why do small movements on most small reptiles and amphibians such as turning heads are quick and short? Making them look jittery when doing these movements in quick succession
In: Biology
Consider that humans can also involuntarily turn their heads very quickly, for example, when there’s a loud bang or a fight is starting. When we sense something that could be a threat, we move quickly. The “reptilian” parts of our brain take over when we don’t have time for even the low-order thinking that we constantly do without noticing.
The smaller you are in size, the more of a threat the world becomes, and survival will depend on assessing threats and food sources more quickly than your predators and competitors (especially if your main food source is fast-moving insects). Same with cats and especially wild cats, or small dogs versus big dogs. The smaller animals move more quickly.
And size also means that a small lizard’s head is far easier to move quickly than a human head. If we moved our heads like small lizards all the time, we’d need bigger neck muscles. Not only because of scale, but gravity – the smaller you are, the less mass you have to move against gravity and inertia.
(Compare the wingspan of a hummingbird in relation to its body size with that of an eagle or a condor – large birds need more wing surface area to achieve lift than birds with less body mass.)
So “small” is the keyword here. Komodo dragons are lizards, but they’re very large and AFAIK, they don’t normally display the jerking head movement you’re asking about.
Since I pulled up this ELI5 from my general knowledge, there are certain in-depth parts missing that I can’t give you without thorough research. What you might ask next is:
– how exactly, when and why does our “reptilian brain” take over? Does it have priority in emergencies just because it’s closer to the spine, or is there an additional mechanism to “drown out our thoughts”?
– Is there a formula to determine maximum size vs. muscles and Earth gravity, the law of diminishing returns etc.? (I’m sure there is, but I just haven’t looked into it)
– Is there also a minimum size? (If a human were scaled down to lizard size, they’d be incredibly weak compared to the other animals. We’re already much weaker than animals our own size, e.g. lions. It’s our intelligence and social cooperation that make us “stronger” than lions, not our muscles.) So, if a lizard had a small-size version of the human muscle structure, could it even climb rocks to survive, or run long distances through the desert?
Latest Answers