I’ve been thinking quite a bit lately about the fragility of life (for pretty straightforward reasons – see my previous post). I’ve also been thinking a bit about the sheer improbability of being alive.
Here’s the most dramatic personal example I can come up with of what I mean:
Members of one of the families from whom I’m descended, specifically my father’s mother’s mother’s family, emigrated from Ireland to Virginia sometime in the late 1600s, establishing a nuclear family household there. Sometime shortly thereafter, this household was wiped out in a raid by local Native Americans, except for an infant son, my ancestor, who was left alive, found by other members of the Euro-American community and taken in.
Whatever their particular grievance, whether against the specific family or against Europeans in general moving into the area, and there were likely plenty of grievances to choose from, had this particular raiding party chosen to completely finish off the household, the world today would be little if any different in any big way, but I wouldn’t be here. Likewise if the child had died of starvation or exposure before being found and taken into another household. Even if the Native Americans in question had chosen to adopt the child into their own community, a not unlikely scenario in the circumstances, that child might have had descendants alive today, but I wouldn’t be here.
In many more mundane ways, my mere existence depends upon a highly improbable concatenation of little decisions having been made by untold numbers of people. Upon having his job as an engraver transferred from a paper plant in upstate New York to a new plant outside of Pensacola, Florida in the early 1950s, had my grandfather and grandmother decided that job or not job, they weren’t moving to muggy Northwest Florida in those pre-air-conditioned Jim-Crow-era days, then my mother and my father would have been around, but never met, resulting in no me.
Given that the human species did evolve, and given that the Neolithic transition occurred (both improbable to varying degrees beforehand), I don’t find it particularly improbable that there are people around now, or even that there are 6 billion people around now, but each of those 6 billion people, as individuals, is the result of an astronomically improbable chain of prior human actions and decisions.
Perhaps not the most profound or original thought (it is, after all, a basic premise of the movie Back to the Future), but something I’ve been thinking about lately.
Showing posts with label probability. Show all posts
Showing posts with label probability. Show all posts
Friday, June 20, 2008
Thursday, October 11, 2007
Possible, Plausible, Probable, Proven
I wrote this post for the blog I write for a course, Peoples and Cultures of the World, and originally intended it primarily for a student audience. However, I think it fits well here as well.
“Possible,” “Plausible,” “Probable,” and “Proven” are terms used to indicate rough degrees of statistical probability of something happening or some proposition being true. (My use of the “probable” here reflects the vernacular. When we say that something is probably true, we don’t mean that it has just any level of statistical probability, but specifically that it is quite likely to be true.)
The terms do reflect an ascending order of probability (and a nested one – anything that is plausible is also possible; anything proven is also probable, plausible, and possible), though not in a numerically precise way. They represent a sort of qualitative statistics. When we can realistically indicate precise probabilities, that is obviously a useful thing, but even a rough sense of degree of probability is far more useful than no such sense at all.
Errors in thinking arise whenever we jump up this ascending ladder of probability without evidence, or without sufficient evidence (though admittedly, knowing what counts as sufficient evidence is always tricky business). Just because it’s possible that Bigfoot could be running around the Pacific Northwest or elsewhere doesn’t make it plausible, much less probable or proven.
The Possible
Saying that something is possible simply means that it does not violate the basic laws of logic. In the realm of empirical scholarship, one could also add that it does not violate basic physical laws, that something is both logically and physically possible.
The existence of Bigfoot is possible – it violates no logical or physical rules, but given the overwhelming lack of evidence, there’s no reason to regard Bigfoot’s existence as having anything but the lowest degree of probability. The same goes for claims about extraterrestrial influence in building the Egyptian Pyramids or Stonehenge or the Nazca Lines.
The Plausible
To say that something is plausible is to indicate that it has a higher probability than the merely possible - it is believable, it makes sense. But claims that are merely plausible (that is, that are not also probable) lack the evidence to be taken as having a high degree of probability of truth.
Thor Heyerdahl’s famous voyage on his Kon-Tiki raft from South America to Polynesia certainly proved that it was possible for people to have traveled from the one place to the other using fairly simple watercraft. He even made it plausible that Polynesians could have made voyages to South America, but his voyage alone did nothing to make such notions probable, much less proven. (See this news article from this past summer from Live Science on both Heyerdahl and more recent evidence of Polynesian voyaging to South America that I’ll discuss below.)
An article I encountered this morning on Science Daily, “Early Apes Walked Upright 15 Million Years Earlier Than Previously Thought, Evolutionary Biologist Argues,” makes what I’d consider a plausible claim. “An extraordinary advance in human origins research reveals evidence of the emergence of the upright human body plan over 15 million years earlier than most experts have believed. More dramatically, the study confirms preliminary evidence that many early hominoid apes were most likely upright bipedal walkers sharing the basic body form of modern humans.” So long as there’s evidence, it’s plausible that hominoid bipedalism might be much older than previously thought, but this is an extraordinary claim, and as such requires not simply a single study with good evidence, but a body of good evidence in order to be taken as probable, much less proven by many scholars.
The Probable and the Proven
To say that something is probable means that it is very likely to be the case, that it has a high degree of probability. To refer to something as proven implies that a claim is definitely true, though given the ever present possibilities of faulty observation (even systematic faulty observation), partial understanding or misunderstanding of empirical materials, nothing (at least outside the abstract realm of pure logic and mathematics) is ever demonstrated to be completely and irrevocably true. Instead, to say something is proven is really to say that it has such a high degree of probability of truth that we can pragmatically assume it to be true (though ideally keeping an open mind towards potential counter-evidence).
When Pizarro and his Spanish soldiers reached Peru, they encountered chickens (an Old World domesticated bird) already there. There are at least a couple ways the chickens could have arrived in the New World – they could have been brought by the very earliest European voyages to the Caribbean and Central America in the 1490s and 1500s and very rapidly diffused southward; or they could have been brought by Polynesian voyagers to South America (the only problem there being, at least until now, a lack of evidence of such Polynesian voyages having actually occurred).
When Captain Cook and other explorers encountered a variety of Polynesian islands in the late 18th century, they encountered sweet potatoes, among other crops being grown. As I understand it, there’s no definite evidence of how these South American plants reached Polynesia. They could have been brought by the Spanish to the Philippines early in the Colonial period and diffused from there to Indonesia, Melanesia, and ultimately Polynesia, or they could have been brought back from South America by Polynesians themselves.
New evidence released this past summer addresses this situation. Chicken bones were recovered in Peru that, according to carbon dating, predate Spanish voyages to the Americas by about a century. Further, genetic evidence links the chicken bones to Polynesian varieties of chickens. (See the previously cited article from Live Science and also this article from New Scientist.)
If the carbon dating and DNA evidence hold up (always an important consideration with important new claims), this proves that Polynesian chickens reached Peru at least on one occasion. Given the highly implausible nature of chickens making the voyage on their own (though not logically impossible), it makes highly probable if not proving claims that Polynesians came to South America on at least one occasion. It makes highly probable that the chickens seen by Pizarro were of Polynesian stock as well. I’d even go so far as to say that this new evidence makes probable the idea that Polynesians brought sweet potatoes back from South America directly, though the distinction between plausible and probable is a bit more ambiguous in this case.
“Possible,” “Plausible,” “Probable,” and “Proven” are terms used to indicate rough degrees of statistical probability of something happening or some proposition being true. (My use of the “probable” here reflects the vernacular. When we say that something is probably true, we don’t mean that it has just any level of statistical probability, but specifically that it is quite likely to be true.)
The terms do reflect an ascending order of probability (and a nested one – anything that is plausible is also possible; anything proven is also probable, plausible, and possible), though not in a numerically precise way. They represent a sort of qualitative statistics. When we can realistically indicate precise probabilities, that is obviously a useful thing, but even a rough sense of degree of probability is far more useful than no such sense at all.
Errors in thinking arise whenever we jump up this ascending ladder of probability without evidence, or without sufficient evidence (though admittedly, knowing what counts as sufficient evidence is always tricky business). Just because it’s possible that Bigfoot could be running around the Pacific Northwest or elsewhere doesn’t make it plausible, much less probable or proven.
The Possible
Saying that something is possible simply means that it does not violate the basic laws of logic. In the realm of empirical scholarship, one could also add that it does not violate basic physical laws, that something is both logically and physically possible.
The existence of Bigfoot is possible – it violates no logical or physical rules, but given the overwhelming lack of evidence, there’s no reason to regard Bigfoot’s existence as having anything but the lowest degree of probability. The same goes for claims about extraterrestrial influence in building the Egyptian Pyramids or Stonehenge or the Nazca Lines.
The Plausible
To say that something is plausible is to indicate that it has a higher probability than the merely possible - it is believable, it makes sense. But claims that are merely plausible (that is, that are not also probable) lack the evidence to be taken as having a high degree of probability of truth.
Thor Heyerdahl’s famous voyage on his Kon-Tiki raft from South America to Polynesia certainly proved that it was possible for people to have traveled from the one place to the other using fairly simple watercraft. He even made it plausible that Polynesians could have made voyages to South America, but his voyage alone did nothing to make such notions probable, much less proven. (See this news article from this past summer from Live Science on both Heyerdahl and more recent evidence of Polynesian voyaging to South America that I’ll discuss below.)
An article I encountered this morning on Science Daily, “Early Apes Walked Upright 15 Million Years Earlier Than Previously Thought, Evolutionary Biologist Argues,” makes what I’d consider a plausible claim. “An extraordinary advance in human origins research reveals evidence of the emergence of the upright human body plan over 15 million years earlier than most experts have believed. More dramatically, the study confirms preliminary evidence that many early hominoid apes were most likely upright bipedal walkers sharing the basic body form of modern humans.” So long as there’s evidence, it’s plausible that hominoid bipedalism might be much older than previously thought, but this is an extraordinary claim, and as such requires not simply a single study with good evidence, but a body of good evidence in order to be taken as probable, much less proven by many scholars.
The Probable and the Proven
To say that something is probable means that it is very likely to be the case, that it has a high degree of probability. To refer to something as proven implies that a claim is definitely true, though given the ever present possibilities of faulty observation (even systematic faulty observation), partial understanding or misunderstanding of empirical materials, nothing (at least outside the abstract realm of pure logic and mathematics) is ever demonstrated to be completely and irrevocably true. Instead, to say something is proven is really to say that it has such a high degree of probability of truth that we can pragmatically assume it to be true (though ideally keeping an open mind towards potential counter-evidence).
When Pizarro and his Spanish soldiers reached Peru, they encountered chickens (an Old World domesticated bird) already there. There are at least a couple ways the chickens could have arrived in the New World – they could have been brought by the very earliest European voyages to the Caribbean and Central America in the 1490s and 1500s and very rapidly diffused southward; or they could have been brought by Polynesian voyagers to South America (the only problem there being, at least until now, a lack of evidence of such Polynesian voyages having actually occurred).
When Captain Cook and other explorers encountered a variety of Polynesian islands in the late 18th century, they encountered sweet potatoes, among other crops being grown. As I understand it, there’s no definite evidence of how these South American plants reached Polynesia. They could have been brought by the Spanish to the Philippines early in the Colonial period and diffused from there to Indonesia, Melanesia, and ultimately Polynesia, or they could have been brought back from South America by Polynesians themselves.
New evidence released this past summer addresses this situation. Chicken bones were recovered in Peru that, according to carbon dating, predate Spanish voyages to the Americas by about a century. Further, genetic evidence links the chicken bones to Polynesian varieties of chickens. (See the previously cited article from Live Science and also this article from New Scientist.)
If the carbon dating and DNA evidence hold up (always an important consideration with important new claims), this proves that Polynesian chickens reached Peru at least on one occasion. Given the highly implausible nature of chickens making the voyage on their own (though not logically impossible), it makes highly probable if not proving claims that Polynesians came to South America on at least one occasion. It makes highly probable that the chickens seen by Pizarro were of Polynesian stock as well. I’d even go so far as to say that this new evidence makes probable the idea that Polynesians brought sweet potatoes back from South America directly, though the distinction between plausible and probable is a bit more ambiguous in this case.
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