2. It Takes Two

It may take two to make a baby - but not necessarily two to bring it up. So what makes a parent decide to stay or go? Especially if that parent is a dad. From the California mouse mother who has to kickstart her partner's paternal instincts, to Adelie penguin parents who can't leave their eggs alone for five minutes; from cheetah mums practicing promiscuity to keep the dads on side, to flamingo parents both producing milk for their young. We see just how far these incredible parents go in order to protect and nurture as many offspring as possible through to adulthood.