What if all animals had human intelligence?

If all animals had the rational thinking and self-awareness than humans do, our species (and the planet) would be in for a hard time.

Imagine a world à la Planet of the Apes, where every animal species has the same intelligence humans do. Chances are, it would be a messy disaster.

It is however, very difficult to make even a speculative guess as the defining trait in determining and measuring intelligence across species is usually done by comparing the brain to overall body mass ratio. However, since you stated that they were simply ‘as intelligent’ and not sentient or sapient I suppose this would leave us relatively unaffected in certain cases.

Larger brains equate to larger energy requirements, especially for endothermic organisms like mammals and birds. Evolution has always been an ‘arms race’ of sorts, with intelligence being one of the most sought after weapons. Predators learning better hunting tactics and prey learning newer defensive strategies such as counter attacks using numbers.
 

Predators would require to hunt far more frequently than they currently do. Chances are that they might end up heavily competing with other predators with even greater ferocity than they already do. Prey animals would always attempt to stay ahead of their predators in order to ensure their survival.

As for us; we might have ended up relatively unaffected. As the only organisms to have conquered fire, something all animals tend to be instinctively afraid of, this could have provided us with a sort of survival advantage; confined to simply watching from the shadows as the rest of the world wages a war of survival between the hunters and the hunted.

Why would they? Humans have developed the intelligence they have as a result of experience over the past 7 million years. No other animal species has shared this experience. Animal intelligence reflects the evolutionary experience of their species. Humans (who are also animals) can only reflect their own evolutionary experience. Human intelligence is not at the top of some scale to which all living things aspire — which is what the question seems to suggest.