First of all, what a long-winded way to tell us which sentence to look at. We are trying to strengthen the following sentence:
"Furthermore, the widespread assumption that cooking could not have had any impact on biological evolution because it's practice is too recent appears to be wrong"
In the passage, we learn that the earliest evidence of cooking dates back 250,000 years. The author is saying that the assumption that cooking occurred too recently to result in evolutionary change appears to be wrong, meaning the author thinks 250,000 years is enough time.
Answer choice B shows an example of evolutionary change in humans that is the result of a practice that dates back 5,000 years. If evolutionary change is possible within 5,000 years, well then of course it is possible within 250,000 years!
I hope this helps. Please let me know if you have any other questions.