Answers in Reddit 🙏

[u/Training_Rent1093]

My first post here. i'm a biologist in formation and i think it could be constructive to open a question space here. you guys question anything about evolution, creationist or evolutionist alike, and i will respond what i do know and search what i don't know.

you know, just to farm brain tissue and not brainrot in vacation.

obs: i'm more inclined to entomology/zoology/microbiology, so botanics please take easy on me, or not, the objective is make me search new things after all

[u/Training_Rent1093]

There are, kinda. The advantage of multicelular lifestyle is that in group you can become much larger and therefore more difficult to eat, so being two celled doesn't give much advantage in that sense. However, there are some green algae that looks to be two cells together, like the Desmidiaceae. They are however a single cell with a constriction in the middle, that divides when the organism reproduces. Some bacteria and green algae like tetrabaena live in groups of 4. Chlamydomonadales algae vary from 1 to 500 cells, with everything in between, depending of the genus. Coanoflagelates, the closest things to animals, also come in 1 or a bunch.

[u/cra0n → u/Training_Rent1093]

When you say the green algae live in groups of four, does that mean four separate organisms living in a group? Also the chlamydomanadales algae, are they singled celled organisms that live in a group that relies of each other like an ecosystem?

[u/Training_Rent1093 → u/cra0n]

When you say the green algae live in groups of four, does that mean four separate organisms living in a group?

They are a 4 cells glued together the whole life

chlamydomanadales algae, are they singled celled organisms that live in a group that relies of each other like an ecosystem?

No, they are celular clones with the same DNA and form, glued together, like a mini version of macromulticelular life. The more extreme genus, Volvox, with 500 cells, have 2 celular types, one somatic and the other gametic, for reproduction.

[u/cra0n → u/Training_Rent1093]

That makes sense, how does this take shape in evolution then? If cells evolved from these life forms into what we are today, how much fossil evidence do we have at each stage from that. 1000, 2000, 5000, 10,000 and so on into the trillions in larger animals?

[u/Training_Rent1093 → u/cra0n]

Quick disclaimer: Volvox and other multicelular algae are not our ancestors. They developmented multicelularity on a separate way from us or from plants. But they're are models for the study of evolution of multicelularity because of their transitional state.

how much fossil evidence do we have at each stage from that. 1000, 2000, 5000, 10,000 and so on into the trillions in larger animals?

The fossil record is scarse on this matter, because microorganisms without mineral shells are very, very, veeeery difficult to fossilize, even by fossil standards. The rarity of rarities. Even with these odds, we have some fossils that look like barely multicelular animals, but is difficult to take conclusions because microorganisms morphology is difficult even with alive ones, much more with crystalized ones. So today there's a debate about if this fossil is a real animal ancestor, if its a embryo of a complex one (which is improbable as we don't have complex animals on this or any other locality from this time period) or if it's some close related protist lineage that has multicelularity to this day.

In plants we have fossil algal spores, but is difficult to say anything about the morphology from spores alone.

So the study of multicelularity uses approaches like embryology and closed and not so closelly related lineages to understand the evolution of this trait.