There is evidence in the way animals behave in situations, and the lack of language development (ie written language, or comprehensible vocal language). So the evidence is that they so far, have lacked the ability to express that they have the intelligence. the moment i'm read Descartes by a budgie, that's the moment i'll consider something equal.
In regards to Understanding Why, and animals.Do you know what the dog 'guilty' look means? it's fucking terrified. The dog doesn't understand that shitting on the floor is bad, it just knows that the thing that feeds it, and it loves (probably) is making loud angry noises. It might eventually make the connection but they don't reason it out, it's beaten/drilled into them.
Meaningful communication and You!
Meaningful communication in this sense would be something that can convey an idea, not an experience. noises of pain are not meaningful because they are not conveying the idea of pain, they are expressing pain is happening. Important difference.
>that sentence is just logically indefensible.
Well considering i used the word meaningful, again being something more than the basics, it's perfectly defensible. Please tell me how a cry of pain indicates anything other than pain.
A baby is an undeveloped person, comparing it to a fully grown pig is asinine and throwing straw into the fight. It's communicating pain, nothing else can be CLEARLY gleaned from the cries, Ie; it's not meaningful. Which again, means that it conveys ideas and concepts, not just what is currently happening.
I assumed you are a Vegangelist because you are cheapening what it means to be human
If we are no better than animals, then we wouldn't condemn rape, murder, exploitation, selfishness and dickery. We wouldn't have formed civilization if we were not better than a cat, or pig or dog. If we weren't more developed.
We needed MEANINGFUL, communication to do all of that.