From StrategyWiki, the free strategy guide and walkthrough wiki

[edit] Level summary

This is the start of the game. There is no way to die. To continue to the next level you must fill the DNA evolution progress bar by moving around eating the DNA food cells until you've eaten 30 of them. There are no enemies or symbiotes in this level.

[edit] Other creatures

Always Smaller: DNA Cells

Varies: None

Always Bigger: None