Is evolution determinate?

[wildman]

In the latest Scientific American, there was published a discussion between the fellow who wrote The Skeptic and Richard Dawkins about what intelligent life on other plants would look like. Basically it was around the idea of how determinate is evolution. In other words, are certain results inevitable? The Skeptic was saying that the chances of there being intelligent life that looked like us was almost zero. Dawkins wasn’t so sure.
So my question to you all is: “How determinate do you all think evolution is? For instance, I look at the Cephalotaceae and the Nepenthaceae. They are in completely different phylogenies and yet their insect traps are almost identical. And there are zillions of other examples. Convergent evolution seems to be the rule rather than the exception. So what do you all think? Could it be that evolution is not random but rather controlled by determinate rules that we don't yet understand?

[biohazard]

If there was an exact or near-exact copy of the planet Earth and there would also be similar large-scale events (like great volcano eruptions and meteor impacts), I assume the outcome would be surprisingly similar than what we see here on Earth. However, having intelligent species like humans might still not be 100% sure, because there obviously isn't very high pressure towards intelligence in this kind of environment - after all we're the only ones.

This being said, it is very unlikely that such a close copy of our planet exists, so I'd assume there might be hugely different outcomes. On most planets, I believe, the life forms would be far less complex due to higher number of planets that have much harsher environment than the Earth has. Of course, there might be also some much more pleasant places and they might have much more complex life forms, who knows :)

But at least our closest stars don't seem to be swarming with high intelligence species, otherwise we would probably have spotted some kind of signal from them, either intentional or unintentional. Radio or such signals at least if nothing else. Although even the way to the nearest star after the Sun is pretty long...

[mith]

it's stochastic

[wildman]

it's stochastic

If so why are so many of the birds in Australia dead ringers for Northern Hemisphere birds. For instance the sittellas http://en.wikipedia.org/wiki/Sittella look and act just like nuthatches even though they are not even remotely related or the Scrub-robins http://en.wikipedia.org/wiki/Scrub_robin look and act just like birds in the Thrush family (again not even remotely related). Convergent evolution is even more dramatic in the plant kingdom as I mentioned in my first post.

[JackBean]

First, the question is, whether they would use the same stuff like we do. The DNA, RNA, proteins. Will they have 4 bases or more/less? Will they have 20 amino acids? Will they have ours 20 amino acids? etc. etc.

[biohazard]

Goog point, JackBean. But if the rules of natural selection were the same (that whatever the blueprint is, it tries to multiply itself and the fittest ones keep reproducing most) then, in the end, this might not matter!

[robsabba]

So my question to you all is: “How determinate do you all think evolution is? For instance, I look at the Cephalotaceae and the Nepenthaceae. They are in completely different phylogenies and yet their insect traps are almost identical. And there are zillions of other examples. Convergent evolution seems to be the rule rather than the exception. So what do you all think? Could it be that evolution is not random but rather controlled by determinate rules that we don't yet understand?

Although the Cephalotaceae and the Nepenthaceae are not closely related by typical standards, the fact is they are related and share most of their genome. That baggage from heredity and similar physical constaints mean there are only so many solutions to similar problems. An organsim that evolved on another planet would share no ancestry with any on this world. Only similar physical constraints (assuming a similar planet) would serve to produce some form of convergent evolution.

[JackBean]

There are plenty of convergent evolution, but also of divergent one

[wildman]

Although the Cephalotaceae and the Nepenthaceae are not closely related by typical standards, the fact is they are related and share most of their genome. That baggage from heredity and similar physical constaints mean there are only so many solutions to similar problems. An organsim that evolved on another planet would share no ancestry with any on this world. Only similar physical constraints (assuming a similar planet) would serve to produce some form of convergent evolution.

Ah, that is why maybe the mammals are less convergent. The constraints are less than with flying animals such as birds. Right?

[robsabba]

Although the Cephalotaceae and the Nepenthaceae are not closely related by typical standards, the fact is they are related and share most of their genome. That baggage from heredity and similar physical constaints mean there are only so many solutions to similar problems. An organsim that evolved on another planet would share no ancestry with any on this world. Only similar physical constraints (assuming a similar planet) would serve to produce some form of convergent evolution.

Ah, that is why maybe the mammals are less convergent. The constraints are less than with flying animals such as birds. Right?

Hmmm. There certainly are plenty of examples of convergent evolution among mammals. Placental mammals and Marsupial mammals from Australia come to mind. However, the physical contraints involved in flight are indeed pretty demanding. There is only so much variation possible with the "design" of a vertebrate flying animal. In addition, terrestrial mammals fill a much wider number of ecological niches than birds do.

[Darby]

In most of these examples, the constraints on the convergence is other organisms (catching insects) or the basic starting structures (birds). If other different starting conditions are possible (is cellularity a necessity?), then it's tough to know too much about eventual forms.

Yes, you would get things like streamlined swimmers, but we have fish and squid and amphipods, fairly different animals doing similar things. You could predict the existence of streamlined swimmers in an extraterrestrial world, but they wouldn't necessarily look like fish. Some form of photosynthesis makes sense, which would make sort-of plants, but would convergence produce land plants like ours? Maybe superficially.

[wildman]

First, the question is, whether they would use the same stuff like we do. The DNA, RNA, proteins. Will they have 4 bases or more/less? Will they have 20 amino acids? Will they have ours 20 amino acids? etc. etc.

This is an interesting question. It may be that our stuff is the only stuff that is possible.... Or maybe not.

The impression I get from this discussion is that the answer to my question (whether evolution is determinate) is yes and no. The environment seems to set constraints on how far the random processes can range. However, with only one example planet to look at, it is hard to know where the constraints are.