Exobiology - how might humanoids evolve on various planet types

My view is that different animal body plans weren't the result of prior engineering, they were the result of heritable changes in the developmental biology of very simple multicellular pre-cambrian organisms, changes that occurred more or less at random (given how the heredity system works and the likelihood of various kinds of events happening on the molecular scale there) and selective pressures subsequently acting on the phenotypic results. The outcome might resemble the results of engineering, but it isn't. A lot of it was fortuitous and contingent, the result of how the history of life happened to unfold (and it might have unfolded in many different ways). It isn't always going to produce the simplest, most efficient and most elegant solution to a problem.

As evolution proceeded and organisms grew more complex, they became locked into their very early ancestral body-plans. It's possible to imagine turning a jelly-fish inside out and that change turning out to be more effective in some environmental situations, but turn a human inside out during fetal development and it would be a spontaneously aborted disaster. So the cambrian explosion was a one-off that set most of the animal phyla on the course that they've taken ever since.

 

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Indeed. Good example.

 

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Yup.

There's no reason to think that any highly-evolved plan is the best, simply that a plan is the best it could do with what it had.

You're not going to get three-fold symmetry spontaneously evolving from two-fold symmetry once its advanced past a certian point.

 

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And your "loaded" claim that the justification was invented gives insight into your own motivation.

 

That's odd. It's like you're chiding him for taking a stance in the discussion. Was he being secretive about it?

I think the point is, it is much easier to argue that what we are is the most likely. It is very difficult to think in terms of the unknown unknowns.

If we were all living isolated in a giant baby's playpen, it would not be hard to argue that everyone else's floors will be soft and fluffy, so they don't crack their heads.

 

Hi Dave. You may recall I earlier offered this response to Killjoy Clown "I was not necessarily agreeing with Conway Morris' view of humanoid evolution. I was correcting Dave's observation that "There's no reason to think that exo-critters would evolve to a humanoid shape on other planets". One might think that the view of Conway Morris and yourself is needlessly anthropocentric."

I was certainly chiding him for using an absolute qualifier, namely invented, without providing a single piece of evidence or argument to justify such an absolute claim.

I find Conway Morris' ideas on this interesting. I am not entirely convinced by them, but I am confident that he did not invent his arguments. I observe that he arrived at them by careful examination of the facts and reasoned argument. This does not make him correct, but it should protect him from casual and unsupported claims of invention.

Two final points:
1. While it may be , as you say, that "it is much easier to argue that what we are is the most likely", this does not necessarily mean that such a view is wrong.
2. I have recognised this risk earlier by suggesting Killjoy Clown and Conway Morris may be guilty of anthropomorphism.

Executive Summary: I am wholly opposed to absolute statements.

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That was me.

I must have missed the absolute qualifier, and the use of the term "invented".

Ah. Post 20 Yazata says "invent reasons" for stereo vision, etc. That's not an absolute qualifier, though I see how it can be seen to put a spin on the Conway's reasoning. I did not interpret it as such. I simply saw it as an argment that Conway might have been guilty of anthropomorphism. He may not have intended to invent, but that doesn't mean he didn't. Generalizing from a data point of one is risky.

Perhaps. Though it is tantamount to drawing a general conclusion from a data point of one. That's not a very tenable position, and should be regarded critically.

 

If you don't like my use of invent, how would you like to characterize it?

We have a result of an evolutionary history, namely ourselves. That's our factual given, the rest of our biological speculating about it is our own invention.

One can point to various anatomical features that we display, and then try to invent arguments about how evolution everywhere is bound (or at least most likely) to result in those features and hence in beings very much like ourselves. That's why I imagined a hypothetical tripedal trilaterally symmetrical alien scientist making the same kind of argument, that intelligent life elsewhere in the universe will have three legs (the fewest necessary for stability) and three eyes (the fewest necessary for a 360 degree stereoscopic field of view. Makes perfect sense from that point of view.

My motivation is trying to avoid anthropomorphism when trying to imagine aliens' anatomies. I don't believe that there's any cosmic predisposition towards producing humanoid lifeforms, any need for them to be humanoid (even if we would feel lonely if there aren't aliens sufficiently like us out there). I think that the appearance of humanoids on Earth is largely an accident of our own evolutionary history, only one of an unknown but doubtless large number of possibilities that might have been realized instead, and might be out there among the stars.

 

I would have to read his book to see if he draws any hasty conclusions.
It's easy to say he's wrong, as long as we go with our idea of his logic, rather than his.

 

Which almost precisely captures the point I was about to make, but is much more succinct.

Yazata, an invented explanation is one - in my lexicon - that is consciously deceptive. Conway Morris constructed an explanation through the use of logic and data.

 

Correction:

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It's apparently rather controversial. See this review from Nature:

http://www.nature.com/hdy/journal/v93/n3/full/6800536a.html

I'm fairly confident that it doesn't represent the consensus of evolutionary biologists.

 

Excerpts:

...aaaaand I've read enough.

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In my lexicon, to invent something means to originate, create or devise it as a product of ingenuity, experimentation or contrivance. Suggesting that just about any scientific hypothesis can be said to be an invention of those proposing it. That's probably the most obvious place where creativity enters into the scientific process.

 

I'd hazard to say that your use of invention was conflated by Ophie with your suggestion that title of his book belies an agenda.

As it turns out, you seem to hit the nail on the head.

Excerpts from the review:

[It is] underpinned by a degree of theological conviction seldom made so explicit in a scientific book

The final major chapter entitled 'Towards a theology of evolution' does not sit well with the rest of the book.