evolution: hard to fathom instances

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Re: evolution: hard to fathom instances

Postby Interactive Civilian » Thu Aug 07, 2008 8:15 am UTC

Guest wrote:I obviously believe in evolution, but from my high school biology days I was left with the impression that a lot of people just pull random explanations for things out of the air without really knowing. Things like "X developed long necks so it could look over tall grass better". Is there actually solid evidence for stuff like this or is it just an educated guess? I don't really know much about it so if it's a misconception feel free to clear it up.

A bit of both. The problem with statements like that, or at least the big problem I have with those statements, is that it seems to indicate that evolution has goals to meet and always tries to make the strongest thing.

A more accurate statement, using your example, would be something like this: "Members of X that had long necks could see over the grass better, so they were able to spot and avoid predators more easily than their short-necked brethren. So, they were able to survive and pass on the traits for long necks."

If someone then asks why they had long necks, the answer is "Variation. It's the same reason I have brown hair and you have blond hair."

Organisms don't evolve traits in order to do something. They either have those traits or they don't and then those traits are either positive or neutral and probably get passed on, or negative and get selected against.

Unfortunately, a lot of teachers have difficulty conveying that effectively, probably including me, since I don't know how much sense this post makes to you. :?
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Re: evolution: hard to fathom instances

Postby chickendude » Thu Aug 07, 2008 1:53 pm UTC

btilly wrote:
cephalopod9 wrote:Another anatomical feature I've never fully understood, the whole neck arrangement. I guess I can see some advantages in range of vision and such, but putting all the thinking* (seeing, smelling, hearing, tasting) matter in one place, and that place being the far end of the body connected by only the neck seems like kind of a bad idea. That would probably make more sense if I understood biology better tho'.

Think about it from the point of view of a fish. You have a mouth. For ease of reaching prey, your mouth is at the tip in front of you. For ease in sensing food and getting your mouth to it, you want your eyes and ears to be close to that mouth. Both for simplicity of wiring and for reaction speed, it now makes sense for your control center to be close to the eyes and ears, which means close to the mouth.

Congratulations, you now have a head.

We haven't changed that basic arrangement since. We've just elaborated it and adapted it for life out of the water.


By the way, the word for this is cephalization and it occurred far before the fish (in flatworms).
Also, the mouth moving to the head was actually the final stage of cephalization. It occurred because having sensory organs in the FRONT of a worm was useful, because that is the direction of movement.

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Re: evolution: hard to fathom instances

Postby Thisisnotausername » Thu Aug 07, 2008 3:15 pm UTC

crowey wrote:True, but I don't think it lost nipples, more that they never evolved in the prototherian line.
So, either the common ancestor for prototherians, metatherians and eutherians had nipples and produced milk, then the prototherianss lost the nipples. Or it didn't have nipples but produced milk then the eutherianss and metatherianss evolved nipples as an addition to the system while the prototherians stayed on the no nipple front. I'm pretty sure that the second is the accepted course? I have no sources for that though, I'm just recalling my undergrad course from a few years ago :roll: .

My point still stands though, that cephalopod's example was of nipples evolving not of milk production evolving.


Say, where do I sign up to be a member of the no nipple front? :lol:
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Re: evolution: hard to fathom instances

Postby crowey » Thu Aug 07, 2008 4:10 pm UTC

ew, it would look so wrong :lol:

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Re: evolution: hard to fathom instances

Postby cephalopod9 » Sat Aug 09, 2008 10:17 am UTC

chickendude wrote:
btilly wrote:
cephalopod9 wrote:Another anatomical feature I've never fully understood, the whole neck arrangement. I guess I can see some advantages in range of vision and such, but putting all the thinking* (seeing, smelling, hearing, tasting) matter in one place, and that place being the far end of the body connected by only the neck seems like kind of a bad idea. That would probably make more sense if I understood biology better tho'.

Think about it from the point of view of a fish. You have a mouth. For ease of reaching prey, your mouth is at the tip in front of you. For ease in sensing food and getting your mouth to it, you want your eyes and ears to be close to that mouth. Both for simplicity of wiring and for reaction speed, it now makes sense for your control center to be close to the eyes and ears, which means close to the mouth.

Congratulations, you now have a head.

We haven't changed that basic arrangement since. We've just elaborated it and adapted it for life out of the water.


By the way, the word for this is cephalization and it occurred far before the fish (in flatworms).
Also, the mouth moving to the head was actually the final stage of cephalization. It occurred because having sensory organs in the FRONT of a worm was useful, because that is the direction of movement.

Alright, cehpalization makes sense, having all that in one place, but I don't see that quite as an explination for necks, having it all out on a limb, so to speak.
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Re: evolution: hard to fathom instances

Postby Mr_Rose » Sat Aug 09, 2008 1:56 pm UTC

cephalopod9 wrote:
chickendude wrote:
btilly wrote:
cephalopod9 wrote:Another anatomical feature I've never fully understood, the whole neck arrangement. I guess I can see some advantages in range of vision and such, but putting all the thinking* (seeing, smelling, hearing, tasting) matter in one place, and that place being the far end of the body connected by only the neck seems like kind of a bad idea. That would probably make more sense if I understood biology better tho'.

Think about it from the point of view of a fish. You have a mouth. For ease of reaching prey, your mouth is at the tip in front of you. For ease in sensing food and getting your mouth to it, you want your eyes and ears to be close to that mouth. Both for simplicity of wiring and for reaction speed, it now makes sense for your control center to be close to the eyes and ears, which means close to the mouth.

Congratulations, you now have a head.

We haven't changed that basic arrangement since. We've just elaborated it and adapted it for life out of the water.


By the way, the word for this is cephalization and it occurred far before the fish (in flatworms).
Also, the mouth moving to the head was actually the final stage of cephalization. It occurred because having sensory organs in the FRONT of a worm was useful, because that is the direction of movement.

Alright, cehpalization makes sense, having all that in one place, but I don't see that quite as an explination for necks, having it all out on a limb, so to speak.
First you need to accept as axiomatic that evolution is fundamentally conservative - it doesn't delete a working system (only non-working systems ever get "deleted" and frequently not completely so) in one place just to make the same or a similar system work in another. In fact there's probably a proof out there that it can't.

Anyway, given that cephalisation happened before heads needed to turn (since heads can't need to turn before there are any heads) and that flexible spines developed for other reasons, the development of an extended part of the flexible spine, enabling head movement relative to the body and all the benefits that come with that, seems fairly intuitive to me.
As for why thee aren't any examples of eye-stalks or mobile mandibular sections with the brain kept inside the ribcage, we can't be certain that there weren't such creatures at some point. In fact it seems likely that there were. We don't see them, however, because the conditions that pertained when such things were still around evidently made those adaptations unfavorable. Basically, you have to remember that everything alive right now has already been selected; it's only the offspring of those organisms which will be the next round of selection.
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Re: evolution: hard to fathom instances

Postby McHell » Sat Aug 09, 2008 5:34 pm UTC

iop wrote:
proof_man wrote:i've always been curious about the evolution of fangs that inject venom. i'm not sure how the mechanism for delivering poison through the teeth could have been beneficial before it was fully operational or how the modified teeth and glands developed in a coordinated fashion.

First, you start to produce poisonous saliva. Then you start to have a groove in one or several of your teeth (mambas, adders). Then the groove gets covered (vipers). No coodrinated development needed, functional at every step.

Late to it all, but still:

important distinction to make is poison and venom. Here we're speaking venom --- something highly toxic to the prey (and often the predator itself) when injected in the bloodstream and/or nerve system, but pretty harmless when passing through the digestive system (where product of course end up in the bloodstream afterwards).

So basically those snake (and lizard!) poisons are indeed saliva, full of enzymes and helpful in digestion, with then additional further extra stuff that's helping to paralyse the prey. See also spiders, who basically sting their prey and wait until it turns into a shelfull of nice thick broth to slurp... Read also last wednesday's Nature article on the evolution of fangs; it's the third by the same group who've been unveiling the lineage and found very interesting things (like the fact that the Komodo dragon and the often-kept bearded dragon are actually poisonous --- so that story that Komodo's have so many bacteria in their mouth that you die of septicemia is not highly true). (Disclosure: I might have taught maths&stats to the first author.)

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Re: evolution: hard to fathom instances

Postby McHell » Sat Aug 09, 2008 5:44 pm UTC

cephalopod9 wrote:Another anatomical feature I've never fully understood, the whole neck arrangement. I guess I can see some advantages in range of vision and such, but putting all the thinking* (seeing, smelling, hearing, tasting) matter in one place, and that place being the far end of the body connected by only the neck seems like kind of a bad idea. That would probably make more sense if I understood biology better tho'.

A far stranger thing to me is that all mammals have the same number of neck vertebrae --- from neckless molerat or sperm whale, to longnecked giraffe. While reptiles (or even smaller sets, like colubrid snakes or even lower classification orders) or birds have very variable numbers (many for a swan, few for a blackbird). Why? This is just highly inconvenient!

I kind of know some explanations for it, have read the papers, but cannot really fathom it. Yes, because the arrangement happens during a crucial phase early in development, any mutation there has catastrophic consequences (survival rate between conception and birth for humans with an extra neck vertebra is something like 5% apparently, and those that make it have scary high cancer rates of a whole host of different types); but I'd guess arranging those vertebrae should happen in a similarly important phase in birds and reptiles.

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Re: evolution: hard to fathom instances

Postby tantalum » Sun Aug 10, 2008 2:35 am UTC

There are some hypothesis that when evolution happens, it's not so much the actual proteins that are being modified, but the regulators of those proteins that are being modified. So this means that there is a gene saying "elongate neck vertebrae for X period of time" and another saying "create 11 vertebrae", and the first is safer, to tinker around with.

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Re: evolution: hard to fathom instances

Postby hipp5 » Sun Aug 10, 2008 2:40 pm UTC

Guest wrote:I obviously believe in evolution, but from my high school biology days I was left with the impression that a lot of people just pull random explanations for things out of the air without really knowing. Things like "X developed long necks so it could look over tall grass better". Is there actually solid evidence for stuff like this or is it just an educated guess? I don't really know much about it so if it's a misconception feel free to clear it up.


You're right, you do have to be very careful. I think I posted earlier on this topic about the giraffe. Ask the general public why a giraffe has a long neck and you'll probably get some variation on, "well long-necked giraffes could reach higher branches and thus had more access to food and were better evolutionarily fit." Well, a group of scientists challenged this idea and took a closer look at what's going on. It turns out the the long necks of the giraffe most likely evolved as a battering ram in males for competitions over mates. They think that females have them (no need for battering ram) because of genetic linkages that made it impossible for them to avoid the elongated fate of the males.

This serves to show that nature isn't always as it seems and that you should be careful about making assertions as to how things work without proper data.

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Re: evolution: hard to fathom instances

Postby jmorgan3 » Sun Aug 10, 2008 3:29 pm UTC

Really? Giraffes' necks cause them to be extremely vulnerable when drinking water, and cause all sorts of blood pressure issues that require special workarounds. I'm surprised that a little advantage in agonistic competition is enough to offset all of those problems. I'd think that females with longer necks would have all the disadvantages without any advantages, and would be worse off enough that the gene is not selected for on average.
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Re: evolution: hard to fathom instances

Postby crowey » Sun Aug 10, 2008 4:15 pm UTC

any chance of a reference for that? It seems very unlikely....

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Re: evolution: hard to fathom instances

Postby hipp5 » Sun Aug 10, 2008 7:20 pm UTC

jmorgan3 wrote:Really? Giraffes' necks cause them to be extremely vulnerable when drinking water, and cause all sorts of blood pressure issues that require special workarounds. I'm surprised that a little advantage in agonistic competition is enough to offset all of those problems. I'd think that females with longer necks would have all the disadvantages without any advantages, and would be worse off enough that the gene is not selected for on average.


Yeah I'm aware of all the issues having long necks brings up. I guess the math works out so that it's still an advantage to have the long necks.

any chance of a reference for that? It seems very unlikely....


I'll see what I can dig up. It was in my second year population genetics class and all my books and materials for that are back at school.

EDIT: This is a research paper that paraphrases the conclusions. I believe the "Simmons, R. & Scheepers, L. (1996). Winning By A Neck: Sexual Selection In The Evolution Of Giraffe. The American Naturalist, 148, 772-786." reference is the paper we looked at in my genetics class.

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Re: evolution: hard to fathom instances

Postby cspirou » Sun Aug 10, 2008 10:54 pm UTC

The one I'm wondering about is electric eels. How the hell does the ability to produce a large electric field come about?

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Re: evolution: hard to fathom instances

Postby sakeniwefu » Mon Aug 11, 2008 3:14 am UTC

Meteorswarm wrote:
cspirou wrote:The one I'm wondering about is electric eels. How the hell does the ability to produce a large electric field come about?


Muscles and nerves naturally produce small electric fields, and many organisms (sharks, rays) can passively sense electric fields. There are fishes, like the Elephant nose fish, that actively sense their surroundings with electric fields, so it's not too big of a jump to zapping things.


As a little zap isn't very useful, they probably started using it for display against rivals of their same species. Eventually, the weapons escalation got so high they could use it to paralyze their preys.
About the fixed number of vertebrae for mammals, it is not very difficult to understand. Dependencies by themselves are non deleterious and if the gene that depends on the number of vertebrae was positive or neutral but introduced with a positive mutation, the chances that it stays there forever are high. This is why we have the whole development movie in embryos. When nature cannot improve on existing genes it patches them to fix the mess afterwards.

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Re: evolution: hard to fathom instances

Postby sakeniwefu » Tue Aug 12, 2008 4:39 am UTC

Meteorswarm wrote:A little zap could be plenty useful. It could stun insects for prey, for example.

It wouldn't be little anymore or they would have to get very close to the prey. Maybe they developed a useful zap in one step but confusion at a distance, even of much smaller preys requires some very strong magnetic field. If the zap was weak at first it makes much more sense in the context of electricity sensitive creatures than in a broad interaction spectrum.

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Re: evolution: hard to fathom instances

Postby Mr_Rose » Tue Aug 12, 2008 8:08 am UTC

sakeniwefu wrote:
Meteorswarm wrote:A little zap could be plenty useful. It could stun insects for prey, for example.

It wouldn't be little anymore or they would have to get very close to the prey. Maybe they developed a useful zap in one step but confusion at a distance, even of much smaller preys requires some very strong magnetic field. If the zap was weak at first it makes much more sense in the context of electricity sensitive creatures than in a broad interaction spectrum.

If anything, an extreme-short range zap would be most useful as a defensive option, "bite me and your jaw hurts for a week" style. Are there remnants of defensive warning patterns on proto-electric eels?
Or if the majority predator hunts by field-sensing, the zappy charge build-up cold serve as a warning in itself...
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Re: evolution: hard to fathom instances

Postby crowey » Tue Aug 12, 2008 10:17 am UTC

Mr_Rose wrote:Or if the majority predator hunts by field-sensing, the zappy charge build-up cold serve as a warning in itself...


Or as camoflage in the electric field? If you make a field big enough to obscure your outline maybe the electro-sensing predator can't see you?

Pure speculation there though....

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Re: evolution: hard to fathom instances

Postby sakeniwefu » Wed Aug 13, 2008 1:58 am UTC

crowey wrote:
Mr_Rose wrote:Or if the majority predator hunts by field-sensing, the zappy charge build-up cold serve as a warning in itself...


Or as camoflage in the electric field? If you make a field big enough to obscure your outline maybe the electro-sensing predator can't see you?

Pure speculation there though....


As always. We cannot know without being there or seeing something that might be an intermediate form and this being soft tissues anything dead for more than a week doesn't cut it.
However, it turns out that according to the Wikipedia such intermediate form exists. As the Amazon river is very muddy the related gymnotus fishes use a weak electric field to PING other animals. Eventually their PING became strong enough to not only DoS small preys but also attackers.
Speaking about strange adaptations, what's up with all the dinosaurs, and more relevantly the aves group, that lost their teeth? They don't add much weight and seem to be clearly more advanced and variable than a toothless beak.

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Re: evolution: hard to fathom instances

Postby psyck0 » Wed Aug 13, 2008 2:42 am UTC

jmorgan3 wrote:Really? Giraffes' necks cause them to be extremely vulnerable when drinking water, and cause all sorts of blood pressure issues that require special workarounds. I'm surprised that a little advantage in agonistic competition is enough to offset all of those problems. I'd think that females with longer necks would have all the disadvantages without any advantages, and would be worse off enough that the gene is not selected for on average.


Traits that provide a direct advantage in competition for mates are VERY strong, because they lead directly to more offspring. Those that reduce survivability only lead indirectly to fewer offspring (through death). If a certain proportion (a minority, although probably not a tiny one) of the disadvantaged giraffes make it to mating, they are likely to produce more offspring than their competitors by winning the competition itself, thus resulting in a net increase in the trait's prevalence.

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Re: evolution: hard to fathom instances

Postby cspirou » Wed Aug 13, 2008 8:18 am UTC

Meteorswarm wrote:
cspirou wrote:The one I'm wondering about is electric eels. How the hell does the ability to produce a large electric field come about?


Muscles and nerves naturally produce small electric fields, and many organisms (sharks, rays) can passively sense electric fields. There are fishes, like the Elephant nose fish, that actively sense their surroundings with electric fields, so it's not too big of a jump to zapping things.


I would think it would be the opposite pressure. If sharks can sense electric fields then the ones that survive are the ones with an electric field that hard to detect. Why would ones with strong electric fields be favored in this case?

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Re: evolution: hard to fathom instances

Postby hipp5 » Thu Aug 14, 2008 2:15 am UTC

sakeniwefu wrote:Speaking about strange adaptations, what's up with all the dinosaurs, and more relevantly the aves group, that lost their teeth? They don't add much weight and seem to be clearly more advanced and variable than a toothless beak.


Ever held a bird beak? They weigh almost nothing. Teeth DO add a lot of weight. Some of the birds we work with where I work are only 9 grams, the weight from teeth will make a huge difference here.

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Re: evolution: hard to fathom instances

Postby liquidspoon » Wed Aug 20, 2008 9:11 am UTC

I just read a Wikipedia article about Echinoderms (a phylum of invertebrates that includes starfish and sea urchins). Apparently every species in the phylum has fivefold radial symmetry. Does anyone know where the five comes from, and why it would be preferred to other radial symmetries (3,4,6...). I would think that the lower number symmetries would be more likely to evolve - 3 should be more likely than 4 and so on. So 5 should have a really strong justification. Is there any fossil evidence of predecessor species with other radial symmetries?

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Re: evolution: hard to fathom instances

Postby btilly » Wed Aug 20, 2008 11:58 am UTC

liquidspoon wrote:I just read a Wikipedia article about Echinoderms (a phylum of invertebrates that includes starfish and sea urchins). Apparently every species in the phylum has fivefold radial symmetry. Does anyone know where the five comes from, and why it would be preferred to other radial symmetries (3,4,6...). I would think that the lower number symmetries would be more likely to evolve - 3 should be more likely than 4 and so on. So 5 should have a really strong justification. Is there any fossil evidence of predecessor species with other radial symmetries?

The different symmetries arose early in the evolutionary process. I have no idea what is thought about why different symmetries got tried. But once established, your symmetry is not easily changed through the process of evolution, and so remains conserved across an entire lineage. Which is why everything in the entire phylum would have the same symmetry.

That said, there are other symmetries out there. http://en.wikipedia.org/wiki/Symmetry_(biology) gives as examples that many jellyfish have a 4-fold symmetry, sea anemones and most corals have 6-fold symmetry, there is an order of corals (which is not really related to the 6-fold one) with 8-fold symmetry.

Interestingly 5-fold symmetry is very common in flowering plants (cut an apple crosswise for instance). I have no idea why.


Incidentally the idea that certain things (like symmetries) are evolutionarily conserved shows up in other apparently puzzling places.

For a famous example the vertebrate eye has a stupid arrangement with the nerves running in front of your photoreceptors, thereby blocking the light. And resulting in a blind spot where the nerves converge and dive down. This arrangement is not universal though - the octopus puts the nerves behind the eye and has no blind spot. Why, then, do we? Well in the primitive eye it is sheer chance where the nerves go and the eye is so inefficient that the placement of the nerves is not significant either way. But once established, that doesn't change.

For a far less famous example, Gould had an interesting essay on why the kiwi bird would produce such a large egg (15-20% of the mass of the adult bird) which I believe was based on http://www.jstor.org/pss/1307538 (unfortunately not a free article). The theory is that it is a result of allometric scaling. Allometric scaling is the principle that as a an organism scales up or down in size, each part scales up or down at a different rate. For instance in many species of insects a larger insect will have appendages that are larger relative to the body than a smaller insect, and this kind of relationship within a species tends to be conserved across species as well.

Anyways across kiwi species there is an allometric relationship between the size of the bird and the size of the egg where a smaller bird will have a larger egg relative to its mass than a larger bird. If you project that relationship out you will find that a 1.5 meter tall kiwi would have a normal sized egg. Therefore, the theory goes, the kiwi has a large egg because it is descended from a large ancestor that underwent evolutionary pressure to become small, and the allometric mechanics of becoming small left it with a large egg relative to body size. In support of this theory I note that the genetic evidence suggests that the kiwi is related to the New Zealand moa and the South American rhea (both large birds) and is in the same group as the African ostrich, and Australia's emu - all of which are large birds.

This example is important because it demonstrates that some puzzling characteristics may not have been evolutionarily selected for at all! They came about as a side product of some other trait that was selected for.
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Re: evolution: hard to fathom instances

Postby McHell » Thu Aug 21, 2008 10:31 pm UTC

sakeniwefu wrote:About the fixed number of vertebrae for mammals, it is not very difficult to understand.[...snip...]

As pointed out, other vertebrates have no problem switching these numbers in a relatively short time, and over and over again (even within snake families you get different numbers). So why do mammals have this problem? Nothing in your text explains this --- the essence of the embryo-thing you refer to is that all vertebrates go through these stages, so why can lizards and birds happily switch numbers?

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Re: evolution: hard to fathom instances

Postby Cloudchaser » Sat Aug 23, 2008 3:09 am UTC

Someone already brought up colonial insects, but more specifically, I'd love to know how honey bees evolved the "location dance" for communicating the rough locations of pollen sources to the rest of the hive. Scent trails are pretty straightforward, but the idea of a dance to convey a spatial location between insects is just astounding.

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Re: evolution: hard to fathom instances

Postby Izawwlgood » Sat Aug 23, 2008 5:20 am UTC

It's like memes, but found in an organism who's 'brain' is barely more complex then a cluster.
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Re: evolution: hard to fathom instances

Postby 4=5 » Sat Aug 23, 2008 6:18 am UTC

McHell wrote:
sakeniwefu wrote:About the fixed number of vertebrae for mammals, it is not very difficult to understand.[...snip...]

As pointed out, other vertebrates have no problem switching these numbers in a relatively short time, and over and over again (even within snake families you get different numbers). So why do mammals have this problem? Nothing in your text explains this --- the essence of the embryo-thing you refer to is that all vertebrates go through these stages, so why can lizards and birds happily switch numbers?

we probably lost some gene coordinating thingy

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Re: evolution: hard to fathom instances

Postby alexh123456789 » Wed Aug 27, 2008 1:25 am UTC

Isn't it more likely that there's just no pressure to change? For humans, unlike snakes, it doesn't matter all that much
how many vertibra we have.

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Re: evolution: hard to fathom instances

Postby sakeniwefu » Wed Aug 27, 2008 6:48 am UTC

McHell wrote:
sakeniwefu wrote:About the fixed number of vertebrae for mammals, it is not very difficult to understand.[...snip...]

As pointed out, other vertebrates have no problem switching these numbers in a relatively short time, and over and over again (even within snake families you get different numbers). So why do mammals have this problem? Nothing in your text explains this --- the essence of the embryo-thing you refer to is that all vertebrates go through these stages, so why can lizards and birds happily switch numbers?

It was implied, they just were more lucky than the mammal common ancestor.
Somewhere in the evolutionary line having N vertebrae was tied to a gene that is necessary for survival. As species X had N vertebrae it was not a deleterious mutation for them. Eventually species X was the last of its kind and became the ancestor of all mammals(I don't know enough about mammal evolutionary morphology to know if this was the first amniote in our line or a monotreme-like mammal living with the dinosaurs). When some characteristic becomes tied to important genes it becomes more difficult(although not impossible) to remove it successfully.

Let's think hypothetically. We are Black Animal A. Hormone Z regulates brain growth. At some point a random mutation causes it to become tied to black pigmentation as well. It's not a problem because we are black animals living on volcanic soil. At some point we get blown off our territory to a white land. And then we become everyone's favorite meal. Black Animal A then asks "WTF! Why can't we change our pigmentation like everyone else!?". The answer is "Blame God". :twisted:

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Re: evolution: hard to fathom instances

Postby gmalivuk » Wed Aug 27, 2008 9:25 pm UTC

alexh123456789 wrote:Isn't it more likely that there's just no pressure to change? For humans, unlike snakes, it doesn't matter all that much
how many vertibra we have.

For humans, sure. But there are other species of mammals living in very similar niches to those occupied by bird or reptile species with widely varying numbers of vertebrae. The fact that not a single mammal species has a different number of neck vertibrae very strongly suggests that something else is going on here.
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Re: evolution: hard to fathom instances

Postby zealo » Mon Sep 29, 2008 11:37 am UTC

blowfish poison any animal that eats them, so anything that eats a blowfish will not be eating another one in a hurry (as an added bonus, the surviving blowfish can feast on the corpse?)

i don't see how the 'proto-poisonous' blowfish would have had their genes positively selected for :/
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Re: evolution: hard to fathom instances

Postby Monty40xi » Mon Sep 29, 2008 2:54 pm UTC

zealo wrote:blowfish poison any animal that eats them, so anything that eats a blowfish will not be eating another one in a hurry (as an added bonus, the surviving blowfish can feast on the corpse?)

i don't see how the 'proto-poisonous' blowfish would have had their genes positively selected for :/

Proto-poisonous blowfish had families. The martyrdom of one blowfish reduced the population of predators with an instinctive taste for blowfish, allowing the families (who also had the poison gene) to prosper.

The one I have trouble with is wings. It seems like a well-developed wing is a great advantage, but a partially-developed wing is useless and should never have arisen. I've seen one attempted explanation for dinosaur/bird wings, where the little feathered dinosaurs flapped their decoratively-feathered arms really fast and this helped them go up steeper inclines, supposedly, and more wing-like arms helped more. Personally I think an environment where running up steep inclines mattered would push small creatures away from wings and towards gripping paws, like squirrels - it's a much simpler way to get the advantage, especially when the creature you're starting with already has good claws on all 4 limbs. Why would their shoulder joints even be capable of so much sideways extension for flapping motions?

The other three separate developments of flight - bats, pterosaurs and insects (was there just one development for insects or several?) - also leave a lot of questions for what a protowing was good for.
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Re: evolution: hard to fathom instances

Postby ccccc » Mon Sep 29, 2008 7:16 pm UTC

My most-difficult-to-explain:
* Flowering plants and foraging-insects, which seem to need each other to survive.
* RNA and the proteins required to sequence it, for the same reason.
* The lichen thing.

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Re: evolution: hard to fathom instances

Postby Monty40xi » Mon Sep 29, 2008 9:09 pm UTC

Hm, aquatic paddles as protowings for insects? Maybe... have you heard of any fossil evidence for that?
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Re: evolution: hard to fathom instances

Postby cspirou » Mon Jul 19, 2010 5:02 pm UTC

Hi everyone.

I was thinking about something and I thought it would be better to resurrect this thread instead of starting a new one.

What is the evolutionary pressure that led to the left side of the brain controlling the right side of the body and vice versa?

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Re: evolution: hard to fathom instances

Postby Charlie! » Mon Jul 19, 2010 5:21 pm UTC

cspirou wrote:Hi everyone.

I was thinking about something and I thought it would be better to resurrect this thread instead of starting a new one.

What is the evolutionary pressure that led to the left side of the brain controlling the right side of the body and vice versa?

Just lucky I guess :P

(i.e. I think had to happen some way, and this is just the way it happened)
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Re: evolution: hard to fathom instances

Postby Argency » Mon Jul 19, 2010 7:05 pm UTC

Actually, I'm pretty sure that its more than luck. I seem to remember some famous biologist (Dawkins?) talking about the head rotating 180 degrees at some point in embryo development, exorcist style, as an evolved trait. Apparently at some point in the past we went from needing to have eyes in the back of our heads, to needing them in the front. So what was originally the right hemisphere became the left, and vice versa.

I suppose that's not so whacky as it first sounds: I mean, salamanders and lizards and snakes and mud-walkers all have eyes that are on the opposite side to their bellies. I guess nothing interesting ever happens underneath them, so they spend all their time looking forwards or up. A ground-dwelling mammal, on the other hand, spends most of its day looking at the ground, or at its forepaws, so I suppose its much more useful that way. Then again, if a salamander rotated its head 180 degrees, its mouth would be in the middle of its forehead, so maybe that's not exactly how it happened. Ideas anyone?
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Re: evolution: hard to fathom instances

Postby Interactive Civilian » Tue Jul 20, 2010 12:45 am UTC

Argency wrote:Actually, I'm pretty sure that its more than luck. I seem to remember some famous biologist (Dawkins?) talking about the head rotating 180 degrees at some point in embryo development, exorcist style, as an evolved trait. Apparently at some point in the past we went from needing to have eyes in the back of our heads, to needing them in the front. So what was originally the right hemisphere became the left, and vice versa.

That doesn't make sense to me. Even if the head rotates why would that affect things in the head, like the "wiring" of the eyes?

That said, I have no idea what evolutionary pressure or adaptations would have caused the cross wiring. How is it in other verterbrates? Do fish, for example, have the same cross wiring? If so, then what about invertebrates like arthropods and molluscs?

It's definitely an interesting question, though. Is it actually an adaptation? Or is it more of a fixed accident from the early evolution of more centralized nervous systems?
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Re: evolution: hard to fathom instances

Postby Argency » Tue Jul 20, 2010 5:09 am UTC

Actually, that's true. I hadn't considered the eyes. What the hell, evolution...
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