Alien Evolution

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PsychoticEpisode

It is very dry in here today
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Since the environment, climate and geology of a life sustaining alien world would be different than ours can we expect evolution to behave the same way as here on Earth? Perhaps behave is a bad word but we have a good idea of what pressures life faced on Earth to provide the impetus for adaptation and change. It should be an entirely different story on another world, should it not? That is to say we may be witnessing evolution in a can here, with an entire cupboard of unlabeled cans waiting to be opened.

I think there's an exciting new field for alien research awaiting future biologists. So with that in mind, what do we expect to find? I'd like to hear some opinions about certain scenarios not similar to the Earth's. Such as how a planet's proximity to a star, a planet's mass or even an entirely watery world would affect evolutionary rate, if there is such a thing.

Also are there factors that could limit evolutionary development? Conditions that prevent further evolution or never allows it to get started or allows it to advance much more rapidly than here.

I suppose there's a myriad of scenarios and the gist of my thread suggests that I believe evolution may be totally different on alien world's but I have to believe that the process is universal. What we see happening here is happening elsewhere. Am I being too narrow minded? Should we be ready to expect the unexpected? If so then what would be considered unexpected?
 
I would expect overall designs to be quite similar.
  • Carbon based biochemisty, probably double helix DNA.

  • Bilateral symmetry is likely for larger vertabrates, especially for land dwellers.

  • Radial & spherical symmetry only for water dwelling creatures.

  • No large animals with 6 or more limbs.

  • No huge Scifi insects.
A zoologogist with a lot of knowledge of evolution could come up with lots more thots on this issue.
 
Dinosaur said:
I would expect overall designs to be quite similar.
  • Carbon based biochemisty, probably double helix DNA.

  • Bilateral symmetry is likely for larger vertabrates, especially for land dwellers.

  • Radial & spherical symmetry only for water dwelling creatures.

  • No large animals with 6 or more limbs.

  • No huge Scifi insects.
A zoologogist with a lot of knowledge of evolution could come up with lots more thots on this issue.
Click to expand...

I totally agree.

I was having a discussion [debate?] with a friend and she was giving me all these examples as to why aliens would look truly "alien". I disagreed on account of all the life that has evolved here. Every imaginable form has been tried.

In our case, and in the case of all land dwellers, the "bilateral" configuration has evolved, numerous times, as the superior form. We descent from fish. The most efficient way to swim is to flex side to side (or up and down). The side to side flexing forces a "two sided" evolution. An eye on each side. A fin on each side. A two lobed brain. Gills on each side. Etc.

As those creatures crept onto land, they used their fins to drag themselves out of the water. You can see where I'm going.

Would the aliens have eyes and ears on their chest or hands? No. Eyes and ears transmit critical information, that is highly complex and requires (often times) immediate reaction. These receptors would have to be located near the "processing center" (i.e. brain). Eyes, ears and brain would be located up front (on the fish) where the action is. Since aquatic life dines by swimming towards their food, the mouth would also have to be located up front.

After dragging itself onto land, the distinct head, arms, body and legs could evolve from that form. And from that form our proto-simian ancestors would evolve their form.

It's not that I wouldn't expect some odd forms to evolve on alien worlds, because I'm sure we'd be surprised by the insanely different life. But the carbon based life that exists on land would most likely have a form that is recognizable to us. Having two legs and two arms, a distinct body cavity with all the "vitals" protected inside, opposing thumbs, a mobile head with brain, ears and eyes, and whatnot all have distinct advantages that are hard to beat. It's why that form has evolved on earth with such success. It's why, after all the millions of trials and errors in our history, this form has come to be seen most animals alive.

~String
 
I must say I do disagree that alien creatures will look familiar. The number of different possible bodyplans that have been tried by evoluton here on Earth has been constrained by the shape of the ancestral species; given different ancestral species, the evolutionary path will look entirely different. For instance the tetrapod form of land-based vertebrates is a result of the evolution of such animals from four-finned fish, the Sarcoptergii; if the first fish to crawl onto land had had six limbs, or two, or none, then so would we.

There are two kinds of feature that one might expect in an alien biota- universal features and parochial features.
Universal features are those which one might reasonably expect to find in creatures anywhere in the universe; parochial features are those that are peculiar to one particular planet. You might find certain parochial features occuring on more than one planet- but they will not occur on all of them, or necessarily in the same combinations.

Universal features include the support structures such as bones, either internal or external to the body of the creature, or both. Even on Earth some major classes of macroscopic creatures, such as the octopus, do not have hard skeletons; but it is likely that a land-dwelling descendant of the octopus would evolve some sort of support structure. It would, however, bear no resemblance to the vertebrate bauplan. Other universal features would include locomotory limbs (which can be a few as one, as seen in the gastropod, or as many as several hundred, as seen in the millipede. And sense organs and a gut of some sort, although the exact details of both features are generally parochial in nature.

Parochial features include the pentadactyl limb, the vertebral column, the jaw, the skull, tetrapody and even the eye. Despite what many people believe, all eyes on Earth are descended from an ancestral eye, and all creatures with eyes share a certain number of genes associated with eye production.
see http://en.wikipedia.org/wiki/PAX6
On a planet where the ancestral eye did not evolve, some other sense organ would take its place. Bear in mind that any alien biology would not share any genetic material whatsoever with the creatures on Earth- so everything would need to evolve entirely separately.
 
Dinosaur said:
I would expect overall designs to be quite similar.
  • Carbon based biochemisty, probably double helix DNA.

  • Bilateral symmetry is likely for larger vertabrates, especially for land dwellers.

  • Radial & spherical symmetry only for water dwelling creatures.

  • No large animals with 6 or more limbs.

  • No huge Scifi insects.
A zoologogist with a lot of knowledge of evolution could come up with lots more thots on this issue.
Click to expand...


Darn I was hoping for some monsters like "The Mist, Cloverfield, and maybe Evolution.
 
Eburacum45: I disagree with your basic POV. I would not expect all of the Earthly life forms living and extinct to be duplicated elsewhere. I would expect some to be missing. A person with more imagination than I have could probably imagine some designs different in significant details from any of our fauna, but I would not expect anything radically different. Ignoring other issues you posted, I will discuss the following two.
. . . . . . . For instance the tetrapod form of land-based vertebrates is a result of the evolution of such animals from four-finned fish, the Sarcoptergii; if the first fish to crawl onto land had had six limbs, or two, or none, then so would we.

. . . . . all eyes on Earth are descended from an ancestral eye, and all creatures with eyes share a certain number of genes associated with eye production. . . . . . .On a planet where the ancestral eye did not evolve, some other sense organ would take its place.
Click to expand...
A quadruped design for large land dwelling vertebrates is both advantageous & efficient. Larger land dwelling vertebrates with either one leg or none would not be able to compete with either quadrupeds or bipeds. They would be easy prey & ineffective predators. Land dwelling quadrupeds are much better runners than bipeds, making them more likely to be evolutionarily successful than bipeds.

Ignoring the problem of predators, herbivores with one leg or none would be at an evolutionary disadvantage compared with herbivores with two or more legs. They would have trouble coping with a local drought or other change in the local environment, requiring them to move to a locality with a better food supply. Even if a local food supply was stable, their population would be restricted by the amount of food available locally. Herbivores with two or more limbs would be better able to forage over a larger area & move to a new locality in response to changes in the local food supply.

Three legs seem to be an evolutionary possibility, but I strongly suspect that a quadruped would be able to outrun a 3-legged vertebrate. I also suspect that a 3-legged design would be unlikely to evolve within an overall bilaterally symmetric design. I would expect a 3-legged vertebrate to be radially symmetric, which seems like a reasonable design for sea dwelling creatures, but not for land dwellers.

Note that evolution has a strong tendency toward efficiency/economy. A fifth or sixth limb would not result in much (if any) increase in running speed or jumping ability. The overhead of additional limbs is significant. Additional food must be ingested & digested to supply energy & provide for the maintenance of extra limbs. In addition: More blood vessels, bones, & nerves, as well as a larger brain would be required.

If a fish with 6 fins had been the evolutionary ancestor of the first land dwelling vertebrates, I would expect two of the fins to be lost or to evolve into something other than two more limbs.

All of the above leads me to believe that the larger land dwelling vertebrates (if any) elsewhere in the universe will be quadrupeds.

A visual system dependent on an eye sensitive to some section of the electromagnetic spectrum seems to be incredibly useful from an evolutionary POV. Given 2 billion years or more, I would be surprised if some such system did not evolve. Even pin hole camera or multi-faceted (insect-like) designs would provide an advantage over a sightless creature. What sense organ would be a worthwhile substitute for the ability to use the electromagnetic spectrum?
 
A six-finned fish-like precursor could evolve into a tetrapod with additionl manipulatory limbs; that would be extraordinarily useful. Centaur-like tetrapods might be widespread.

Bipeds (particularly with horizontal 'spines' like theropods) have been extraordinarily successful back in the Mesozoic. I think that various forms of biped might be widespread too.

Limbless smakes are quite successful, and plenty of other creatures have a limbless bauplan. But they lack manipulatory appendages, so might seem limited in their potential. But a worm-like creature with complex mandibles could diversify into a wide range of creatures, including ones which use the mandibles for walking. Eventually you have a biped, triped or even quadruped crature derived from a limbless creature.

For more speculations on possible alien evolution see this website- written by a dinosaur fan, so the creatures look a bit too dinosaur-like for my taste. But they are excellent nevertheless.
http://www.nemoramjet.com/snduterus.html
 
Dinosaur said:
I would expect overall designs to be quite similar.
  • Carbon based biochemisty, probably double helix DNA.

  • Bilateral symmetry is likely for larger vertabrates, especially for land dwellers.

  • Radial & spherical symmetry only for water dwelling creatures.

  • No large animals with 6 or more limbs.

  • No huge Scifi insects.
A zoologogist with a lot of knowledge of evolution could come up with lots more thots on this issue.
Click to expand...

I agree with this too, the basis is all there. :worship:
 
The best we can say is that a fraction of worlds will have lifeforms which are reasonably similar to Earth lifeforms; but at present it is not possible to say how large that fraction would be.

One way to look at it is that all lifeforms on Earth are unique to this planet.
There are no annelids on other worlds; there may be creatures which resemble annelids, but they will only occur on a fraction of worlds, and we don't know how large that fraction will be, and we don't know how closely they resemble annelids.
There are no arthropods on other worlds; there may be creatures which resemble arthropods, but they will only occur on a fraction of worlds, and we don't know how large that fraction will be, and we don't know how closely they resemble arthropods.
There are no chordates on other worlds; there may be creatures which resemble chordates, but they will only occur on a fraction of worlds, and we don't know how large that fraction will be, and we don't know how closely they resemble chordates.
There are no fish on other worlds; there may be creatures which resemble fish but they will only occur on a fraction of worlds, and we don't know how large that fraction will be, and we don't know how closely they resemble fish.

Fish-like creatures do not evolve on worlds which do not first evolve chordate-like creatures.

There are no mammals on other worlds; there may be creatures which resemble arthropods, but they will only occur on a fraction of worlds, and we don't know how large that fraction will be, and we don't know how closely they resemble mammals.

Mammal-like creatures do not evolve on worlds which do not first evolve chordate-like creatures or fish-like creatures.

Other biospheres may include animals that are as successful as the mammals but have evolved from phyla which are entirely different to the precursors of mammals so have an entirely different bodyplan.
 
Here's another speculative alien biosphere
Furaha

Like Snaiad, this is a comparatively Earth-like world.

It seems entirely possible to me that many life-bearing worlds will be either much larger than the Earth, (superterrestrials) so life will quite probably have many legs to support the bodyweight; or possibly smaller than the Earth so life might favour fewer legs or even flight. Note that there is not a clear correlation between atmospheric thickness and gravity in our solar system; worlds such as Venus and Titan have thicker atmospheres than the Earth, despite being smaller and with less gravity.

On a world which has a biosphere yet is not Earth-like, most ideas of parallel or convergent evolution should be abandoned.
 
eburacum45 said:
if the first fish to crawl onto land had had six limbs, or two, or none, then so would we..
Click to expand...

Have to disagree there. If the second fish species to crawl on land had a different number, and was more successful, we would be descended from it, not the first.

Also, it's wholly possible for the first fish to lose a number of appendages if they no longer served a useful purpose. We know there are 'snakes' today that are actually legless lizards, and they have vestigial appendages to show their lineage.

We would have genes that allowed for those extra limbs, but they would be turned off (controlled by HOX genes iirc?)
 
I would suggest that on a planet with a biosphere and gravity significantly greater than Earth's, a six-legged or eight-legged creature would have the advantage. How significantly greater I wouldn't like to guess. One day we may know the answer to this sort of question; but that will be far in the future, when we can examine these biospheres at close range.
 
you guys are assuming too much they are going to be very similar to us. Creation is great and very varied but they have several limitations in the range of creation, if you don,t believe me wait and see...ex. water exist like our water in the three stages we know, liquid, solid and gas all over the Universe, believe me this is a fact
 
Salt water with a wide range of salts dissolved in it, acidic water, alkaline water, supercritical water, ice II, ice III, ice IV, ice V, ice VI, ice VII, ice VIII, ice XI, and so on. Water is much more varied than you might think.
 
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