The BBC has made an extraordinary new documentary, presented by Sir David Attenborough, which will reveal the discovery of a fossilised skeleton that may be a vital ‘missing link’ in human evolution. The centrepiece of the programme is the unveiling of the first-ever complete skeleton of an extinct animal called an adapid

Dr Alice Roberts re-traces the greatest ever journey taken by our ancestors. Thousands of years ago one small group of our species, Homo sapiens, crossed out of Africa and into the unknown. Their descendants faced baking deserts, sweat-soaked jungles and frozen wildernesses and risked everything on the vast empty ocean. Within 60,000 years they colonised the whole world... How did they do it? Why do we, their descendants all look so different?

Intelligence and adaptability allow primates to tackle the many challenges of life, and this is what makes our closest relatives so successful. This resourcefulness has enabled primates to conquer an incredible diversity of habitat. Hamadryas baboons live on the open plains of Ethiopia in groups up to 400 strong. Strength in numbers gives them some protection from potential predators. But, should their path cross with other baboon troops, it can lead to all-out battle, as males try to steal females from one another, and even settle old scores. Japanese macaques are the most northerly-dwelling primates and they experience completely different challenges. Some beat the freezing conditions by having access to a thermal spa in the middle of winter. But this privilege is only for those born of the right female bloodline. For western lowland gorillas, it's the male silverback that leads his family group in the rich forests of the Congo basin. He advertises his status to all with a powerful chest-beating display. Most primates are forest dwellers, and one of the strangest is the tarsier – the only purely carnivorous primate. As it hunts for insects the tarsier leaps from tree to tree in the dead of night, using its huge forward-facing eyes to safely judge each jump. Good communication is essential for success in primate society.

Sir David Attenborough investigates whether the world is heading for a population crisis. While much of the projected growth in human population is likely to come from the developing world, it is the lifestyle enjoyed by many in the West that has the most impact on the planet. Sir David examines whether it is the duty of individuals to commit not only to smaller families, but to change the way they live for the sake of humanity and planet Earth.

The world is affected by an obesity epidemic, but why is it that not everyone is succumbing? Medical science has been obsessed with this subject and is coming up with some unexpected answers. As it turns out, it is not all about exercise and diet. At the centre of this programme is a controversial overeating experiment that aims to identify exactly what it is about some people that makes it hard for them to bulk up.

Horizon uncovers the secret world of our dreams. In a series of cutting-edge experiments and personal stories, we go in search of the science behind this most enduring mystery and ask: where do dreams come from? Do they have meaning? And ultimately, why do we dream? What the film reveals is that much of what we thought we knew no longer stands true. Dreams are not simply wild imaginings but play a significant part in all our lives as they have an impact on our memories, the ability to learn, and our mental health. Most surprisingly, we find nightmares, too, are beneficial and may even explain the survival of our species.