What if mankind never had/gained the ability to travel by sea?

I think the problem I see here, is that we can travel quite a ways down a river simply by holding onto a floating log. And, effectively, a canoe is simply a dug out floating log. So, we have to go a bit beyond Alien Space Bats for this, and postulate some kind of serious mental block. Put another way, if mankind was stupid enough that it couldn't figure out how to hollow out a log, what exactly IS mankind capable of doing in your scenario? So, I'd say if mankind is mentally deficient enough that they can't figure out how to travel by "sea" -- which, I assume includes rivers or lakes, too -- that we'd have been superseded by some more intelligent life form by now. Or, possibly, wolves domesticate men, rather than the other way around? Actually, elephants can travel by sea to some extent, they can swim 10 or 20 miles in open ocean and survive. So, possibly elephants are the dominant intelligent life form in your scenario. On the other hand, maybe we're just hydrophobic, and fear proximity to seas and rivers, whether in boats, or otherwise. In this case, all trade and commerce is overland, so I would suspect roads and road making technology become much more advanced, much earlier. Also, the horse collar and stirrup are invented much earlier. The land based economy forces adaptation to more arid climates, so the camel would likely be very popular worldwide, as well. Irrigation would have to be extremely sophisticated, because farming, as all human activity would be isolated from the seas and rivers, and in more arid areas. No fertile crescents, so, civilization is likely delayed. Society is likely Nomadic, for a very long period of time, rather like the camel caravans in the traditional Sahara or Gobi deserts. Possibly, advanced technologies for extracting water from the air are developed much earlier, leading to the possibility of great civilizations inland, as well as unique advances in chemistry and materials technology.