580 million years ago, life on Earth began a rapid period of change called the Cambrian Explosion, defined by the birth of new life forms over many millions of years that ultimately helped bring about the modern diversity of animals.

While fossils can help palaeontologists chronicle the evolution of life since the Cambrian Explosion, drawing a picture of life during the 3 billion years before the Cambrian Period is challenging because the soft-bodied Precambrian cells rarely left fossil imprints; early life forms did leave behind one abundant microscopic fossil, DNA. 

Scientists have studied human brain samples to isolate a set of proteins that accounts for over 130 brain diseases and found an intriguing link between such diseases,  the leading cause of medical disability in the developed world, according to the World Health Organization, with an economic costs in the USA exceeds $300 billion, and the evolution of the human brain.