If I understand it correctly, albeit in layman’s terms, Darwin reckoned that the fittest (healthiest) specimens of a given species would go forward to populate the earth. The weak and sickly wouldn’t survive.
But … don’t many species reproduce, passing on faults or conditions that do not become evident in the parent until after bearing offspring? In other words, the weak and sickly may well survive long enough to proliferate, the ‘problem’ only showing up after it’s too late to stop it spreading to the next generation.
I’m looking for examples of such diseases/conditions over a mixture of recognisable species… plants and/or animals.
Try visiting http://www.talkorigins.org for some basics about evolution. Especially try the FAQ. After you read that, come back here if you still have questions.
Aw hell, I’ll give you some help. No, Darwin didn’t say that ONLY the “strong” would survive. Just that all organisms compete for resources, that organisms vary, that part of that variation is hereditary, and that organisms that have favorable hereditary variations are going to be over-represented in the next generation compared to the others.
This is true. Diseases that appear after an organism is done reproducing are not selected against.
For many organisms it is just natural death. They die of old age after they are no longer able to reproduce. There also is cancer, which affects nearly every multicellular organism.
For instance, it is more likely that the animals that are more resistent to diseases will continue better than others.
my own 2 cents
And just because one may develop a question that does not seem to be explainable by certain theories does not prove the existence of mythological superstitions
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*Originally posted by Qadgop the Mercotan *
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He was given the above assignment and I think he should not only read the book, but should also turn in his book report no later than August 18th. And no fair using…[list][list][list][list][list][list]cliff notes[list]
Unfavourable mutations that are expressed after the reproductive phase can still be disadvantageous to the offspring, particularly in creatures like elephants (and humans) where the offspring are reliant on the parents for a considerable time.
I think that the OP was referring to disorders which don’t show up in a carrier, but might in the carrier’s offspring. In that case, a carrier might have plenty of children, but few or no grandchildren, which are just as important, evolutionarily speaking.
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*Originally posted by Blown & Injected *
And just because one may develop a question that does not seem to be explainable by certain theories does not prove the existence of mythological superstitions
I don’t understand this point. Please could you clarify?
More homework: The works of Thomas Henry Huxley on the subject of evolution and especially natural selection.
Most people forget that everyone thought Darwin was insane until Huxley weighed in on the subject. Also keep in mind the fact that Darwin never used the phrase “survival of the fittest.” The attribution of these words to Darwin is indicative of the most common misunderstanding about his theories.
An important thing to remember when talking about Darwin is that his theories are posited in the context of geologic time (as my favorite high school English teacher always said: look it up).
The OP has not promulgated any alternative position on speciation, or biological diversity, superstitious or otherwise. An assumption that such an opinion is intended demonstrates a prejudice on the part of one making such an assumption.
Stronger, better, or fitter are not necessarily traits that will be selected for by natural selection. If a plant produces several colors of flowers, the colors might provide no specific benefit to the plant. A great diversity of color could become common. If a grazing species develops an aversion to a different plant that has blue flowers (which causes gastric distress in the grazer), that has no direct hereditary effect on the original plant. But if the grazing species flourishes, and overgrazes the range of the original plant, the simple fact that those grazers tend to avoid blue flowers can change the frequency of the trait for blue flowers drastically.
Over time, the species might have only blue flowers. Blue flowers were a benefit for survival. Thousands of years or even millions of years later, the benefit of blue flowers no longer exists, but the genetic heritage remains. It is possible that many such traits exist, although they have no current survival benefit, simply because they survived in different circumstance. Disease resistance is an example that can be critical for a specific generation and completely unimportant for a thousand more. That does not take into account the evolution of the disease, of course.
Tris
“It is even harder for the average ape to believe that he has descended from man.” ~ Henry Louis Mencken ~
It seems I haven’t got the hang of replying with a quote, perhaps it’s the tiny screen on my PDA, my black & white browser, or just me so I’ll comment here.
Qadgop the Mercotan et al. This may be controversial, but I do not intend to read “Origin of the Species” at this juncture. (I feel sure that it is as compelling as Erasmus Darwin’s hand-written and beautifully hand-illustrated works) I wish to examine the ‘loophole’ first. By reading yesterday’s horoscope many predictions may seem to fit better.
kniz, you (too?) have made assumptions.
I’m really looking for identifiable instances where the ‘unsuitable’ (the maladapted, if you like) are not weeded out before reproduction occurs. It is perhaps excessively applicable in humans nowadays because much of the world’s population has access to medical services, without which many wouldn’t survive long enough to reproduce.
Here’s a couple of bad examples (I could use some good ones!):
Wouldn’t Haemophilia be much less prevalent if medical facilities for testing/treatment did not exist? Perhaps the disease, in a fully expressed form got mainly weeded out of females because those which survived so far tended to die in childbirth (if the menstrual cycle didn’t get them first!?) but then that would still have been too late to stop it getting to the next generation should the child survive. (I’m guessing here, please inform me!)
Something like senile dementia , on the other hand, is extremely unlikely to get bred out because it only surfaces some years after reproduction is finished. …and the medical care of such people wouldn’t make any difference to the next generation inheriting it. If initial signs of it could be detected at, say, puberty, I wonder what difference that would make.
El Cid: The end result ( and there isn’t one really, since it is an ongoing process ) of Natural Selection is not the “super-organism”, but rather the “muddling-through” organism. No, not every maladaptive feature gets weeded out. Some because they are, on balance, more adaptive than maladaptive, like Sickle-Cell Anemia. Some, such as vulnerabilities to parasites and disease, represent losses, or at least parity, in the evolutionary “arms race”. Some are rarely expressed genetic defects that linger in the genome simply because they are rarely expressed. Some, your senile dementia for example, are irrelevant because they would generally surface after breeding age and therefore are less significant ( though if it surfaced too young it could conceivably have a negative impact on descendant generations - conceivably ). And if we’re talking humans and their domestic animals, some are deliberately propagated for sundry and bizarre reasons - i.e. inbreeding and hemophilia in the old European royalty .
English Cid, I’m not entirely sure what you’re asking, but if this:
is your point, then…I think you’re missing the point. Natural selection is ultimately all about reproduction - only those traits which prevent an organism from reproducing will be weeded out. Once an organism reproduces, it’s done its job, evolutionarily speaking.
So, if a genetic trait, whatever it may be, affects juveniles of a species in such a way that they are unable to reproduce upon reaching the appropriate age (or, perhaps, by being prevented from reaching such age), then, yes, this trait will be selected against. If the organism reaches sexual maturity and reproduces, then natural selection has no further say, so to speak. Other factors may later work to weed out the sick or the weak, but these have little bearing on evolution.
Medical science has allowed humans to circumvent natural selection to a degree. We may be able to treat certain genetic traits, which left untended might otherwise prevent a child from reaching sexual maturity and subsequently reproducing; such traits may well continue in the gene pool.
This is a bad example. To give some context, haemophilia is caused by a gene on the X chromosome. Women don’t develop the condition because the gene is recessive compared to the normal copy on their other X. Men however have a Y chromosome and so male carriers do suffer from the disease. Half the sons of a carrier (of either sex) will be haemophiliac, half the daughters will be carriers.
It’s a bad example of what you seem to be arguing because, pre-20th century, haemophilia did tend to get quickly eliminated from families by natural selection. Male carriers died before maturity and with only half the females being carriers the gene tends to die out in time. Why the disease occurs at all is because the original mutation that introduced it to families is relatively common as mutations go. In the most famous example, I think the mutation arose a generation or two before Victoria and I’m pretty sure it’s at least almost eliminated from all branches of her unusually large and medically well-cared-for family. (With a little help from the Bolsheviks.) Perhaps half a dozen generations for it to be selected into extinction.
There are plenty of genetic diseases that aren’t selected against because they don’t appear till after childbearing - and several have already been mentioned in the thread.
I wouldn’t second the advice to read Darwin himself as a way out of your confusion. (It’s a brilliantly argued book, but not for someone with basic misunderstandings.) A little Dawkins and lots of Gould might be more helpful. Also Why We Get Sick (Times Books, 1994; Evolution and Healing, Weidenfeld and Nicolson, 1995, if you’re in the UK) by Randolph Nesse and George C. Williams might be worth a look. It’s a consistent feature of Williams’ writing to worry about when genes are active and what influence this has on selection, so there’s quite a bit about this sort of issue there.
For background, one of the recurring, interminable topics in the ‘Great Debates’ forum is evolutionism v. creationism. Creationist thought often focuses on apparent ‘mistakes’ in the theory of evolution as proof of creationism. The topic line you gave to this post could have been leading that way, which may have triggered this comment.
Your actual OP and subsequent comments indicate an attempt to understand the theory of evolution, which is a good topic for a General Question. If the thread turns into yet another ‘creationism v. evolution’ debate, you can expect a friendly moderator to move it to GD.
) of Natural Selection is not the “super-organism”, but rather the “muddling-through” organism. No, not every maladaptive feature gets weeded out. Some because they are, on balance, more adaptive than maladaptive, like Sickle-Cell Anemia. Some, such as vulnerabilities to parasites and disease, represent losses, or at least parity, in the evolutionary “arms race”. Some are rarely expressed genetic defects that linger in the genome simply because they are rarely expressed. Some, your senile dementia for example, are irrelevant because they would generally surface after breeding age and therefore are less significant ( though if it surfaced too young it could conceivably have a negative impact on descendant generations - conceivably ). And if we’re talking humans and their domestic animals, some are deliberately propagated for sundry and bizarre reasons - i.e. inbreeding and hemophilia in the old European royalty 
.