Scientists say there are 15 million insect species, 2 million marine species, more millions of bird and animal species. Yet, only one- humans - developed language. If evolution is true - that species evolve continually higher and better - why haven't other species developed language?
If evolution is true - that species evolve continually higher and better - why haven't other species developed language?
I'll discuss that question first, and then move on to what we know about languages in animals.
"Species evolve continually higher and better" is not what evolution actually postulates; there is no real sense of progress towards ever-smarter ever-better organisms; merely that the frequencies of genes in populations follow dynamics that is dependent on the relationships between the traits they are responsible for and the relationships between traits and the environment which further determine how many offspring a carrier of a given set of traits are likely to have.
Secondly, new traits don't pop out of nowhere; for a trait to appear in a population, let alone spread through a population, mutations that generate those traits must happen in the first place. That species don't evolve along some imagined ladder of progress has nothing to do with the veracity of evolution.
Coming to languages ; there are recorded instances of bonobos using modulations of their calls to communicate information; which is, simply put, language. Whales do it to a limited degree as well; communicating clan identity through ultrasound.