A biologist studying abnormal stripe patterns in zebras says humans could be partly to blame for their strange look — and that it could be an early sign of problems for the species. In a study published in the journal Molecular Ecology, Brenda Larison and other researchers looked at DNA from 140 plains zebras across Africa, including seven with abnormal stripes. They found increased levels of inbreeding among zebra populations with unusual patterns on their coats. The researchers say it could be a consequence of habitat fragmentation. Habitat fragmentation happens when a large habitat area is broken up into smaller areas by human-made developments like fences or roads. According to the study, the total population of plains zebras has declined by about 25 per cent since 2002. The International Union for Conservation of Nature estimated there were about 500,000 plains zebras as of 2016.