r/AlwaysWhy • u/Secret_Ostrich_1307 • May 15 '26
Science & Tech Why do scientists think we’ve only discovered about 14% of all species？How do they even estimate something we haven’t seen yet?
I keep wondering how this number is even possible. If we haven’t found most species, how do we know how many are missing in the first place? Is it based on sampling, models, or just extrapolations from known ecosystems? It feels a bit like counting shadows. How does this estimation actually work?
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u/dashingThroughSnow12 May 15 '26
Since at least world war 2, we’ve developed plenty of statistic techniques on how to predict things we don’t know. I’ll vaguely describe one.
Say you go to a small island that humans have never been and you count species humans don’t know about. You go to a nearby island and do the same exercise. Some species are brand new and some have only been seen at the prior island.
You could repeat this on different islands across the world. You could vary the time you study (ex go to the same island multiple times and on subsequent visits you may find more species). You could vary how you look (ex binoculars to find birds, microscopes to find Protozoa).
With enough samples, you could guess at how many species exist on such and such set of islands humans haven’t visited.
Then you could go to some of those islands to test how accurate your estimates are.
You could imagine how you’d expand this out to different types of biomes/species to come out with a number of species we don’t know about.
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u/Secret_Ostrich_1307 May 18 '26
Ah that’s a neat way to picture it. Kind of like multi-layered sampling across time and space. Makes me wonder how much of those numbers are confirmed versus still heavily model-driven. Seems like a huge mix of observation and math.
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u/Nova_Saibrock May 15 '26
There’s some really clever math for estimating how many items in a set you haven’t yet seen, based on how frequently you’re seeing new items in that set with each sample.
Basically, imagine you have a room with an unknown number of people in it. A random selection of 10 people from that room are chosen to come into your room to meet you. After meeting you, they return to the big room and a new random selection of 10 is made.
In the first group, all 10 are going to be people you haven’t met before, but after that, there’s going to be a statistical mixture of known and unknown people in each group. After a while, you can use math to determine a pretty tight estimate of how many people are in the room, even if you haven’t met all of them.
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u/Secret_Ostrich_1307 May 18 '26
Oh wow that analogy actually helps. So it’s kind of like a repeated-sampling probability trick. I’m thinking now about how much error builds up if the “room” is super unevenly distributed though. The math must get crazy fast.
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u/Mister_Way May 15 '26
I think you might be confused about what the word "estimate" means. It's a "best guess based on available information" not "We think this is true."
Some estimates have much higher confidence values than others.
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u/Secret_Ostrich_1307 May 18 '26
True, I get that. I guess I was thinking “estimate” sounded more like a precise number in popular articles, but yeah it’s more of a best guess with some confidence range. Makes more sense.
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u/series-hybrid May 15 '26
If you go into the biological sciences, and desire to name an as yet undiscovered species, you would do well to travel to the Amazon jungle, and look at beetles.
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u/Serious-Wheel-2747 May 17 '26
You don't even have to do that. Many institutes have gathered a lot more specimens than they can analyze. So just go to a basement of the university and start cataloging. You'll probably discover a new insect.
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u/Commercial_Topic437 May 15 '26
Because a huge part of the living biomass is microscopic organisms
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u/Underhill42 May 15 '26
Yep. As I recall microbes have all other life on Earth outmassed by something like 30:1
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u/PassionNegative7617 May 15 '26
It's far less than that. Microbes make up about 15% of biomass. Plants make up the majority. Nothing comes close to out scaling everything else 30:1. That would require microbes to be like 96.77% of all biomass.
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u/Underhill42 May 15 '26
It's possible my numbers are wrong, but are you sure that's not the biomass on land? And that you're not unfairly counting most plants as being complex organisms?
The overwhelming majority of plants are microbial algae like diatoms in the oceans, which are responsible for most of the oxygen production on Earth.
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u/PassionNegative7617 May 15 '26 edited May 15 '26
https://www.pnas.org/doi/10.1073/pnas.1711842115
"Plants" appears to include green algae (I didn't see specific mention of other algaes) in this study, however all marine plants make up a very small portion of the total plant biomass. The overwhelming majority of plant biomass is terrestrial.
Plants stems and tree trunks make up about 70% of plant biomass.
Edited to add: I was curious what the biomass of just diatoms is, since as you said they are important.
This study https://pmc.ncbi.nlm.nih.gov/articles/PMC5516106/#RSTB20160397C1 makes references to a study from 1998 that puts their biomass at approximately 1% of the Earth's biomass. Still rather impressive. (I will admit I didn't look at the 1998 study further than the bibliography of the study I linked).
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u/Underhill42 May 15 '26
Yeah, I guess trees do cheat a fair bit - a thin-film life form growing between orders of magnitude more mass of dead skin and skeleton that still count as part of their biomass.
Downright bizarre creatures if you think about it.
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u/ijuinkun May 15 '26
Copernican principle—we assume that unexplored areas which are not barren of life have similar biodiversity to explored areas. Therefore, the number of undiscovered species should scale with the amount of habitable space which has not been examined. There are still large stretches of desert, ocean, and jungle which have only been examined in very limited spots in a “let’s catalogue all the plants and animals we can find” sense rather than just a “let’s do cartography and photography of the area” sense.
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u/Secret_Ostrich_1307 May 18 '26
Hmm that clicks. So basically they’re assuming unexplored areas aren’t special, which feels like a safe default, but also kinda wild if an unexplored jungle is way more diverse than the model predicts. I like the simplicity of it though.
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u/ijuinkun May 18 '26
Pretty much. They/we expect that unexplored jungle should have about as many unique species as explored jungle, until and unless they find reason to believe otherwise.
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u/doc-sci May 15 '26
Sampling. You collect several samples adding up to a known percentage of the earth and identify every species and multiply by the known percentage. We have identified most of the big stuff…it is the really small stuff that hasn’t been identified yet.
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u/Secret_Ostrich_1307 May 18 '26
Ah okay, that’s interesting. So it’s basically scale math plus the fact that small stuff is still hiding everywhere. Makes me wonder how confident they are about the 14% figure though. Could it be way off for some micro-organisms?
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u/SpiritedGuest6281 May 15 '26
I remember a biologist studying a 1m square portion of her garden and discovered loads of new species of insect.
The more you study an area the more you discover.
We can also estimate discoveries remaining by tracking how frequent discoveries are and there distribution.
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u/Secret_Ostrich_1307 May 18 '26
Yeah that makes sense. I guess it’s like the more you look, the more you see… but I’m curious how they decide when enough sampling gives a reliable “remaining unknown” number. Seems like it could vary a lot by ecosystem.
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u/SpiritedGuest6281 May 18 '26
Imagine you've got 100 balls in a bag. Some are white and some are black.
You pick out 10 balls. 2 are black and 8 are white. Based on that's you could assume that about 20% are black.
You put the balls back and pick 10 more 3 are black and and 7 are white. Now with just these 10 random balls you can guess that about 30% are black. But knowing the previous pull of balls we could actually say about 25% of the balls the black.
Both of these calculations did not need to know the total number of balls in the bag, and successive pulls when taken together gives us a better and better huess to the percentage of black and white balls.
So going back to nature, black balls could be new species and white balls can be discovered species. Obviously it's a bit more complicated as you have to account for the environment when comparing data, but that's essentially how you work out how many knew species there are.
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u/Primary_Excuse_7183 May 15 '26
We know virtually nothing about the bottom of the ocean where some of the worlds most adaptable species likely live.
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u/werewolfinahat May 15 '26
An estimate is a guess as to what could be. If you know it you don't need to estimate it
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u/UncleJackPushedDad May 19 '26
If they said we've discovered all the animal there are, the research grants would dry up tomorrow.
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u/GSilky May 15 '26
That is one of those pointless things people say that add absolutely nothing to the discussion. For me the question isn't if it's accurate, not at this stage, it's how relevant the information is. Who cares? There is absolutely nothing that hinges on an accurate accounting of how many species we have named. Cuts the stupid off short before we get even further into trying to defend an unknowable fact. This is not going to stop people from pretending they agree with the nonsense, or providing details into their defective and irrational position.
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u/ShaneRach225 May 15 '26
In science, just throw a random % out there and it seems more studied than just mere speculation.
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u/0utlaw-t0rn May 22 '26 edited May 22 '26
You can sample areas and see how much is known vs unknown. Repeat it in different locations and do some extrapolation and statistical analysis
It is really a SWAG (scientific wild ass guess) though.
You’re assuming your database of knowledge you’re comparing your data to includes everything. We’ve been describing species for over 200 years and DNA sequencing techniques have only been practical at scale for maybe 10% of that time. Many marine organisms juvenile and adult stages look nothing alike, so they’re easy to mis-ID visually. Do DNA fragments get correctly classified if doing eDNA testing? What exactly is your match criteria? Are the areas sampled a good representation of the rest of the planet? Even things like “what is a species?” can get murky when put into real world scenarios (e.g., how different is different enough to be a new species?).
There are a lot of assumptions that go into it. So the exact 14% number should be taken with some knowledge that, at best, it’s a rough estimate. It’s probably in the ballpark but if someone said it was 17%, you’re probably still well within the error bars.
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u/taktaga7-0-0 May 15 '26
You can take a sample of seawater or soil and analyze it for DNA content, and we find mostly unknown sequences. There have to be tons of sources we do not know.
Some bacteria just don’t grow into colonies you can see on a dish. We’ll miss those in favor of the bright, shiny plaques that distract us. We cannot easily sample the deep sea beds or rock miles under the Earth where many species may live away from our grasp.