Before you all go nuts, I accept that evolution is real (we Europeans don’t have as much trouble with it as our cousins from across the pond ), but only because most biologists say its real, and, well, they should know.
There are however, several things that I don’t understand about it, and I was wondering if people had any good, easy-to-understand sites that I could look at (non of this dogmatic “if you don’t believe you’re stupid” crap).
Specifically, I was wondering about the timeline of evolution, since apparently it takes millions of years to change an animal, but through selective breeding it only takes us a few centuries to turn a wolf hound into a sausage dog. My WAG is that it has something to do with the consistancy and focus of the breeding (ie, the desired trait always wins out).
Also, I don’t get how natural selection works for multiple traits. For instance, I can see how the height, shape, fur length, toungue shape etc can change over time (again look at breeding), but I don’t get how these changes are selected simultaneously over time. My understanding is that more than one change occurs at the same time, yet it seems to me that its unlikely that more than one trait would appear in one organism at a time. For instance, for a hypothetical prey species, being bigger might only be advantageous if the prey also had a certain defense mechanism, but the defense mechanism would only work on a bigger creature. It just seems to me that certain adaptions are dependant for their advantage on the existance of each other.
Finally, I saw this on a website, and I couldn’t think of an answer; certain adaptions woul not be an advantage until fully formed. A new leg, or a complex organ like a liver, would not really be any use until fully formed. Similarly, a little nub on the side of an aurochs head, when it was growing horns, would have been useless.
Remember, you don’t have to convince me to believe in evolution, I just want to unerstand the mechanics of it.
Any (all) Richard Dawkins books are good. River out of Eden is one, available thru Amazon for a few dollars or at your local library for free.
Steven J. Gould is another good author.
Random variation coupled with survival of the fittest is your answer.
Due to errors in digital copying of genetic material, some organisms have a better chance of living and therefore reproducing. Their offspring carry the same “error”, which has proved to be useful. These are very small changes and may take a long time to weed out the less useful characteristics, altho Gould postulates that some changes are more rapid than others believe.
And you are certainly right that certain adaptations are dependent on other species; the prey get better at avoiding the predators, the predators get better at catching the prey. It’s one of the things that drives species changes.
As far as multiple traits, these may be selected individually or several at once. Sometimes one trait affects the selection of others. Overall, the most adapted organism must, on average, be better able to survive and reproduce regardless of why or how.
It’s a fascinating topic, and I hope you find it interesting enough to investigate.
Well, it doesn’t have to be an advantage. It only needs to not be a disadvantage. Evolution is almost entirely negative. It weeds out maladaptive traits but useful and neutral traits are passed on because they don’t interfere with reproduction.
I’m not an expert, but here are a couple of points:
evolution has no purpose. It can take a long time to produce something, and what it looks like depends on the enviroment, predators, food etc.
selective breeding by man is not as random as natural evolution. If you start breeding wolf hounds, but only continue breeding with the puppies that more resemble your sausage dog ‘target’, then you produce ‘desired’ changes quicker (and therefore reach your result faster too).
I’ve always wondered what the evidence for this is.
I can see how it’s possible for evolution by natural selection to produce the kinds of species we see around us even if it’s “almost entirely negative.” But what’s the evidence that it is almost entirely negative?
Is it just that maladaptive mutations are more common than adaptive mutations? Or does the claim mean something more interesting and informative than that?
I don’t have citations or facts to offer, but I can speculate as to how this can be possible.
Suppose I invent machine A and machine B for two separate purposes. But one day I notice if I put the two together in the right way, I can accomplish a third task. (If you imagine very simple machines, like a rock for hitting things with and a stick for leveraging things or something, you can see how this could happen. And every now and then, you might even get a pair of complex machines that accidentally “fit” together in this way.) So I put them together into machine C. But then later, I see some ways to improve the design of C, so I carry out this improvement, getting machine D. And it could be that the design improvements I carried out on C to get D in fact erase the distinction between A and B–in other words, it could be that I can no longer take D apart to get A and B.
In such a case, D might appear to be “irreducibly complex” as some people put it, while still having been historically selected by means of mutation plus the putting together of simpler parts.
I’m no good at concrete examples, but hopefully you can fill in the blanks in some creative way yourself.
It’s negative in that there is no force making any particular organism evolve any specific trait. Mutations randomly occur and those that aid in reproduction get passed on. A mutation that makes reproduction more difficult hinders passing itself on to the next generation. Neutral mutations are just along for the ride. The reason for variances in population are because as a group spreads throughout an area they encounter different terrains, climates, vegetation, etc. and begin to evolve different ways of surviving. And because evolution is not a set process, two similar populations in two similar but separate locations may evolve differently because different random mutations occurred. That’s why I, at least, characterize evolution, or perhaps natural selection would make more sense, as negative.
I’m sorry to hammer on this a bit, but nothing in that paragraph seems to support the conclusion that natural selection is in some sense fundamentally, or even just usually, “negative.”
You mention mutations that “aid in reproduction,” that “hinder” reproduction, and that are “neutral,” in a way that appears to imply that none is any more usual or more important than the others. And you attribute speciation to diffusion through different environments, which seems to say nothing about the relative importance of “negative,” “positive” or “neutral” mutations.
But I have seen the claim that evolution is “almost completely negative” made by people with varying levels of expertise on quite a few occasions, so I think the idea must at least make some sense. It’s just that I don’t know what the evidence for the claim is supposed to be.
Ida thunk evolution is “almost entirely neutral” rather than negative. But why isn’t it?
Selective breeding is the result of what Darwin termed “artificial selection”, while adaptation is the result of “natural selection”. Both are essentially the same process, but they differ in who or what does the selecting.
Artificial selection is when humans do the deciding of which individuals in a population get to breed, based on certain characteristics those individuals have - typically, characteristics the breeder finds useful or aesthetically pleasing. The characteristics thus selected for can be fine-tuned in a relatively short time-period, as measured in generations.
Natural selection, on the other hand, is the process whereby those who are best able, in the wild, to procure resources, including mates, are the ones most likely to do so and thus leave offspring, thus making the population “more like them”. There is no entity doing the selection here, it’s just each individual doing what they do, and the cards falling where they may, so to speak. Because there are no guarantees in natural selection, it can take a much longer time period to fine tune a population, relative to its environment. But, also, see below…
Multiple traits aren’t selected for (or against) simultaneously. Individuals are selected for against, based on their ability to procure the aforementioned resources. The relative frequency of those particular traits they have, be they positive,negative, or neutral, are thus increased however slightly in the overall population. Certain traits of those will bestow greater advantages or disadvantages than others, depending on the circumstances. Also, those traits, because they are based on variations of existing traits, will be present in several individuals at a time.
So, you’ve got a prey population with, say, an average size. Some individuals will necessarily be smaller, some larger, than average. Now, if it happens that individuals who are larger are thus less susceptible to predation than the “average” or “small” critters, then those individuals will be more likely to mate successfully and pass on their largeness to their descendants (assuming said size is hereditary, of course). Over time, then, assuming that largeness continues to provide an advantage, the average physical size of individuals in the population will continue to increase. During the time of size increase, certain other traits can come into play which further aid the individuals possessing them, such as bony tail knobs or spikes, horns, etc. (or such traits could have already been present, and their effectiveness enhanced by larger size, etc.).
Another important, and oft-overlooked, feature of so-called mosaic evolution is that much of evolution occurs during development. Small changes during development can result in drastic and widespread changes in the adult. Pleiotropy is the term which describes such developmental changes and effects, and can be responsible for a good chunk of the simultaneous changes you mention.
In addition to the fact that many complex traits have simpler precursors, which allows for numerous intermediate stages to be advantageous to an individual, there is the concept of exaptation, whereby a structure can change function at some point in its evolutionary history (perhaps even changing function several times, at various stages). Thus, the bony fins of fishes could be used to somewhat support and propel the critter in shallow water, while at the same time being able to propel the critter in their normal fashion in deeper water. Over time, the function of the fin can change from one of “propelling through the water” to “support and location on land”. Or, the swim bladder of fishes can evolve from a lung-like precursor. Or wings can evolve from forelimbs. And so on.
False. Natural selection can operate for or * against*. That this is true should be self-evident based on even a cursory understanding of natural selection, so I’m not sure how this idea continues to propagate.
If an individual is better able to procure resources than his fellows, and is subsequently more likely to mate, then those traits that make such possible will be selected for; those traits will likely increase in frequency in the population in subsequent generations. If an individual is similarly less able to procure resources than his fellows, and is thereby less likely to mate, those traits that are most responsible for his shortcomings will be selected against; those traits will likely decrease in frequency in the population over time.
Were natural selection a killer only, adaptation would be impossible, as the “superior” would have no inherent advantage over the “average”. Indeed, there would only be “average” and “inferior”. It is the selection for superior individuals which drives adaptation, and it is this selection that is the creative force of evolution.
I often sit out on the back porch and watch the birds at the bird feeder, where I notice a lot of individual variability in behavior - more or less skittish, bigger/smaller, and so on. I can certainly see how an individual small bird that has better eyesight could eventually lead to larger soaring birds over many generations. But I’ve always gotten stuck at trying to see how non-flying creatures became flying creatures. At some point, it seems that the flap of skin along a forelimb that could help a creature soar from limb to limb would have to make a pretty large leap to an appendage that would allow real flying. What is the current state of thought on how birds evolved from dinosaurs (I presume that’s still the accepted view).
I’m not clear on what the difficulty is supposed to be here. Isn’t it pretty easy to imagine wing A and wing B where A and B are very very similar to each other but where A only allows gliding and where B allows for just a little bit of lift?
Seems like this would just be a matter of a slight change of angle in something or other. But it’s been over thirty years since I took an aerodynamics class. And I’m thirty years old. So maybe it’s not as easy to imagine as it seems to me.
Note that gliding implies lift.
There are a number of critters that fly with low efficiency - for example, flying squirrels and snakes. They can’t actually gain altitude, but can do a lot better than if their bodies had no adaptions for flight. It’s easy to imagine these shapes evolving toward greater aerodynamic efficiency.
The lift part I understand. But the difference between a flying squirrel and a cardinal is pretty significant. I realize that it’s not a matter of one day there’s a flying squirrel and the next there’s a cardinal. At some point, though, the skin between the forelimb and the body that provides the lift has to separate to form much more of a wing-like structure, and the creature moves from being land-based with a gliding advantage to being air-based with some ground mobility. It just seems to be a very interesting transition, and one that is not as intuitive to me as moving from sea to land, for instance.
That’s the key point, between transitioning between being a paw or a claw to being a wing, there does not have to be any point at which the existing forelimb has to be a detriment or useless. It might seem to us like an awkward webbed claw and unable to provide flight but if it provides an advantage or no disadvantage, and it stays.
The “flap of skin” issue really isn’t a big deal with birds, of course, since their lift-generating structures are formed with feathers, rather than skin flaps (as is the case in bats, and was the case in pterosaurs).
For bats, it’s not that difficult to imagine, really: observe the skin flaps between your own fingers. Extend those gradually, and you can get some nice parachuting-capable structures, as in a variety of tree frogs and such. The skin flaps between the arm and the body, as well as between the legs and body are more novel; indeed, we don’t fully understand the evolutionary lineage of bats (or pterosaurs, for that matter), since the fossil record is rather lacking regarding their immediate ancestors. However, as I alluded to above, a significant amount of phenotypic evolution happens during development. And, indeed, that is where folks are currently looking for answers about bat evolution. It’s looking more like a relatively sudden change than a gradual one, brought about by relatively minor changes in developmental gene regulation.
As for your original question about the current consensus regarding bird evolution, the issue isn’t so much whether birds evolved from dinosaurs at this point, but rather how did powered flight evolve. There is some debate as to how, exactly, that happened.
), but only because most biologists say its real, and, well, they should know. 