There is little doubt that all life-forms – plants, animals and humans – communicate. There is still, however, quite a scientific debate whether animals have thoughts (eg, Aeon, my 2016 blog, Theory of mind in animals). There is also a scientific debate whether having thoughts is required for using (written) language, or the other way around (Wiki).
The basic methods of communication are through the use of (organic) chemicals (all), colour/light (all), gestures, electricity, seismic, sound, speech, thermal, touch, visual, and written language (humans only). See animal communication and plant communication on Wiki.
The evolvement from communication to thoughts to (written) language is a scientific mystery. Animal speech and human language are taught (ie, Nurture) rather than inherited through genes (ie, Nature). A recent study even discredited the earlier attributed FOXP2 gene. Without teaching by its parents, no animal develops speech, and no human develops a language.
The origin of written language is (as often) attributed to the Sumerian civilization, which is another mystery in and of itself. Source: “Writing was used exclusively for accounting until the third millennium BC, when the Sumerian concern for the afterlife paved the way to literature by using writing for funerary inscriptions.”
The debate on the (missing) link between thoughts and language received new meaning following the introduction of Artificial Intelligence (AI). New Scientist: “computational logic in AI is, arguably, the missing link that connects language and thought”. Note LO: quote slightly adapted.
Research on human babies (eg, Boston) and animals (eg, apes, dolphins) clearly suggest that both do have thoughts. Interestingly, these suggestions follow games and these are always crucial in learning and teaching, whether for animals or for humans.
A 2018 Psychology Today article states that “The human capacity to learn exceeds that of any other animal. Indeed, our massive memories and impressive computing power are the engines of all that makes us different from other animals, rooted mostly, but not entirely, in language.”
Adulthood in humans starts at 18 (legally) or 25 (brain), which represents some 20% to 30% of our average lifetime. It would be hard finding similar percentages in animals. This (absolute and relative) vast amount of time available for (social) learning must be responsible for the differentiation in communication, thoughts and language amongst species.
Learning and teaching, first by parents and later by schools, must be responsible for the evolvement from communication to thoughts to (written) language. This thought seems so logical that it’s almost absurd to call this a scientific mystery.
Note: all markings (bold, italic, underlining) by LO unless stated otherwise