Ecology, Evolution and Genetics. Solutions to many of the world's most pressing environmental issues require a basic understanding of nature at the organismal, population and ecosystems level.
Average. On average, women start to show around the fourth month of pregnancy, between weeks 14 and 17. By week 17 the uterus usually has expanded to just an inch and a half below the navel, making the pregnancy more obvious.
1 Girls usually start to show the physical changes of puberty between the ages of 9 and 13, which is slightly sooner than boys. 2  The female sex hormone called estrogen and other hormones cause the physical changes. 3  Many girls are fully developed by the age of 16.