High in the eucalyptus trees of Australia, koalas (Phascolarctos cinereus) are often seen curled into tight, fluffy balls, barely moving for hours at a time.

There are so many koalas in some places that food is the issue – while elsewhere populations are threatened by habitat loss. And there are no easy fixes ...

Kangaroo Island koalas have many more, and longer, stretches of identical DNA inherited from both parents. Scientists call these stretches runs of homozygosity, and they are a hallmark of inbreeding.