The reptile would now evolve into mammals likes rats. They would adapt to different temperatures and climates. They might have moved around and adapted to their new habitats. This could be reasoning why they grew fur over time. As time went on the animals would grow both intellectually and physically.
Life began deep within the ocean many years ago, we think around 3.5 billion years ago. The first living thing was called a single cellular organism. Scientist are still not sure how it came to be but they believe life was formed due to chemicals clashing in the ocean.
Many years later the rat like animals would reproduce giving their offspring new characteristics. Eventually there came apes. These apes, after many years would go on to creating highly skilled and intelligent humans.
These single called organisms eventually morphed into multicellular organisms as the environment around them changed.
The single cellular organisms would harvest energy from the sun resulting in the process of producing oxygen called photosynthesis. With more oxygen in the air, this helped change within the organisms. When the habitat around living things change, it can very well change as well.
As time went on bacteria (single or multicellular organisms) formed plants and coral in the ocean. These evolved into fish. They would move onto eventually coming out of the water and breathing air. These animals could be in the water and out. This would create a reptiles like lizards etc. The organisms had to adapt to the new environment. This creates new characteristics within the organisms.
The apes developed into humans. Humans are not just Homo sapiens though. There are many humans that came before us (21 century). All of the humans originated in Africa and from there spread out in the world. They had to adapt to different areas around the world. This led to many different characteristics being passed down generations. As time continued the humans got smarter and smarter. There bodies, and minds changed. This was the beginning of the human species.