How Did Life Transition from Single Cellular to Multicellular?

[BillTre]

Here is a Science News article on life's transition from single cellular to multi-cellular life.

This is an important transition in the evolution of more complex life forms.
Unlike situations like the origin of life and the generation of eukaryotic life forms, the transition ot multicellular life occurred several times and an is not considered such a difficult hurdle for evolution.
In addition, it can be studied in the lab, where multi-cellular forms can be selected for and the hanges underlying the changes can be studied.

Several ratchet mechanisms are also mentioned. Once a multi-cellular entity exists, ratchet mechanisms make it less likely for the cells to revert to their old single cellular ways.
An example, that would result in a reduction in a single cell's ability to survive and reproduce would be the increased cell death rate found in multi-cellular yeast clumps. This produced more (and smaller) yeast cell clumps which can grow and reproduce faster, but would just reduce the rate of population growth for single cells.

 

[KenJackson]

The article quotes an evolutionary biologist as saying, "What this group of algae has taught us is some of the steps involved in the evolution of a multicellular organism." But all of these "steps" seem to involve fully formed genes. Those seem trivial compared to evolving the genes. Where are the genes-in-progress? How do new genes come to be?

The article does talk a lot about "repurposing" existing genes, but that doesn't sound like it even requires a mutation. There's also an awful lot of conjecture about various aspects.

Wouldn't the most difficult steps of all be along the path to producing a new gene? Where are those steps illustrated? How does that happen?

 

[BillTre]

But all of these "steps" seem to involve fully formed genes. Those seem trivial compared to evolving the genes. Where are the genes-in-progress?

The "genes-in-progress" appear to be already existing in the organisms studied and doing something else (yet to be determined).

How do new genes come to be?

New genes (apparently not involved in these studies) can arise in a number of ways.
They could arise from sequence changes of nucleotides that do not encode anything. This is thought to be long and unusual, since it is unlikely that a functional sequence would arise by chance changes in sequence.
Alternatively they can be generated by gene transfer, or a pre-existing gene could be duplicated (so one copy maintains the old function of the gene) and changed (by either point mutations (single changes in sequence) or by combining block of sequence from other pre-existing genes. These kind of results are frequently seen. They do not require so many low probability steps (as assembling a useful sequence from nothing) to result in a functionally result.

The article does talk a lot about "repurposing" existing genes, but that doesn't sound like it even requires a mutation.

Repurposing genes refers to using already existing genes for a new purpose.
In this case the gene might need a new controlling mechanism to get it expressed at a useful time. This would most likely involve evolving new binding site for genetic control mechanisms, such as a transcriptional activator binding site or a promoter site in the DNA adjacent to the gene.

These are mutations, just not massive new constructs that would be an unlikely occurrence that might take a long time to happen.

There's also an awful lot of conjecture about various aspects.

Conjecture is the mother of hypothesizing, for follow-up studies.

Wouldn't the most difficult steps of all be along the path to producing a new gene? Where are those steps illustrated? How does that happen?

Yes, if they were needed, they would be difficult.
But since they are not needed, the quicker path to satisfactory results (for an organism) is what we find (the successful results of evolution) because that is all an evolving biological system needs.
A bit of gene evolution was discussed above. More in depth discussion would best occur in a new thread on that issue.

 

[Laroxe]

Many single celled organisms will under the right conditions form biofilms that begin to act in a coordinated way and appear to adopt some specialisation within the group, this implies the ability to influence each other using signaling molecules, indeed some biofilms can contain several species of bacteria. It might be that the loss of the ability to revert back to individual functioning may be as important as the evolution of new traits. This describes some of the issues;
https://www.khanacademy.org/science...ism-ecology/a/prokaryote-interactions-ecology
and some evidence
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006655