Every morning you wake up as a new person. Yesterday was Joel 12889, tomorrow I will be Joel 12890, and seventeen years ago I was Joel 7001. Each Joel is fundamentally different than the rest. Many are very very similar, especially recent models where life has not changed much, but they all still are different.
Joel 7001 is nearly unrecognizable as “me” when I think about him. His recent experiences were vastly different than my recent experiences. He had goals that were very different. His skills set was different. In many ways, people with a twin might be as similar or even more so than I am today to who I was 20 years ago.
I believe a possible cognitive bias humans have is this illusion of self being the same or very similar through time.
We definitely have an Us vs Them cognitive bias. This usually most fundamentally is your basic self vs all other individual humans out there. Next is your family vs all other families. Then comes your city / state / company / football team vs all the others. Then we have us vs them between races. As each of these levels of us us them passes, people are able to empathize less with the them. They are willing to sacrifice others in these outgroups for their own gain.
Humans are 99.9% genetically identical. Genes mix so much anyways that if you look a few generations back or forward from yourself you will see people who are as nearly as much different than you as a random people on the street.
We are hardwired to look for differences, not similarities though. When we find these differences, we lose sympathy and often gain fear. Fear leads to anger and anger to hatred according to our dear friend Master Yoda. This hatred leads to dictators who oppress those around them, warfare between nations, and refusing to render aid those who need it.
The differences between my current self and my earlier self are smaller than the differences between you and I. However, I think there are far more similarities between us than differences. At a global scale, we are essentially the same.
The more we all open our eyes to our similarities and try to help one another out, the better the world will be.