Sweating: Human bodies sweat when under humans need to cool off, this allows us to easily cool off no matter what is happening. Us humans don't need to stop to pant like other Earth animals. Many alien species like the Grays expel their heat through a gland near their feet. This gland makes it difficult to move around when letting go heat.
Facial Geometry: Human faces have a lot of characteristic to them. Due to our relatively short lifespan and small population count, humans (as a whole) gain new traits faster than aliens. Plejaren live for up to 5,000 human years.
Spoken Language: Although not entirely exclusive to humans, most aliens surprising do not make any meaningful verbal output. Some alternatives include: Using instruments to vocalize info, reading, and images.
Internal Structures: As you might know already, all alien races evolved separately from each other. This segregated evolution means all aliens (and us) have different internal structures. However, humans digestive track includes a stomach. Most other alien species deal with this issue of breaking down food by extending the intestines.
Preferred Living Space: Usually alien races either live with a massive group of people in one common living area (like wasps), or live entirely alone. Humans love having a family relationship. Garibalds are heterosexual creatures that find it socially awkward to live near their offspring.
