How rare is life in the universe?

[spuriousmonkey]

We can actually have a closer look at the group of animals from which tetrapods evolved.

The so-called lobe-fins.

Here is a picture:

The lobe fins were a new evolutionary structure that enabled the fish to interact in new ways with the bottom. To get extra support? To crawl? To prop itself up to breath air?

The lobed fin ancestor happened to have 2 pairs of lobed fins. These evolved into proper limbs in tetrapods.

Now, how can a structure evolved for a certain mundan purpose such as crawling on the bottom, be any indication of how an intelligent species' limbs should look like?

We have 4 limbs because of an 'accident'. A 4 lobe finned ancestor gave rise to us. There was no pre-knowledge that 4 limbs would be good for locomotion, for tool-handling.

It's all unsubstantiated speculation to assume 4 limbs are related to certain aspects of a 'determined' evolution as Dinosaur is proposing.

-------
edit
It also could have been a different picture. Like the following:

A 'fish' ancestor with 6 lobed fins and eyes all around. The front lobed fins evolved into a flexible structure similar to the elephants trunk, the hind pairs into legs.

As long as the structures do not defy the logic of small steps that do not go down the 'hill of evolution' (simplified and wrong analogy) you can think of anything you want. 4 limbs are last seasons fashion.

 

[spuriousmonkey]

A vertebrate is defined by having a backbone, not four limbs. The number of limbs on terrestrial vertebrates is a derived characteristic.

Are we done trolling now?

Fuck off dick. You got the point I was trying to make.

 

[RHaden]

Fuck off dick. You got the point I was trying to make.

My, what intelligent language...

Yes, I understand that land vertebrates' four limbs are the result of an evolutionary "accident".

 

[spuriousmonkey]

My, what intelligent language...

Yes, I understand that land vertebrates' four limbs are the result of an evolutionary "accident".

reported for derailing a thread.

 

[Dinosaur]

A large land animal with 6 or 8 limbs seems to be a design with no evolutionary advantage and some disadvantages. If fish originally had 6 or 8 fins, I would expect evolution to trim back to 4.

Note the evolutionary history of the tail. It is useful for some mammels (squirrels), not so useful for large primates. Evolution got rid of it for some species, a fate I would expect for an extra pair of limbs.

 

[spuriousmonkey]

It's all speculation what you give.

If you really want to show that 4 legs are the most efficient solution you better start explaining why there are trends in evolution towards no legs and 2 legs.

Evolution is all about history. It has to work with what is there. If there are 6 legs to start with it will work with six legs. If there are a million legs, then it will work with a million legs. If there are 4 legs it will work with 4 legs. Sometimes reducing them to nothing. Something changing the function of 2 legs into wings, into arms, or using all legs to put a flap of skin in between to make them into legs.

Obviously the most optimal solution to make wings would be to start from scratch. That's hardly ever an option in evolution. That's why legs are transformed into wings.

Evolution depends on history. Evolution doesn't follow the best engineering solution.

 

[orcot]

Evolution depends on history. Evolution doesn't follow the best engineering solution.

it doesn't but it gets mighty close, anything large with a big brain that doesn't fly will proberly have 4 legs.

 

[Novacane]

it doesn't but it gets mighty close, anything large with a big brain that doesn't fly will proberly have 4 legs.

Yep......Elephants and Rhinos have the smallest wings on the planet.

 

[swivel]

Fuck off dick. You got the point I was trying to make.

I see a pattern here.

1. Spuriousmonkey says something ignorant.
2. Someone points out what a moron Spurious is and corrects his mistake
3. Spurious curses at the person and tattletales on them at the same time
4. Spurious cries "ad hominem" when attacked person dares to defend themself

 

[madanthonywayne]

We have 4 limbs because of an 'accident'. A 4 lobe finned ancestor gave rise to us. There was no pre-knowledge that 4 limbs would be good for locomotion, for tool-handling.

You're probably right. But you must admit that four limbs is the simplest and most stable configuration for a bilaterally symetrical organism.

 

[spuriousmonkey]

You're probably right. But you must admit that four limbs is the simplest and most stable configuration for a bilaterally symetrical organism.

You can't beat a millipede in stability. However, the chances that a 4 limbed bilateral symmetrical organism will arise are probably pretty good. Probably good enough to put a bet on it. It is not however a sure outcome in my opinion.

 

[Ophiolite]

Attention all dumbasses. Yes, this means you (unless you are francois - the only person who has an understanding of the Drake equation).

Point 1: The Drake equation was introduced over forty years ago. It has stood the passage of time remarkably well.
Point 2: It was created in order to provide a framework for a meeting on the possibilities of extraterrestrial life. It was not intended as an absolute way of computing the likelihood of such life.

Those of you who have been glibly criticising it have utterly failed to consider its pedigree and purpose.

 

[Dinosaur]

MadAnthonWayne: I do not think that stability is the main issue in the design of a large vertebrate.

But you must admit that four limbs is the simplest and most stable configuration for a bilaterally symetrical organism.

A 3-legged vertebrate could be bilaterally symmetric and stable, but would be a lousy design for running speed.

The mutation facet of evolution is generally believed (with good reason) to be random, but the natural selection part strongly tends to result in designs which are both functionally effective and reasonably efficient. My main objection to more than 4 limbs is little (if any) additional running effectiveness with extra requirements in energy and brain/nervous system circuitry.

Ophiolite: I agree that the Drake equation often gets put down for the wrong reasons.

The concept is good. The downside is the lack of objective criteria or evidence supporting any of the guesstimated parameters.

 

[Novacane]

You're probably right. But you must admit that four limbs is the simplest and most stable configuration for a bilaterally symetrical organism.

Whales are a pretty symetrical organism too, bilaterally speaking.

 

[kaduseus]

Why does life exist is the question, apparently it's because earth isn't too hot or too cold....which is bollocks.

WARNING: crackpot theory below.....

Life exists because of diatomic bonding, diatomic bonding exists because the background environment, Earth, is unstable (has a wobble (because of a single moon)).
So if you look for planets with wobble, like earth, you have a pretty fair chance of finding life.
The other known planet with high instability is Uranus, but i'm not sure as to wether it's instability isn't somewhat muted by the fact it has more than one moon.

If Planets with single moons are unstable, lead to diatomic bonding and life, there must be alot of life out there.
Question is, are planets with single moons only found around stars like the sun, is the sun diatomic(has a sister star), how many star pairs are there........




...........Life on Uranus...because it's wobbly......

 

[Maast]

I remember reading somewhere we owe our moon two big debts of gratitude;

1. It gave us large daily tides thus prompting evolution of terrestrial based animals

2. It stabilized the Earths rotation and made our fair planet a good deal more friendly towards life, else Earth would have wobbled on its axis more frequently and to a much greater degree thus leading to extreme variability in climate.

Maybe any intelligent ETs we meet will be much tougher physically than we are due to life having to adapt to a rather hostile planet. Our soft squishy bodies would be no match for them

 

[madanthonywayne]

Life exists because of diatomic bonding, diatomic bonding exists because the background environment, Earth, is unstable (has a wobble (because of a single moon)).

Please explain how a planets wobble increases diatomic bonding.

 

[kaduseus]

"Please explain how a planets wobble increases diatomic bonding."

Duh.......coz it's wots jelly is made of innit

However i must point out, that if your going to point out, that the universe is mainly hydrogen, and therefore diatomic hydrogen exists everywhere, then i have to point out that hydrogen existing throughout the universe is an assumption.
I'd also point out that we perceive things within a local reference frame.
And then i'd ask you for your opinion as to where chemistry comes from, to which you will reply it's universal, which is another assumption.

hehe. i love sciforums

 

[Syzygys]

One element is missing from the Drake equation. It is the chance of having 2 civilizations occuring at the same time. Let's count human civilization from building cities and having societies, so humans in about 10K years reached the level of ability to complete selfdestruction (nukes).
From this point of being able to whipe out themselves, civilizations can exist for a long time, but also could disappear very quickly. Thus if we count this 10K years as an average length of interesting to have a meeting between 2 civilizations/lifeforms, we have to introduce this into the Drake equations and will reduce the chance of meeting of 2 intelligent lifeforms greatly.

Now let's say we can go to other solar systems and visit other planets. Sure, visiting a planet that is in the age of our Jurassic Age can be interesting, but most likely we would like to meet other intelligent life/civilizations. And please note that 10K years is really nothing a minoscule compared to the timeline that Dino posted...

 

[Novacane]

One element is missing from the Drake equation. It is the chance of having 2 civilizations occuring at the same time. Let's count human civilization from building cities and having societies, so humans in about 10K years reached the level of ability to complete selfdestruction (nukes).
From this point of being able to whipe out themselves, civilizations can exist for a long time, but also could disappear very quickly. Thus if we count this 10K years as an average length of interesting to have a meeting between 2 civilizations/lifeforms, we have to introduce this into the Drake equations and will reduce the chance of meeting of 2 intelligent lifeforms greatly.

Now let's say we can go to other solar systems and visit other planets. Sure, visiting a planet that is in the age of our Jurassic Age can be interesting, but most likely we would like to meet other intelligent life/civilizations. And please note that 10K years is really nothing a minoscule compared to the timeline that Dino posted...

In terms of finding other intelligent life forms out there? The results so far to date are Zerooooooooooooooooo! It's still being hotly debated whether or not Earth currently has intelligent life on it. You know after reading the paper this morning, I'm not sure either.