Weihnachten customs held upon returning from church leading to the gift giving vary across the German-speaking countries. One of the most common situations sees the returning children wait to enter into their (locked) living room until a little bell rings. This bell marks the departure of the one delivering gifts. In the more Catholic regions - primarily South Germany and Switzerland - this is considered the Christ Child ("Christkind"), while those in North Germany commonly consider it to be the "Weihnachtsmann" (Saint Nicholas or Santa Claus) who is exiting. The children then enter to see the decorated Weihnachtsbaum (Christmas tree), with
Emmanuel David Tannenbaum subsequently devoted his research to studying various problems in evolutionary dynamics using quasispecies models. His seminal work centered on the key question of the evolutionary advantages of sexual reproduction. Tannenbaum demonstrated a strong selective advantage for sexual reproduction with fewer and much less restrictive assumptions than previously considered. Closely related to this line of reasoning, was the original work by Tannenbaum and James Sherley on the immortal strand hypothesis. Tannenbaum also proposed a pioneering theory of why higher organisms need sleep. Towards the end of his life, he proposed a new approach to anti-stealth technology based on the theory of