|This isn't my MRI, but it demonstrates the"string of pearls" pattern of watershed area stroke damage in my brain.|
Here is how I described watershed stroke damage in my Skeptical Inquirer article:
My neurologist told me that the reasons I've recovered so well are I was younger than the average stroke victim, and most of my brain damage was in the watershed areas. Watershed areas lie between two major arteries. By the time blood reaches these sections, there’s less oxygen in it. It’s a bit like a wetland fed by two trickling tributaries. Together, they provide just enough water, but when the flow diminishes, the land between the tributaries dries up. As she explained, watershed areas don’t generally control vital functions. They die more quickly than more important regions, but also spring back faster after damage has occurred. Ain’t evolution grand?But why is this natural selection in action? I'm glad you asked. What would aid your survival if you experienced a sudden loss of blood or blood pressure to your brain--say a sabertooth chomping down on your skull? It looks like you're about to be sabertooth cat chow, but in the nick of time, members of your tribe come to your rescue. You've lost a lot of blood, but you're still alive. So far, you're brain has sacrificed the areas that will cause the least amount of long-term damage. You won't be the same for some time, but you will eventually recover. Fortunately for you, humans instinctively help others who need assistance (especially if they are kin), as indicated by some of the crippled skeletons of early humans and our close cousins, the unfairly stereotyped Neandertals. Now it's only a matter of time before you recover enough to once again be a productive member of the clan.
Substitute sepsis for the sabertooth, strokes for the cranial trauma, and writer for the productive member of society part, and you have what happened to me.
What evolution gave my survival in general is humanity so intelligent in the aggregate that it could develop medicine and technology advanced enough to maintain my life while my other bodily systems recovered according to their evolved survival mechanisms. An early modern human in my situation would have indeed been toast.
As I mentioned in the article, dialysis and a respirator gave my kidneys and lungs time to begin healing so that they could eventually start working again. Later, the nursing home permitted my body time to recover enough to begin walking somewhat. Still, the evolution of care in our society, namely our healthcare "system," meant that Kaiser handed me my walking papers when I could still barely walk.
Further proof that evolution is not unidirectional.