Question

Write a narrative on the origin of multicellular life.

I just would like some tidbits on the topic. Thank you for helping me!:)

Answer 1

Life as we know it came from a single celled organism. Something like bacteria. Once the bacteria could produce its own energy(ATP), it started to grow. Things like choloroplast and mitochondria engulfed the bacteria through endosymbiosis and it seemed to work great for both of the organism. Then somehow the bacteria started to stay together and could get the best nutrients when it worked together. Then came sex to create its clones but then by randomnization of DNA, we started to get different organisms with different tasks. Then comes evolution.

Answer 2

Ok I think this question deserves a complete answer. There are of course, those who believe that the earth is 6000 years old and all, but here is the mainstream scientific theory on how life cam about.

I am going to briefly discuss prokaryotes, since they were here first (about 4 billion years ago!). It is important to note that even before life developed, there was a form of evolution. At some point, a molecule capable of making copies of itself formed at random. Once this happened, there was a "replicator" that evolution could act on. Over time, small changes added up and mutant replicators began to compete. These first replicators were most likely RNA, since RNA can do both the work of proteins (although not as efficiently) and carry information (but not as faithfully as DNA). So eventually we get more and more complex replicators, leading to the first prokaryotes. It is important to note that these are not the same prokaryotes that we know today, evolution has been acting on them ever since and they are only distant relatives of the first true cells.

Ok, now that we have a base to work with, eukaryotes next (developed about 2.7 billion years ago). The true defining attribute of the eukaryotic cell is the nucleus and membrane bound organelles. The nucleus developed over the generations, in fact there are a few prokaryotes with a simple form of a nucleus that hint at this evolution. Mitochondria and chloroplasts, arguably the two most complex organelles, formed via endocytosis. That is, at some point the common ancestor to all eukaryotic cells enveloped a smaller cell. Most likely, at first the relationship was more parasitic, but over time they began to benefit each other more and more. I am simplifying to keep this brief, but support for this theory is strong. Sequencing of mitochondrial DNA reveals that it is related to Richetsia (spelling?), which is an intracellular parasite. Chloroplasts are distantly related in a similar fashion to cyanobacteria. Both organelles can no longer live on their own, and have evolved in their own way to be specialized and efficient organelles. It is also important to note that at some point, sexual reproduction developed. It is not clear exactly when, but probably fairly early in the history of eukaryotic life it developed as a defense mechanism against parasites.

Now for the evolution of multicellular organisms. We have just begun to realize how social cells are, even prokaryotic cells. For example, even the prokaryotic organism myxobacteria is in a way, multicellular. Large groups of related individuals move around in the soil in a "swarm" looking for food. About 530 million years ago, the Cambrian explosion produced multicellular organisms. The Cambrian explosion was a sudden "burst" of evolution. It is under some debate, but it seems logical to me that once cells were able to accumulate the amount of DNA necessary to code for enough proteins to communicate with and coordinate large groups of themselves that many such multicellular organisms would develop in a short time. Anyhow, this is when cells first developed into cooperative organisms. Once simple multicelluar organisms developed, this again changes the way that evolution can function. Now it was able to act on large groups of cells, favoring those that worked together more efficiently (made better bodies). It is hard to say what the first multicellular organisms were, since they had no bones or hard tissues to be fossilized, but you can imagine they were likely simple things only a few cells in size. This all changed quickly however as evolution favored new body designs...

I think you can see where this is going so ill stop here cause its getting long. Its a broad topic and i left a lot out, so look around because its a fascinating subject! Hope all that helped.

Answer 3

There are various mechanisms by which multicellularity could have evolved.

http://en.wikipedia.org/wiki/Multicellular_organism