I'd probably call them "chemical analysis organs" as that is what those senses are - one from a distance, one from closer up. Otherwise they'd probably eat indiscriminately.

I'll buy that. There may well be species without eyes, of course, but I think a great many will have some form of visual receptor. Light and dark is just too fundamental to life.

Unless life has evolved on the moons of giant planets which are not orbiting any star - said moons being warmed by tidal interactions.

I suppose that depends on the fluid medium - whether atmosphere or water. I imagine there may be some that hear with their whole bodies.

Seems likely, although tentacles and elephants' trunks might be common too or instead.

As opposed to... yuck!

Reproduction yes, as that's a basic definition of life. But sex might not be commonplace. Or else there might be several sexes. I don't think there's a definite reason why there are only two on Earth - particularly as that doesn't apply to all creatures.

Seems likely.

As opposed to inflating a bladder with a lighter than air gas? But yes, I think we will see wings.

Ah, now that's where you're certainly wrong. We will see human faces... regardless of whether they are there or not! We see human faces in hedges, clouds, and Phil Plait even saw one in his shower curtain.

Seriously though, as long as there are two eyes together, there will be some resemblance to a face.

Uncommon, I'd guess, but not nonexistent.

There might be coincidental resemblances - and again people will look for these - but I reckon any cat-like aliens that we do encounter will have a totally different internal system, and it won't meow.

I agree with the most, but there might be some.

There's a huge scope for variation there. A language of clicks where the vocabulary is the length of pause between clicks rather than the sound of the clicks, for instance.

I'm guessing there might be some languages we can imitate, but there will be many more that depend on sounds that are outside the range we are capable of delivering, and many more still that are not sound-based at all, or are only partly sound-based.

This is very speculative. The idea that we can transfer our consciousness as easily as a Word document is a very attractive one, but it may well prove impossible.

Good speculation, Ronald.

As for Meatloaf, I think the confusion arises because "but" is the wrong conjunction - "and" would make more sense. You might say, "I will you make you my highest priority and I will never let you down," but you would not say, "I will you make you my highest priority but I will never let you down," which is what Mr Loaf appears to be saying.

Ooh! Let me play the game of "how many can I disagree with"? (I'm sorry, my personality does naturally tend toward instinctive skepticism...it's a tendency I do try to keep under control with a second step of skepticism of my own skepticism...)

I disagree with this one--if you mean a distinct organ like a "nose" or "tongue". Many animals essentially smell/taste through their skin, either throughout large areas of their body or concentrated at the ends of their "fingertips". Having a distributed sense of smell/taste is useful for burrowing animals and may be useful in general for avoiding caustic substances--much like our distributed sense of temperature allows avoiding hot or cold objects.

It could be that in most alien environments, there are usually lots of caustic acid pools or lots of poison producing molds. Distributed sense of smell/taste throughout the skin might be the rule rather than the exception. Specialized smell/taste organs might be as uncommon as specialized temperature sensors here on Earth (pit vipers can directionally sense heat with crude thermal vision "eyes").

I'll agree with this one, but note that there's an incredible variety in potential designs (as evidenced by the various types of eye mechanisms in life-as-we-know-it), and the frequency band(s) of sensitivity will greatly depend on what's available.

Agree. Certainly there will be some ability to sense vibrations, and having sensors specialized for this is pretty useful.

Disagree. See any joints in starfish or mollusks? No. Even we have a useful non-jointed manipulator (open your mouth). Many mammals have useful prehensile tails or noses, in addition to jointed limbs. Obviously, there are animals with only non-jointed limbs, and clearly non-jointed limbs can be useful even in animals with jointed limbs. Therefore, aliens with non-jointed limbs are viable. There is a vast families of creatures without jointed limbs, so I don't think we can say for sure that jointed limbs will be common.

Note that we can trace all vertebrates with jointed limbs to a particular progenitor lobe finned fish. That might have been a freak occurrence. Snails made it on land.

Disagree on this one. It may sound gross, but there are animals which inject or spit digestive juices into its food and slurp up nutrients rather than stuffing more or less unprocessed food into their bodies. This strategy may be quite an advantage if most prey plants/animals are protected by a tough exoskeleton.

Also, there are multi-cellular creatures which simply absorb nutrients directly from the soil and air/water. Actually, almost all life-as-we-know-it absorbs at least one nutrient from the air/water (oxygen). In my speculations on non-predatory intelligent aliens, the aliens get all of their energy from sunlight, and absorb nutrients from the water and air. While this sounds unusual, we don't know...it might be the rule rather than the exception.

I disagree. Evolution doesn't require sexual genetic material exchange, and it's not at all obvious that genetic material exchange is always going to win out. One example of an extremely fast evolving creature is the AIDS virus. Pretty much its only defense against our constantly shifting natural and artificial defenses is the ability to not copy itself well.

But I'm more intrigued by the opposite possibility--creatures where individuals don't even have just one genetic code. We take it as a given that a creature will have just one genetic code, but that's not true of lichens, and it's not true of chimeras. In the extreme, aliens might be gestalt collections of genetically distinct sub-creatures. They could even have genetic variation on a cellular level...even a sub-cellular level (like a slime mold, there could be multiple genetic nuclei within each cell). Such gestalt creatures might have a distinct advantage in highly volatile environments requiring constant adaption.

What if that's the rule? It might be that most aliens are hyperadaptors that evolve on a cellular level rather than an organism level. On a macroscopic level, they just directly pop out offspring buds. They might find our lumbering evolution process of sex, death, and natural selection rather fascinating in its bizarre inefficiency. The entire concept of disease may be alien to them. "Viruses? That's something that only happens to computers!"

Disagree. We're biased toward liquid water and oceans/lakes. But looking at the solar system, open pools of liquid water look rather uncommon. For all we know, it might be that life is rather more commonplace than open pools of liquid anything. Without something to swim in, you won't get swimmers.

Disagree. Similar to the above. We live on a planet with a thick atmosphere, but most planetary bodies we've seen so far lack a thick atmosphere. Maybe life usually evolves on planetary bodies without an atmosphere. Without an atmosphere to fly in, there are no flyers.

I agree with all of the above, with the possible exceptions of size and language. There might be some inherent "sweet spot" for size, when it comes to technological creatures--maybe related to available brain power, visual resolution, and tool using muscle power, vs sheer numbers. Also, there might be some inherent "sweet spot" for the frequency range of sound communications, and some inherent advantages to the human language style of breaking up things into syllables/words.

Maybe. Okay, I'd bet against it.

Yes, but they'll plausibly have a cultural tendency to stick with reflections of the past.

I just remember the movie Alien & Predator.

In middle age, many men grow another useful limb. Young women grow a similar limb, but it generally goes away within about nine months.

BTW, I took Ronald's post to mean, "These are things that will be sufficiently common that we will see them at least some of the time," rather than, "These are inevitable because no alternative exists."

Middle age?!

Young women grow a "limb?!"

My beer belly is very useful for holding books, my wallet and so on, and for steering my car while driving along the motorway, leaving my hands free for knitting or doing a Rubik's cube.

[None of my posts relating to an abdomenal limb are meant to be serious.]

An interesting discussion. I agree with what most people have stated as to life forms being very different from us, because of the multitude of different evolutionary factors involved. I do however think that because of the sheer size of the Universe, life probably takes on similar shapes from time to time. Kind of like a horse and a sea horse having somewhat similar looking head shapes, even if one animal is a land animal and the other is a sea animal.

With billions of stars making up an average galaxy and billions of galaxies out there; I bet somewhere out there, there is something that looks or looked like us. When you have a huge range of possibilities, I wouldn't count out the ole Star Trek type aliens out completely. Who knows, maybe there is or was, a Jubba the Hutt out there in some other galaxy, far far away.

It is certainly possible that there is a human looking species out there somewhere. Though given your Sea Horse analogy appearances can of course be deceptive - the large volume on top of such a creatures head may not be for a large brain but for some other purpose it might not be the dominant species on its world and might occupy a very minor niche in it's planet's biota.

However unlike in Star Trek the occurance of such humanoid forms is more likely to be the exception rather than the norm. Furthermore I would offer very long odds against them existing in our galactic neighbourhood. If your search area extends out to include around 50 galaxies then then odds of finding a humanoid species might just be worth considering but finding any humanoids within 300 light years of us? I doubt it.

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Define 'human face'. Some features of the human face are environmentally optimal - having two, forward facing eyes for one. Having your nose adjacent to your mouth allows them to share receptors (seeing as they have similar functions) and having them on the same side of your head as your eyes allows you to put things in your mouth or put them under your nose to smell them. You've a lot of elements of the face right there.

Again, our bodies are fairly well optimised for getting around whilst retaining the capacity to hold/manipulate stuff. Why won't our joint structure be found on other planets?

This I agree with.

The number of organisms a given environment can support is dependent on the size of those organisms, and for intelligent beings there is presumably a delicate balance between being big enough to support a complex brain, and being small enough to allow a large population that can start a civilisation.

So, I suggest if you go to a populated Earth-sized planet, you've a good chance of finding roughly Human-sized people.

I suspect (although I'd need to check) that our aural range is pretty much optimal for our environment (as we don't need echo-location). So at a similar temperature and pressure, why wouldn't an alien language be audible to humans? And some humans can be extremely talented in creating non-language vocalisations, so it might even be possible to speak it.

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I agree with this. I would think that it is very unlikely to have another lifeform that resembles humans anywhere very close to us. I would think the odds are that there is probably nothing like us in our galaxy at the moment. Like the lottery, it is very unusual for two winners to come from the same neihborhood, but from time to time, it does happen. If you have enough possibilities, the unlikely will happen sooner or later.

Unless you live in the Netherlands...
From 01101001's post here.

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Every SF alien I ever read of fell into one of two groups:

1. Communicates by sound within human hearing range, and humans learn to understand and speak its language with no more difficulty than learning some tougher Earth languages.

2. COmmunicates by ultrasound, radio, chromatophores, etc. In all these case humans need some artificial interface.

I think that sound generation is a very efficient method of communication, and it is entirely possible that we could hear an alien speech. What I do not believe is that we could process it. Just like our visual brain center is tuned to recognize and analyze human faces, our audial center is tuned to recognize and analyze human sounds. We can hear fine distinctions between human sounds; we can not hear equally fine distinctions between nonhuman ones.

If that does not make sense, here is an example:

Rhesus monkeys have at least 30 distinct cries. Each cry has a distinct meaning -- a cry for "eagle!" calls for very different response than a cry for "snake!".

Primatologists needed digital sound analysis to identify these cries. To a human ear they all sound the same.

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As seen in some creatures of the Kingdom Monera.
I'm going to have to stop talking about how I hope there are "Europan Jellyfish", then.

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I mean a biologist would see that it was different from earth jellyfish, not that jellyfish like creatures are extremely unlikely.

I'll expand a little on what I wrote before about what might be fairly common amoung intelligent aliens. First I'll mention that I am writing about aliens that are roughly analogous to life on earth and that we could look at when it's active and say, "Yep that's alive!" For all we know the most common form of life in the universe lives in molten metal, the photospheres of stars or the metallic hydrogen layer of gas giants, but I feel the need to limit myself.

The things I mentioned are characteristics I think might be fairly common among beings at a "Wear your old biological body" party on Vega. (Please correct me if I'm wrong KaiYeves.) I don't think they are things we will definitely see, just what seems likely to be popular. Basically they are things that have evolved independantly on earth several times which suggests they are broadly useful adaptions that may help ooffworld species as well.

Jointed limbs of one sort of another have evolved among diverse groups of animals, suggesting that joints are fairly popular. Even starfish have jointed limbs but this demonstrates how very different joints can be. An alien with human limb proportions is unlikely to exist because even our closest relative, the chimpanzee, has significantly different limb length from us. Then look at a cow or an emu leg and see just where they locate their toes, ankles and knees, and they are all just modifications of the same basic design, alien motility limbs could be very different.

Some things have only evolved once on earth and so these are unlikely to be common. For example, vertebrates (phylum chordata) are the only animals that breath through their mouths. Since this is unlikely to be repeated on other worlds it makes it very unlikely that alien communication will involve making sounds that humans can easily replicate. It also means that there won't be human like faces with a "nose" above a mouth.

Since humans have a habit of seeing faces that aren't really there it's possible we might think we have found an alien's face when actually the alien will be wondering why you spend all your time trying to communicate with its butt (And no doubt the aliens will refer to earth as planet of the buttfaces, but this sort of confusion does make those alien abduction stories you hear just a little more believable, doesn't it?)