p4. Animals much like modern humans first appeared about 2.5 million years ago.
For countless generations did not stand out from the many other organisms they shared a habitat with.
No different from chimpanzees, baboons. Nothing special about humans. Prehistoric humans: insignificant animals; no more impact on their environment than gorillas, fireflies or jellyfish.

p5. We are members of the family called the Great Apes. Closest living relatives include chimpanzees (closest), gorillas and orang-utans.
Human => 'an animal belonging to the genus Homo'; used to be many other species besides 'Homo Sapiens'. For the last 10,000 years we have been the only human species around.

p6. Human populations evolved in different directions based on their environments. Humans in Europe and western Asia evolved into Homo neanthalensis ('Man from the Neander Valley'). Eastern regions of Asia were populated by Homo erectus ('Upright Man') - survived there for close to 2 million years - most durable human species ever. Island of Java in Indonesia lived Homosoloensis ('Man from the Solo Valley') suited to life in the tropics.

p8. In 2010 scientists discovered, using genetic analysis, a previously unknown human species (Homo denisova) when excavating the Denisova Cave in Serbia.
Who knows how many lost relatives are waiting to be discovered. The cradle of humanity (East Africa) continued to nurture numerous new species; Homo rudolfensis ('Man from Lake Rudolf'); Homo ergaster ('Working Man'); Homo sapiens ('Wise Man').
From 2 million years ago until 10,000 years ago, the world was home to several human species (at least six). Our current exclusivity is peculiar and perhaps incriminating.

p9. Humans have extraordinary large brains compared to other animals. 60kg mammals have average brain size of 200 cubic centimetres; earliest men/women (2.5 million years ago) had brains of 600 cubic centimetres; modern sapiens have brain of 1,200 to 1,400 cubic centimetres; Neanderthal brains were even bigger. Why are giant brains so rare in the animal kingdom? Jumbo brain is a jumbo drain on the body. In Homo sapiens brain accounts for 2-3% of total body weight, but consumes 25% of the bodies energy when the body is at rest (hard to fuel). Other apes require 8% of rest-time energy to fuel their brains. Archaic humans paid for their large brains by having to spend more time foraging for food/energy and their muscles reduced in size (reduced strength, weaker).