system
Given the following post, respond as if you're commenting on Reddit:
human
Do species with a shorter lifespan evolve faster than those with a longer lifespan?

I got to thinking about insects and the other species with really short life spans and noticed that they almost always have more complex eye systems, nervous systems, and more limbs. 

Is this just coincidence did having more focus on development of the brain functions for complex thought, etc, lead species into another direction? or does having a shorter life span have an effect on evolution?
gpt
The answer to your main question is that yes, shorter generation times (lifespan itself doesn't really matter) allow faster evolution, more or less by definition since evolution is a change in allele frequencies from one generation to the next.

But the underlying premise is mistaken:

> insects and the other species with really short life spans and noticed that they almost always have more complex eye systems, nervous systems, and more limbs

* Insects' generation times vary just like those of other organisms, and there are plenty of non-insects with shorter generations than plenty of insects
* The animal kingdom is full of complex eyes, insect or not
* Insects aren't really toward the high end of nervous-system complexity
* What does number of limbs have to do with anything?
* The things with the fastest generation times, single-celled organisms or viruses, evolve very quickly but also tend to have the simplest anatomies

It sounds like you're imagining insects as somehow "more evolved" than longer-lived animals. Do you suppose lions and tigers are on their way to developing an extra pair of legs if you just wait for them to reach the same number of generations? Will mice get there before elephants?

The "design space" of eyes or brains or body plans is vast, and different lineages have gone down different routes that lead to different places. After billions of years of evolution, we can generally assume anything is pretty stably adapted to the environment it's been living in all this time, and the rate of adaptation only becomes important when the environment itself is changing.