Even though silicon is similar to carbon in terms of its valence, it doesn't form the kinds of complex compounds as carbon, with anything like the functional groups that make carbon organic chemistry so interesting. Also, silicon dioxide is such a stable byproduct of silkicon chemistry that an oxygen rich environment would probably be fatal to silicon-based life.
The theory of evolution never implies humans evolved from octopi. And if you consider the more intricate elements of our eyes and octopus eyes, it seems clear they developed to a similar state along two different paths. Once "nature" finds a successful "design", it tends to replicate it rather than starting from scratch - the heart, circulatory system, digestive system, all quite similar among mammals, because as a system they work extremely well in our situation. But since evolution is not predestined, there is no guarantee that life on other planets would converge to the same state, or become intelligent - it seems a lot of people assume that "intelligence", at least as we define it, is a given when it comes to aliens, some people even assume that they must for some reason be more advanced than us. Evolution only aids the survival of creatures - in our case, having brains with a greater capacity aided our ability to survive and reproduce, but consider all the millions of other species on the planet who are not evolving bigger brains, even though they could. Its not worth the cost to them since it would not necessarily aid their survival, and for that reason, you cannot assume that intelligent life would evolve anywhere else on Earth, yet alone on any other planet.
I think that intelligence is a by-product of a larger brain. I don't think that the course of evolution intended for us to be intelligent. For some reason, we developed a larger brain (possibly just to power our complex internal systems), and as a result, intelligence flowered. I think that, as evolution continues (on other planets), that larger brains are required to run more complex lifeforms. Therefore, I believe, intelligence will develop elsewhere if lifeforms are allowed to evolve.
But that assumes that more complex lifeforms are a necessary product of evolution, which isn't true or there would be no single celled organisms left today. Evolution beyond simple organisms enables organisms to beat their competition for resources, but if there was no competition to drive evolution, it would not continue. Consider the evolutionary arms race between lions and gazelles. As the lion evolves and improves its ability to hunt, the gazelle develops better evasive capabilities. The net result of this evolutionary pattern is zero, yet both sides are becoming more and more "advanced" in their capability to survive. Survival instincts and competitiveness are the only things driving this race - if lions suddenly became extinct, gazelles would likely cease to evolve until a new challenger emerged.
Non-sequitur. Evloution is not at an endpoint. It continues around us. And there are ecological niches for all manner of life forms, from the least evolved to the most. As long as a niche exists which increased intelligence favors, in telligence will eventually develop to dominate that niche.
Agreed. One must also watch out for the fallacy that evolution has purpose. It has neither purpose, nor motive, nor wish, nor intention. It's a numbers game. Probabilities played out in numbers large enough and time-scales long enough to see actual consistent values and patterns arise.
Hello, Im new here but I have a few ideas why we haven't made contact yet. SETI has only been operating for a few decades. It's possible that the radio signals they're looking for originated from a planet so far away they just haven't reached us yet. Or that they are closer than that to us but they're actually behind us in developing technology. They don't know what radio signals are yet. Maybe they're still in a phase comparable to our colonial period. Or they are so far ahead of us they have found us first but for some reason have chosen not to contact us. We are a terribly warlike species and they could be snobbish intergalactic pacifists and have simply turned their noses up at us. also they could be waiting for us to mature to a point where they think we're deserving of their contact. Or they could already be in contact and are being kept quiet by the world's governments.
Sorry, I didn't mean to imply humans evolved from octopi, I meant that we have a common ancestor (as does every living creature on earth) and that despite our ancestor lacking eyes, we (octopi and human beings) nonetheless evolved them completely separately. Of course intelligent life isn't going to evolve on every hospitable planet, but the sear number of such planets, given what's been found in a very, very small sample thus far, I think, errs on the side us being rare, but in the larger scope of things, no rarer than finding twenty bucks on the side walk.
That's not necessarily true. Life could have developed in multiple isolated hotspots all over the world. I doubt a sole single celled organism was the only thing alive to start with. I dare say, all humans have a common ancestor, but not the entire biosphere.
