Here is the link to the Radiolab program on hygiene and hookworm:
Excellent NPR piece on microbiota diversity:
Here is an image from the recent Yatsunenko et al. study published in Nature this year, showing the differences between adult and infant microbiomes. Malawians take a little longer time to adopt the adult pattern of microbiota, compared to a US population (a). Infant microbiotas are significantly different from the microbiota of adults (b). CLick on the image to take you to the article.