Ah but that's not right. You just don't see macroevolution. Evolution is basically only the change in allele composition (that is gene variations on a given on a locus in the chromosome) in a population. This even does not necessarily need to lead to a change of (visible) phenotype distribution.
One thing to remember with species is that they don't have to look startlingly different in order to be separate species; they just need to be reproductively isolated (if we're using the biological definition of species). Some of the fly work does show the beginnings of this sort of reproductive isolation: drosophila populations were kept for several generations on media containing either maltose or lactose, & then cross-breeding experiments were carried out. Males from the maltose population preferred to breed with females from the maltose population, and not the lactose population, & vice versa. The other thing is, if we're talking flies in lab populations, that unless they're exposed to dramatically different selection pressures then there is unlikely to be any movement towards a population that is morphologically different from another. (This can be seen in the very well documented evolution of the different drosophila species on the Hawaiian islands: definitely different species (genetically & reproductively) but not substantially different in the physical sense.) Evolution can and has certainly led to novel features (feathers from scales would be one case in point) but this is not going to be something you see in a little glass jar full of little black flies - in these conditions there's unlikely to be any adaptive benefit to obvious novelty. Physiological novelty... that's a different issue.
Speaking of flies in labs... Why not? Has anyone tried to force evolution's hand, so to speak? Breed fruitflies in a totally dark environment for severel years, perhaps. Or slowly increase the amount of a selected chemical, that would be poisonous in large quantities, in the air over many generations. Perhaps, devise a way to keep them from landing for longer and longer periods of time with each new generation working towads zero landing time. Or, the opposite, pull off the wings of every child (or perhaps only every male child) in each generation for may generations. One of the greatest benefits to working with fruitflies is theuir short lifespan and quick generational turnover. Why not take advantage of that, and force evolution's hand towards speciation?
One_raven, what you propose wouldn't work for the most part. Breeding fruit-flies in the dark would probably result in a flies with a dysfunctional visual system (as its development usually needs environmental stimuli), BUT it won't lead to genetic changes. As such they won't pass on any genes involved in eye development and as such it's progenies would be normal, regardless of how many generations were bred. The same goes to ripping of wings or changing their behaviour, it will not affect genes therefore it will not change the following generations and thus there will be no evolutionary effect. The poison experiment could work, but in a different way that you might think, though. If you apply poison and only the surviving flies can reproduce you will get an increase in the amount of poison resistant flies from generation to generation. But they will not be necessarily more resistant than their parents.
That's where current understanding fo evolution starts to fall apart for me. If breeding them in the dark will not affect their evolution because it will not affect their genes, why are some breeds of moles born blind? Why have bats evolved echo-location? Why do limbs evolve into flippers? Camoflauge, mimicry, wings, opposable thumbs... There are so many examples of evolution appearing to follow need or function.
They might appear so, but they don't. This would be the so-called lamarckism (giraffe's got long necks cause they stretched them so much). But especially modern genetics showed that this is not the case. Maybe you want to check my example of basic evolution in the other thread...
Actually, I would very much like to. Are you referring to This Thread? You wouldn't be referring to any specific posts that you could point me to, would you? Did you address the general sentiment I was speaking to in This Post or This One? If not maybe you would care to comment directly to them. Essentially, it seems to me that Natural Selection of random mutations simply is not thorough enough. Something, though I do not know what, is missing.
Hi one_raven. Natural selection of random mutations seems completely adequate to me. Animals that live the dark will eventually lose vision not as an adaptation, but as a result of vision not being selected for. It's simply useless, so that flies that are born bling are not at a disadvantage and therefore pay no penalty for being blind. However, if a fly is born with a better than average set of chemical receptors, it will generally out-breed flies with less developed receptors. Traits that are not constantly selected for are doomed to atrophy in the long run (millenia) since there's no survival advantage to maintaining them. Yeah?
Like I said in the Gaia thread, though, what about snake-headed moths, stick bugs, leaf bugs, dead horse arums... Imitations, defenses and the extraordinary balances between some symbioptic relationships... Parasites that control the behavior of the host to it's own advantage (we could go on for days -or even entire careers- about some of the simply astounding parasite/host realtionships)... Do you really think that segmented fingers on each hand would be a result of what would have to be thousands (if not millions) of random gene mutations over many many generations being arbitrarily selected for? Again, flippers... People always talk about whales once being land animals, right? Well, why are there NO OTHER land animals that have evolved bodies that are streamlined for swimming and living at great depths under the ocean, but still live on the land? Whales, it seems to me, must have had some kind of impetus for evolving flippers. There are more than a few animals that have hardly changed at all in millions of years, yet others who have evolved quite a bit in that same time. When animals are isolated in an environment, they evolve much more quickly. Are you willing to accept that the other animals have had just as many "random mutations" over those years, but none happened to be selected for because they were of no direct advatange? The isolated animals in say Madagascar, Australia and Galapagos evolved more rapidly because their random mutations were selected for because they gave them a niche advantage, I would certainly agree with that. I, however, think that is an incomplete picture. Another thing... How could a common feature atrophy in a population by lack of use, but the opposite neccesarily be impossible? Scientists say that from conception to death, your DNA does not change (another dubious claim, if you ask me), so if there is no mechanism available to generate change due to function, use necessity or impetus, how could there be a mechanism for an attribute to atrophy? Disadvantage would certainly cause a trait to disappear, and advantage would cause a trait to become more prominent (see Daphne Island Finches) however, if there is no mechanism to generate change to suit (such as flippers evolving in land animals spending more time in water) then there could necessarily be no mechanism for atrophy of a trait for simple lack of advantage.
one_raven: Of course. Why should there be? That would require highly specific adaptations for two wildly different environments. Of course. You can swim better with flippers. What's the problem? Not true. Isolation alone has little to do with it. If there's no selection prerssure for an animal to change in its current environment, it won't. Of course. Why??? I don't understand this. What scientists say this??? And whos DNA? The heritable changes in DNA only apply to the gametes (sperm and egg cells). Your sperm carry many different sets of genetic mutations. But there is a mechanism. Perhaps examining a specific example of your choosing might help.
one_raven, sorry, I thought I put a link in it. I'll just copy the stuff over here: "First evolution. As I said in other threads already, evolution merely means that the allels in a population (that is the gene variants in a single place, or locus on the chromosome) change. Assume three different allels a, b, c. In a starting population there is, say 50% a, 20% b, 10% c. Now let's futher assume that for one reason or another the distribution changes. Let's say that individuals with allel a are more susceptible to a certain poison that enters the population and c less. Now, many generations later under this selective pressure the distribution could be 20% a, 20% b and 60% c. This is evolution already without that new phenotypes arise. That is, no new traits were developed Now to seperation of populations. What you are talking about here is a special event during evolution, namely speciation. This is the process during which a new species arises. Isolation, together with genetic drift can together lead to the rise of a new species, but it is only part of evolutionary processes. Furthermore the size of a population can affect the speed of evolution, but again, it does not necessarily mean a better adaptation. Assume again a population with 50% a, 20% b and 30% c. Further assume that it is a very large population. In this case changes in allel distribution as in the above example can easily be reverted, once the selective pressure ceases (e.g. if the poison vanishes). Now assume that out of the large population, a very small one gets isolated for some reason. let's say 10 individuals with the above allel distribution. That makes 5 individuals with a, 2 with b and 3 with c. Now let's also take genetic drift into account. By a purely randome reason (not connected to the allels in question), say, a rockslide, both b bearers die. In the large population this wouldn't have an effect, but in the small one it leads to a complete extinction of allel b. This leads to a drastic change (fast evolution) in the allel distribution: change to 63% a, 0% c and 37% c in a single generation. Now due to the different starting allel distribution, different ecological niches and thus selective pressures and so on, this population might deviate from the main population from which it was separated and together with mutations and (in case of e.g. microorganisms and plants) gene flux, gradually a new species might arise that due to its slightly different genetic make-up cannot bread with the original population anymore. This model btw. is the reason of the punctuated equilibrium theory proposed by gould, in which on the fringes of large populations or isolated pockets of them seem to undergo sudden and fast speciation evolutionary events (such as speciation)." I haven't followed the discussions in the other threads, but maybe or maybe not this basic model might help you...
I did read this, but thank you for posting it here. It is a concise run down of Natural Selection. I understand it well and find no fault in nor take any issue with any of this. I would like you (or someone else, if you don't want to) to backtrack a bit. Why do the alleles change? Also, please scroll up a bit (if you haven't) to see what I was trying to clarify to superluminal. Either superluminal was not understanding me well, or I was not understanding him well. What I pick up from scientists who talk about evolution regarding the specific changes to alleles: Genetic mutations are random. They do not follow function or necessity. Genes simply mutate due to external forces (such a=radiation, parasites, disease etc) or no external forces at all (it just seems to be "written" into DNA "code" that random mutations happen). A mutation can have one of three results (taking countless factors (many unforseeable) into account). It can be beneficial to the species in its localized enviroment. It can be harmful to the species in its localized envirnment. It can be neither, and simple be a change with no affect on the species. This is where natural Selection (CharonZ's post above) comes in. How am I doing so far? Where I start to lose faith in the theory, and would like to see what it is that I am missing is the idea that the random mutations are the only thing causing changes to alleles. I want to be convinced that lamarckism (or some parallel or complementary theory) is not correct. I want someone to show me why it is that the scientific community does not believe that form follows function. With the apparent limitless number of forms available, why is it that so many unrelated water species have very similar appendages? Now, don't tell me it is Natural Selection, because I fully understand that when a creature evolves to have a flipper instead of a hoof, it would most certainly be beneficial to it in the water environment, therefore will be selected for. What I am after is before it is selected for. Why do so many different animals that happen to live in or near the water have the such similar "random" mutations? The only thing I can think of that makes sense (outside of direction, aim and intention of some sort being attributed to evolution) is that every life form's DNA is incessantly "trying" every possible combination of mutations and the ones that happen to be selected for in that species are the ones that are passed down. In that situation, however, why do Polynesians not have webbed feet? This is very difficult for me to clarify and I apologize if I am not making my point clearly enough. I am not asking why flippers will "spread" throughout a species, I am asking how they get flippers in the first place.
Explaining the difference between webbed feet in ducks and chicks is easy. BMP signaling through the limb induces apoptosis of the interdigital regions. In ducks gremlin is expressed in these areas. It is a BMP inhibitor preventing apoptosis of the cells between the digits. You simply have to shift the region of gene expression. This can be done by regulation of existing genes. Minor mutations can do this. http://www.sinauer.com/milestones-devbio/Gilbert7e_538-539.pdf
OR, Of course form follows function. The form of a dolphin flipper is superbly in accord with its function as natural selection would drive it there. Ok. Good question. An animal (a Proto Dolphin, PD) lives comfortably on the margins of the sea, making its living off the animals (seals, penguins, otters, etc.) that come onto land to breed or whatever. A new and better hunter/predator, NP, moves into the area due to climate change and begins seriously competing with PD. NOTE: There is no guarantee that PD will not be driven to extinction by the more well adapted predator. If PD fails to find a new way to survive (not consciously of course), it will die out as have 99+% of all species that have ever existed. Extinction is the rule, adaptation the exception. Now, PD had a penchant for swimming short distances once in a while for a snack. NP hates the water. Many PD's die in the water by predation from sea creatures and such. Some, however are much better swimmers, by virtue of having shorter forelimbs, bigger paw pads, shorter toes (all giving less drag and more power in the water). Over many, many millenia, the PD's are driven nearly to extinction and have only survived due to luck and a large initial population with a liking for water. We now see though, a population of PD with greatly foreshortened front legs and toes and very large paw pads (the forelimb is almost all paw) which are almost useless for walking. It's more flipper now that paw. PD begins to make a comeback, living exclusively off of fish. Natural selection has bred for those PD with short forelegs and toes and large paw pads. Do you see how this happens? There are so many creatures with similar flippers because of two things: 1) there were, by luck, structures that could form a general flipper shape, and 2) flippers have nearly ideal physics for the job they have to do. There are other creatures that pulsate, undulate, squirt, or bottom crawl for locomotion in the sea. It's luck, preexisting structures that can be modified, and the buffet of possibilities offered up by mutation. Most mutations kill the host, and most hosts go extinct given environmental changes. What we see (us included) are the amazingly lucky few with the preexisting structures that allowed them to be successful in a new environment. Helpful?
You mean inherited "accumulated" change(s) at a locus or loci on a chromosome(s) within a population that somewhere along the line eventually does lead to a phenotypic change, or else it is termed "neutral." Without an eventual phenotype change, there is no evolution of any sort.
Did you happen to catch the NOVA program today explaining the Coelacanth evolution to tetrapods? Although DNA evidence supports the fact that lungfish are more closely related to humans (tetrapods), after watching this clip I would side with the Coelacanths. They showed live filmage of the way they move their flippers in the water just like humans walk: forelimb out front while hind limb back and adjacent limb opposition: front-to-back. The skeletal structure is similar and they give birth to live young. On top of that they recently discovered a new colony of Coelacanths in Indonesia that DNA evidence proves this subspecies diverged from the Madagascar Coelacanth millions of years ago. Fascinating!
Actually, it was. Thank you. I still have difficulty making the jump from that to stick bugs, leaf bugs, some of the most extraordinarily complex parasite/host relationships and such.
There is no such thing as luck in evolution but you can attribute these adaptations to accumulated random chance mutations that proved favorable to the environment that the creature lived or lives in. Flippers (swimming), web-feet (gliding), feathers (insulation), then wings (flying), flying fish, gliding frogs, whales and dolphins (both originally terrestrial tetrapods) went back into the water and those ancestrial traits that they once had reemerged to allow them to adapt to the new environment (flippers again). The structure itself was already there in the embryo: vestigial rudimentary structures (remains from the past). Evolution builds on itself: on the structures and designs that came before it (ontogeny: Haeckel's "biogenetic law"), or else it's called "convergence of form" (analogy) where two distinct unrelated ancestrial lineages develop similar anatomical structure that are adaptive to the similar environmental conditions.
