Overview: Our DNA can determine attributes from eye color to medical predispositions. An extraordinary technology called CRISPR allows us to edit human DNA, possibly eliminating genetic diseases or choosing our children's features. But how far should we go?

DVD Verdict: A string of discoveries beginning in the 1990s has led scientists to a revolutionary tool known as CRISPR.

It comes from the immune-like response of bacteria that can chop up the DNA of invading viruses and incorporate it into their own, creating a "memory" of the invader in case it attacks again.

This simple but powerful gene-editing tool has now been harnessed by humans to edit DNA - including our own. The ability to make targeted edits to the genome could mean a cure for genetic disorders like sickle cell disease.

It could also lead to editing of human embryos for specific traits. But how far should we go? Is it wrong to engineer soldiers to feel no pain, or to resurrect an extinct species? Is there harm in allowing parents to choose their children's features, like eye color or height?

And is something lost, even in editing out "harmful" things like disease? The scientists who pioneered human genome studies and CRISPR grapple with the ethics of editing the very code that makes us human.

What we learn as we watch along, is that Genome editing is of great interest in the prevention and treatment of human diseases. Currently, most research on genome editing is done to understand diseases using cells and animal models.

Scientists are still working to determine whether this approach is safe and effective for use in people. It is being explored in research on a wide variety of diseases, including single-gene disorders such as cystic fibrosis, hemophilia, and sickle cell disease.

It also holds promise for the treatment and prevention of more complex diseases, such as cancer, heart disease, mental illness, and human immunodeficiency virus (HIV) infection.

Ethical concerns arise when genome editing, using technologies such as CRISPR-Cas9, is used to alter human genomes. Most of the changes introduced with genome editing are limited to somatic cells, which are cells other than egg and sperm cells.

These changes affect only certain tissues and are not passed from one generation to the next. However, changes made to genes in egg or sperm cells (germline cells) or in the genes of an embryo could be passed to future generations.

Germline cell and embryo genome editing bring up a number of ethical challenges, including whether it would be permissible to use this technology to enhance normal human traits (such as height or intelligence).

Indeed, based on concerns about ethics and safety, germline cell and embryo genome editing are currently illegal in many countries. Learn more than this about a subject I'd like to bet you knew nothing, or very little of, now on this PBS-released DVD 'NOVA: Human Nature.' This is a Widescreen Presentation (1.78:1) enhanced for 16x9 TVs.