Halloween is one of those weird "holidays" no one really knows why we do it. And oddly, I'm going to try and give a biological perspective to it. Often we think of the celebration of death or the occult and all the weird things that center around those as the "reason" for Halloween. Fortunately, that isn't entirely true, though their is that element of it. Our version of Halloween in the United States today is really a hodge-podge of all sorts of holidays from all over the world. Historically, Halloween like celebrations were much closer to Thanksgiving celebration except with more singing, dancing, games, and fun stuff like that. Many cultures have their own version of the holiday to celebrate the end of and abundance of the harvest season. This is partially where all the pumpkins come in being they often are harvested in October. So the end of the harvest which does line-up well with the end of October is a great biological perspective we can have of Halloween. Honestly, Thanksgiving in the end of November is far too late to be celebrating the summers harvest (OK just my opinion!).
Jack-o-lanterns obviously are a well established Halloween traditions that also rooted in the harvest celebration. This tradition was founded in Britain and Ireland during the 1800's. For hundreds of years prior to this people made turnip lanterns, which seems much less exciting and much more difficult to make. These vegetable lanterns were part of a pagan form of trick-or-treating.
One of the latest Halloween traditions, and one of the most exciting I think, is the growing of gigantic pumpkins. People that grow monster pumpkins learn all kinds of secrets about how to breed and grow these giants. The entire process can be quite intense and people have been producing pumpkins over 1000 pounds for many years now. Competitive growing of pumpkins is advancing in the United States so fast that world records are made nearly every year. This fall the world record was broken again with a 1810 pound gourd! It won't many years before a 2000 pound is grown.
"Everything you want to know about pumpkins"
Dentists also give us another perspective on Halloween. As you would guess, they hate it because too much candy really does rot the teeth. But several dental studies have asked the question, "How can we eat trick-or-treat candy and not rot our teeth?" Common sense tells us that maybe if you eat it a little bit every night it will be better for you. In this case however common sense is wrong and research has shown it is better to gorge yourself and eat it all in one night. Which I am sure most people want to do but rather use some misguided "common sense." When I tell people this they say, "Of course, then you will get sick and never want to eat it again." While there probably is some truth to that, the real reason dentists say it is better to eat it in one night is because then your teeth are only covered in sugar for one night as opposed to being covered in a little sugar every night for a longer time. Here is an article on the subject: