Why were animals and insects so much bigger during the time before humans?
In: Biology
You see bugs don’t have lungs so they can only grow big when there is more oxygen .And when they were the biggest there were a lot of trees
It wasn’t in “the time before humans” it was during “the time of lots of oxygen”. We used to have a much more oxygen rich environment which meant everything could grow larger.
[deleted]
The animal cells are depended on oxygen and food to function. However, only rich-oxygen environment isn’t enough to make an organism bigger. If it is advantageous for species, genetic adaptations through evolution codes DNA to make an animal bigger. Eventually in a environment containing enough oxygen concentration and proper genetic mutations, any kind can be big. Similar logic applies for being small.
There are a lot of separate things going on here:
First, not everything was bigger in the past. Blue whales are probably the biggest animals to have ever lived.
Second, the above fact is kind of remarkable because you’d expect, just due to random chance, many of the biggest things to have lived in the past. Most animals that have lived are extinct, so if you just picked a random one to be the biggest, it would probably be in the past.
Third, giant insects specifically (but not other giant animals) require higher levels of oxygen in the earth’s atmosphere. This is because insects don’t have proper lungs but breathe by diffusion of oxygen through tubes. This is inefficient, and limits the size of insects. But it’s not the only limiting factor. The level of oxygen has gone up and down through history, and while insects were huge the first time levels got high, the second time it got high they didn’t get huge. By that point there were other flying animals around that could outcompete and probably eat them.
Dinosaurs got huge for a variety of reasons related to their biology that let them get particularly large. High oxygen levels had nothing to do with it, in fact oxygen levels were actually lower at some points. But dinosaurs had efficient birdlike lungs which is one reason they could get huge at all. Many dinosaurs also had air sacs in their bodies and bones which probably helped them stay lighter and get larger. There’s a lot of factors involved in their huge size, probably.
Ice age mammals were larger than modern fauna for yet another reason….basically, the modern world has very few species of large mammals (and other land animals) compared to basically any point for millions and millions of years (since mammals first got large after they took over from the dinosaurs). Why? That’s a matter of debate….some will tell you climate, some hunting by humans. I personally think the latter answer is the better one, for various reasons, but the main point is that all the mammoths and giant sloths and the rest mysteriously went extinct recently. But they weren’t really that much bigger than our surviving large land animals like elephants and rhinos…the ones that managed not to go extinct.
Scarcity of sources of energy in general during several catastrophic events in the past meant that species with advantageous traits survived through those events. Less oxygen/sunlight/food would tip the scales towards smaller varieties since they could survive on less.
Before humans animals used to goto mcdonalds but now humans eat all the mcdonals so human 1 animal 0
What blows my mind is the age that there were giant lizards roaming the earth. Evolution is fascinating. Lots of documentaries on youtube on The Age of Reptiles.
Can I just suggest you watch Cosmos? It’s really amazing in terms of explaining science to commoners. This is one of the things they show and explain real nice.
Because humans killed everything big.
It takes a lot of time and energy to get big. And humans are good at killing big things.
Latest Answers