How do we know that a species has definitely gone extinct (as opposed to just being extremely rare/elusive)?
In: Biology
Well, we don’t. In science “definite” answers are few and far between. However, there isn’t much difference between having 10 animals and having 0 animals. That population of 10 is too small to preserve genetic diversity and survive in the long run.
We can’t be sure, that’s why some species “come back to life” after years of supposed extinction.
>*Evolutionary biology isn’t always a perfect science. Researchers themselves have even given a name to species that they mistakenly believed to be extinct. Named for the legendary Lazarus who came back from the dead, Lazarus species are the wide variety of animals that have seemed to do the same thing. They’ve gone from officially not existing to existing once again. It’d be miraculous if they hadn’t actually been alive all along. When these creatures had gone unseen for years upon years, scientists just wrote them off. When they reappeared (sometimes more than 100 years after last being seen!) they totally shocked the world. We can only hope that some of today’s endangered and extinct species will pleasantly surprise us with Lazarus status in the future.*
[Whole article](https://www.thetravel.com/14-creatures-scientists-thought-were-extinct-but-arent-11-gone-forever/)
There is a show on animal planet called ‘extinct or alive’ which is just a guy going to find animals that have supposedly went extinct. So it’s really j7st a guess.
Take the Northern White Rhino. It is big enough that we know exactly how many are left: two females, neither of whom could carry a calf to term, no living male. It’s extinct, with the caveat that scientists MIGHT be able to produce an embryo from frozen sperm and eggs that MIGHT implant in a southern white rhino, and MAYBE carry to term. But for all intents and purposes, it’s gone.
Littler creatures can be deemed to be gone if X number of years go by and none have been reported, and it is known to have a limited range. We know for example that orangutans have a very small range, constantly being lost to palm plantations. There will still be a population in captivity when the last wild ones are gone, but probably not enough to provide adequate genetic diversity.
We don’t. Science is based on the weight of the evidence forming a consensus in publications. If we haven’t seen something in 50 years, sure we’ll say it’s extinct. Then we’ll turn right around and say it isn’t if some are found.
Once the numbers in viable remaining habitat fall below the minimum needed for genetic diversity to reproduce to a sustainable population is basically extinct.
Even if a few breeding pairs remain, the inbreeding will eventually make them sterile,…or vulnerable to disease, or predators.
As everyone else has said, we don’t. One of the poster child cases for captive breeding programs is the [black footed ferret](https://en.m.wikipedia.org/wiki/Black-footed_ferret) which was thought to be extinct until a population of 18 was discovered. Now the population is over 1000 in multiple locations to help protect them from complete extinction.
More recently, [the widely thought extinct Vietnamese mouse deer](https://www.cnn.com/2019/11/11/asia/mouse-deer-vietnam-chevrotain-rediscovered-scn/index.html) was captured on game cameras by biologists after having not seen it for 30 years.
I know that when you’re investigating how many different species there are in an enviroment, you can use [rarefaction](https://en.m.wikipedia.org/wiki/Rarefaction_(ecology)) in order to determine whether or not you have sampled enough of the enviroment to get an accurate look of that area’s richness. I’m not an expert, but I would imagine that a similar thing can be done with a specific species in order to tell how likely it is to be extinct
Basically, when we don’t see any members of the species for a while. They could be extinct, or they could be good at hiding. The Zanzibar leopard is an example that is or was thought to be extinct, but there is some evidence to suggest they may still be alive and just really good at living around humans without being seen.
Quick shout out to ‘Extinct or Alive’, a show on Animal Planet that shows this exact question and in my opinion is really well done.
Latest Answers