Is physical weakness the catalyst that started Human evolution?
What would make you think that? Have you read the link explaining evolution? https://www.physicsforums.com/threads/learn-about-evolution-evolution-introduction.543950/
I don't even understand the question. Physical weakness of who/what? Start of evolution? There is no such thing for an individual species.
That possibility has been debated, sometimes rather hotly. Obviously human migration from forest to the savanna brought new challenges. I don't think there is much disagreement that would provide increased selection pressure. It appears the points in dispute principly relate to the logic and timing behind specific adaptations. For discussion see: http://www.npr.org/blogs/13.7/2014/...ans-evolve-on-the-savanna-the-debate-heats-up.
I wouldn't apply such a blanket statement to the whole of human evolution. But there are some cases in human evolution that you might interpret that way. For instance, smaller jaw muscles (a mutation you might consider a weakness) may have led to bigger brains.
teleology: the explanation of phenomena by the purpose they appear to serve rather than by postulated causes.
This is what is happening with the original concept posted.
Evolution is an emergent process - it has no predefined purpose or intent; it has no direction; it has no ultimate goal. It is not smart nor is it stupid. The process is purely driven by environmental factors and changes that enforce different survival rates. Survival == successful reproduction. Those governing differences are the genetic differences in a group of organisms in the environment you are considering.
D Hosfstadter proposed a reason for why we do this kind of teleological thinking. Humans have hard-wired templates for analyzing new concepts.
If you see a log laying over a stream you walk on the log, rather than wade through the stream. Humans that have never seen a man-made bridge implicitly understand what it meant is for. Sometimes these templates lead us astray. In this case, applying human pre-defined "causes" to the current point of human evolution when there is none.
Separate names with a comma.