Question: How is that some animals and insects only live for one day but humans live longer.

Reka Nagy answered on 14 Nov 2016:

Tough question!

The first thing to consider is that the basic instinct of every animal (including humans) is ultimately to survive and keep making babies to ensure that the species continues to exist.

Different animals use different strategies to keep their species going, however, and differ in the age at which they are able to start reproducing.

For example, insects tend to live for a shorter time than humans but they lay a lot of eggs, and they can do so very soon after they hatch. The parent doesn’t spend a lot of energy staying around and making sure that all their eggs hatch, so some eggs will become insects while others never will, but the continuity of the species will be ensured, so evolutionarily speaking there is no requirement for these insects to stick around for a long time.

Compare to insects, humans produce a lot fewer offspring but they spend a lot of energy making sure that these babies survive and reach maturity. Additionally, it takes a lot of years before humans are able to reproduce, so their parents need to stick around for even longer.
Once we pass the age after which we are no longer able to reproduce, our bodies have no reason to keep us alive, other than to help raise children.

Generally, we notice that the larger a species is (and the larger its brain iscompared to its body), the longer-lived it tends to be. This is because smaller animals need proportionally more energy to keep themselves alive, so ‘burn out’ faster.

One interesting thing to note is that while we have managed to extend our average lifespans with the introduction of many medicines and changes to our hygiene, we are also seeing a rise in diseases that tend to affect older people, such as a lot of different types of cancer, and diseases such as Alzheimers. It’s not that these diseases didn’t exist before, but very few people used to reach old age so they were not so prevalent. The problem is that because these diseases usually start after we stop being able to reproduce, we have no way of overcoming these naturally as evolution has no means through which it can act.