system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why do people with downs look similar

I've met a few people in my life who has downs and noticed no matter the race they all mainly have the same features. Larger forehead, inflammation of the body and puffy eyes are the general features I see in downs patients.  Is this a genetic marker of downs or has anybody thought about downs being a part of evolution?
gpt
Yes, those differences in appearance are caused by one genetic abnormality that causes all the other symptoms of Down's syndrome.

If the other symptoms of Down's Syndrome made it easier to live life as humans, attract a mate and have children, then it could become part of what you could call 'evolution'.

Persons with Down's syndrome look similar to you for the same reason that persons of a race that you are not very familiar with look the same - your brain mostly notices how they look different from the 'norm' of human appearance. If you think about it, this is how you tell your friends apart - seeing, and also exaggerating, the differences in their appearances.