"No purpose other than to become an ancestor.

The purpose we share with other animals.

We are no different.

In fact, many other species have been more successful than humans.

Success is not defined by what species do but by how long they last. "

When you say there is "No purpose in life" what you might mean is that there is no ultimate or absolute purpose of life.
In other words there is no purpose which has an higher objective value than compared to any other purposes someone may have.

Which helps explain why liberty is a highest value.

If there was an ultimate or absolute purpose of life then liberty as a consequence would be required to be secondary to that purpose.

So, whether or not the entire biological process has assigned mandate or requirement or somehow knows what it wants is not something science can determine at the moment.

And as far being different from other animals, it seems fairly obvious to me that humans are significantly different than other animals. Though there also many similarity between all life and a big difference between life and things not living.