We are told, “When facing a predator, single cells sometimes unite to defend themselves, paving the way for more complex multicellular life forms to evolve:
One theory posits that single-celled organisms evolved multicellularity through a specific series of adaptations. First, cells began adhering to each other, creating cell groups that have a higher survival rate, partly because it’s harder for predators to kill a group of cells than a single cell. But this defensive adaptation comes at the price of a lowered reproduction rate; only through adaptations acquired over generations do cell groups become better at reproducing than single cells.Stephen Johnson, “How evolution shifts from unicellular to multicellular life” at BigThink (July 14, 2021)
The theory was tested on algae:
After six months, all the algae strains that faced the predator had evolved into cell groups. Meanwhile, only four of the 10 algae strains without predators evolved into groups. Surprisingly, this transition toward simple multicellularity occurred relatively quickly, over just 500 generations or six months. (The algae replicated about once every 9 hours.) …
After cell groups boosted their defenses against predators, they were able to increase their reproductive rates. The researchers noted that these adaptations occurred on the genome level and were heritable, suggesting that with enough exposure to a selection pressure, like predation, the evolution toward multicellularity might be inevitable.Stephen Johnson, “How evolution shifts from unicellular to multicellular life” at BigThink (July 14, 2021)
The paper is open access.
But wait. Before we get carried away, botanist Margaret Helder writes to say,
Lots of algae exhibit clumping together in groups. This is not the definition of multicellularity. There are quite a number of colonial relatives of Chlamydomonas, for example like Eudorina, Pandorina and Volvox. They are not evolving into anything.
Multicellularity, by definition, involves differentiation of cells into different tissues with different roles.
This study seems very simplistic. One wonders if the referees knew anything about algae.
The referees do know that claiming a breakthrough is good for business.
Generally, a colony of cells is not a multicellular body, even if the cells co-operate. It takes more than that. They must be obligate members of a system.
Here are the study’s vids:
Here’s a Volvox colony: