Why do humans cannot grow as giant where dinosaurs and some plants in prehistoric times can?

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Is it related to food? Or genetics or climate or something else? Thank you!

In: Biology

Humans ancestor’s weren’t as big as giants, it’s genetics. Our genes do not allow us to grow to the size of dinosaurs.

Well, you can’t just scale up a human and expect everything to work. Your leg bones wouldn’t be strong enough to support your weight, and you’d overheat because your volume (and thus heat generating capacity) goes up as a factor of a cube of your height, while your surface area (ability to dissipate heat) goes up with the square.

If you’re asking why we didn’t evolve to be that sort of size, there are hard limits on how big a mammal can grow due to the requirement to carry the young internally and give birth to them live–this is a difficult and error-prone process. Seaborne mammals like blue whales are helped by being able to be supported by the water, land creatures don’t get that, which is why the largest mammals around are elephants–and their children spend nearly 2 years in the womb before being born!

There is an an incredible amount of oxygen missing from the earth’s atmosphere that gave to the growth of giant flora and fauna. Also, modern humans evolved from tiny ancient mammals and not giant lizards.

It’s genetics. First and foremost, there’s natural selection. Natural selection will only keep those traits that give an advantage for survival, and for humans being much bigger than we are is actually a disadvantage. Neanderthals, for example, were noticeably stronger than homo sapiens (us) and, scientists think, probably smarter too. But because they were so much stronger and faster than us they never developed tools to the extent that our ancestors did, which led to them being out-competed and going extinct.

Also, there’s the square-cube law to consider. The absolute largest a human could get without significant changes to our anatomy is around 8 or 9 feet. Any bigger than that and the structures of our legs couldn’t handle the weight. In fact, the one man in history to actually get that big (Robert Wadlow, 8’11”) had to use a cane and leg braces to walk due to the strain on his legs. He weighed over half a ton despite being pretty slim. That’s the square-cube law in action.

We could grow to the size of an elegant but there is no selective pressure to do so. Once we evolved the brains a spear requires a lot less energy than a larger body. Also being on two legs makes it so you can’t grow as tall. The spine just can’t take it. If we did we would either need to grow tails and begin leaning forward or revert back to all fours

One consideration is the square cube law, as size increases propotionately, surface area is sqauared and volume is cubed. So you get heavier very fast, which takes different strategies to counteract. The tallest humans that have lived have had many health problems as a result.

Thank you all for your explanation!! Any sources can I read more?