Surviving through each and every day of your life used to be something that you had to worry about as a human. Some humans still have this worry today, but for those of us with computers and other modern luxuries, we pretty much take surviving into old age for granted.

Even today we can not survive without a group of other humans helping us out. A naked infant left in the wild won't survive. Some species on earth are born and never see their mothers again but we as humans survive by being in a group. Maintaining that group is critical to the survival of each member. Without elderly members to pass on a lifetimes worth of life-saving information, the young would die. For example, during a famine an elderly member can remember back to when they were just a child and point out a root that is not eaten by current members but is abundant and was what his/her tribe ate when they went through a similar famine. Without young members to hunt and gather food, the old would die.

As an aside, the reason elderly are no longer respected could be due to the ability of recording history in books. We no longer have to rely on the elderly to tell us what to do in a situation that we are unfamiliar with and which they already lived through. Elderly are no longer valuable resources since the information they contain is available in books. This is not entirely correct though, due to their longer existence the elderly have the potential to have learnt more and processed more data. This could give them a broader outlook and provide them with more informed opinions. It does not always turn out that way but the potential is there.

Without cooperation, the group would die. Due to the critical nature of maintaining the group, those humans that did not exhibit cohesive group dynamics ceased to exist. Natural selection produced humans that were successful in groups. Our behaviors and decisions reflect this group living. In teenagers for example, being part of a group is what drives their behavior. They base their self-worth on how they are valued by their group. They act in accordance with their group whether rational or not since it is about trying to conform as much as possible so that they are considered a successful member of the group.