Why is it argued that speech is only possible in modern homo sapiens and not in homo erectus or homo neanderthalensis? the brain wiring is not set up properly the capacity for language may be innate homo sapiens is the only species with a large enough oral cavity and a low enough larynx to allow for speech production. the areas for speech and sound recognition are not developed in other primates?

homo sapiens is the only species with a large enough oral cavity and a low enough larynx to allow for speech production. 

One line of evidence that speech only possible for modern homo sapiens is the anatomy of their throat. Speech depends on certain anatomical arrangements and the Homo sapiens is the only species with a large enough oral cavity and a low enough larynx that would allow speech.

burning of wood and coal

explanation:

the panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in earth's temperatures over the past 50 years.