduce? For example if I have some genes that are maladapted to refined carbs but have already popped out a kid before it has killed me how is natural selection taking place even over say 20 generations? I mean how often do people really die of refined carb related illness before they can squeeze out a kid?
2) If we have been around for 2.5 million and grains have been around for 10k how much adaptation has taken place?
3) I guess I am asking is natural selection the only way we evolve or are there smaller feedback loops on like a cellular level. I just donít get it.
I think there are mechanisms of evolution operating that are different from natural selection, which is more short term as you say.
Pottenger's cats, infertility caused by hyperinsulinemia, lactose/gluten tolerance of Caucasians, and other evidence suggests that effects besides death before offspring contribute to genetic adaptation.
Something that is emerging in evolutionary biology is a shift towards looking at the distribution of a gene across a population as opposed to focusing on the "fitness" of one individual. From this perspective we have a potentially much larger sample size with a given gene (or set of characteristics) interacting with the environment. It is here that we see a population wide tendency to show favorable or unfavorable adaptations to a given environmental stressor.
In the situation you described you, me and our immediate ancestors have not been impacted to a degree that makes it impossible for us to reproduce. In general we do however have smaller brains, less robust frames and decreased fertility vs our HG ancestors. Certainly a slide away from a better pairing of our genes and the environment.
Now we (as a species) have passed through the: Agricultural, Industrial, and information revolutions. Each of these steps have decreased our activity level and refined our diets, and our health has suffered. We are now facing a time when our diet is SO refined and activity levels SO low that children are failing to enter puberty due to hormonal derangement. Things have gotten bad enough that some WILL be weeded from the gene pool before being able to reproduce. The folks who go on are better adapted to: refined foods, low activity and crushing boredom as a lifeway....unless things shift so dramatically that fertility as a whole drops to un-sustainable levels. That is unlikely to happen but it's not necessary to die early to be removed from the gene-pool.
In addition to natural selection there is epigenics which is the interaction of the organism with the environment. This can effect gene expression to a remarkable degree, although most geneticists do not think this changes heritable traits ala Lemarkism. Good follow up reading includes:
The Blind Watch Maker
1. Right...we are seeing maladaptation and infertility occurring in obese kids. That is a form of natural selection. Beyond that, in a natural environment, which humans do not exist in any longer, natural selection doesn't necessarily have to kill you before you procreate, just before you outprocreate that with the beneficial traits. If you die after having 1 child, who dies after having 1 child, who dies after having 1 child, ad infinitum while Ben lives to have 3 kids, who live to have 3 kids, ad inifinitum, whatever beneficial trait Ben has passed on will eventually overcome and outcompete your underperforming genes.
Note: the above story is not intended to insult anyone's DNA. The author has not examined the named subjects DNA.
2. Little adaptation has occured. It seems that most people have some level of gluten intolerance, obviously some exhibit overt symptoms and are hypersensitive. I would think those people are in a better situation than those that are slightly sensitive and damage their bodies for their entire life because "it doesn't bother me."
3. I think this is splitting hairs. If it knocks one out of the breeding cycle, whether at the cellular level or because you have short legs and can't outrun the tiger, it is natural selection at work.
Edit: Robb replied while I was posting...sorry for any duplications/discrepancies.
This might be why we are attracted to 'healthy looking' people. People who are far out of shape, extremely overweight, extremely underweight, etc are less likely to find mates.
Health and strong reproductive traits are what our sex drives are based upon.
The problem is, many people these days are starting to develop skewed opinions because of society(unnaturally skinny woman as 'healthy', extremely ripped men as attractive, and on the opposite side of the spectrum - being obese is okay, etc).
Being skinning is not healthy.
Being 'totally ripped' is not a good thing.
Being obese is not okay.
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