I am looking for a science-fiction book that features genetic engineering, in a way. It is about a science team sent from Earth to an alien planet. On that planet, there used to live an intelligent species, but they are long gone. The team was sent there to explore why they vanished. They find out that the alien species went extinct because they valued “good genes” very much, and therefore bred themselves into extinction. One of the scientists actually builds a "suit" that he wears to emphasize and feel like the aliens! The team realizes that the ship, coming from Earth to take them back home, is not coming. They then decide to all get together to have as many kids with each other as possible in order to have enough genealogical diversity to kickstart a new civilization on the planet. However, they run into difficulties. Does anyone have a hint?
This is Total Eclipse by John Brunner
As you remembered, it's about a human archeological expedition to a planet with extinct aliens, and the aliens were eventually discovered to have destroyed themselves by breeding themselves into "perfection".
This review discusses the suit you mention
He eventually comes up with a plan to make crab suit (!) to simulate the creature’s movements, way of visualizing the world, and even the psychological impact of the creature’s evolving sexual stages.
From the novel itself, this quote confirms the genetic theme:
We found out that the Draconians inbred to the point of simple genetic collapse because they used commitment to fertilise each other as the basis for their medium of exchange.