Hi bridget! Interesting question. Although the Earth has undergone many pole reversals in its history, there is not direct evidence that such events have disrupted the Earth’s biosphere (i.e. we don’t observe mass-extinctions correlating with any pole reversals). Even humans have survived a few reversals in our history (including the last one around 780,000 years ago!). The one major threat I can think of is radiation exposure. The Earth’s magnetic field protects us from vast amounts of cosmic radiation. It is possible that during a pole reversal, the magnetic field could weaken, limiting our protection from such radiation. This radiation could cause mutations, including cancer. But the most detrimental effects (seeing as humans have clearly survived past events) would be to our technological devices – all of them are susceptible to sun storms! Imagine no protection – all our electronics might fail! That probably would be the worst case scenario of a pole reversal and is something ancient man would not have had to worry about!
Sara is right that we don’t know for sure what would happen, but that technology might be more vulnerable than living things. Be very careful with averages though. We don’t actually know what caused historical pole reversals, and the fact that the current interval is longer than “average” isn’t necessarily meaningful.
When you were a baby, your nappy was changed every couple of hours. It’s been years since that happened – OMG a drastic nappy change is way overdue!