Sagan discusses the story of the Heike crab and artificial selection of crabs resembling samurai warriors, as an opening into a larger discussion of evolution through natural selection (and the pitfalls of intelligent design). Among the topics are the development of life on the Cosmic Calendar and the Cambrian explosion; the function of DNA in growth; genetic replication, repairs, and mutation; the common biochemistry of terrestrial organisms; the creation of the molecules of life in the Miller-Urey experiment; and speculation on alien life (such as life in Jupiter's clouds). In the Cosmos Update ten years later, Sagan remarks on RNA also controlling chemical reactions and reproducing itself and the different roles of comets (potentially carrying organic molecules or causing the Cretaceous–Paleogene extinction event).

Adam Rutherford meets a new creature created by American scientists, the spider-goat. It is part goat, part spider, and its milk can be used to create artificial spider's web. It is part of a new field of research, synthetic biology, with a radical aim: to break down nature into spare parts so that we can rebuild it however we please. This technology is already being used to make bio-diesel to power cars. Other researchers are looking at how we might, one day, control human emotions by sending 'biological machines' into our brains.

The film explores the revolutionary gene-editing tech now giving humankind the freedom to redraw the blueprint of biological life itself. We investigate not only the tremendous potential the technology holds, whether in the fight to eliminate diseases or in transforming agriculture to adapt to unprecedented climate extremes, but also probe the inherent risks involved and the potential for widespread abuse, dangers that could take our future down a very dark, dystopian path.

We humans often like to think we're the end of the line when it comes to evolution. But if we rewind through our short time on Earth as a species, and the many changes that have occurred to us along the way, we find we're still very much a work in progress. Renowned geneticist and author Spencer Wells reveals how changes in our genetic code have fuelled major changes in our appearance and capabilities over time, and why scientists believe we're continuing to rapidly evolve today. By understanding these changes, we are better prepared for the future.

Professor Brian Cox grapples with science's darker side, asking why, when science has done so much for us, it often gets such a bad press. Starting with the original Frankenstein - the grisly 19th century tale of George Foster's hanging and subsequent 'electrocution', Brian confronts the idea that science can go 'too far'. From the nuclear bomb to genetic modification, British science has always been at the cutting edge of discovery, but are British scientists feckless meddlers, or misunderstood visionaries whose gifts to humanity are corrupted by the unscrupulous?

Some 30 million Americans have sent their DNA to be analysed by companies like 23andMe and AncestryDNA. But what happens once the sample is in the hands of testing companies, and how accurate are their results? The film explores the power of genetic data to reveal family connections, ancestry, and health risks—and even solve criminal cold cases.