Sorry, I forgot all about this shit.
So you know pretty much everything about us biologically comes down to gene expression. If you remember in high school biology, you can use Punnett Squares to figure out the likelihood for offspring to express certain traits. Well, we have a huge but finite number of genes in our genetic code and the traits that each gene can express vary, but they are also finite. In other words, there is a finite number of different combinations you can get from human gene expression. That number is massive, but the majority of those genes have nothing to do with phenotypic features, so when you take away genes that have nothing to do with how people look, you get a smaller number of combinations.
Again, that number is probably still huge, but now let's take into account the fact that not every phenotypic trait holds the same weight when we see people. Things like eye shape, nose shape, and lip thickness stand out more than things like ear lobe type, eye color, or eyelash length. If you broke it down, two people "looking alike" could really mean they have as few as ten key phenotypic features that are the same. So, for example, if for simplicity sake, we say that each of those 10 genes had 5 possible expressions, the likelihood of getting a particular combination would be 1/(5^10) or 1 out of 9,765,625. That's a far shot, but remember there are more than 7,000,000,000 people on this planet, so statistically you're pretty much guaranteed to have multiple sets of people running around with similar enough combinations of phenotypic traits that people would consider them to look alike even.
That explanation is super simplified. It doesn't even account for the fact that people with similar backgrounds are more likely to have certain traits in common off top. That's why people who don't often see Asian people say they all look all like. You can also consider the fact that phenotypes don't even have to be exactly the same for people to say people look similar. If two black people have very similar facial features, people will still say they look alike even if their skin tones aren't an exact match.
