Why do people pronounce English differently in different parts of our country? Why don't speakers from Northumberland sound the same as people from Norfolk? Why is the Somerset accent different from the Suffolk accent?

There are two different ways of answering 'why' questions like this. If the question means: 'how did it come about that people from different places have different accents – what is the reason?', then we know the answer. All languages are constantly changing, and they change in different ways in different places. Even if you started off with everybody speaking the same, after some generations regional variation would start to set in.

But – and this is the second 'why' question – why does that happen? What is the purpose? What on earth is the point of different accents?

Dr Emma Cohen, an anthropologist at Oxford University, has argued that there was an evolutionary advantage to the development of accents. When early human beings lived in relatively small groups, you could always tell whether someone was a member of your group or not because you knew everybody personally and could recognise them. Outsiders were easily identifiable as such. But when groups got bigger, that was no longer the case.

However, once different communities developed different accents, then you were able recognise outsiders just by listening to them. If someone had even a slightly different accent from you, you would instantly know that they were not a member of your group, that they might be hostile, and that you should be careful.

Accents functioned as badges of membership. And, crucially, they were badges of membership which were rather secure against being used fraudulently. For early humans, there was an evolutionary advantage to the fact that, after childhood, it is very difficult to acquire a new accent perfectly. Someone attempting to imitate your group's accent and getting it wrong would be a person to be particularly wary of.

Sadly, in modern England, these badges of membership are often misused to make sure that outsiders stay outside – for example by denying them access to certain jobs. A report which came out last year found that elite firms in this country are still heavily dominated by people from privileged social backgrounds, because companies are systematically excluding bright working-class applicants from their workforce by including a candidate's accent in their selection criteria.

Firms like this may be elite, but they are also dismayingly palaeolithic.

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