According to your argument then aliens should look exactly like us because we all come from the same single point called Big Bang. My point is that mutations h

According to your argument then aliens should look exactly like us because we all come from the same single point called Big Bang. My point is that mutations happens a lot (see current situation where the pandemic might actually become endemic exactly because the virus mutates so much) and diversity will always happen. And in the grand scheme of time measured by millions of years the diversity will 100% happen to fill all the free niches, regardless of the founder.