English: Geographic location of Guinea-Bissau and present-day settlement pattern of the ethnic groups. The main ethnic groups now present in Guinea-Bissau were already settled in the region in the 15th century, at the time of arrival of the Portuguese. With the establishment of the Atlantic slave trade the region experienced an input of Europeans, in their vast majority males, whose genetic imprint is undetermined. Many of the ethnic barriers were brought down, in particular the endogamic practices, promoting an intense cultural contact and higher levels of admixture between groups than before.