Before humans made their fortunes, the mammoth, a hair-clad behemoth, was probably the most widely distributed mammal on Earth, shuttling between Eurasia and North America, arguably the most important and influential mammal on Earth at the time.
You may have heard that about 10,000 years ago, before the end of the last ice age, these epochal species went extinct without waiting for dawn.
However, this was not the case, and while the global mammoth was heading for extinction, a small group of the species survived. They entered Wrangel Island 200 kilometers away from the Siberian coastline at the time of the Ice Age, and then they were trapped on it with the end of the Ice Age.
In the "post-mammoth" era, this group of mammoths trapped on Wrangel Island multiplied until about 3700 years ago before they really became extinct, when the Chinese Yin Shang had just overthrown the Xia Dynasty and truly opened the era of writing history.
If a human had entered Wrangel Island at this time, it might have recorded this group of interesting animals, but humans did not have enough technology to enter the island until 3,000 years ago, when all mammoths were extinct.
However, to the surprise of modern paleontological researchers, the mammoths of Wrangel Island are far from the mammoths we are familiar with, they can only grow to about 1.8 meters and weigh only about 2 tons, while the mammoths of the mainland can grow to 3.2 meters and weigh more than 6 tons.
Pictured: Pygmy mammoth on Wrangel Island
It seems that it only took 5,000 years for the mammoths trapped on the island to slim themselves into "miniature mammoths."
For biological evolution, 5,000 years is only a blink of an eye, so what exactly makes mammoths change so dramatically in such a short period of time?
Island rules: big animals get smaller, small animals get bigger!
You may have heard of Komodo monitor lizards before, which can grow to 3 meters and weigh more than 130 kilograms, making them the largest lizards in the world.
You may also have heard of elephant birds, which can be more than 3 meters tall, weigh up to 500 kilograms, and are almost 1 times larger than their continental relatives, and did not become extinct until 1,000 years ago.
What both species have in common is that they both live on isolated islands, which seem to make them larger, the exact opposite of island mammoths.
Elephant Bird, Credit: The Paleo Page
In 1964, a man named J. Bristol Foster's PhD graduates were the first to describe changes in the size of island animals, simply by saying that smaller animals become larger after being isolated by islands, a situation now known as "island gigantism", while larger animals themselves become smaller when isolated, sometimes called "island dwarfism".
Personally, he believes that this is the rule for animals to survive on islands, and he also gives why organisms evolve in this way.
He believes that in an island environment, small organisms will face fewer predators and competitors, giving them enough space to get bigger.
But large animals like elephants don't have to worry too much about predators or competitors — their main concern is the lack of resources to sustain themselves.
So for these very large animals, the smaller habitat means they have to be smaller to survive.
This explanation seems reasonable, but the size of the island creatures is much more complicated than this.
Pictured: Iguana
Island animals that don't play by the rules
In 1978, another young biologist named Ted Case discovered that some organisms did not evolve according to this rule.
He personally studied a large iguana, chuckwalla, and to collect more data, it looked for traces of chuckwalla on various islands in the Americas.
According to the rules of the islands we mentioned earlier, chuckwalla should be larger on the island, but Keith found that the island did not always make chuckwalla larger, in fact on some islands chuckwalla became larger, and on some islands it became smaller.
In addition to this, Keith also found an interesting phenomenon in which he studied the island of Chuckwalla on angel de la Guarda
Half-meter-high Giant Rabbit of Minorca, Source: NobuTamu
There are two species of rattlesnakes that also live – the red diamond rattlesnake and the spotted rattlesnake – that also do not evolve according to island rules.
On the mainland, the red diamond rattlesnake is twice the size of the spotted rattlesnake, but on the island of Angel de la Guarda, on the contrary, the spotted rattlesnake is almost twice as large as the red diamond rattlesnake.
These two animals that share the same ecosystem should, according to island rules, grow larger at the same time, but the truth is that one has become larger and the other has become smaller.
In later studies, Case found that spotted rattlesnakes were more differentiated from mainland relatives than red diamond snakes, meaning that spotted rattlesnakes isolated on the island earlier and evolved on their own.
This allows the spotted rattlesnake to integrate into the island ecosystem faster, and it makes itself larger through the rules of the island, while the red diamond rattlesnake has already occupied its living space because it landed later, so it can only quickly shrink to adapt to the new environment to find its own niche.
Haast hawks attack moa, which are particularly prone to getting bigger on islands, Credit: John Megahan
Keith redefined the rules of the island for his new discovery, arguing that the core factor driving changes in the body shape of a living organism is energy expenditure, and that all changes stem from the animal's energy needs and how much energy it can get in any given amount of time.
In terms of energy consumption, animal sizes have distinct advantages and disadvantages. Large animals do better when it comes to competing for resources, and they are better at storing energy in case they need it.
But critters need fewer resources in the first place, and they are more capable of reproducing, which means they are better able to cope with environmental crises and survive dramatic changes.
Pictured: Mammoth teeth
In short, whether the island's animals have grown larger or smaller has less to do with their initial size and more about what kind of support the island's existing ecosystem can provide.
In fact, the huge changes in the animal that cause energy requirements to occur not only on the island, it happens everywhere, but the island amplifies this result, because the determinant of how much energy the organism can get on the island is very single.
In addition, the energy demand is not only affected by the size, other characteristics are also affected by this, but it is easier to change the size of the body, which is why the mammoth lost 4 tons in just 5,000 years.
Pictured: Antarctic circulation
At last
So far, there have been many controversies between "island gigantism" and the so-called island rules, but personally, I still believe that it is energy that controls all this, after all, the activities of living things are energy-driven.
I don't know if you have ever thought about where the biggest island on earth is? How will creatures evolve on such an isolated island?
In fact, there is a perfect giant island on Earth, that is, the Antarctic, and the oceans around it.
Antarctica has a current that surrounds the entire continent from west to east, which is the strongest ocean current on Earth and the main reason Antarctica is so cold, it isolates external resources from entering Antarctica waters.
At the same time, deep-sea animals tend to move toward larger sizes, which is called "deep-sea gigantism", so some people think that antarctica may have giant animals that are not discovered in the world.