Scientists learn more about enigmatic archaea (2021)
nature.com
nature.com
The ancestors of the mitochondria organelles you see today in every cell in your body were once free swimming bacteria, in a world where there were no animals, and no eukaryotic cells. Planet earth then, and for its first 2 billion years, was populated exclusively by bacteria, or single celled organisms. These cells were about one hundredth the size of the cells in your body.
How did life on earth become more complex?
Billions of years before the Cambrian explosion, when the number of animal species exploded into the millions, something much more basic happened at the cellular level. Cells became more complex.
How?
Maybe cells engulfed other cells, and the engulfed cells survived, forming a partnership or a colony.
Or maybe different types of cells hung out in close proximity, in colonies, which eventually merged into a network of DNA exchanging nodes that keep growing in complexity and interdependency.
We don't know.
This new effort to grow and study archea in vitro gives us something to study and experiment with.
1: https://en.wikipedia.org/wiki/Chloroplast#Lineages_and_evolu...
The History of Evolutionary Thought → 1900 to present → Endosymbiosis: Lynn Margulis
https://evolution.berkeley.edu/the-history-of-evolutionary-t...
Lynn Margulis and the endosymbiont hypothesis: 50 years later
Maybe same goes for cilia, centrioles, golgi body, nerve cells ..
Bacteria are just one of the types of single celled organisms that populated the earth before multicellular organisms emerged.
The author more or less concludes (highlighting also limitations of the science and current knowledge) that our cells were arachea which absorbed a methanophile bacterium that became both our today's mitochondria and a parallel process for the chloroplasts in plants (with possibly a common ancestor if I remember well).
I'll grant my view is mainly driven by the question of how much complex life exists off of Earth, and therefore how hard/unlikely it was for Earth life to reach its current complexity. If it happened a bunch of times on Earth it's probably not a blocker, and therefore not relevant to my interests. :D
Anyway, the evolutionary gradient that drove complexity in the genome is what I'd really like to know about. How it works, how it got started, why it apparently only happened once, etc.
It took only 2 billion years from that to the Cambrian Explosion!
The arrival of mitochondria, or the "merger" of the bacterial ancestors of mitochondria and the archea "host" was pivotal.
Bacteria and archea have been around for billions of years, ~a billion years longer than eukaryotes. Only once, as far as we know, did they blossom into the complexity of the eukaryotic cell, via a very specific endosymbiotic event. Most of the bacterial DNA ended up in the (newly developed) nucleus, where, in addition to coding proteins for the mitochondria, it could also take on lots of new functions.
We don't have a bunch of intermediate states between prokaryotes and eukaryotes-- it's a huge gulf that suggests a one time event that left most offspring unable to reproduce.
Whether we are talking about life on earth or other worlds, this seems very, very lucky, and very relevant to your interests-- it is why we got the big complexity gradient, and why, even billions of years later, you don't have "complex" bacteria or archea.
Citation needed. There is a hell of a lot more to being a eukaryote than having mitochondria. They're defined by having a nucleus, not mitochondria, and I think that's a good definition.
If mitochondria were a necessary step to modern eukaryotic complexity, it could only be by providing a bigger power budget, which could have happened lots of ways. Again, cellular endosymbiosis is common, other notable examples being chloroplasts and red algae serving as chloroplasts for brown algae.
So, I'm not saying mitochondria are not important, but I don't think they were the blocker to eukaryote evolution.
For a citation, see The Vital Question: Energy, Evolution, and the Origins of Complex Life [see https://www.amazon.com/gp/product/B00OD8Z4JW/ref=dbs_a_def_r...]. I think you'll like it.
(Among other things, it suggests that the nucleus itself developed because of the inflow of bacterial DNA and the need to parse out meaningless intron segments of genetic code.)
Note also that the subsequent endosymbiotic absorption of chloroplasts is not a "common" event, although of course it is very important-- at least to us, as we wouldn't be here without it.
* Some have lost them, when they are involved in symbiotic relationships that supply the required energy, or, as part of multicellular organisms-- for example, our red blood cells. Note that our red blood cells also lack nuclei.
The nucleus is a result of the endosymbiosis, not something that just picked up some extra fuel cells...
On the contrary! In billions of years of evolution it happened only very few times (successful), and only once really successfully. It is a rare event.
It traces how we got to some of these new ideas from pre-Darwin, through Lynn Margulis, to present day nanopore sequencers via the guy who discovered Archea.