ahem As I was saying before the board outage rudely interrupted me…
Ninjaed by lazybratsche! 
This touches on the concept of irreducible complexity - the creationist argument that extant complex biological structures/functions could not have evolved on their own, since evolution (so goes the claim) wouldn’t select for any of the expected intermediate structures/functions between “no photosensing at all” and “fully formed vertebrate eyeball”. As WhyNot and lazybratsche have shown, there are plenty of intermediate forms (many of which are also extant in other species) that provide useful functionality that can be selected for by evolution. There’s that Haldane quote, “The world is not only stranger than we imagine, it is stranger than we can imagine,” and it serves as the counterpoint: a person arguing for irreducible complexity demonstrates only that the world is stranger than he can imagine.
First stage is a patch of light-sensitive molecules on the surface of a cell.* All that they can show is that there is more light on one side of the cell than the other, but that is still useful–it can trigger the cell to ooze or rotate its cillia/flagella in a way that moves it towards or away from the light. Even bacteria have those.
Second stage is having versions of those light-sensitive molecules on the surface of patches of cells on a multi-cellular organism. Again, all they can show is that there is more light in one direction than another.
Third stage is having those patches of cells in a shallow pit, which allows the direction of the light to be more finely determined.
Fourth stage is having the pit become deeper, and partially closed over. This allows for a pinhole camera, and finally an eye that can form an image.
Fifth stage is forming a transparent membrane over that partially closed pit roof. This becomes a lens.
Every single step along this progression is useful, and earlier stages look “primitive” only when compared to later progressions.
*and at least one family of unicellular organisms has actually evolved an “eye” with a lens!
Ooh! That’s cool. Creepy, but cool!
Folks who’ve been trained from a young age to be dogmatically incurious often have very weak imaginations. And darn little knowledge of the immense variety actually available in the world which needs no imagining at all; merely the desire to learn and explore.
Not really. When you look around and see species with developed senses that they need, they didn’t get them because they need them. It’s more a case that they’re still here because they have them.
Within the framework of evolution, the most common response to needing something you don’t currently have is simply failure to survive.
The vast difference in rate of change between these two messes up a lot of things.
For example, there might one trait now that isn’t so good for us but in a more advanced society 500 years from now will be advantageous.
Evolution is not just playing catchup, the goal posts keep moving around as well as getting farther and farther away.
One human problem that has arisen due to rapid change is so many people falling for lies. Language developed too quickly that the countermeasures to tell when someone is scamming us haven’t developed to keep pace. Will we ever evolve the ability to spot BS?
What he said.
Whether or not a species needs something to survive has no effect on what mutations occur.
Regards,
Shodan
Although other posters have covered the uses of a proto-eye, the book In the Blink of an Eye goes into depth about the possible evolution of sight, including numerous examples from both the fossil record and modern animals. I found it an interesting read.
I’ll also note that trilobites had crystalline eye lenses that, in some cases, have been preserved intact in fossils. Meaning it is possible to actually look through the actual eye lens of a creature that lived half a billion years ago, still in working order. So, not a layer of transparent cells, but a layer of deposited mineral.
Overweight people actually live longer.
Interesting book maybe, but best read while holding a grain of salt. (Yes, I’ve actually read it myself, but so long ago that my memories of the details are vague at best.)
A good summary of trilobite eyes from probably the best trilobite info site on the web (the work of one person, and has been around practically forever in web-years.)
I read somewhere that eyes appeared to have evolved independently up to 40 times.
One place that evolution might take place and even quickly would happen if we somehow succeeded in wiping out malaria, whether by a gene drive mechanism or otherwise. You would see the sickle cell trait disappear rather quickly in evolutionary terms. Maybe with a few dozen generations or certainly a few hundred.
On the other hand, we are unlikely to evolve a lack of appendix. I am very sensitive to this because I am one of three none of whom would have survived to reproductive age without the availability of appendectomies, which is the sort of thing that ought to generate strong evolutionary pressure. But the other side of this coin is something I read somewhere that smaller appendices are more likely to get infected than larger ones. So the appendix is unlikely to wither away, although I suppose it could just disappear somehow.
This illustrates the fact that evolution can work only with the material it has at hand. It can happen quickly or slowly, but every step has to give a selective advantage.
You’re all neglecting sexual selection, which roughly uses female (mostly) intelligence to predict the reproductive success of the potential offsprings. This is a much faster evolutionary pathway, and in fact there are a number of human genes that had significant evolutionary pressure in the past few thousand years.
As others have said, Cool!
Thanks
The Dope never ceases to amaze…
Several people have described the evolution of light-sensitivity to functional eye. Some creatures have eyes on aim-able stalks IIRC; one can see the evolutionary advantage of shrinking the stalk to make it less vulnerable until it retracts into the body (sumo style) so only the lens is exposed, but still retaining some aim capability.
Another point is that a lot of the intermediate products (half-way there eyeballs?) disappear as the creatures that had them lose the evolutionary battle to the better model.
Even a pit with a few dozen light-sensors gives the creature an idea whether it has ventured out from under a rock, for example, and should reverse course and duck under cover again. Evolution advantage…
The key to any evolution change is - does the advantage allow the person to have more children than others and allow those children to survive into adulthood? The latter is critical because humans have a notoriously longer childhood than many species, before they can fend for themselves. In fact, modern human society is directly countering many evolutionary tendencies - welfare generally means that even the least capable persons survive to reproduce; modern medicine and vaccines reduce the risk of childhood mortality, and that child welfare systems ensures those children survive to adulthood even if the parents don’t. Birth control reduces the tendency of differential reproduction rates; you may have a great mutation, but if you choose to use protection, you will not pass it on to more children than your rivals. One study I read suggested that regardless of abortion, or available birth control, most women in western society tend to have as many children as they want and no more. Regardless, biological “fitness” is less of a criteria for how many children one raises to adulthood. Indeed, it’s possible that irresponsibility and immunity to the effects of birth control hormones may be the major factors being selected for.
(We had a long thread earlier about the issue of whether modern medicine is causing the reverse, genetic dilution with traits that would be detrimental to survival outside the modern support system; do eyeglasses and insulin and antibiotics and IVF result in generations that contain a more tech-dependent population).
Of course, partly that selection is aimed at evaluating the ability of the male to help feed and protect the woman and offspring while the children cannot survive on their own… again, the extended childhood of humans. Hence the attraction of a man’s large… wallet. 
Glasses are only a partial weapon against evolution. Beer goggles overcome them. And ladies, don’t kid yourselves. You wear them, too. 
Not really, chronic pain isn’t a problem for people in their teens, 20s and 30s for the most part. Even if it is and a parent becomes disabled, that isn’t going to affect whether the children survive to adulthood or mate themselves. I know someone in their 30s who has chronic pain and it is impacting her ability to be a parent. But her children will have grandparents, cousins, aunts, uncles, etc. to pick up the slack. She has 2 kids. Irrelevant of whether she is disabled by chronic pain or not, both of those kids will survive until they finish puberty and I doubt it affects the quality or quantity of mates they find.
Right now Africa makes up about 14% of the human population, 1 billion out of 7 billion. By 2100 they could make up 40% of the human population, 4 billion out of 10 billion. They have more kids in Africa.
Evolution rewards whatever mates the most, and whose offspring survive to adulthood and themselves mate.
Sadly,right now evolution is selecting against positive traits like long range planning or education. Less educatedwomen have more children. People who reflect on how serious raising a family is have less kids than people who just fuck like bunnies. Wealth is also selected against on a national level, nations with a per capita income below $6000 have far higher fertility rates than nations above this level. So right now evolution is selecting for poorer, less educated individuals. Sucks.
I do wonder if evolution would select against obesity because obese people are less sexually desirable and they have lower fertility rates. However, who knows how long that’ll take. Realistically we will probably have a cure for obesity in 20-50 years, so I doubt evolution would matter much after that.
We’ll probably also be able to augment our intelligence and perhaps stop aging. That would restore natural selection in favor of positive traits, since if we’re not aging and dying of natural causes then the morons get themselves killed in other ways.
Not really. Note my beergoggles post. We are stuck being the product of our stupid genes. Any hope otherwise is cute. Totally cute. Enough to find me cute. Far too long to waste genetic material on cute losers. Y’all fucked. 