Is there anything particular you have in mind that differentiates humans from other apes?

Is there anything particular you have in mind that differentiates humans from other apes — Kenosha Kid

Several traits differ us from other apes. Just as several traits differ a chimp from a gorilla. What exactly is the relevance just out of curiosity? All I'm simply saying is would it be likely in a universe where the same conditions are required for life that the same type of life would emerge and thus civilisations capable of contacting us would look very similar? Perhaps not.
But as far as I know physics and chemistry still exerts the same effects by the same laws and combinations. And natural selection I cant imagine would work particularly differently anywhere else.

What exactly is the relevance just out of curiosity? — Benj96

Just that the characteristics you cited weren't unique to humans but you were asking if aliens might necessarily have those characteristics and be like us. If the characteristics you had in mind were things like a head, eyes, skin, facial and bodily hair, why would you expect the result to be necessarily human-like and not gorilla-like or chimp-like or even sheep-like? What differentiating characteristics are you thinking of?

What differentiating characteristics are you thinking of? — Kenosha Kid

Ah okay fair I see what you mean. I'll clarify. Would aliens be bipedal with hands/opposable thumbs and look characteristically like us more so than we do to our closest biological relatives and secondly would their biodiversity have the same kingdoms and relatively consistent taxonomy to earths? Due to the fact that organisms fill levels and modes of existence that are available. Such as parasitism, symbiosis and other interactions.

As in if I went to their planet would I have an intuitive sense of their version of something? Or would their lifeforms be unrecognisable even in the same environmental and physics parameters - an earthlike planet

Okay, so on bipedalism, the benefit for us was that it freed up our hands in an environment conducive to upright mobility, particularly useful for carrying babies, hunting and gathering. This is because we evolved from quadrupeds: we couldn't just evolve a new pair of arms; evolution had to work with what our ancestors had.

Obviously freeing up our hands was important for developing more diverse technology, and we might assume that alien visitors also had this requirement in their evolutionary history.

But I can't think of a reason why they must have evolved from quadrupeds and not, say, an octoped. Quadrupedalism goes back through our evolutionary heritage to common ancestors of amphibians and reptiles: fish with bony fins, essentially. There's no obvious reason why four is better than six or eight, or why even here on Earth, by fluke, the first bony-finned fish mightn't have had more limbs.

But I can't think of a reason why they must have evolved from quadrupeds and not, say, an octoped. — Kenosha Kid

Because we have octopeds and they arent our direct descendants. As you explained bipedalism was conducive to the development of the human hand. So an Octoped is probably not conducive to the same outcome considering the large degree of more change (loss of limbs) that would have to occur in the same timeframe in order to get the the same evolutionary form as an outcome. And I'm a firm believer that biological pressures (like water) take the path of least resistance using the minimum amount if energy required to propagate survival of a species. In that sense it's more efficient for a quadraped to begin with, which can migrate in both directions to those which have no legs and those with have numerous. Rather then beginning at an extreme/pole regarding a characteristic.

Here's hoping for sentient blob networks and eusocial insect civilizations. No more dirty apes!

Life probably would look a lot similar on the same kind of planet but there are probably countless alternative ways to achieve our current functionality and it need not occur.

We have evolved to look as we are today through natural selective pressures in an environment conducive to life.

Few of our physical qualities are particular to humans. Generally, most traits are common to many species because they endure the same environments; intensity of sunlight, gravitational forces, composition of the atmosphere, abundance of certain elements etc. We have skin with certain UV absorbing pigments, hair for insulation, eyes at the front of our heads for hunting, the list goes on.

Now let's make an assumption for a moment. The assumption is that the exact conditions we observe on earth are the only ones that permit the emergence of life. That is to say that earth somehow fits with a very narrow and defined spectrum of conditions that will allow it to have biology.

The right amount of gravity, air pressure, magnetism, distance from the star and type of star etc.
Now if that set of conditions always leads to the same environmental pressures one could deduce that probably the same niches will develop and the same level and type of biodiversity will emerge in roughly similar order; unicellular- marine - amphibious - reptilian- mammalian and so on. Meaning that a humanoid niche will eventually emerge.

If that is the case shouldn't all aliens be very similar to humans; ie. Have hands, facial and body hair, similar skin etc. Thus is excluding their potential to be more advanced and genetically modified. I mean in a natural state, I think an alien would just look like another race of humans even if a bit peculiar perhaps. — Benj96

In order for an intelligent alien to rival us, i agree that they would have to be similar to us. However a derivative of cockroaches will probably out live humans in my opinion. This is in consideration of the premise "all things held equal". I think we assume very often what traits guarantee ultimate adaptability and cockroaches and things like cockroaches are the most similar to bacteria and viruses. Bacteria and Viruses are the best animals or creatures if you prefer the term creatures at survival. Once again this is in consideration of the basic premise of "all things held equal".

:up:

Because we have octopeds and they arent our direct descendants. — Benj96

That is not a reason why octoped descendants can't have freed-up arms. That's just saying that evolutionary pathway wasn't explored here on Earth. Evolution history is limited by what is possible, not vice versa.

Begs to differ:

It could be argued that has dinosaurs not been made extinct they , in 65 million, years could have evolved well beyond our feeble minds. This planet supports millions of life forms, I do not think our physiology is the only one that could support mental ability, Dolphins are a case in point.

Evolution history is limited by what is possible, not vice versa. — Kenosha Kid

If evolution is limited to what is possible on earth (earthlike conditions) then wouldnt it progress in a similar fashion on any planet if said earth-like conditions are essential to life?

https://en.m.wikipedia.org/wiki/Convergent_evolution

I do not think our physiology is the only one that could support mental ability — paganarcher

No I dont believe our physiology is the only one that could foster high mental ability. I agree. Many other animals could be equally intelligent if not maybe even more than us. But it seems that only human physiology and anatomy enables such a mental ability to take charge/ dominate a planet and created tools and technology to such a degree as to be considered apex and likely the subject of alien/interstellar travel and communication.

I think it's likely that any aliens we might encounter would have what we would call hands and humanoid features that go along with it (primate genetic line) rather than flippers or tentacles or paws

If evolution is limited to what is possible on earth (earthlike conditions) then wouldnt it progress in a similar fashion on any planet if said earth-like conditions are essential to life? — Benj96

I expect that the starting conditions might be similar, even the importance of water habitats for complex life. And obviously the rules of natural selection would be similar. That aside, no, I don't see that. I think there are certain features, like you said, that would likely always be perfected if crude versions evolved: eyes, limbs for mobility, opposable thumbs for dexterity, etc. But I don't see why the details (number of eyes, number of limbs) would be constrained.

The evolutionary history of life on our planet owes more than anything to its habitats, especially catastrophic changes in habitat. Differences in natural history would be expected in different environments, just as species diverge in isolated habitats (Galapagos, Australia) here.

However a derivative of cockroaches will probably out live humans in my opinion — tilda-psychist

Yes agreed...should several catastrophic natural extinction events occur on other planets just as they have on earth one would imagine advanced alien civilisations would be derivatives emerged from basic and numerous lifeforms especially those that have dormant survival forms for harsh conditions such as bacteria, moulds and fungi which are inherently difficult to exterminate. As well as those things that parasitize bacteria etc like viruses (bacteriophages) and maybe cockroaches are there superior radiation protection.

However, consider the minimum time required for the re-evolution of multicellular and complex life, as well as the establishment of diverse ecosystems necessary for the development of brains followed by tool making and harnessing of fire, the creation of agriculture, technology and civilisation. This may well be a long enough time such as that said bacteria, moulds and cockroaches would have already diverged due to pressures into typical lineages; mammals, reptiles, trees and plants, insects protozoa etc.

I see know reason why -regardless of the original catastrophe survivor (mould bacteria etc) - humanoid features would not yet again be functionally selected and progress to humanoid aliens. And should a catastrophic intervention and destroy the process that it would not just re-emerge again

. But I don't see why the details (number of eyes, number of limbs) would be constrained. — Kenosha Kid

They arent constrained. What you're referring to is differetiation of species. An ape with three eyes is not an ape, but it is like an ape. Just as a dog can look like a bear but it is not a bear. Considering all primates have two eyes this animal would likely have it's own lineage as it would violate logical association genetically to apes. Some features are shared by all lifeforms; genetic code, ribosomes, mitochondria, and many others are shared by kingdoms, less so by classes orders and genus and the exact same variations of traits are shared by a species.

Secondly these features are likely constrained by one another. You dont see fish with arms because arms are not streamlined, you dont see mammals with the same amount of eyes as insects because the size difference negates the sensitivity requirements to light, perhaps multiple eyes requires other non mammal traits like metamorphosis or insect like metabolism which again is proportional to size or the degree to which one species is likely to be prey (requiring better vision and from multiple angles).

It's not as if the details as you said - of the number of components is free to be what it wants nor where they are located any more then the quality or function of the component, as they work in integrated systems and must conserve payoffs like the ratio of energy required to sustain 7 limbs: and the degree of function they offer in sourcing that energy. Why have 4 noses when when the most sentsitive singular nose that exists could detect 80% of all chemicals that would ever be necessary to detect in a habitat?

Which brings me back to the belief that life evolves in a relatively organised, ordered and strict narrow defined way. Such as that the same kingdoms necessarily and must coevolve to support one another. And therefore the same ecosystems and environments develop and proceed to generate life that is essentially similar in quality to what we see on earth both in the types of anatomy and the number of its parts

It could be argued that has dinosaurs not been made extinct they , in 65 million, years could have evolved well beyond our feeble minds — paganarcher

Dinosaurs did not go fully extinct, only the majority went extinct. Those who remained evolved into turtles, crocodiles, lizards, snakes, birds etc. As far as dinosaurs go they achieved predator status but have yet to achieve societal/technological status. I reckon without primate hands it would be very difficult to command the dexterity required.

That is not a reason why octoped descendants can't have freed-up arms. That's just saying that evolutionary pathway wasn't explored here on Earth. — Kenosha Kid

Yes but our arms as we know them -the tools we used to create civilisation, function and are structured in such a way as to work as a pair, to only require X amount of our total body energy on account of what we can hunt and whether said arms have the dexterity to cook. To work relative to lengthy arms and a particular shoulder so as to enable what sort of movements and therefore how many digits, bones and muscles are required... and also that they are suspended and therefore not requiring the weight bearing qualities offered by feet.

The "freeing up of an arm" is defined as what exactly? And how does the number of such arms determine how many are freed up? I dont thing octopeds could have the same arms as us. Whether there arms become sophisticated enough to manipulate materials and build, design and construct or use tools I would imagine very much depends on whether this creature is a land animal or sea, whether is swung from trees or was better galloping with the limbs. And before you know it the octoped you're describing is actually a bipedal primate.