[General Battuta]

I believe that 'arm' is the other leg, curled up.

[Wobble73]

Doh! Of course, it just looked too far up the body at first to be the leg.

[Stormkeeper]

... Then where did you get the second leg from?

[Turambar]

He expected two legs on the ground so he saw two legs o the ground. Same for me. :<

[Wobble73]

He expected two legs on the ground so he saw two legs o the ground. Same for me. :<

Yeah, just one of them tricks of the mind, I "saw" the other leg behind the first. Sorry about that Slayer! 

:sheepish:

[Stormkeeper]

Hmmm. Human mind. Like the fact that you'll be able to read a word if only the first and last letters are in the right position, and the length is correct.

[Mongoose]

I look at that and can't  help but think of this guy.  Surely he is the missing link between dinosaurs and birds!  



...somehow.

[StarSlayer]

Burninating all the peoples and their THATCH-ROOF COTTAGES!! THATCHED-ROOF COTTAGES!!

[Black Wolf]

I do believe there is actually a scientific theory about that Kosh, that the more 'radical' type of life is too fragile to environmental change, so as evolution passes (I recoil from using the word 'progresses') the gene-pool gets cleaned of the edges, so life is more resilient, but not as experimental in nature.

That's an oversimplification... some very specialized animals have survived very long periods in the fossil record, and radical change can drive evolution quite quickly if it gives the ability to exploit new niches, or old nieches in new ways. What I think you're trying to describe is the tendency for rapid and often highly unusual speciation into new niches following major extinction events. There's generally a brief delay, followed by a rapid diversification of the survivors into the niches vacated by extinct animals or plants. During this time, interspecies competition is generally fairly low, and so all sorts of relatively poorly adapted animals can survive. As time goes on though, and the vacant niches fill up, the evolutionary arms race starts again and a lot of these less well adapted animals are outcompeted.

Yet another example of very likely irreversible evolutionary path would be the cetaceans. They started as quadruped land animals and ended up with behemoths almost completely adapted to living in oceans, and for them to become capable of land life again they would need to first of all develope a mutation that makes their hind legs grow back, then reduce their size and go through some immense skeletal and morphologic changes for them to step away from water. It's very difficult to see that happening within normal evolution.

Actually, cetaceans with back legs do occur - it's not common, but the fact that they occur at all suggests it's a relatively easy mutation. But you're right that most cetaceans are unlikely to get back onto land, unless there was some sort of land based major mass extinction that left a lot of vacant niches (after all, fish did it, and they were much less well adapted to living on land). However, you'd still (potentially) have seals, turtles and lots of other better adapted animals that'd probably beat the cetaceans onto those land based niches.

Besides regarding feathers and dinosaurian/avian features, isn't it at least a very credible possibility that part or even majority of dinosaurs were feathered to begin with? Making scaly birds sounds more like kickback to reptilian ancestry rather than dinosaurian. Now, make me an ostritch that has teeth, tail and arms that it can use to grab stuff... and I'll say it is a dinosaur.

Of course, I consider all avian species to be higly specialized branch of dinosaurs and only named differently due to historical reasons...

You're basically right that birds are specialized dinosaurs, and we have a really much better idea of the evolution of feathered dinosaurs into birds thanks to fossils out of China over the last 10-20 years. We've actually got some really impressive fossil impressions of both scaly dinosaur skin and feathers - it's generally assumed that feathers were a feature of the theropods, so the majority of other dinosaurs were almost cetainly scaly - it's hard to imagine something like a brachiosaurus or an ankylosaurus needing feathers. In fact, they'd be a physiological detriment to animals that were that big due to their tendency to insulate, which'd be bad in an animal that would probably be relying on gigantothermy to maintain temperature stability.

Evolution is not directional. Defined at its simplest, evolution is simply a change in allele frequency in a population over time (if I recall correctly.) This is something a lot of people (including most of the anti-evolution blowhards) don't understand: evolution does not imply 'progress', it does not imply motion in a particular direction.

No, you're misunderstanding. The frequency of alleles in the human population as a whole is changing more rapidly than it has in the past (not merely 'mixing about'). This is the definition of evolution. Ergo, our species is evolving faster than it ever has.

That's a poor definition of evolution IMO. What you're describing is genetic drift, and while genetic drift can lead to speciation, evolution as its understood today implies natural selection. In that context, I'd say human evolution has definiutely slowed, since there's no real adaptive progress or elimination of less reproductively fit individuals, although we probably are still developing some minor disease resistance (though that too is being prevented by modern medicine keeping people alive). However, we're only talking on a very small scale in geological time... I'm not sure that, with hindsight, anyone would recognize an evolutionary pause here. In fact, given how precarious our position is on the globe (I'm talking about vs major natural disasters like meteor impacts and whatnot) we're likely to have another major catastrophe trigger massive population kill, and potentially speciation before too long. The only question is whether we can get humans off earth before that happens to maintain the species.

Certainly, we're not going to evolve anything like Mika suggested ("Weaker lower limbs? Curved back? Smaller frame? Decreased brain volume?") due to office work. That's Lamarckian. We'll only evolve along sexually selective lines, which are being badly muddied by modern medicine and whatnot, so it's extremely difficult to predict. I'd suspect we're just going to drift along until the next big catastrophe.



As for the actual topic of the thread, I very much doubt this guy is intending to replicate a T-Rex with a chicken. He's probably talking about getting the individual features of saurian anatomy out of a modern bird, like a toothy jaw, a long tail, clawed wings, scaly skin etc. Some things will be easier than others - scaly skin, dor example, is probably triggerable by turning off a very basic, very old gene that triggers feather development. By contrast, wings would be much harder to turn into limbs because of the (likely) many genes working in conceret to produce them - it'd be difficult if not impossible to find a single gene that could revert them back.

[General Battuta]

The basic definition of evolution given in most textbooks and classes is the change in allele frequency over time in a population. That's it. Additional components like natural selection, speciation, sexual selection, genetic drift, etcetera are plugged in to flesh out the full theory of evolution, but they're not part of the core definition per se.

[Kosh]

Natural selection was a key part of Darwin's original theory, not something that was added on later.

[General Battuta]

I didn't say anything about what was or wasn't present in Darwin's original theory of evolution. I just defined what the core of the theory was.

[karajorma]

The basic definition of evolution given in most textbooks and classes is the change in allele frequency over time in a population. That's it. Additional components like natural selection, speciation, sexual selection, genetic drift, etcetera are plugged in to flesh out the full theory of evolution, but they're not part of the core definition per se.

That's pretty close to the way I was taught it. Natural selection, etc. are the mechanisms by which the change occurs. That doesn't mean they are unimportant, simply that they aren't part of the definition.

An analogy would be the definition of a power station (A building where a fuel is converted to make electrical energy). Coal, gas, nuclear, etc are the fuel. Very important parts of the system but in no way necessary for the definition.

[General Battuta]

Precisely!

[da1edwin]

I have to disagree with the idea that evolution's core is simply the "change in allele frequency over time in a population". That same phrase is consistent with intelligent design, for instance. Darwinian evolution is a specific mechanism by which that frequency change occurs; change in allele frequency over time in a population is a tautology. It's the difference between a mathematical equation and a scientific theory, and evolution is an example of the latter.

[Ace]

Somebody here doesn't work with population genetics.

[General Battuta]

I have to disagree with the idea that evolution's core is simply the "change in allele frequency over time in a population". That same phrase is consistent with intelligent design, for instance. Darwinian evolution is a specific mechanism by which that frequency change occurs; change in allele frequency over time in a population is a tautology. It's the difference between a mathematical equation and a scientific theory, and evolution is an example of the latter.

Read again:

The basic definition of evolution given in most textbooks and classes is the change in allele frequency over time in a population. That's it. Additional components like natural selection, speciation, sexual selection, genetic drift, etcetera are plugged in to flesh out the full theory of evolution, but they're not part of the core definition per se.

I didn't say anything about what was or wasn't present in Darwin's original theory of evolution. I just defined what the core of the theory was.

That is the basic definition given in most textbooks and classes. Now, the entirety of evolutionary theory is far more complex, but that's what evolution is, in the same way that 'gravity' is defined very simply whereas a theory of gravity is tremendously complex.

And it's silly to say that 'the same phrase is consistent with intelligent design' because a) intelligent design is not a scientific theory, it is an ideology, and b) as in the above example, so what? A simple definition of gravity is consistent with Flat Earth 'theory', but that doesn't make the definition itself any less valid.

You yourself pointed out that Darwinian evolution is a mechanism by which evolution occurs. That's precisely correct. You defined what you were trying to say, which is in complete accordance with the statement you're attempting to contradict. Nonetheless, evolution is simply a change in allele frequency in a population; that's the definition.

And Ace is correct. In many fields you don't need to bring in all the components of evolutionary theory to see 'evolution' occuring. Simple equations and observations about allele change still demonstrate evolution.