Why is there only one human species? | BBC

[liferocks]

It's not faith. We know what parts of our brains control language and speech, so if Homo erectus didn't dedicate much of its brain to this region, it was not very adept at communication. By studying brain injuries in humans and determining what parts of the brain are damaged and what functions are lost, we know what part of the brain does what. No faith needed.

I do believe that science holds many valuable answers for us , but FaithNoMore, you say that brain injuries in humans can be studied. That is because the actual brain or subject are present to question, dissect, analyse. Fossil records have no brain matter intact and the subject, in this case the "Erectus", is not present for inquiry.
I was taught evolution in high school, never questioned it then but things like this are now what I am seeking to answer. What you say to me now is in relation to what we know of human biology in regards to present human beings, not lower life forms or erectus that science claims no longer exist. This is one line of my thinking that as of yet still remains in dispute.