branching pattern is you know if you have you know people who then make babies and then they each make two babies and make two babies off that you get a tree that bifurcates into two of each generation on the other hand it could be that one one branch bifurcates into three one branch bifurcates doesn't at all and so you can get asymmetric trees and and it turns out that the way the characterization of that asymmetry of the trees turns out to follow a scale invariant behavior and that's that's what um that's all was discovered about about NUMBER_TOKEN NUMBER_TOKEN years or so ago um by us also independently and a bit earlier by another group and um and what we discovered was that actually this could be an outcome of the interplay between ecology and evolution and and and the idea being that that when organisms change their environment by their activity i think you know the usual example is beavers you know eating trees damming rivers causing lakes and then getting invaded by plants and fish and things like this so so the activity of an organism in its environment can literally change the evolutionary history of that entire ecosystem and and so when you try to model that effect in a very in a very crude way what do you find is that it also it can produce this scale invariant behavior so then to your question your question was well what does that have to do with the tuning so remember that we talked about the scale interference in the magnetic system that there's a vein over which there is a times a spatial scale where things are correlated there's a range where the atoms sit on the lattice which is angstroms and it's the scale interference between that very small scale in space and a very large scale in space for the correlations that scale interference the fact that you can't neglect the smallness of the lattice is what causes the critical phenomena so in the evolution problem it's an it's a normalization effect like that of scale interference but it's in time rather than a space so when you think about ecosystems you think there's a time scale which the ecosystem adjusts when you think about evolution you think there's a time scale over which evolution occurs you know millions and millions of years and you would think well i can neglect you know the time scale of beavers eating over here trees and chopping them down and causing a mess in in in the ecosystem and damning rivers i could ignore that time scale compared to millions of years well it turns out you can't and if you if you make values if you ask what happens if you don't make that common sense assumption then you can explain the the fractal behavior the scaling laws that you see in in the evolutionary history of of uh of life alert so it is an interesting kind of tuning in some sense i mean the the ising model example gives us the impression that you know we are an external actor and we have to carefully tune it whereas in in examples like this i think probably both turbulence and in evolution there's some internal dynamics that naturally takes you to that critical point is that a fair thing to say that's right in other words in the limit if you just look at the evolutionary time scale as being just a little bit bigger than the ecological time scale you will not see this scale invariant behavior so just like in the in the fluid if the viscosity is small but not
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