system
Given the following post, respond as if you're commenting on Reddit:
human
If we say sharks as a species are roughly 400M yrs old, does this mean that sharks from back then could theoretically interbreed with today’s sharks?
gpt
They couldnt interbreed, but thats not the defining feature. Differnt species of shark cant interbreed today, thats how we define species, if two of the same animal can breed to make fertile offspring. When they deviate enough that two cant breed anymore its called speciation.

When they say sharks are 400M years old that means that 400M years ago speciation occured to create the clade Selachimorpha which we commonly refer to as sharks.

A bit oversimplifying but you get the idea.