You don’t need to meet another intelligent species to know that it is the nature of intelligence to create intelligence. There are 7 billion other intelligent creatures on this planet to observe.
You are making a cop out because this offends your atheist sensibilities.
Their is one intelligent species on this planet but fine, if you want to go with individuals, how many of the 7 billion intelligences will create intelligence?
My atheist sensibilities are fine it is my science sensibilities that are hurting.
Almost all - if not all - animals and plants have some level of intelligence. The question is degree. To be intelligent one must have senses to receive input and the ability to process that input to make a selection or choice. Most animals and plants do this instinctively and are not conscious of the selection. Humans are different. Yes, we have instincts and impulses but we can override our instincts and impulses.
Humans are beings that know and create. We have built a technological society. As such we have created a myriad of technologies that mimic intelligence. They have sensors and they have processors. They receive input from their surroundings and make predetermined responses.
This should be so self evident that I am at a loss how you can be arguing against this. Therefore, I concluded that this offends your atheist sensibilities.