Eight Animals That Break the Rules of Biology
A shark that may live 400 years, a frog that freezes solid, a mammal that barely ages, and a fish that can fill a bucket with slime in seconds.
Biology has some firm expectations — that animals age, that vertebrates need a backbone, that freezing kills. These eight ignore at least one of them.
1. The Greenland shark, which may reach 400
Radiocarbon dating of the lenses of their eyes put one Greenland shark at somewhere around 400 years old, and the method suggests they do not reach breeding age until about 150. The oldest individuals alive now were swimming before Newton published.
2. The naked mole rat, which barely ages
Nearly everything's chance of dying rises steeply with age. The naked mole rat's does not seem to, which breaks a rule thought to apply to all mammals. They also get cancer vanishingly rarely, survive with almost no oxygen for long stretches, and feel no pain from acid or chilli.
3. The axolotl, which regrows limbs and never grows up
Axolotls regrow legs, tails, jaws, parts of the eye and even parts of the brain, without scarring. They also never leave their larval form — they keep their feathery gills and stay in the water for life, breeding as what is effectively an overgrown tadpole.
4. The wood frog, which freezes solid
Through an Alaskan winter a wood frog can let roughly two-thirds of its body water turn to ice. Its heart stops, its breathing stops, its brain activity stops. It floods its cells with glucose as antifreeze, and in spring it thaws and hops off.
5. The hagfish, which has a skull but no backbone
Hagfish have a skull and no vertebrae, which puts them awkwardly at the root of the vertebrate family tree. Threatened, they release a protein that turns litres of seawater into slime in seconds — enough to choke a shark's gills and make it let go.
6. Bdelloid rotifers, which gave up sex millions of years ago
These microscopic animals appear to have reproduced without males for tens of millions of years, which theory says should be a dead end. They also dry out completely and come back, and in 2021 Russian researchers revived individuals from Siberian permafrost dated to around 24,000 years old.
7. The horned lizard, which squirts blood from its eyes
Cornered by a coyote or a fox, some horned lizards raise the blood pressure around their eyes until vessels burst and fire a jet of blood up to a metre or so. It tastes foul to canines, which is the point.
8. The platypus, which breaks four rules at once
It is a mammal that lays eggs. It has no stomach to speak of. The male has a venomous spur on its hind leg, painful enough that morphine is reportedly little help. And it hunts with its eyes shut, finding prey by the faint electrical signals of their muscles. When the first specimen reached London, scientists assumed it was a hoax stitched together from other animals.
For more of this sort of thing, see twelve animal facts that sound completely made up.