Why complex life probably evolved only once

[Geriatrix]

http://www.newscientist.com/article/dn18734-why-complex-life-probably-evolved-only-once.html

The universe may be teeming with simple cells like bacteria, but more complex life – including intelligent life – is probably very rare. That is the conclusion of a radical rethink of what it took for complex life to evolve here on Earth.

It suggests that complex alien life-forms could only evolve if an event that happened just once in Earth's history was repeated somewhere else.

All animals, plants and fungi evolved from one ancestor, the first ever complex, or "eukaryotic", cell. This common ancestor had itself evolved from simple bacteria, but it has long been a mystery why this seems to have happened only once: bacteria, after all, have been around for billions of years.

The answer, say Nick Lane of University College London and Bill Martin of the University of Dusseldorf in Germany, is that whenever simple cells start to become more complex, they run into problems generating enough energy.

It required a kind of industrial revolution in terms of energy production," says Lane. "[Our hypothesis] overturns the traditional view that the jump to complex eukaryotic cells simply required the right kinds of mutations."

"It is very, very convincing, in my opinion," says biologist John Allen of Queen Mary, University of London, on whose work Lane and Martin have drawn.
Growing costs

To become more complex, cells need more genes and more proteins – and so they need to get bigger. As the volume of any object increases, however, its relative surface area falls: an elephant has less surface area per unit of volume than a mouse, for instance. This is a major problem because simple cells generate the energy they need using the membrane that encloses them.

Lane and Martin calculate that if a bacterium grew to the size of a complex cell, it would run out of juice. It might have space for lots of genes, but it would have barely enough energy to make proteins from them.
Folds don't help

In theory, there is an easy answer to the energy problem: create lots of folds in the cell membrane to increase its surface area, which in turn will increase the amount of energy the membrane can produce. Indeed, many bacteria have such folds. But this leads to another problem as they get larger.

Producing energy by "burning" food is playing with fire. If the energy-producing machinery straddling the membrane is not constantly fine-tuned, it produces highly reactive molecules that can destroy cells. Yet fine-tuning a larger membrane is problematic because detecting and fixing problems takes longer.

These obstacles were overcome when a cell engulfed some bacteria and started using them as power generators – the first mitochondria.

By increasing the number of mitochondria, cells could increase their membrane area without creating maintenance problems: each mitochondrion is a self-contained system with built-in control and repair mechanisms.
Birth of complexity

Once freed from energy restraints, genomes could expand dramatically and cells capable of complex functions – such as communicating with each other and having specialised jobs – could evolve. Complex life was born.

So if Lane and Martin are right, the textbook idea that complex cells evolved first and only later gained mitochondria is completely wrong: cells could not become complex until they acquired mitochondria.

Simple cells hardly ever engulf other cells, however – and therein lies the catch. Acquiring mitochondria, it seems, was a one-off event. This leads Lane and Martin to their most striking conclusion: simple cells on other planets might thrive for aeons without complex life ever arising. Or, as Lane puts it: "The underlying principles are universal. Even aliens need mitochondria."

Journal reference: Nature, vol 467, p 929

 

[Keeper]

meh.... I think if it can happen once, it could happen multiple times too (maybe even two or three times on the same planet)

 

[solo7]

can you sum that all up... quite a lot to read there..

 

[stricken]

what a load of toss. the universe is full of complex chemistry. ffs. how many times should we repeat ourselves: man once thought the earth was flat - it was round. thought the earth was the center of the universe. nope... thought the sun was... nope... anything else? life is a natural "anti"-entropy reaction that occurs when you have high enough energetic yield in entropic flow. like a strong river flowing in one direction will have pockets of flow flowing in the other direction (using energy from the main flow) at places, although, over the long term, everything ends up flowing downhill. ie. we all die and go from high energy to low energy state after spending our lives being the reverse.

 

[Valis]

what a load of toss. the universe is full of complex chemistry. ffs. how many times should we repeat ourselves: man once thought the earth was flat - it was round. thought the earth was the center of the universe. nope... thought the sun was... nope... anything else? life is a natural "anti"-entropy reaction that occurs when you have high enough energetic yield in entropic flow. like a strong river flowing in one direction will have pockets of flow flowing in the other direction (using energy from the main flow) at places, although, over the long term, everything ends up flowing downhill. ie. we all die and go from high energy to low energy state after spending our lives being the reverse.

Could you give some examples of this "complex chemistry" elsewhere in the universe please?

 

[porchrat]

can you sum that all up... quite a lot to read there..

summary: The idea is that cells didn't become eukaryotic (having nuclei etc.) until after they engulfed mitochondria. The presence of mitochondria is what allowed complex multicellular life to emerge.

This seems to ignore the textbook idea that mitochondria and these cells existed in a sort of symbiosis before the absorption and conversion into organelles. Absorption may be a rare occurrence but what about close interrelations of different strains of bacteria?... that is not so rare I have always considered that sort of relationship to be the starting point of the modern mitochondria.

 

[Techne]

Related article:
Energy Revolution Key to Complex Life: Depends on Mitochondria, Cells' Tiny Power Stations

ScienceDaily (Oct. 21, 2010) — The evolution of complex life is strictly dependent on mitochondria, the tiny power stations found in all complex cells, according to a new study by Dr Nick Lane, from UCL (University College London), and Dr William Martin, from the University of Dusseldorf.

Artist's rendering of basic cell structure, including mitochondria. (Credit: iStockphoto/Sebastian Kaulitzki)​

Well, I am not too sure about this idea that eukaryotes only evolved (i.e. main reason) once because of the lucky few endosymbiotic events that allowed mitochondria to form. We are only beginning to understand the massive importance that viruses play in the evolution/change of life. For example:
Virus-like particles speed bacterial evolution

In the ocean, genes can hop between bacteria with unexpected ease, thanks to strange virus-like particles that shuttle genes from one species to another1. These particles, called gene-transfer agents (GTAs), insert DNA into bacterial genomes so frequently that gene transfer in the ocean may occur 1,000 to 100 million times more often than previously thought. This suggests that GTAs have had a powerful role in evolution.

"We know there's a lot of gene shuffling going on in bacteria, but nobody had come up with a good mechanism by which it happens," says John Paul, a marine microbiologist at the University of South Florida College of Marine Science in St Petersburg, and an author on the study that finally succeeded in uncovering a mechanism.

GTAs, which harbour bits of their host's genome inside a protein coat, reside in bacterial genomes. When they exit, they take some of their host's genes with them. For 30 years, they have remained obscure objects of occasional study in the lab...

Genes are shuttled between ocean bacteria many times faster than was previously thought.​

There are likely more factors that played a role, for example environmental pressures such as the emergence of an oxygen rich atmosphere and several preadaptations.

 

[zulgin]

'probably also not true'