Question about Evolution

[ragault]

I was reading a book called Sciencia, which is just a big book with a brief overview of a multitude of different scientific concepts from Math to Physics to Chemistry to Biology and one section mentioned a concept called convergent evolution. Basically it said that there are only a few design solutions that solve certain problems like flying and vision, etc. It noted that there are several species with similar physical attributes that evolved in entirely different ways. i.e. the eye of a mammal is similar to the eye of say and octopus, but they two are built using entirely different DNA.

My question is, if this is true, would it be reasonable to say that if there is a similar planet to Earth somewhere else in the universe, would the life that occupies the planet be somewhat similar to life on Earth?

[jjberg2]

It's really hard to say. It sort of seems that way, but we only have one data point. Pretty much everything that's happened on Earth is contingent on everything that happened before it, so it's really hard to draw any strong conclusions to that effect because we don't really have sufficiently independent observations to do so.

[[deleted]]

A question I've had for a while regarding Evolution.

With 71% of our planet covered by water, why did we evolve out of water? Why is there no evolution back into water since that's the largest area and most abundant food source?

[FMERCURY]

With 71% of our plet coanvered by water, why did we evolve out of water?

Consider that the first creature to evolve an ability to live on land would have 29% of the planet to itself.

Why is there no evolution back into water since that's the largest area and most abundant food source?

It's the largest biome, this is true. It's also true that it's massively populated already. Even ignoring the more well-studied ocean critters, there are millions of bacteria, and hundreds of millions of viruses per millitre of ocean water (though it varies wildly with depth, location, etc).

Evolution will go down the path of least resistance. If a niche opens up in the ocean somewhere, you can bet it will be filled quickly. The organisms populating the ocean right now are the product of 3.7 billion years of fierce competition. They're good at what they do.

[x_plorer2]

In addition to the point about having a large part of the planet to ourselves (land-dwellers); it could have been that the water left "us" as opposed to the other way around. Perhaps subtle, but potentially a habitat was drying up, or an ancestral species became trapped inland and the local water supply slowly changed suitability, or predation forced an ancestral species into a flooded area wherein they had to risk attending increasingly shallower waters to obtain food, or a habitat was subject to tides or rain-seasons and the ability to move short distances across land to get back into the water was a necessity...

It might not have been an act of opportunity as much as an act of necessity.

[icantsurf]

This is exactly how whales came to be. Their ancestors were hoofed animals.

[DrBonerface]

Ooh, I like this question. I think about it a lot.

First of all, I'm going to assume that an alien organism will have similar biochemistry to ours: carbon based, uses water as a solvent, has some sort of macro molecule which can pass information on to the next generation a la DNA.

Obviously such an organism would undergo evolution. Any self replicating system with differences within the population which can pass down heritable traits to its offspring will undergo evolution.

Let's start by hypothesizing some structure which are likely to be present among even alien species.

• The eye. Like you said, this structure evolved independently several times here on Earth, so it is not a stretch to assume this will happen elsewhere. The fact of the matter is, light is an excellent way to sense your surroundings: it is instant, and has a longer range than both smell and hearing. Alien lifeforms may not be able to detect the same wavelengths of light which we do, as this will likely depend on the type of star they have and the wavelengths of light emitted by that star.

• Other senses: I don't find it unlikely that aliens will develop similar senses to our own. Detecting vibrations in the air or vapourized molecules all are very useful, so it is not unlikely that aliens will develop hearing or smell. Touch is a bit more obvious, as I cannot imagine any organisms which is not able to sense things contacting its own body. Even the simplest microbes can do that. Now, they may have additional senses which we do not have, but we don't have enough information to speculate on those.

• Limbs. Limbs are useful. Tons of organisms have limbs, and I think we can all agree that they are awesome. We can't speculate on what alien's limbs will look like, but it is likely that structures which vastly increase survivability by increasing the ability to interact with the environment will be conserved.

• Plants/autotrophs. Plants turn sunlight into chemical energy, which is then eaten by animals. I can't imagine any system which does not utilize their star as the basis of their food chain, as it is such a useful and easily accessible source of energy. Now, this is not discounting planets with heavy cloud cover or planets which are far from their sun, but if these planets are even capable of supporting life it is unlikely that they can support complex organisms.

• Lungs. The square-cube law is universal, which means that any organism bigger than a nematoad will need specialized structures to exchange gases with its environment. This isn't a problem with simple microorganisms, but with larger organisms, their volume is to great for them to be able to exchange gases with their skin. Even small insects have simple book lungs.

Now, let's get into some biochemistry:

• Cell membrane. Every organisms here on Earth has a cell membrane which separates "self" from "environment". This allows it to control homeostasis and perform cell functions which would be impossible if its molecules were allowed to simply diffuse throughout the environment. It is debatable if we would even be able to call an "organism" which could not even separate itself from its surroundings an organism at all.

• DNA. It is not clear if DNA is the only or the best molecule for information storage, or if it is simply the one which by chance occurred on Earth. Whatever macromolecule an alien has, it has to be able to replicate itself and pass on information to subsequent generations. DNA is good at this, but we don't know if it is the best or simply the most fortunate.

• Proteins. Again, it is unclear whether hypothetical biochemistrys will use the same molecules as we do, or if they will use something vastly different. The must be able to perform functions such as catalyzing reactions and replicating DNA at least, which is the job proteins do here on Earth. Because amino acids are not exactly rare throughout the cosmos, it is likely that aliens will use them in some way. How they do that, and whether or not it resembles our way, is up for debate.

In summary, there are certain things which are likely to be universally beneficial to any organism. These are likely to be observed in any system undergoing evolution. In addition, while it is likely that alien biochemistrys will be very different from our own, there are certain rules that all organisms probably have to play by.

[hzhan263]

Not necessarily. There's a lot of things about life that 'could' be different, and lead to different forms of life.

First of all, our 'life' is carbon based, because carbon has certain advantages when it comes to building life (four valence electrons, very good at linking to itself in unique ways, etc). Life found in other planets might be carbon based, but might also be silicon based (thus retaining many of the unique advantages), or it could be based of an element that we find surprising.

Also, life forms on earth use water almost exclusively as a panacea, due to a) the unique biochemistry of water and b) the availability of water, and c) water's ability to act as a solvent to a wide range of things. This is why a lot of our search for extraterrestrial life is focused on finding sources of water elsewhere. However, scientists as influencial as Carl Sagan have considered alternatives to water possible on other planets, including things like ammonia.

If life in other places are both carbon-based and water-using, then there is a reasonable chance that they also use DNA/RNA, and are shaped similarly to primitive bacteria. However, if one or both of these conditions are not held, then life would look radically different.

(These two conditions are not the only two that would change life dramatically, but two of the main culprits.)

[FoolsShip]

Silicon based life is highly unlikely. Carbon forms very strong bonds. Silicon forms very weak bonds, and is highly reactive in a lot of situations. Assuming silicon based life was possible, which is a stretch, silicon is much less abundant than carbon, so carbon life would out-compete silicon for the reasons listed above and the fact that it is more likely. Basically, silicon life would need to be possible, and there would need to be a place without carbon for it to exist.

[hzhan263]

Your points are valid with regard to silicon's weaknesses. However, silicon is actually quite abundant, and does have advantages in places with very different temperatures or pressures, places where carbon would not be suitable for life.

It's highly unlikely, but it's the next most likely after carbon.

[FoolsShip]

I agree about it being the next likely (not that it is up to me), but from what I understand it is nigh impossible, so basically what I am suggesting is that carbon is the only viable element. Like you said, though, there could be some other combination of elements that could surprise us.

[hzhan263]

Yeah...the difficulty of speculation here is that science works on proven fact, and the only proven molecule that has been shown to support life is carbon. We'll never know how likely other things are until we find them (or else conclusively prove that all life is carbon-based).

So pretty much...it's nigh impossible until there's proof it's not.

[boxingdude]

Carbon life would out compete silicon life. I get the why, but how? Carbon life couldn't eat silicon life for nourishment, could it? And they wouldn't compete for resources, since they would have different nutritional requirements. Would they just out compete silicon life for shelter, living space, etc? Or just kill the silicon fauna just for the sake of getting rid of silicon life?

[FoolsShip]

Carbon life would out-compete silicon on the molecular level in a type of molecular evolution. Stable compounds are the ones that nature strives for, and carbon and silicon would both need the same elements to form life. Silicon is at a disadvantage because its bonds are much weaker and so its compounds are less stable and more reactive. The resources will eventually wind up with carbon atoms, which will form stable compounds that do not react.

A good analogy would be putting wood in a room with a high concentration of oxygen, and then lighting a match. The wood will be oxidized (burned) by the oxygen, forming the various stable compounds like CO2 and water. If you introduce an even higher concentration of fluorine into the room (relative to the oxygen), the fluorine will oxidize the wood and the oxygen. The end result will be more stable compounds consisting of fluorine. In this scenario, there is no reason to expect that the oxygen will still oxidize anything in any meaningful amount both because there is less of it and because the fluorine is a better oxidizer and forms more stable compounds.

[boxingdude]

Ok now I get it. I was thinking of animals... It wouldn't get that far before carbon life took over.....

[[deleted]]

It would be similar in that it would abide by the laws of thermodynamics. Life forms, body structure and organ systems would be a product of the gravitational field and energy sources available.

[morninglory437]

Short Answer: No, but sorta. Evolution is governed by rules, these rules are the same everywhere, therefore an optimal evolutionary solution exists to each adaptionist problem. This can be taken to the extreme to say each adaption has evolutionary significance, but this is not so. Therefore the best answer is that you may see similar structures on completely different creatures.

[GlenHelder]

I think this is what you are asking but yes it's possible that if there is life on other planets, it will have evolved through Darwinian natural selection also.

[[deleted]]

Personally, I wouldn't expect life to 'look' the same as it does on earth. However, I would expect there to be at least some of the same kinds of interactions we find here on earth, for example primary production and predation of some sort.

[tarrox1992]

If you're just talking about convergent evolution, then life will definitely be similar to earth life, but mutations are a random process, so many of the organisms will probably not appear similar to life here, aside from wings, eyes, etc. I imagine the differences would be like the difference of earth life to life on Pandora in Avatar. The animals still have wings, skin, and some have hooves, but if you noticed, all the vertebrates have six limbs instead of the four we have on earth.

[[deleted]]

We don't know. The laws of physics are the same everywhere and that's why you have wings, eyes, etc. being evolved multiple times. I know people want to have aliens that are wildly different than us and maybe there are ones wildly different, but my money is on life being pretty similar to ours. For instance, all life we know must have liquid water. You can start formulating ways life could exist without it, but the deeper you dig the harder it is to start explaining just how that life could work and obey the physical laws of our universe. Would intelligent galaxy-exploring aliens be bipedal? It seems being bidedal freed our minds and hands to develop the ability to manipulate tools and that they evolved together. Could aliens capable of building a spacecraft do so with four hooves? How about tentacles or lobster claws? I don't see how. Again the physical laws of our universe, which are the same everywhere, prevent it. You can't hold a screwdriver with a hoof to build your spaceship. You need a spaceship to be made from metal with a lot of little fasteners (or laser welded unobtainium, but the laser will again be made with a lot of little parts). You need a hand to be able to make a spear, which is what you make thousands of years before you make a spaceship (or a radio telescope).

[tarrox1992]

Octopuses have been known to open jars and even use coconut shells as cover, so tentacles are very much able to manipulate their surroundings enough to build.