How do we study language evolution?

Language evolution in humans, dogs, and other animals

source: W. Tecumseh Fish
New Scientist vol 208 no 2789, 4th December 2010 
starts pii, two pages long

Language allows humans to express thoughts as signals, and to turn signals into thoughts. Dogs can give information about themselves and the outside world through barks, but they cannot provide complex information, such as an account of their lives as puppies. Vervet monkeys can give calls signalling eagle predators and different calls signalling leopard predators, allowing the group to take appropriate evasive action, under cover or in a tree. This ability is innate, so they are unable to develop it to signal novel predators. Honeybees can signal the location of
resources, though not with detailed information, such as the colours of flowers.

Shared traits can come from common ancestors, and these traits, called homologies, contrast with convergent traits, which develop separately in different species, in response to changes in the environment, which in turn affects selection pressures.

Many animals, such as dogs, can learn to understand words, or new signals. A border collie, Rico, has learnt hundreds of names of objects. A bonobo called kanzi has done this and perceives word order differences. Neither Rico nor Kanzi can produce words in human language. A seal called Hoover learnt to talk human sentences, but did not understand what they meant, and mostly used them to impress females seals at mating times.

Some animals can be trained to interpret and produce words. Alex, an African grey parrot, could talk and use appropriate words for numbers, shapes and colours. Being able to produce
complex sounds may be a later development than understanding their meaning.