Alternative Evolution

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One of the things I like to think about is the possibility of extraterrestrial life. In particular, I wonder what physical forms alien species could take. Just what would they look like? Unfortunately, it doesn't seem like many others put forth serious speculation here. Most scientists simply say "they could look like anything" or "they'll look completely different from us". While I certainly think both of those statements are true, I also feel that they are both something of a cop-out. By using either of those phrases, they can avoid the possibility of looking silly by speculating about, to put it bluntly, what aliens might look like.

Well, there's another interesting way to come up with valid possibilities for "alien" creatures, and that's to figure out paths for alternative evolution right here on Earth. It's been often said that, if another solar system formed just like ours, life on the third planet would turn out completely different. With that said, what are the "what-if" scenarios that you believe to have been possible in Earth's history? How would those scenarios have made life on Earth different today? I'll wait to see some of your ideas before adding my own.

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Happy speculating!

- Rob

 

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From a bio-mechanical perspective, a planet with features that are similar to our's would create bipedal humanoids. This is not anthropomorphism, just common sense. Convergant evolution among species, on this planet, illustrates how very different animals with completely different evolutionary paths, will come to resemble each other if they are steeped in the same medium. Cetacions and fish, bats and birds, etc...

 

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Nonsense. I would wager there is not one other instance of humanoid life in our galaxy outside the Earth; there may be bipeds, but they probably resemble iguanodontids rather than erect bipeds. This is not anti-anthropomorphism, just common sense; erect bipeds have only evolved twice on our planet, hominids and penguins. As a bodyplan, erect bipedalism is rare.

Almost all examples of parallel evolution cited are members of the same subphylum - vertebrates. No wonder they resemble each other.
Here is a hint - there are no examples of that particular subphylum anywhere else in the universe. Sure, some groups might resemble vertebrates, but the only true mammals, birds and so on are found on one planet only. This one.

 

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True, because there are no examples of life anywhere else in the Universe. So, to make a definitive statement such as that a priori is fallacious.

 

The reason most scientists will not speculate is, quite rightly, that speculation that far out is not science, but amusement. Plenty of scientists have indulged in amusement in this field.
There has been a series, on the Discovery channel I think, that looked at alternative life forms on other planets, and another, on BBC(?), which looked at life on Earth in one hundred million years following a KT event type catastrophe that wiped out not only man, but most/all mammals. In this case squid came onshore and developed an arboreal lifestyle, swinging through the forest canopy and evolving into squibbons - a gibbon like equivalent.

Here are some of the key events in the development of life on Earth:
Emergence of the cell as the basic unit of life
Development of multicellular life
Development, probably simultaneous with, but not necessarily tied to multicellular organisms, of cellular differentiation
Development, etc, of morphogenesis
Emergence of vertebrae as a support mechanism, facilitating emergence onto land

So, we have five hugely important steps, at least, before we even get to the vertebrates. We now have a diversity of possible body plans from penguins to possums, armadillos to zebras, only a handful of which are vaguely humanoid.

Now, just how likely are those first five steps to have occured? At present we simply do not know. They may be inevitable. They may be rare, or even unique. Without at least four of those first five steps life may be so different from what we know as to be almost unrecognisable. I suspect this is the position that eburacm45 finds himself in.

Agitprop view seems closer to that of Conay Morris, who believes intelligent life on other planets will emerge looking distinctly humanoid. His logic is well structured. His error, if error it is, lies in his premises.

I'll go along with QuarkMoon: we really can't say. Extrapolating from a single data point is always a risky business, but then, as long as we don't mistake it for science, it can be fun.

 

I don't think humanoid life is inevitable. Just look at the millions of species on Earth - how many of them are humanoid?

What might have helped to create humans in their current shape:

1. Our sun is a single star though most other stars are double systems that cannot have planets.
2. Distance of our planet from the sun.
3. Our planet is covered with liquid water, but not entirely.
4. Our single large moon causes tides. Tides helped to permanantly dissolve minerals in the oceans which provided the building blocks for the creation of the first forms of life. Tides later also helped life to leave the water.
5. The moon stabilizes the Earth's axis.
6. The Earth's magnetic field stabilizes the atmosphere and protects the earth and us from sun wind and radiation.
7. The Kuiper Belt as well as the huge planet Jupiter work as cosmic vacuum cleaners that prevent Earth from being hit by meteorites and other large objects too often.
8. A catastrophe approx. 65 million years ago probably caused the extinction of dinosaurs and the subsequent rise of the mammals.

Did I forget something?

So any variation in this combination of facts and events might have led to other evolutionary results. Most of them probably ending with less developed life forms.

 

Extra-terrestrial organisms?

 

No. Atmospheric life (read: Atmospheric Biology).

 

From what I really hypothize...other evolution possibility is something like a water planet like Earth...like dolphins developing to be as intelligent as we are.

 

Without DNA?

 

Sure. Atmospheric biology is comparatively in it's infancy in terms of understanding as other scientific fields. And the findings are hardly conclusive at this point. The chances of extra-terrestrial life floating down through space from an asteroid or comet and surviving the entrance into the Earth's atmosphere are astronomically smaller than the explanation that these are Earth organisms.

 

As far as the 'red rain' in India is concerned, please read this official report into the matter.
http://www.geocities.com/iamgoddard/SampathAbstract.pdf

Quote -
The spores were found to grow well in alga culture medium. The alga was identified as a specie belonging to the genus Trentepohlia.

 

Good to have that sorted out!

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Many quadrapeds will assume an erect posture while using their 'hands' like racoons and lesser primates and members of the bear family. It is quite reasonable to assume that evolution favors those individuals, who use their paws/hands the most.

Given a few eons, chimps, racoons, prosimians, etc...could well be walking erect. Bipedalism confers an advantage on the individual animal as it creates evolutionary pressure within the species. This is a dynamic process, so to state that only 2 animals ARE bipedal, fails to account for potential change. If you fail to understand these basics,you don't understand the most basic elements of bio-mechanics.

 

If its such a bloody good system how come there haven't been more bipedal animals throughout the Earth's history? Prattling on about potential is irrelevant. If this were an intrinsically sound system, then it should have emerged repeatedly in the march of evolution.
Bipeds are slower than quadrapeds. Full stop. Period. No debate. This places them at a disadvantage as predators or prey - unless - unless they are also smart. It is the combination of intelligence with bipedalism that made it such a winning combination. Either by themselves is of little use.

 

There were a few other erect bipeds (all birds) in the past; the flightless Auk for instance. But it has been a very rare bodyplan.
I think that the evolution of self-awareness, language and or tool-making is not necessarily tied to body plan at all; for instance our language skills seem to have developed as a result of sexual selection within a social context. Such a chance event could potentially happen to any advanced species on any world; language ability plus toolmaking will possibly lead to a technological species.
But the creatures which develop those crucial traits could come in a wide variety of shapes and physiologies, and perhaps will be accompanied by a wider range of psychological characteristics.

 

Of course tool-making requires an set of manipulatory appendages, and a set of eyes or some comparable imaging sense; but this too permits a wide range of possibilities.

 

Evolution is usually economic, so you can assume that the two arm, two leg body plan of most reptiles and mammals would morph into an upright stance with two arms and two legs, no more and no less.

The eight legged arthropod/arachnid plan is fantastic for spinning webs, but demands so much in specialized mental processing, that evolution of a brain that does anything but, is unlikely. The body plan and brain would have to devolve a set of successful functions in tandem with it's form, while it quickly evolved another entire set.

Evolution of land based higher intelligence constrains body form to one type. Different planet, different gravity, etc....it could be different.

 

I am glad to see that my initial message has sparked a good discussion so far.

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For now, I would like to pose the following:

1. Are there any other possible endoskeletal configurations that would serve just as well as the typical notochord/vertebrate plan?

2. Is there any way that creatures with exoskeletons could reach the size of a man or larger?

3. What conditions, if any, could have given rise to hexapods (i.e. six limbs) instead of tetrapods on land?

I look forward to your responses.

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- Rob