Instructions: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: ALMOST everyone wants to get smarter. We struggle to improve our memory, intelligence, and attention span. We drink cup after cup of coffee to help us get through the day. However, a new study published in the journal Current Directions in Psychological Science warns that there are limits to how smart humans can get, and trying to increase your thinking ability could beurisky. Each of our body parts evolved in a certain way for a reason. For example, we are not 3 meters tall because most people's hearts are not strong enough to send blood up that high. Scientists are now saying that our thinking ability works in the same way. A baby's brain size is limited by a series of factors, such as the size of the mother's pelvis  . If our brains evolved to vbe bigger, there could be more deaths during childbirth.  The study of Ashkenazi Jews  , who have an average IQ much higher than other Europeans, showed that they were more likely to develop diseases of the nervous system. This might be because of their increased brainpower. If intelligence cannot be improved, can we at least get better at concentrating? Not really, say scientists. They studied drugs like caffeine that improve attention span. They found that the drugs only helped people with serious attention problems. For those who did not have trouble paying attention, the drugs could have the opposite effect. Scientists say that this suggests there is an upper limit to how much people can or should concentrate. Our memory is also a "double-edged sword  ". People with extremely vivid   memories could end up having a difficult life because they cannot forget bad things that happen to them. Thomas Hills of the University of Warwick in the UK, one of the authors of the paper, said that considering all the problems in trying to get smarter, it's unlikely there will ever be a "supermind". 
 Answer: there are limits to people's intelligence
Output:
Our heights and babies' brain size are mentioned to prove that   _  .