How did vision originate?

[md2000]

Some points to ponder -

Every characteristic comes with a cost as well as a benefit. If an organism evolved decent light senitivity, then the chemicals and energy needed to produce and maintain that characteristic cost. So a patch of light-sensitive skin requires less cost and upkeep for the orgnaism than a fully photosensitive skin. If the patch does the same job as an enie skin, the patch orgnaism is more able to survive in marginal conditions (i.e. shortage of food).

The advantages of light sensitivity are many and obvious. Moving to and away from light - away from approaching predators, under shelter (away from predators) toward where food (photosythetic organisms) may be found, etc.

As pointed out about snake IR, a pit or photosensitive material adds a secondary level of information. You get directional detail if you have more than 1 sensor, you get movement sense, etc. It is easy to see why this would lead to an expansion of scale - the more separate sensors, the more detail the organism receives. (Assuming it is in an environment that provides relevnat information.)

If the pit then evolves a tough but somewhat transparent cover to prevent damage to a critical element of the creature’s survival, then that gives it even more advanage and you are halfway to real eyes.

[Broomstick]

@Blake

Did you actually read the post?

Yes.

Did you read the bit where I said “We animals are all evolved from plants. Or more correctly, we are all evolved from single celled photosynthetic organisms.”

Animals did not evolve from plants, so why did you make that statement?

Do you realise that “Plant” is not a scientific term?

Yes

Do you realise that most people consider kelp or cyanbacteria, for example, to be plants?

Yes.

So… if you know that already, why did you conflate “plant” and “photosynthetic organism”?

Do you realise that when I say “We evolved from plants. Or more correctly, we evolved from single celled photosynthetic organisms”, not a single evolutionary biologist in the world would gainsay me as you appear to be doing?

That is what I disagree with. And why I asked you on what you based that statement. Are YOU an evolutionary biologist? If so, what are your credentials? Why should I take your word over that of any other random person I encounter on the internet?

What is your point? That rhodopsin didn’t evolve as a photosynthetic pigment in prokaryotes?

What that the primary reason for cells retaining it, or was it because it was useful as a light detector?

That animal rhodopsin isn’t almost identical to rhodopsin in sulfur bacteria, and isn’t universally agreed by evolutionary biologists to be homologous?

That is not in dispute. However, because it IS so widely distributed it is not indicative of a life form being in a particular division of life. For example, chlorophyll is found in plants, and something with chlorophyll in cell organelles is going to be classed as a plant. Something with mitochondria will not necessarialy be so classified, because mitochondria are not limited to plants, animals, or eukaryotes. Rhodopsin is even more widely distributed than mitochondria, being present not only in eukaryotes but also prokayrotes as well.

That rhodopsin isn’t a key component in animal visual systems as well as in the bacterial photosynthetic systems in which it first evolved?

No one is disputing that rhodopsin isn’t a key competent in animal visual systems. As for photoreactive chemicals in life, there are a LOT of them beyond chlorophyll and rhodopsin but you seem to be ignoring them.

In short, what precisely is your point here Broomstick?

On what basis do you claim that animals evolved from plants and not from a common ancestor that was neither? That simple, really. If what you state is the truth you should be able to point to the evidence on which you base that statement.

And can you clarify what you meant by that nonsense about the prokaryote lineages diverging 3.5 billion years ago and provide a reference to these source who have been writing that for decades?

That is not what I claimed, and if you were honest you’d know that.

I said that animals did NOT evolve from plants, they evolved from a common ancestor that was neither. I did not impose a timeline or make all those other assumptions you did. I did simplify by saying “photosynthesis” instead of “chlorophyll based photosynthesis” but thought you could make the leap there. Apparently you can’t, or it’s more important for you to prove someone else wrong than to be accurate yourself.

Chloroplasts are a strongly defining characteristic of plants. That marks the split from the other eukaryotes (NOT “prokyarotes” as you maintain). Unless you can come up with something other than “I said so” to refute that.

[Ruken]

@Ruken

For those of who need things spelled out all slow-like:

That was supposed to read “for those of us…”

I do wonder what other sorts of stuff we have in our bodies that was originally used for totally unrelated functions.

[Blake]

In other word’s Broomstick’s entire contribution to this thread has been pointless nitpicking of an explanation that I specifically noted was simplified into layman’s term’s. Oh so typical of him.

I shall ignore him henceforth..

And for those who are interested in fighting ignorance:

@Broomstick

..the last common ancestor of plants and animals occurred prior to photosynthesis evolving.

This statement is complete and utter ignorant nonsense.

The last last common ancestor of plants and animals was a eukaryote.

Eukaryotes evolved billions of years after photosynthesis evolved.

The last common ancestor of plants and animals occurred billions of years after photosynthesis evolved.

Broomstick did not read anybody saying anything remotely like this ridiculous statement in the past decades. No evolutionary biologist has believed such a ridiculous claim since the 1920s, at least.

Broomstick’s claim that “the last common ancestor of plants and animals occurred prior to photosynthesis evolving” is ignorant nonsense of the highest order. Anybody who cares to think about it for a second could have worked this out for themselves, for the reasons I gave above.

[xoferew]

Thank you Blake for that explanation. My gobbling blob idea was way off base! So would an organism have to evolve quite a bit to be able to use light sensitive chemicals to move AWAY from light? Cockroaches are an example. Can an organism be much simpler than a cockroach and still avoid light?

[Blake]

@Ruken

For those of who need things spelled out all slow-like:
So the common ancestor of modern plants and animals did not have photosynthetic capabilities.

Probably not. We can’t actually know for sure. There are certain features of eukaryotes that suggest that the common ancestor was a heterotroph, and that photosynthesis was re-acquired with the acquisition of chloroplasts. However we can’t be absolutely certain that all photosynthetic ability had been lost.

Since you wrote this:can I assume that this common ancestor evolved from an organism that was photosynthetic, but which lost this ability?

That is the most widely accepted hypothesis.

The ability of certain facultatively photosynthetic bacteria to tolerate oxygen placed them in a unique position when the cyanobacteria started to poison the atmosphere. When most “predatory” bacteria were forced into sediments and the deep ocean to avoid the poisonous gases on the atmosphere, the facultative photsynthates had unfettered access to the cyanobacteria, which themselves were not predatory. These photosynthetic organisms became the apex predators on helpless prey.

And like predators in other ecosystems, they became huge to enable them to engulf their prey more easily. Being successful predators they also no longer required photosynthesis, and at that stage they presumably lost the ability.

In the process of engulfing their prey, they either became infected by certain anaerobic pathogens or deliberately incorporated them into their bodies. Either way, they eventually became symbiotic fusions of both the aerobic photosynthetic ancestor and the anaerobic symbiont. That composite organism became the first eukaryote.

Of course there are dozens of alternative theories. The whole thing becomes hopelessly convoluted because the ancestral eukaryote seems to have incorporated at least 4 different bacterial lineages, including mitochondria, chloroplasts and the movement and antibiotic resistance systems. And with each acquisition, at least little of the DNA has bled across to the nucleus.

So at this stage we are truly composite organisms with multiple ancestral lineages. But at least one of the very earliest ancestors was photosynthetic and then lost that ability, only to later re-acquire it through the incorporation of chloroplasts.

[Punoqllads]

Y’know, Blake, for all the attitude that you know so much about Broomstick, why do you keep calling her ‘him’? She took your statements about the photosynthetic common ancestors of animals and plants to mean chloroplast-containing common ancestors. That’s not what you meant, though.

[Blake]

@xoferew

Thank you Blake for that explanation. My gobbling blob idea was way off base! So would an organism have to evolve quite a bit to be able to use light sensitive chemicals to move AWAY from light? Cockroaches are an example. Can an organism be much simpler than a cockroach and still avoid light?

Yeah, there is at least one microbes that moves away from light. It’s pretty tricky.

The rhodopsin system works in conjunction with a protein that pokes through the cell membrane, with one end sticking outside the cell and one end sticking inside. Think of it like a pipe poking through a rubber sheet. Under normal conditions, the inside of the pipe latches onto positively charged chemicals, and the outside latches onto negatively charged chemicals. When light strikes the system the protein turns a somersault, taking the positive charge outside and bringing the negative charge in. The charged chemicals are them released and the proteins spins back to its normal position. That’s how the electrical charge builds up.

So to avoid light you need to invoke a really complex and convoluted evolutionary pathway.

You turn the protein upside down.

Seriously, that’s it. The protein gets inverted, so the inside is outside and the outside is in. Now, when light strikes the system the positive ions are pumped in and the negative are pumped out. The protein is now actively reducing the electrical charge in response to light.

Complicated, huh?

In fact very few microbes avoid light because it’s not a very good way of doing anything at that scale. They are so small that being seen is simply not an issue. Anything with eyes that wants to eat them is a filter feeder, not a visual predator, and anything small enough to grab individuals is too small to have eyes. If they want to avoid oxygen or heat there are better and simpler ways to do that than avoiding light.

So avoiding light is mostly pointless for microbes. It’s really only useful for larger organisms with visual predators. Nonetheless they can evolve the ability to do so very easily if they wish.

[Blake]

@Punoqllads

Y’know, Blake, for all the attitude that you know so much about Broomstick, why do you keep calling her ‘him’?

Because I don’t give a shit what genitals she has.

I do care about her behaviour, with which we all have plenty of experience.

She took your statements about the photosynthetic common ancestors of animals and plants to mean chloroplast-containing common ancestors. That’s not what you meant, though.

I specifically stated in the third sentence that that is not what I meant.

“We animals are all evolved from plants. Or more correctly, we are all evolved from single celled photosynthetic organisms.”

How could she possibly misunderstand that. Not truly plants, single celled photosynthetic organisms is the accurate description.

Where the hell she got “chloroplast-containing common ancestor” from is beyond me.

Probably the same place she has read in recent decades that the last common ancestor or plants and animals existed before photosynthesis evolved, 3 billion years ago. :rolleyes:

[Broomstick]

@Blake

I specifically stated in the third sentence that that is not what I meant.

Then why didn’t you say that in the first sentence?

[Ruken]

I was confused too. I would suggest leaving the whole “descended from plants” thing out from any further repetitions of this explanation. Easier to just write it how it is rather than make up an oversimplification that is wrong.

[Blake]

@Ruken

I was confused too. I would suggest leaving the whole “descended from plants” thing out from any further repetitions of this explanation. Easier to just write it how it is rather than make up an oversimplification that is wrong.

It isn’t wrong. It is perfectly, factually accurate.

If you believe it is in any way incorrect then you are failing to understand something.

[Punoqllads]

I, too, initially thought you meant that animals descended from chloroplast-containing entities. It was only after reading your follow-up posts that I recognized my error. Perhaps in the future, explicitly mentioning that you don’t mean that would help give a clearer picture to some of your listeners.

[Blake]

Probably, but I can’t predict what totally unwarranted assumptions my readers may make. Plant does not mean “chloroplast containing entity” and I never said “chloroplast containing entity”. I really can’t guess at all the wild assumptions people might read into my posts.

In contrast a statement like “the last common ancestor of plants and animals occurred prior to photosynthesis evolving” is simply wrong on every level no matter what reading you attempt to give it. It’s total nonsense.

[Autolycus]

Vision evolved from midichlorians. That’s why the Emperor said to Luke: ‘you will pay for your lack of vision.’ If Luke had a higher midichlorian count, he could have fought the Emperor mano-y-mano.

[Broomstick]

OK, Blake, you’re saying that an explanation so muddled that even after you told everyone to ignore the first two sentences of your post it still left at least three people misunderstanding you couldn’t possibly be a lapse of clear communication on your part, it’s all the fault of the readers. Uh-huh. Gotcha.

Dude, next time try “preview” and if the first two sentences don’t contribute consider deleting them. Then re-read to make sure it makes sense before hitting “submit”. The communication thing might go a lot smoother, then.