Eric H

quote DR GH
The core issue you seem to have is how do mutations enter into the genome of a species. If you read Late_Cretaceous' responce, particularly their point #2, I think you will get the idea.
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My problem is not how the principle of evolution happens; but it is the numerical amount of times it would have to happen to end up with the first male and female species with four legs that is compatible..

If you look at an average skeleton from an engineers point of view, it has around 200 bones, and about the same amount of muscles and tendons. Every component has an exact job, and just happens to be made from the best material for each job. All the components just happen to move in the right way, and they can also move independently as part of a complete unit.

I know cripples and defects can happen but on the whole the majority of life seems to work in a perfect way from a mechanical point of view.

Peace

Eric

lpetrich

Sexual reproduction originated something like a billion years before multicelled animals or plants, in some very early protists. As to what that original sexually-reproducing protist reproduced with, the answer is simple: one of its numerous identical twins.

Here's a scenario for the origin of sexual reproduction:

* Early protist invents the meiosis-fusion cycle:

Diploid - meiosis - haploid - fusion - diploid - ...

There was only one "mating type" or sex; any haploid-phase organism could fuse with any other one.

* Evolution of anti-inbreeding mechanism -- a haploid organism will refuse to fuse with one that has the same version of some surface protein

The result is multiple "mating types" or sexes, sometimes thousands of them, as in certain basidiomycete fungi. However, in many protists, algae, and fungi, the sexes look alike -- "isogamy".

* Evolution of egg/sperm gamete dimorphism. This is a byproduct of multicellularity; a good start is to produce a gamete stuffed with food. However, a stuffed gamete is a slow one, and if another mating type specializes in fast swimming, that fast swimmer's presence will be selected. This enables the food-stuffed gametes to become further food-stuffed, becoming eggs. And the fast swimmers to be really lightweight fast swimmers, becoming sperm.

* External vs. internal fertilization. The original form is external -- and lots of marine animals and primitive plants continue to do it. Internal fertilization evolved in seed plants and several times in land animals; some marine ones, like sharks, also do it. This helps keep the gametes from drying out as they meet each other; afterwards, it is safe to give a fertilized egg a water-resistant covering.

lpetrich

Eric H:
My problem is not how the principle of evolution happens; but it is the numerical amount of times it would have to happen to end up with the first male and female species with four legs that is compatible.

Their ancestors were already sexually-reproducing. And imagine a swamp fish with a mutation that made its side fins more leglike. It produces a lot of baby fish with similar fins, and if any of them grow up, they can interbreed with each other. Something made likely with leglike fins being more convenient for moving in cluttered water, which enables such fish to survive and reproduce better.

If you look at an average skeleton from an engineers point of view, it has around 200 bones, and about the same amount of muscles and tendons. Every component has an exact job, and just happens to be made from the best material for each job. ...

That's presumably a human skeleton. Vertebrate skeletons vary widely in their numbers of bones. Frogs have only 6 to 10 vertebrae, while snakes have 100 to 600 vertebrae. Our species is in between, with typically 33 vertebrae.

And the number of vertebrae can vary among individuals of the same species, as happens with snakes. I could not find any numbers on that, but I found this lab exercise for counting variations in the number of fin rays (spines) in a fish species.

This suggests that vertebrae are not individually specified, that the spinal cord produces varying numbers of generic vertebrae that get modified in different directions depending on where they are.

The lesson is that evolution does NOT work by adding one piece at a time Different pieces coevolve with each other. Thus, if a bone gets longer, its muscles get longer with it.

lpetrich

How is that supposed to be the case?

There are lots of examples of less-than-perfect performance. And even of some curious design flubs, like the vertebrate-eye retinal-nerve arrangement.

Late_Cretaceous

Eric, the problem is with the way you are picturing the evolutionary process. You are thinking of single individuals, you need to think of entire populations. If ever there was a case of a lone individual representative of a species, you basically have a species right on the edge of extinction. Picture the last on earth dodo bird searching in vain for a mate - no potential for evolution there. Evolution only works with populations, where there are lots of offspring.

The first four legged creatures were part of an active and successful breeding population - not a lone male and female.

Albion

Well, if you have a population of fish and one of them has a mutation that makes the fins slightly more robust, that isn't going to stop it from mating with the other fish in the population, even if they don't have that fin mutation. If the mutation is useful, or even if it isn't harmful, then it's going to survive over many generations, and if another mutation making the fins yet a bit more leg-like comes along, that still won't stop the mutant from mating with otehr members of its population. Eventually, after enough generations with changes like this being selected for because they become useful, you may have a population whose members can't mate with the original ancestors. But the chances are that the original ancestors won't be around anyway, all those millennia later, or if they ARE around, they won't be in the same place because the lobe-finned descendants will have been able to colonise shallow-water areas that weren't optimal for the ancestors.

Eric H

Quote Late_Cretaceous
The first four legged creatures were part of an active and successful breeding population - not a lone male and female.
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I am not interested in how the second generation of anything exists, I am only concerned about the first generation of any four legged creature..

So are you saying that there has to be many male and female of a species before the first pair can breed, in order for a species to survive?

If so, this seems to greatly increase the odds of it happening.


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Quote Albion
Well, if you have a population of fish and one of them has a mutation that makes the fins slightly more robust, that isn't going to stop it from mating with the other fish in the population, even if they don't have that fin mutation. If the mutation is useful, or even if it isn't harmful, then it's going to survive over many generations, and if another mutation making the fins yet a bit more leg-like comes along, that still won't stop the mutant from mating with otehr members of its population. Eventually, after enough generations with changes like this being selected for because they become useful, you may have a population whose members can't mate with the original ancestors. But the chances are that the original ancestors won't be around anyway, all those millennia later, or if they ARE around, they won't be in the same place because the lobe-finned descendants will have been able to colonise shallow-water areas that weren't optimal for the ancestors.
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While you are talking about fine-tuning fins, the body of the fish remains fish like. Too many other features have to change to go from a successful sea creature to a successful land creature.

Maybe a fish could evolve into a lizard or a crocodile type of creature

As I understand it evolution has many limitations on what it can do,

Can a shark evolve into a tiger? Can a whale evolve into an elephant?
Can tigers evolve into horses, can rats evolve into dogs, and can spiders evolve into birds?

How do we get these wide range of creatures existing if different species can’t seem to interbreed through the evolution system?

peace

Eric

Monkeybot

Late Cretaceous is right. Evolution is the change in frequency of an allele within a gene pool - IOW, it means a certain trait becomes more common in a population. Individuals don't evolve, populations do.

Coragyps

You are exactly right: that's why it took about 40,000,000 years, and maybe half that many generations, to get from critters-that-looked-like-fish with funky fins to amphibians that had a fishy-shaped body, and then another 100,000,000 years to get to the first mammal-like thing. No one pair of Acanthostega had kids that walked up the bank - but their distant descendants went to play in the shallows more and more. And then those guys' distant descendants chased bugs even further from the swamp. It was such a gradual "becoming" that you or I could never see it happen - a hundred years, after all, will fit into a million years 10,000 times.

And no, a shark can't evolve into a tiger, as they are both here in the now. But a fishy looking thing like Acanthostega evolved from an odd-looking little swimmer, maybe something like Haikouella, and then its progeny gave us tigers, and lizards, and whales, and bats, and Winona Ryder. It just took a hell of a long time and a whole lot of dead ends to do it.

scigirl

Eric H,

Welcome to infidels - and it's good to see someone interested in learning about evolution - good for you!

I urge you to do a bit of reading about genetics, and embryology. I find that when talking to people who are skeptical of evolution - that they have this idea that 1) base pair substitutions are the driving force for genetic diversity, and 2) body plans are designed like buildings.

Both facts are dreadfully wrong, and it's no wonder people who believe them are skeptical of evolution (my apologies if you don't think in this manner of course!)

Point mutations (one base turning into another base) have played an important role in evolution. But our DNA can do other complex things like allow retroviruses to cut huge chunks out and transport them to other places, or duplicate parts of itself allowing for a gene to branch out its functions.

In terms of our body plan - we are made in a very strange way - genes get turned on and off in unique patterns such that tissues grow, then regress, then grow and regress some more and eventually you get something that looks like a fish or a a human. If you start modifying promotors (sort of like volume control dials for each gene), suddenly you can and do see dramatic changes like a fish giving birth to a banker to use Coragyps' example. Ok maybe not that extreme - but did you know that a single point mutation in the Drosophila genome can cause a fly to grow legs where antenna should be? That's just one base pair change. Couple that fact with all the crazy things that DNA does, the fact that we are created from a series of overlapping programs operating simultaneously, and the fact that the earth has existed for 4 and one half billion years - and suddenly evolution doesn't seem that far-fetched. Amazing and wonderful, but not far-fetched.

scigirl