The Complexities of Life

From New Scientist: Why complex life probably evolved only once.

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.
...
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.

And from Transterrestrial Musings, a stream-of-consciousness report about Craig Vetnor's presentation at

Has synthesized a megabyte chromosome. Everything in the cell was derived from the chromosome and the natural traces were all deleted. They are digitizing biology. Converting analog genetic code to digital. Now they can go the other way, from ones and zeros to living organisms. Huge progress over past two decades. Big breakthrough new algorithm in 1995. New approach to sequencing pieces by breaking them down and putting into the computer....

Yes, and compilers for manufacturing prokaryotes (organisms with no cell nucleus), and later assembling eukaryotes (organisms with a nucleus). Arranging for the organism to make its own membranes has been surprisingly difficult - though programming it has been surprisingly easy.

In terms of cell numbers - your body has ten times as many cells without your DNA in, than with. But the cells with your DNA in are larger and more complex than the swarms of bacteria to which you play host, so most of your mass is you.

A bucketful of seawater has more genetic diversity inside its bacteria than all the complex organisms on the planet put together - and they're constantly swapping DNA in a promiscuous fashion, so new "species" are being created all the time - though the concept of "species" tends to lose its meaning under those circumstances. From Scientific American:

In fact, the bacteria in the wild—the researchers tested microbes in coastal, estuary, reef and open ocean environments—were quite promiscuous with their DNA, busily transferring genes to not only their own species but also other closely related bacteria and even other genera. They were also doing it thousands to hundreds of millions of times more frequently than previously estimated for other methods of gene transfer, such as via phages or bacterial viruses (the method also employed by human gene transfer agents, also known as synthetic biologists).
...
Nevertheless, such horizontal gene transfer is a potent weapon in the bacterial evolutionary arsenal. "Truly novel genes can be taken on instantly. This is why we have antibiotic-resistant superbugs," Doolittle says. In fact, sequencing bacterial genomes has revealed that such gene transfer is responsible for many of the genes present in today's microbes. "Many already accept that HGT is very important to marine microbial adaptation."

And not just for bacteria. Given the apparently vast numbers of such genetic packets—and viruses, plasmids and other bits of genetic material—the ocean can be seen as a bit of a microbial DNA soup.

One off? Maybe not.