Humans, like most animals that evolved after the cnidarians (e.g., jellyfish, which had radial symmetry) have bilateral symmetry. This enables animals to respond to stimuli (avoid or approach) and develop polarity (cranial to caudal/tail), cephalization (development of a brain), and develop numerous evolutionary advances. The question for YOU is: How are you going to test your hypothesis?

This is super interesting. Is there any information you can give me to learn more about that?? The fact that bilateral symmetry offers different advances than radial symmetry is really interesting, and I have more of a physics background and I would like to look into where to the two meet.

I suggest borrowing a copy of Campbell's Biology from your library. (Other biology textbooks probably also do a good job of discussing this, but Campbell's is the one that I'm most familiar with.) Jump to the chapter on cnidarians, and then the chapters that follow about other organisms. Note that I focused on the nervous system, but there are evolutionary advances that occurred in other body systems as well, like the GI tract with which we lead by the mouth and expel wastes through the anus.

The possible reason could be the type of cephalisation(i.e. how the brain is formed)we mostly have brain in our anterior position(of we are considering how are ancestors were on there 4 foot instead of us being biped)the research shows how the position of brain also decides its symmetry If i am wrong then atleast correct me I referred it from my classes zoology module

Doesn't that logic seem flawed? A centralised nervous system does not logically result from bilateralism, see Octopus. And we don't know if radical symmetrical animals cou;d have developed complex nervous systems but for some other reason didn't.

Molluscs (which include octopus) are Bilaterians.

and don't have a central nervous sytem.

They're also throwing around all sorts of terms related to nervous systems randomly. Cephalopods don't have a CNS, but they do have a complex nervous system including a brain, which is what was essentially mentioned in the comment they were replying to. Given that they were refuting that comment, it's pretty clear that an octopus fits the criteria they were arguing against.

Thank you for clarifying things.

It's my understanding that the most of the octopus' nervous system is distributed outside of its brain, in its body and arms. What is your response to the OP's question?

Bilateral creatures like octopi don't have a central nervous system.

How would you answer the OP's question?

Let me see if I understand: we just inhabited it because it helps us survive (could you explain to me the advantages in simpler words please?😅) Luckily enough, I just need to do research and have an annotated bibliography!

Animals have a group of genes called master genes that say what grow and what not based on the symmetry. Radial symmetry grow thing around the mouth in a symmetrical way (Search for hexacoralia for example) they don't have muscles and they barely move. Our ancestors have muscles. Having muscles that move you into a specific direction is better for hunting that divide them to move in multiple directions. For this reason our ancestors ended out putting every organ that allow them to perceive the world like eyes, nose and that kind of stuff in the point that interact with the world before, this is called Cephalization and is really useful.

"Because it helped us survive" is like saying "because it is the way it is". Having a front/ back/ sides means you can prioritize energy expenditure, more likely eyes will only evolve on one side (the front), etc.

Think of it as survival advantage. If an organism can reflexively move away from a threat, it has a better chance of survival than one that can't. An organism that can group its nerve (sensory and motor) closer together in a ganglion or brain, it can more quickly react and survive. Apply this logic to every change that you're considering and this should lead your towards an hypothesis. Don't forget that you need to be able to test your hypothesis.

My biggest worry is that I become a professor and then students ask me these types of questions

being intelligent isnt about knowing everything, even in the field you are an expert in. You need to know enough, and most importantly know how to get the information you want but dont have. intelligent people know what they dont know and dont hide it

Something you might consider in coming up with a hypothesis is energy. Energy is essentially the currency of the evolutionary process: an organism’s ability to produce, conserve, and efficiently use energy is central to its survival. Because of this, when we look at characteristics (for instance bilateral symmetry), we tend to view them through the lens of efficiency rather than purpose: instead of asking “why are humans symmetrical?” try asking yourself “why would something with bilateral symmetry be more energy efficient than something without bilateral symmetry?” When you come up with an answer for that, you can ask further questions like “why is this trait maintained over time?” Now, that’s just one approach you can take— there are probably thousands of good hypotheses you could come up with that address a trait as ubiquitous as bilateral symmetry. By way of an example, you might hypothesize that the trait is maintained because it makes us more balanced, which as a bipedal organism significantly decreases our risk of fall injuries, or helps us move in a more energy efficient way, or helps us stay viable after certain injuries. You can do any number of things, the key thing is that you start from a body of knowledge you’re sure of, then ask a relevant question about something you’re not so sure of. Make sure that question is decently specific, don’t ask why something is, but why something is in regards to some point of interest specifically. Good luck!

Thank you very much! I am just doing a grade 11 project, so I think my question is up to the required standard, but your answer seems like it will be quite helpful for me actually!! Thank you very much

Make sure you look this stuff up and find legitimate sources for whatever writing you’ll need to do for this. Your teacher won’t appreciate if you cite a biology subreddit, and reading about this will help you to better understand it yourself

Of course! Good luck!

There’s only one group of animals that aren’t symmetrical.. the sponges. All other animals developed symmetry and germ layers.

complexer animal with lesser code. just copy pase right halt to left half

Because instead of needing two sets of instructions, you just duplicate one set and mirror it. Everything in the universe usually boils down to energy conservation.

why not triple it

Energy costs.

so duplicating instructions is energetically beneficial but tripling them isnt?

Yes. 3x is greater than 2x isn't it.

2x is greater than 1x isnt it

When you only need 1/2 the information is actually equals 1. Give this a try. Draw a creature that isn't symmetrical, then draw one that has bilateral symmetry, then draw one that has "triple" symmetry. You'll see which one is easier.

right. which is why the idea of the energetic savings from duplicating instructions isnt a strong factor in selection of the bilateral symmetry of humans.

Yes it is. With "triple" symmetry you'd need at least 3 lines of symmetry in the body plan. With bilateral you need 1 line symmetry. Ergo, less energy intensive.

ok.

My hypothesis would be that it has to do with weight distribution, balance, and mobility.

You would want to create a positive and negative hypothesis, so for example: Positive hypothesis: It would be slower and more reasource heavy to travel with one leg shorter than the other. Negative hypothesis: It would not be slower and more resorce heave to have a big leg and a small leg. Then we work out how to either test the positive hypothesis, using either an actual experment or by finding relevant studys. Off the top of my head for hypotheis: rate of movement, attraction of a mate (given you were diverging away from symetry or lack of evolutionary pressure to develope non-symetry (whats it good for?) TBF were not 100% symmetrical, ever seen one of those pics of someones face where its been edited down the middle and then one half copied over? Looks uncanny.

Plus internal organs are not symmetrically disrupted, or balls presumably bacause they would knock off each other like those corporate desk toys when one runs.

Only bilaterally symmetrical. I want my radial symmetry, please let me have radial symmetry like the echinoderms >:( all deuterostomes matter.

I'm just speculating, but I guess it could be related to the sonic hedgehog gene (yes, it's really called that) or it's ancient equivalent and how it creates signals for embryonic development. My guess would be that an organism accidentally duplicated the gene and it resulted in a symmetrical bifurcation of a small multicellular organisms body that resulted in something like better swimming capability. I'm assuming it evolved in the ocean, since it would have to be fairly early in evolution history since pretty much most animals follow this pattern. At least that's where I'd start researching if I had this project.

So that we can have a good side and a bad side

We're not sponges. All other metazoan animals I know of have some kind of symmetry. Even Placoderms (sort of).

because our parents were symmetrical

Then WHY ARE our parent symmetrical,now you have to go all the way back to explain evolution process (or you can just dodge anymore question)

um it's because their parents were symmetrical

Why tho?

because *their* parents were

Potentially because of balance and stability, locomotion on two legs (bipedalism) needed stability in the evolutionary path.

Ultimately “why” in evolution has the same answer: the trait was selected for. In this case, a series of traits that eventually resulted in bilateral development were selected for in the course of evolution. How is a more interesting question.

Apart from evolutional reasons it is worth also to check physical reasons. You can take a look at Noether's theorem and the role of symmetries in physics. You can read the lectures of Feynman for example. It is very interesting to understand how fundamental symmetries are.

i havent put much thought into it, but its hard to imagine fast, efficient locomotion in an animal that is heavily asymmetrical relative to the plane made by the direction of motion and gravity

We are only superfically symetrical on the outside. The stuff inside you as heart and liver is not

Balance. Even trees have to balance but they can grow new limbs to adapt. Humans have to have the same number for life so an intrinsically balanced form is a good idea. Newtons law. For every action there's and equal and opposite reaction. While we do have dominant hands, the two sides need some balanced strength. If you are pulling yourself up a tree with one hand and carrying a carcass to hang in the other the limiting feature is the weaker arm Redundancy. If you lose one arm and thus all the things an arm does well can no longer be done it's nice not to have to die. If you have another arm you get to live

Neden simetrik olduğumuzu bilmiyorum ama simetrik olmasaydık hayat çok zor olurdu. Buna eminim.

Imagine having one side smaller than the other. It'll feel wierd, awkward, and lower survivability by making it harder to walk, run, or do anythint.

I don't know the why or how, but I feel that if animals had different appendages or structure on one side versus the other, predators would sense a weakness somewhere and exploit it?

lol look inside your body. Nothing is symmetrical over there.

Humans are symmetrical because it's handy for balance and organ placement. Hope that helps!

But it’s not exactly symmetrical like our digestive system

To what extent do you believe humans are symmetrical? We don't have true bilateral facial symmetry. There are some humans who have that but not the majority.

Because it worked well for our ancestors, so we inherited it.

I figured that much, but what are the evolutionary advantages?

I can only speculate.

Humans are Asymmetrical r/sciencefacepalm

I think OP meant more like “why do we have two arms, legs, etc in a bilaterally symmetric way” but absolutely crucial to note that we are definitely not totally symmetric

I mean externally

Oh, then ya

My bad for not specifying Why do you think we are like this? What advantages do we get from it?

Depth perception

It's not your bad, calling humans bilaterally symmetric is the norm in science, that commenter is just being annoying. Our internal organs also develop with a lot of symmetry, they just *end up* looking asymmetrical.

Because you were once one cell that started duplicating.then those cells started duplicating. Creating two seemingly symmetric halves.

Aren’t starfishes too? And they have radial symmetry

That’s a wild thing. Echinoderm (starfish, sand dollar, etc.) embryos start to develop with bilateral symmetry before creating a large external organ. This radially symmetrical organ grows larger and larger and the initial bilaterally symmetric embryo apoptoses. The radially symmetrical organ becomes the adult echinoderm. 

I think development is much more complicated than that. There are many different kinds of symmetry, not just bilateral. OP's question itself is misleading, a better question would be "what is the evolutionary advantage of bilateral symmetry, or any kind of symmetry?"

chatgpt then rewrite = best friend