The Origin of Multicellular Life: Cell Specialization and Animal Development

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Күн бұрын

Alright, so we've learned a lot about the origin of life. We learned about how the first organic molecules can have formed spontaneously, and how they might have assembled into the first protocell. From there, endosymbiotic theory tells us how these merged to form more complex eukaryotic cells. But these are still organisms made of one cell. Animals like humans are made of trillions of cells. So how did life make the big leap from one cell to many cells? To answer this, it is helpful to look at embryonic development, because the way one cell eventually becomes an entire animal can tell the story of how life stumbled upon this possibility in the first place. Crazy stuff!
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Пікірлер: 70

@martinwilkinson9395 5 жыл бұрын

Awesome educational videos!

@ninalehman9054 Жыл бұрын

After 4 years, I doubt my comment will be seen, but I have a thought on multicellular life. I suspect that on the way to a multicellular organism like a sponge, life went through advanced biofilm communities. The single celled but multi species films even have lateral gene transfer. Could the different tissue types have originally been different species contributing a unique function to the biofilm community? I’m a total layperson, but the concept of how multicellular life began is fascinating to me. Its origins are buried deep in the past. The first time we see multicellular fossils, they had already gone through a lot of evolution. I love this topic.

@kayseek1248 Жыл бұрын

I see your comment.

@martink592 2 ай бұрын

Cool idea. Although complex mutually beneficial relationships between organisms exist, I don't think this is likely to explain the origin of multicellular life. Remember that all the cells of a multicellular organism have the same genome and come from the same zygote, right? So more likely a zygote that formed by fertilization had a mutation that caused daughter cells to stick together, and contained molecules (cytoplasmic determinants) that would cause parts of the resulting blastocyst to differentiate to have a specific function. If the blastocyst survives better, it would be selected for, and these multicellular organisms would then continue to evolve.

@ninalehman9054 2 ай бұрын

@@martink592 my impression is that we have a “chicken and egg” situation with your scenario. Zygote, fertilization, and blastocyst are all things evolved by multicellular life. It is likely that the first multicellular organisms reproduced by budding, not sexual reproduction. A blastocyst does seem feasible because that is where the different layers of either a 2-layer or 3-layer organism first differentiate. I believe sponges only have two different kinds of cell types (inner and outer). I’m a layperson, so I hope I get the three different layers correct: endoderm, mesoderm, and ectoderm? What was the first creature to develop the middle (meso) layer? How did it give the animal an evolutionary advantage? Also, did plants become multicellular in a different pathway from animals? It seems likely.

@karenjwoods5961 5 жыл бұрын

Thank you for useful explanation

@Worldfoods1 6 жыл бұрын

Good teacher-!

@chillboy8116 4 жыл бұрын

my dad's name is hassan

@nathanphillips7787 8 күн бұрын

This is fascinating! I never thought about the connection between cell differentiation in time and space! 😊

@aidan2849 Жыл бұрын

That was the most information I've ever gotten in an 8 minute video

@hydernewman6332 4 ай бұрын

Hello Prof. Dave, why are there only uni- and multi-cellular organisms, but no bi- or tri-cellular organisms?

@electrum310 3 жыл бұрын

Choanoflagellates have no nuclear receptors while sponge cells have two (RXR and HNF4). Choanoflagellates may look similar to collar cells but the genome has evolved. Therefore, I think sponges are much evolved than a simple aggregation of choanoflagellates. Thanks for the slides that helped to understand.

@carlosandleon 3 жыл бұрын

probably some choanoflagellated became more complex first before turning into sponges

@electrum310 3 жыл бұрын

@@carlosandleon Hello, if you can find any unicellular choanoflagellates that code for nuclear receptors I will give credit to your suggestion.

@carlosandleon 3 жыл бұрын

@@electrum310 I can't, they're extinct

@carlosandleon 3 жыл бұрын

@@electrum310 they're stuck in sponges now

@booJay 3 жыл бұрын

Currently it's debated whether choanoflagellates, ctenophores, or placozoa are the first animals to exhibit multicellularity. Not to mention, there are probably other candidates we don't know about. Capsaspora are also unicellular organisms that exhibit animal-like features.

@RonJohn63 4 жыл бұрын

0:19 I was watching an iBiology video the other day (by a Professor of biology), and she said that they *don't* know how it happened. And that it happened 600-1,000M years ago.

@ProfessorDaveExplains 4 жыл бұрын

Yeah we don't know precisely how. We do know roughly when, and the choanoflagellate thing is an extremely viable hypothesis.

@kasparhauser4472 3 жыл бұрын

Well, Evolution and the Theory of Evolution are only "hot topics" and disputed in the US, at least in terms of the western world...

@edthoreum7625 4 жыл бұрын

2:40 what happened 600mya? 3:30 symbiotic relation,mitochondria & cell

@daniellewilson8527 4 жыл бұрын

Ed Thoreum in algae and plants, a chloroplast joins too

@marinanicole5693 3 жыл бұрын

200,000 years in this scale seem so little. Like we came in a blip and went *what the hell*

@whatabouttheearth 3 жыл бұрын

And human "civilization" (the establishment of sedentary agricultural society) has only existed for about 10,000 years.

@AlbertaGeek 5 ай бұрын

200k years is billions of generations on that scale.

@while.coyote 4 жыл бұрын

Well, damn. We know so much.

@santicruz4012 3 жыл бұрын

Mason G. And yet we know almost nothing

@joelynd.torres3691 2 жыл бұрын

How is the development of complex organisms controlled?

@williamchamberlain2263 2 жыл бұрын

Do you mean embryonic development from the fertilised egg? Chemical gradients control a lot of it; cells produce chemicals/hormones, and sense the chemicals secreted by other cells and regulate gene expression, metabolic pathways, protein synthesis, etc so that they develop specialisation in relation to other cells.

@mikeg1368 6 ай бұрын

Fyi imo, Michael Levin has some intriguing morphogenesis research results

@shipshrekt2156 3 жыл бұрын

But if entropy is the move of all energy and matter to a lower state of complexity why would life even want to develop? Or the universe for that matter. I read that entropy can move in waves up and down but always moves down in the end. Like those reversible chemical reactions that switch colors back and forth. Maybe that explains it. But still. Why would something so simple as atoms and molecules want to come together to be more complex. I wish we had an answer

@ProfessorDaveExplains 3 жыл бұрын

What you are saying is not accurate. If you wish to understand entropy, please visit my classical physics tutorials.

@ProfessorDaveExplains 2 жыл бұрын

I have no idea what you're referring to, and neither do you.

@shipshrekt2156 2 жыл бұрын

@@ProfessorDaveExplains The conservation of energy states that no energy shall be created or destroyed. What im asking is why would something at rest and a low energy state develop into something that is complex and at a high energy state. Isn't that the opposite of the flow of entropy? Everything is supposed to spread out evenly in the universe until there is nothing except radiation flying around in empty space.

@shipshrekt2156 2 жыл бұрын

@@ProfessorDaveExplains Also I appricieate the reply back. I wasn't able to explain what i was thinking about and now that i look at what I said it looks crazy xD. Im not a science denier I assure you. I was just asking if we know exactly how the basic basic building blocks stitched themselves together? or if maybe there was some extra terrestrial intervention?

@ProfessorDaveExplains 2 жыл бұрын

"Complexity" has nothing to do with a "energy states". When atoms and molecules assemble into larger structures this releases energy. Thermodynamics states that the entropy of the universe will increase for every spontaneous process, and the formation of localized order dissipates free energy, increasing the entropy of the universe. Check out my classical physics tutorials to better understand entropy and other concepts in thermodynamics, and check out my two-part response to James Tour to hear more about what we know regarding abiogenesis.

@aaronscottbullock8843 4 жыл бұрын

omnis cellula-e cellula

@MostlyPennyCat 4 жыл бұрын

My answer to this question is almost entirely, "because collagen is sticky"

@namfilemon7614 3 жыл бұрын

Professor how do I master in biology

@suelane3628 3 жыл бұрын

Dear Nam, I might say learn English Grammar. I did a three year course in Acupuncture. Any foreign students applying without a good grasp of English, were advised to take an English course first. This has included some Chinese persons. Before anyone complains: this is not a racist comment! I want equality for all. Keep Safe. (By the way, I initially spelt grammar wrong, lol.)

@suelane3628 3 жыл бұрын

I forgot to wish you luck, but first of all keep safe!

@whatabouttheearth 3 жыл бұрын

Do you mean a "master degree"? To get that you have to get a 4 year bachelors degree first. I would ask a college/university.

@whatabouttheearth 3 жыл бұрын

@@suelane3628 For a Bachelor of Science degree in the US you have to take English classes anyway, even if you are a native English speaker. In an actual college/university you have to take many mandatory classes that are not in the subject you are getting a degree in also. It traces way back to ancient times and the Trivium and Quadrivium and the concept that a "liberal arts" degree should be a well rounded education. Then a Masters degree (after the full time 4 year bachelors) or Doctorate (after the very long Masters program) you take only your specific degree subject.

@avinashkumar-jq6lo 4 жыл бұрын

The teacher is so handsome 😄

@insAneTunA 4 жыл бұрын

I bet that you want to exchange some DNA with him 😄

@SchiwiM 4 жыл бұрын

Don't fall in love with the teacher 😂

@robertrowan9893 3 жыл бұрын

Hot Button issue is one way of putting it. However, buttons likely progressed to zips, and from there all manner of clasps and temporary fixings...et cetera. With luck, that might give some sectors of society something tangible to proverbially chew on. Though, that said, the evidence likely points to way of looking at things is lost on them...despite the overwhelming weight of historical evidence. Now I'm hot under the collar. As such, must release that said button and let off steam...productively.

@whoneverknow9588 3 жыл бұрын

Dear Professor, One should start by identifying the First Organism to suddenly appear on Earth with No simple precursor 3.8 billion years ago. The Stromatolites. You use the word "imagine," which implies an Assumption, not a Fact. Do You consider 3.8 billion years enough time for the DNA Cell to have evolved here on Earth?? And how do You imagine that the Stromatolites came to be here on Earth??

@suelane3628 3 жыл бұрын

I don't understand your question. Are you suggesting that somehow it has taken 3.8 billion years for a 'DNA' cell to evolve? A basic modern metabolism including protein synthesis and DNA would have already been in existence 3.8bya. This is based on molecular dating involving ribosomal RNA which suggests all life on Earth evolved from a common ancestor which existed 3.8bya. (LUCA.) There is no evidence that modern protein synthesis (based on DNA) evolved more than once. Granted this gives less time to evolve a basic metabolism, but we understand more now as to how it may have occurred. Stromatolites are composed of mineral excretions from colonies of Cyanobacteria, and so wouldn't have formed until the evolution of Cyanobacteria which are Eubacteria.

@whoneverknow9588 3 жыл бұрын

@@suelane3628 No sue, stating that 3.8 billion years is not enough time for the Complex DNA Cell to have evolved. The Stromatolite was the very first organism to suddenly appear on Earth with No simple precursor. How did it come about or arrive on Earth??

@suelane3628 3 жыл бұрын

@@whoneverknow9588 Hi, I have never come across the concept that Stromatolites are the first living organisms. Not to mention how to define an organism, since one bacterial cell is a living organism. As far as I am aware, Stromatolites appear in the fossil record 3.5 bya around the same time as Cyanobacteria. Yes, they are easily fossilized, which always helps. But there are earlier signs of life even up to 4.2bya. not long after the Earth cooled enough. Maybe it is not surprizing that the projected earliest life forms are thermophiles such as Sulpholobus, Actinogens and Methanogens. These are chemotrophs which would have preceded photosynthesizers such a Cyanobacteria. Our Last Universal Common Ancestor (LUCA) is believed to have existed around 3.7 bya, quite possibly before cells (Eubacterial/Archaebacterial) evolved, but after the advent of DNA which is universal to all life. (Depending on whether viruses are classed as living.)

@whoneverknow9588 3 жыл бұрын

@@suelane3628 Stromatolites are a microscope organism which appeared around 3.8 billion years ago...

@whoneverknow9588 3 жыл бұрын

@@suelane3628 Sorry, microscopic organism....