Which Species Will Survive the Longest?

Which Species Will Survive the Longest?

We’re constantly seeing headlines warning of potential global disaster. And, as if the wild weather and fluctuating temperatures aren’t a big enough clue, increasing numbers of studies claim that we’re currently in the middle of the world’s sixth mass extinction event – the Holocene extinction. And it’s mainly our own doing. Biodiversity is declining at an alarming rate due to overfishing, all types of pollution and deforestation… And despite many world leaders attempting to plug the geyser that is our current environmental predicament, some scientists speculate that the point of no return is quickly and ruthlessly approaching.

The good news is that the world will keep spinning. Our planet has gone through five previous mass extinction events before, the biggest of which being the Permian-Triassic event – which killed around 90% of all species. But that was around 252 million years ago, and Earth’s ecology has recovered enough to stage two more major extinction events in the years since. It’s clear that our planet will survive. But what else will?

Various species do (and have) withstood extinction events already, although experts are generally puzzled as to why. Many point to the idea of a ‘stable food web’ – a complex ‘who-eats-who?’ set-up, sometimes simply referred to as the ‘food chain’. Like a well-built Jenga tower, a stable food web can survive the odd displacement. And a sturdy-enough web can endure even massive holes in its structure, allowing for the continued survival of its remaining contributors. If an animal or species is part of such a web, and they’re not killed off by the extinction event itself, then they might stand a chance.

Others have pointed to more physical and recognisable traits as being responsible for the survival of specific creatures. Some species bury underground, gifting them protection against dangers on the Earth’s surface. Others are able to withstand massive shifts in climate and temperature. There are also those that have more flexible diets, allowing for easier survival when food becomes scarce. And finally, some species breed faster which, while it doesn’t bring individual safety, all-but ensures their collective continued survival. Another popular theory posits that a species’ continuity depends on its ability not only to withstand changing climates, but to physically uproot and colonize a new location whenever local conditions become too disagreeable. For example, the wasp spider can use its silk threads to float on the wind, allowing it to travel vast distances in short amounts of time – giving it a greater chance of staying safe.

Clearly, there are lots of reasons why various creatures could potentially survive an extinction event. However, we humans are not all that likely to survive at all. History has shown that it’s predominantly the smallest species which fare best, and despite our relative smallness next to some other animals, we are nowhere near small enough to ride out an extinction. Paleontologists have studied the Cretaceous-Paleogene event, AKA the dinosaur extinction, and discovered that it wiped out most species larger than the common dog. In short, we would likely be doomed should a similar catastrophe strike right now.

But then there’s the Lilliput effect to contend with. A pretty fascinating concept, it describes the occurrence of physically smaller body-sizes in species that have survived major extinctions. A 2015 study by Lauren Sallan of the University of Pennsylvania looked at over 1,000 fossilized animals that survived an ‘end of all things’ type event. It found that these animals were smaller than their ancestors before them. So, sharks that previously measured in yards were now mere inches long, while previously dog-sized creatures became cat-sized to survive. Anything that didn’t shrink during an extinction event, including things that actually got bigger, swiftly died off. Meanwhile, naturally small vertebrates had an evolutionary advantage that allowed them not only to survive, but to recolonize the now-empty world.

The reasons for the apparent vulnerability of larger species are many. For one, larger-bodied animals tend to have larger generation gaps. Again, take humans: We have a large, years-long gap between childhood and maturity, whereas other (typically smaller) species mature within a matter of days or weeks. This means we are more susceptible to extinction, as we’re unable to sustain swift continuation. Another factor is the already small population sizes for larger animals. While not such a problem for humans (which number in the billions) for something like the American bison population (which is only 500,000-strong) one world-changing event could spell the end of their dwindling species. Finally, and perhaps most obviously, the larger the animal the more food and energy it needs. Naturally, after (or amidst) a mass extinction, the smaller sorts that require less day-to-day sustenance are more likely to do well.

So, it’s looking good for small-bodied organisms and animals – relatively speaking. But which specific species can feel especially hopeful?

One of the absolute toughest creatures on Earth is the lingula. It’s a sea bed-bound brachiopod with a shell on both halves of its body, and a long, white, fleshly extension called the stalk which helps keep it anchored to the ground. The lingula has been around since the Cambrian Period, at least 485 million years ago. Its incredible hardiness can be attributed to its small size (naturally), but also its burrowing behaviours and simple feeding habits. However it does it, the lingula predates even the Earth’s very first extinction event which began roughly 450 million years ago – meaning that it has survived all five mass extinctions so far. Would you bet against it surviving the next few as well?

Another seriously sturdy organism is the tardigrade, more commonly known as the water bear. These are tiny, eight-legged micro-animals that can be found almost anywhere on Earth, including on the ocean floor, on bleak mountaintops, and inside volcanoes. The tardigrade also dates to the Cambrian period, and its survival has been attributed to its sheer resilience. They can withstand literally anything; extreme temperatures, immense pressure, an immense lack of pressure, the vacuum of space, prolonged dehydration, radiation exposure… The unlikely list goes on and on.

But for even older organisms, we should head back into the water itself. The humble sponge may have first emerged 700 million years ago. It actually helped oxygenate the water, which in turn gave rise to more aquatic species, like the jellyfish. To get real technical, bacteria (in its many, many forms) is the oldest lifeform on Earth, with unicellular microorganisms appearing roughly four billion years ago. So, whatever happens, the most basic building blocks for life aren’t likely to leave Earth anytime soon.

Ultimately, it is extremely difficult to predict specifically which species will survive the longest. There are too many variables to take into account, and unique conditions can create different results. The environmental effects of a massive asteroid strike just don’t match with the drawn-out effects of global warming. And the potential destruction of nuclear war brings a completely different challenge… But our biggest clues can be found through history, and on either side of previous mass extinction events. Smaller species have a much higher chance of survival in general, although the Lilliput effect could serve to preserve some larger beings.

Those wily water bears could be the leading contender for Earth’s longest-living species, though. Because they can survive pretty much anything – from widespread drought to relentless flooding, increased temperatures, decreased temperatures, and a nuclear apocalypse. Failing that, it’s back to bacteria for Planet Earth… But that really is the worst-case scenario.