mandarine

Fault-tolerant design

Let me take you on a detour through aerospace systems design: when we have to engineer spacecraft that will operate for twenty years in geostationary orbit without any maintenance (imagine your washing machine running 24/7 for 20 years without interruption), or when we have to design aircraft that will fly a billion flight hours without an accident (imagine your computer running for 117,000 years without hanging), we need fault-tolerance and robustness. The way we achieve this robustness is through redundancy and diversity. Whenever a system fails, there is a similar backup system that can take over (redundancy). Sometimes, even the redundant system fails eventually. The most frequent case is because there was a common design flaw in both the nominal and redundant systems. When we want to ensure robustness even against such unforeseeable events (we never know where our design will be flawed, but we always know it can be), we design another backup system that is completely dissimilar from the nominal system (diversity). Generally the backup system design is much less efficient, but much more rugged, therefore it has a lot more tolerance to off-nominal situations. This will allow the pilot to land the aircraft or give ground operators time to reconfigure the spacecraft. The more diversity we build into the system, the more robust the design will be.

Biodiversity theorem

I recently read an interesting analysis in a gardening book: the author was showing that there were always ‘magic’ weeds which showed up after an ecosystem had been upset, so that it always seems to be just the right weeds to improve the soil and make it ever more fertile. First it will be grass, to stabilize the upper layer, then it will be dandelions with a very deep tap root which will punch through the denser lower layers, then thorny shrubs that will protect the area from grazing and tramping, then trees, which will provide a lasting source of humus, a lasting protection against erosion, a lasting rock-grinding capability to create more soil, a lasting haven for wildlife, etc. The author was describing this as if the whole process had a purpose, as if there had been a designer who had assembled all the pieces in this clockwork miracle.

Although I am a believer deep down, I am still an engineer with principles, and I never buy into a ‘God made it so’ or ‘Nature wants it so’ arguments. But the whole illustration was striking, and got me thinking. Then I understood something obvious: natural selection does not only apply to species. Our individualistic viewpoint deceives us into thinking that natural selection is only about the evolution of individual species, but there is no mechanism for natural selection to target a species individually: if a fungus and a tree get a mutual competitive advantage, they will thrive alongside and evolve alongside. Natural conditions apply globally to whole ecosystems: if a given ecosystem recovers faster after an upset or a disaster, then it will prevail. Natural selection will favor those ecosystems in which diversity provides a whole range of different tools to thrive, recover, evolve. Just like the evolution of species led to cats and we marvel at how perfectly they are designed for hunting mice, the evolution of ecosystems let to temperate or tropical forests and we marvel at how perfectly they are engineered for fertility and fast recovery.

The ecosystems that we observe today have survived for millions and millions of years (otherwise we would not observe them today). They have gone through tens of thousands of upsets and disasters, and have always recovered. They were the most robust. As robustness comes with diversity, this explains why natural selection has generated such an extraordinary diversity (instead of narrowing down to a few ‘best’ species, in our naive Darwinian interpretations). And it explains why the ecosystems that we observe today (at least those that are reasonably pristine) seem to have built-in recovery mechanisms for every sort of disruption. QED. Fires, landslides, drought, floods, frost, there always seems to be a set of processes or species that had been waiting for the event to occur to make themselves useful and mend the wounds, and then go back to their hiding places for the next twenty thousand years.

Application case: my life

I never know what tomorrow will be made of. Just because the economic and social backdrop has been relatively stable for the last twenty times the Earth went around the sun does not mean it will go on forever. Humans have a very bad habit of considering that three years in a row makes an eternal rule. I know that there is a 100% probability that a major disruption will hit my vicinity of space-time before I am a grandfather. Trying to imagine what it will be is a vain game, just like listing all possible unexpected failure cases in system design.

But I know that a diverse system is always more robust. Therefore I want to build more ‘biodiversity’ into my life.

What can that mean? I have only just started to express this need explicitly, but here are a few examples:

• diversify work. This is probably the keystone of the process. Work ethics and social conventions force us to have a single, full-time, monetary-only job. To me, this looks just as biodiverse as a 100,000-acre GM soybean field. I have to break out of this box. I am already working only part-time (4 days a week), and I will definitely seek to carry on in that direction. I could choose to have two jobs, but I believe there will be much much more potential for diversification if I just reduce my main job and do non-monetary work in the time that is thus freed: build my house, grow my food, create local and global networks of friends, work for the public domain, just do the right stuff.
• diversify food sourcing. I wish to grow at least half my food in two years from now.
• diversify friends, know more different people. When all I do is work; when all my colleagues are aerospace engineers; when all engineers come from the same social background and the same schools, then that’s monoculture again. I am not a people’s person, but now is the time I started doing some real networking and get to know people I would never have met if I had stayed in my hole in the ground. And not only in blogland.
• diversify knowledge. If you just think for a minute, one’s culture is hugely limited by what is considered culture within one’s social and cultural background. I am going to open the windows much wider than that — my curiosity will know no limits.

Epilogue

And diversity is so much more FUN!!

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