Mammals and birds tend to grow, reach maturity, and stop growing. Conversely, many reptile and fish species keep growing throughout their lives. As you get bigger, you can not only defend yourself better (reducing your extrinsic mortality), but also lay more eggs.
So, clearly, we must have the same for humans. If we became progressively larger, women could carry twins and n-tuplets more easily. Plus, our brains would get larger, too, which could allow for a gradual increase in intelligence during our whole lifetimes.
Ha ha, just kidding: presumably intelligence is proportional to brain size/​body size, which would remain constant, or might even decrease...
So, clearly, we must have the same for humans. If we became progressively larger, women could carry twins and n-tuplets more easily. Plus, our brains would get larger, too, which could allow for a gradual increase in intelligence during our whole lifetimes.
Ha ha, just kidding: presumably intelligence is proportional to brain size/​body size, which would remain constant, or might even decrease...