This is The Guardian.

Two years ago, the Russian opposition leader Alexei Navalny died in a remote Arctic penal colony.

Now, the UK and several of its European allies say blame lies at the feet of the Russian state,

alleging to have uncovered the lethal poison used.

In a joint statement, the governments of the UK, France, the Netherlands, Germany and Sweden said

they had analysed samples from Mr Navalny following his death and found traces of a toxin found in poison dart frocks from South America.

Incredibly, this was not the only chemical originating from South America in the headlines this week.

A psychedelic drug called DMT, which is also found in ayahuasca, has been shown in a small

clinical trial to swiftly and significantly improve symptoms in people with treatment-resistant

depression. The fact that a mystical, hallucinogenic trip where you might need an otherworldly

being can transform and reorganise the

brain state speaks to the many complex mysteries of the mind but there's a more strange and

obvious enigma just five or six inches further down. The chin.

Yes?

The chin.

Scientists this week appear to have finally answered the burning question.

Why do humans have chins?

Because, believe it or not, we're the only animals that do.

So today I'm sitting down with science correspondent Nicola Davis and my co-host science editor Ian Sampal

to discuss the stories of the week.

From The Guardian, I'm Madeline Finley, and this is Science Weekly.

Ian, we're starting today with a trial that's had some exciting early results in developing new treatments for depression.

...