[mike_hock]

Sure, organisms that already share a massive amount of commonalities can diverge and then converge again.

What about the branches that happened early on? We essentially have only two lineages of macroscopic organisms that are actually fundamentally different: Plants and animals.

I would expect any kind of macroscopic extraterrestrial life to be at least as distinct from Terran plant and animal life as they are from each other.

[depressedpanda]

> We essentially have only two lineages of macroscopic organisms that are actually fundamentally different: Plants and animals.

That's not true, we also have fungi as a macroscopic lineage.

Or maybe you put them in the plant group? If so, that's a mistake, as they are more closely related to animals than they are to plants.

[uh_uh]

I think it's fine to lump fungi together with plants for the spirit of this discussion. The distinction between plants and fungi are made on the basis of metabolism but in this thread people are clearly talking about external behaviours observable with the naked eye.

[godelski]

Metabolism influences external attributes (I think behavior isn't the right word you're looking for). A larger creature requires higher caloric intake than a smaller creature (and this process isn't linear). A larger creature has different thermal regulations than smaller creatures because surface doesn't scale with volume linearly. The bigger the creature the more it calories it has to expend on the body vs the mind. There are equilibriums here that are physics based.

And then consider the selective pressures from plants vs fungi. A fungi gets its environment. Plants do some, but also need to perform photosynthesis. These have very different selective pressures for these lifeforms.

[hoseja]

If you're talking about lineages you should actually lump Fungi with animals. Also, how are fungi behaviours comparable to plants?

[uh_uh]

If their behaviours are not comparable, then why were fungi lumped together with plants up until the 1960s?

[yourenotsmart]

DNA is extremely flexible, there's no macroscopic form or shape it can't take, as various insects camouflaging themselves as sticks and leaves and what not shows.

So the idea we'll see some vastly different concepts with different starting blocks is possibly unfounded.

Alien life might be very different at low level depending on their environment, but in terms of macroshapes, things like the formation of a head with eyes and mouth, upper and lower limbs, bilateral symmetry and so on will repeat over and over.

We'll see (in another life probably).

[mike_hock]

Yeah, but so what? The geometric shape isn't very interesting. The insect camouflaging itself as a leaf still functions as an insect. It doesn't perform photosynthesis.

Considering that we have a whole class of lifeforms that have nothing like a head with eyes and mouth or limbs, the idea that this would evolve independently more likely than something completely different, is also possibly unfounded.

[harperlee]

Having two eyes, as a simple example, is arguably the cheapest way to perceive 3d at things-may-want-to-eat-me distance: just two points that enable triangulation. Similar constraints reduce the configuration space a lot. It still remains huge, but I don’t think someone that believes about certain convergence to be necessarily naive.

[ClumsyPilot]

Having three eyes, as a simple example, is arguably the cheapest way to percieve 360-degree view of things-may-want-to-eat-me.

Plenty of animals that have 2 eyes and no 3d vision, they try to get as close to 360 coverage as possible.

[spywaregorilla]

> DNA is extremely flexible, there's no macroscopic form or shape it can't take, as various insects camouflaging themselves as sticks and leaves and what not shows.

That feels like a really bold claim given the evidence.

[ncmncm]

Let me know when you spot an animal that drives around on wheels.

[dtech]

Physically you could have wheeled animals, but wheels just won't evolve. They are perfect for somewhat smooth surfaces where you want to travel in a somewhat straight line. Organisms just cannot confine themselves to that and survive.

Unless we find a planet composed entirely of solid smooth rock we won't find wheeled animals.

[jhgb]

How would wheels get fed with nutrition? Would they have tiny mouths?

[mod]

Gears have evolved, though, which is equally cool IMO.

[ncmncm]

Half-gears.

[pvaldes]

rotifers

[ncmncm]

Rotifers do not, in fact, have wheels.