evolution - Why do we assume that the first humans were dark-skinned?

According to the article Dark skin and blue eyes: How Europeans once looked:

It is widely accepted that Man's oldest common forefather was dark skinned, and that people became more pale as they moved further north out of Africa into colder climates with less sunlight.

I thought that humans' oldest common ancestor was light-skinned, because

1. Dark-skinned people have white palms and soles, but light-skinned people have more consistent skin tones. This suggests that light skin is more ancestral and dark skin evolved to protect skin from the sun.


2. Bonobo chimpanzees, our closest primate cousins, look like they have light skin under black hair.

I understand we all originate in Africa, but I thought that the environmental conditions in Africa were different from today. How do we know that the first humans were dark-skinned?

Answer

According to wikipedia, "comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and is the ancestral state of all humans." This is several million years after after the time estimated for the last common human-chimpanzee ancestor, but at least 1 million years before the emergence of Homo Sapiens. This suggests that the earliest species in Homo may have had lighter skin, but that the advantageous genes for dark skin were universal by the time of the first true humans.