Linear distances are small, areas are large. It's easy to drive across an 83km crater, but imagine trying to paint the whole thing.

Volumes are even larger still.

>IIRC the Navy did a couple studies after a rash of collisions and other ship casualties. The net result was to shorten the shifts in certain critical command/control positions - Officer of the Deck, Navigator, helmsman, Weapons Officer, etc.

Perhaps the takeaway really is that we need to invest significant resources into developing better procedures for hand offs that mitigate the negative consequences of them. Then we can shift the equilibrium closer to optimising for the first order effects of shift length itself.

>For what it's worth, the point where unique ancestors would outnumber the population is precisely 30 generations.

I don't think it's necessarily safe to use this as a lower bound for the posed question in terms of how far back we'll be going. Obviously the max number of unique ancestors alive at the same time must be lower than 2^30 (*Edit, maybe not technically, but probably in practice on Earth today - see my edit below), but it does not follow from that that the widest generation must be less that 30 generations ago. What happens instead is that very quickly as you go back generations, the number of additional ancestors in the next generation back starts to grow very slowly, and then in fits and starts as you have individual ancestors who migrated a significant distance.

The more determinative fact will be the distribution of the size the population over time - both the global ones, and the sizes of the populations to which you are likely to be genetically linked. Populations that have grown significantly in the somewhat recent past (but not too recently) will have the max number of ancestors being very recent, because you can hit a number of ancestors alive at the same time that outnumber the people that actually lived in early generations in that population.

But for sparsely interconnected populations that have had stable sizes for centuries/millennia, you could expect to very slowly attain small numbers of new ancestors each generation for well over 30 generations, if the growth rate is low enough.

Edit: Come to think of it, perhaps more important is that the number of unique ancestors in generation X back from yourself can actually outnumber the people who were alive at the same time as any given one of those ancestors. Go back far enough and you'll have ancestors from different parts of your family tree in the same ancestral generation who lived centuries apart. The further back you go, the more pronounced this effect becomes.