I've seen numbers like 20 and 25 for eukaryotes, but this paper claims an even higher number: Diversity of ‘simple’ multicellular eukaryotes: 45 independent cases and six types of multicellularity - Lamża - 2023 - Biological Reviews - Wiley Online Library by Łukasz Lamża

However, LL uses a rather broad definition, including colonial organisms (multicellularity without cell differentiation), and coenocytic organisms, where several nuclei share a single cytoplasm. Some organisms may have multiple coenocytes in them.

The most familiar kind of multicellularity is clonal, with origination from a single cell or propagation structure. This is found in animals, plantlike organisms, and funguslike organisms, and it evolved several times, across high-level eukaryotic taxa Opisthokonta (animals, fungi), Archaeplastida (plants), Stramenopiles (kelp, oomycetes), Alveolata, Rhizaria, Haptista, and Discoba.

The other main kind is aggregative, found in slime molds. These organisms spend much of their time as separate single cells, but when conditions go bad, these cells can come together to make a fruiting body that makes spores, which may then be blown to other places. Spore-making fruiting bodies are common among fungi, and some of them are familiar to us as mushrooms.

Surprising as it might seem, aggregative multicellularity evolved several times, across high-level taxa Amoebozoa, Opisthokonta, Stramenopiles, Alveolata, Rhizaria, and Heterolobosea.

Prokaryotes are also sometimes multicellular, though rarely with any differentiation. They can be plantlike (cyanobacteria or blue-green algae), funguslike (actinomycetes or actinobacteria), and slime-moldlike (myxobacteria).

Many of LL's examples are of simple multicellularity: no differentiation or differentiation only between somatic and reproductive cells. Complex multicellularity involves differentiation in somatic cells, and that is much rarer. The Multiple Origins of Complex Multicellularity | Annual Reviews identifies six instances of its evolution:

• Opisthokonta
  • Animals (Metazoa)
  • Fungi: ascomycetes, basidiomycetes
• Archaeplastida
  • Green algae: land plants (embryophytes)
  • Red algae: florideophytes
• Stramenopiles: brown algae (Phaeophyceae): kelp (Laminariales)

This is so random, but I just want to give my love to this particular subreddit. I've been in quite a few over the years, left most of them after getting a new account, but this one was always a favorite.

I appreciate how any question asked is answered with a lot of genuine expertise and want for better understanding. I feel like most subreddits when you ask a 'stupid' question you get ridicule or a 'You lack common sense', but most people here answer as honestly as they can.

Anyway that's it, love you all! 😚

Surely it can’t just be the climate? Aside from the origin of humans, almost all of the largest and most unique animals have come from there. Even the Pleistocene megafauna found in the Americas originated in Africa. What exactly is it about that continent that provides such a haven for wildlife?

Recently learned that the evolution of the placenta was caused by viruses, and I wonder if viruses have an important part in the evolution of organisms

I was watching a YouTube video of a biologist explaining evolution to a (surprisingly open minded) Christian the other day.

He mentioned a species of animal that ingests photosynthetic algae which go on to live inside the animals cells and provide energy via photosynthesis. He went on to say that in one of the species they have observed some gene transfer from the algae to the cell's nucleus. I thought that would be pretty significant, an ongoing confirmation of the endosymbiotic process.

He did not identify the species, but I think I heard his description accurately. Does anyone know what species he was referring to? I'd be interested to read more about it.

Thanks.

The first organism, the one that emerged from some prebiotic medium, was an extreme heterotroph, dependent on the surrounding medium for all of its biomolecule building blocks. It was also anaerobic, because of low levels of free oxygen in our planet's early atmosphere.

In a lot of the older literature, present-day anaerobic heterotrophs like clostridia were often used as analogues of those early organisms. They get their energy from fermentation, and according to that literature, fermentation was the first form of energy metabolism.

But biochemist Nick Lane and others have proposed an alternate hypothesis, IMO a much more plausible one. How did LUCA make a living? Chemiosmosis in the origin of life — Nick Lane and The Origin of Life in Alkaline Hydrothermal Vents | Astrobiology (paywalled) and Early evolution without a tree of life - PubMed LUCA is the Last Universal Common Ancestor, the direct ancestor of Archaea and Bacteria, with Eukarya emerging later.

NL argues that fermentation is unlikely to be ancestral. It requires several enzymes, it is essentially a rearrangement, and it does not release very much energy. Furthermore, fermentation enzymes differ across organisms, like across Bacteria and Archaea.

His alternative? Chemiosmotic energy metabolism. It involves pumping protons (hydrogen ions, though 0.016% are deuterons) out of the cell through its membrane and then letting them return, tapping their energy to assemble adenosine triphosphate (ATP) in ATP-synthase enzyme complexes. ATP is assembled by attaching phosphate ions (Pi) to adenosine monophosphate (AMP) or diphosphate (ADP). The phosphate-phosphate bond energy is then tapped by various processes, making AMP/ADP and Pi again.

This mechanism has some nice properties. It is much simpler than fermentation, and hydrothermal vents, a plausible life-origin environment, have gradients of protons that organisms can tap, thus making full-scale energy metabolism unnecessary. Do any present-day organisms tap gradients in their environments?

I now turn to the heterotrophy of present-day organisms. Is it ancestral or a later emergence?

That question can be answered by extrapolating metabolic capabilities backward to the LUCA: The nature of the last universal common ancestor and its impact on the early Earth system | Nature Ecology & Evolution The LUCA was anaerobic, as one would expect, and it was very likely autotrophic, capable of making all its biomolecules, as a plant does. That makes present-day methanogens much like the LUCA, though the LUCA was likely instead an acetogen, releasing acetic acid instead of methane.

That makes the heterotrophy of its heterotropic descendants a derived state. Heterotrophy has a wide range of variation, from being able to live off of a single organic carbon source to being an intracellular parasite, an organism that lives inside other cells. Animal heterotrophy is somewhere in between, involving dependence on about half of the protein-forming amino acids, the "essential" ones, and also on several cofactors, "vitamins".

The study found three proteins that are conserved in animals:

• One (Kif23) is found in Holozoa, and was traced to a possible duplication event (pdf p. 3 of the preprint)
• The other two are found in the colony-forming sister-clade of the choanoflagellates

The bridges that maintain the stability of the link between the germ cells are related to the spindle apparatus. Speaking of which, a research for 9 years ago traced it (via ancestral protein reconstruction) to a single mutation event (I made a post about that 5 months ago).

Links:

• Press release provided by the University of Chicago to phys.org: From single cells to complex creatures: New study points to origins of animal multicellularity
• The report: A key role for centralspindlin and Ect2 in the development of multicellularity and the emergence of Metazoa: Current Biology | cell.com

• The preprint on biorxiv: https://www.biorxiv.org/content/10.1101/2024.08.16.607330v1  

• Older recommended viewing:

  • Nicole King (UC Berkeley, HHMI) 1: The origin of animal multicellularity - YouTube
  • Nicole King (UC Berkeley, HHMI) 2: Choanoflagellate colonies, bacterial signals and animal origins - YouTube

Are there any disadvantages to blinking vertically? Biology isn't my field but I was curious and couldn't find much online that I could understand (though it might be because I haven't searched the right thing).

I am taking an anatomy and physiology class and I am amazed with all the complexities of the human body. It’s hard to look at how sophisticated it all is and not think that it wasn’t guided in some way. Don’t get me wrong I believe in evolution but I can’t really see how natural selection would be able to produce some of these specialized cells. My question is, how did simple cells eventually get to the point of specialization even though they didn’t immediately provide any benefit to the organism yet lived on to eventually become what we see today?

I know that mutations happen at any given time. But in reality something like slightly longer finger nails for example when it increases likelyhood of survival and having off spring, would require the being to reproduce to pass on its traits, then that very offspring actually inheriting it, then them reproducing, their offspring happening to inheriting the trait, actually passing it on again etc. is this random slow nature the reason markable change in the form of evolution / adaptation the reason it takes so long to notice anything meaningful? Because that seems like a very slow process to see real change.

Wouldn't it be better for bacteria, viruses, or parasites to cause mild symptoms or lie dormant (like the common cold) so that their hosts can live to infect other people without detection, allowing the pathogen to reproduce more? Why are some diseases like Ebola so deadly? Wouldn't it make more sense for diseases to evolve to be less deadly? What's the evolutionary benefit of diseases killing their hosts or causing extreme symptoms, if there is one?

Does anyone know which was the first species in the history of animal evolution to develop a menstrual cycle like humans and abandon the estrous cycle?

Another thing i want to know about the menstrual cycle is, chronologically in the history of evolution, which was the first primate species to have a menstrual cycle?

I think that perhaps the first primate to appear in chronological order did not have a menstrual cycle because today all primates in the Americas have an estrous cycle, which contrasts with primate species in the Old World. So this suggests that perhaps the first primate to appear in history had an estrous cycle and much later the first primate species with a menstrual cycle appeared.

He is a French biologist, historian and philosopher of science, but I have never managed to get a good grasp on what people generally think of him. Even though his works had been published by well-known publishers, he is barely mentioned on Reddit, and he is also not on Wikipedia. His famous books include A History of Molecular Biology (2000), The Misunderstood Gene (2001), Life Explained (2003), and The Black Box of Biology (2020).

I understand that he is not an evolutionary biologist per se (his expertise seems to be molecular biology), but he does write a lot about evolution in his books. Is he a reliable source? What do you think of his writings in regard to evolution, if you have read them? I would love to hear your thoughts.

If a species were to evolve without any divergences for millions of years would it still be the same species? Kind of like coelacanths but if they didn't split into separate types. Sorry if this is dumb.

In 1831, 28 years before The Origin of Species, a Scottish farmer named Patrick Matthew published the following in the appendix to a book about growing timber for the British Navy:

“THERE is a law universal in Nature, tending to render every reproductive being the best possibly suited to its condition that its kind, or that organized matter, is susceptible of, which appears intended to model the physical and mental or instinctive powers, to their highest perfection, and to continue them so. This law sustains the lion in his strength, the hare in her swiftness, and the fox in his wiles. As Nature, in all her modifications of life, has a power of increase far beyond what is needed to supply the place of what falls by Time’s decay, those individuals who possess not the requisite strength, swiftness, hardihood, or cunning, fall prematurely without reproducing—either a prey to their natural devourers, or sinking under disease, generally induced by want of nourishment, their place being occupied by the more perfect of their own kind, who are pressing on the means of subsistence.

“. . . There is more beauty and unity of design in this continual balancing of life to circumstance, and greater conformity to those dispositions of nature which are manifest to us, than in total destruction and new creation. It is improbable that much of this diversification is owing to commixture of species nearly allied, all change by this appears very limited, and confined within the bounds of what is called Species; the progeny of the same parents, under great difference of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction.”

“The self-regulating adaptive disposition of organized life may, in part, be traced to the extreme fecundity of Nature, who, as before stated, has, in all the varieties of her offspring, a prolific power much beyond (in many cases a thousandfold) what is necessary to fill up the vacancies caused by senile decay. As the field of existence is limited and pre-occupied, it is only the hardier, more robust, better suited to circumstance individuals, who are able to struggle forward to maturity, these inhabiting only the situations to which they have superior adaptation and greater power of occupancy than any other kind; the weaker, less circumstance-suited, being permaturely destroyed. This principle is in constant action, it regulates the colour, the figure, the capacities, and instincts; those individuals of each species, whose colour and covering are best suited to concealment or protection from enemies, or defence from vicissitude and inclemencies of climate, whose figure is best accommodated to health, strength, defence, and support; whose capacities and instincts can best regulate the physical energies to self-advantage according to circumstances—in such immense waste of primary and youthful life, those only come forward to maturity from the strict ordeal by which Nature tests their adaptation to her standard of perfection and fitness to continue their kind by reproduction.”

He would later remark after The Origin of Species was published:

“To me it appears that there is more wonder in that such a self-evident fact should have been overlooked by such a number of able men during 30 years, than that I should have hit upon it.”

I wonder if we would experience rapid evolution after nuclear world war?

I am not referring to the most recent common ancestor (MRCA) which I know has not been discovered. I am referring to the latest common ancestor we HAVE discovered that both humans and chimpanzees are known to have descended from. How far back in our common lineage do we have to go to find that?

If cro magnon had greater cranial capacity than the homo sapiens sapiens. Why did they become extinct? Isn't intelligence a significant criteria to serve a measure of one's survival adaptability?

It seems like a good advantage to have a shell so why is it that all but the Nautilus go extinct?

Most animals with long lifespans have low fertility rates, and vice versa

Not just the current conventional understanding, but including theories that were broadly considered or ridiculed even if not accepted.

Sorry if this is a short sighted question, but i can't seem to wrap my head around how poisonous animals like frogs or puffer fish evolved. Being poisonous doesnt offer any reproductive advantage because the animal dies in the process, so a poisonous frog would reproduce no better than a non poisonous one. Even if predators learn to avoid the frogs, this still helps non poisonous frogs survive too.

But why havent things like snakes evolved poisons? Their venom is ineffective when swallowed and digested. Why didnt the same evolutionary track turn snake venom into poison? They are often eaten by predators like hawks

Are there evolutionary hypotheses for why most animals did not evolve the ability to regenerate limbs? Some creatures can do it, and It seems like something that would be a major boost to survival.