system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does DNA translate to an animal’s natural instincts? As in, how can genetic code give an animal innate knowledge about the natural world while the animal is developing in the lightless womb of its mother?
gpt
Let's look at a very very simple example - ticks.

Ticks have a few instincts - "Move towards warmth" "Move towards the scent of carbon dioxide" and "When the smell of carbon dioxide is very strong - BITE."

These are not learned behavior; a tick starts exhibiting these as soon as it hatches from an egg.  Moving towards warmth means that rather than lying on the ground, where they're unlikely to be picked up by an animal, they crawl to the top of grass, where the warmth of the sun is greater - and where they're more likely to get picked up by an animal.

Once they're on an animal, they start to burrow towards the source of carbon dioxide - the mammal's skin, which is constantly emitting carbon dioxide.  There, the scent is very strong, and the tick bites and starts to feed.

These are all hard-wired into the tick's brain.  The "warmth sensing" brain circuitry feeds directly into the "movement" brain circuitry.

These are simple examples, but the kind of provide a template for more complex examples.  Mammals have a hard-wired desire to stay close to their mother when very young, to seek out and suck on nipples, to flee from loud sounds.