How are scientists able to say that a random species is extinct? Did they have to look everywhere?
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Scientists are actually proven wrong from time to time when they think a species is extinct only to find some tiny pocket of the planet in which it still exists.
They check not only for the animals, but for feces, bones, and other traces and pieces of evidence that the animal is known to leave behind. They also monitor reports by people living in near the habitat to see whether there are any sightings, as well as populations of known prey.
Cannot look everywhere for obvious reasons. They have to do a statistical evaluation. At some point, the odds of the thing still existing when never seen despite being sought in all the places it likes to live, does lead to a pretty good likelihood that the poor lifeform is no longer in existence. And yet, there is an occasional find of something thought to be extinct for quite some time.
Scientists and hobbyists in many places around the world track and report populations of animals. For example, you can track the population of local birds in the US through apps on your phone.
Eventually people stop reporting sightings of a specific plant or animal and they are considered extinct after enough time has gone by. The system isn’t perfect and some animals do reappear, but for the most part once an animal is extinct it is really gone
It’s pretty easy to guess these days because while we can’t track each individual animal, it’s pretty easy to track the loss of their habitats, which is the real driver of extinction. If the forest is gone, the critter that lived in it is likely gone with it.
When it comes to declaring a negative (that something is not true, does not exist, no longer exists, etc) most scientific conclusions are about looking long and in depth enough to say with confidence that we’ve investigated every reasonable possibility and can draw the conclusion that it is *overwhelmingly likely* that things are the way we’re concluding.
Confirming the positive is a lot easier. You know you’re 100% correct the first time you see a giraffe that giraffes are not currently extinct. Not finding a giraffe doesn’t mean you can confidently say it’s extinct just on its own, but eventually when you look long and thoroughly enough to say you’ve checked every place a giraffe could plausibly survive and found no evidence of one, you can say giraffes are likely enough to be extinct that you can treat it as they are.
It’s impossible to prove a negative. So we assume it’s true until proven otherwise. That is, we assume a species is extinct so long as we have no proof otherwise.
So if we found a species, but all the ones we were tracking died, we will assume it’s extinct until we find a new one.
Like all of science, we have to assume the universe is how we perceive it until proven otherwise.
What a good question. Love this. Check out the [Coelacanth](https://en.wikipedia.org/wiki/Coelacanth) discovery.
Short answer is no they don’t. It’s an assumption made when they can’t find evidence of modern encounters.
“Extinct” species are occasionally rediscovered in the wild. There’s also the long-standing issue that the distinction of what constitutes a “species” is more or less arbitrary.
e.g. historically one of the main tests for a “species” is genetic isolation, but to make the example gene-flow between domesticated dogs, Coyotes, and Wolves is quite free to the point that almost all wild coyotes/wolves have some mixed fraction of ancestry between the two species. Morphological distinctions to define species are also arbitrarily applied, to use the dog example again, the gap between a Labrador and a French Bulldog is bigger than many species gaps.
Evidence of absence is evidence. If we know a species makes nests in certain areas and they don’t anymore, then we don’t find the species there anymore. The lack of evidence for it’s continued existence is a type of evidence that helps form our conclusions.
Like if the police want to make sure nobody is in a house, they may stake it out. If nobody comes and goes from the house for a few weeks, they can be reasonably confident that the lack of evidence suggesting a presence means there isn’t a presence.
Of course, should a species be rediscovered because it was forced to relocate deep into say, the rainforest, it’s status would simply change when we got that new information proving they aren’t all gone.
Extinct isn’t so much a declaration of what is, as much as what we can currently find. Extinct means, “We done looked and didn’t see hide nor hair of it. Fuck knows.”
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