Who were the people of ancient India that collected trash and skinned animals?
The people who collected trash and skinned animals were the Pariahs. They were also known as the untouchables or dalit. They skinned animals and handled dead bodies. When the Pariahs traveled they tapped two sticks together so the people in higher castes could hear them coming and have time to move away. Most ancient Indians believed that being near the Dalit was harmful so they were forced to live apart from other ancient Indians. The Dalit lived very dirty lives and didn't belong to a varna.
Arians are an ancient tribe living in western Afghanistan. This can be confused with Aryans, which are the people who live in Northern India. These northern Indians are lighter skinned because of the cooler climate found in North India. Dravidians are those people that occupy South India, and tend to be darker skinned because of the hotter climate in the southern area of India.
It's generally believed that we have been adapted to our surroundings we live in through millions of years. Darker skinned people who had to endure the hot, intense sun and the cold, freezing nights, as well as the likes of mosquito's and wild animals developed wooly hair for the cold, and for sun protection, dark skin and other 'survival based' features, whereas lighter skinned people who had it easier, did not need such traits.