When it comes to evolution, scientists know that life as we know it began in the planet’s seas. At some point, those ancient fish decided to venture onto land, using their fins as crude walking appendages, and some got so good at it that they eventually made land their full time homes. What happened in between, though, was a little fuzzy. To fill in those gaps, researchers from the University of Ottawa and McGill University took the only obvious course of action: They took modern fish known for walking on land, and raised them there for two years.

“Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioural variation, a form of developmental plasticity”, says Emily Standen, a former McGill post-doctoral student who led the project, now at the University of Ottawa. “We wanted to use this mechanism to see what new anatomies and behaviours we could trigger in these fish and see if they match what we know of the fossil record.”

The fish, called Polypterus, is native to Africa and while it spends most of its time in water, it’s capable of “walking” on land and breathing air for extended lengths of time. This made it the perfect candidate for the study.

After two years, what they observed was essentially evolution at work. The “terrestrialized” fish walked much more capably than their aquatic brethren, holding their fins closer to their bodies and their heads more upright. Their skeletons even adapted, developing stronger pectoral attachments and reducing connections with the head, allowing for longer strides and improved head mobility.

“Because many of the anatomical changes mirror the fossil record, we can hypothesize that the behavioural changes we see also reflect what may have occurred when fossil fish first walked with their fins on land”, says Hans Larsson, Canada Research Chair in Macroevolution at McGill and an Associate Professor at the Redpath Museum.

Because this time in prehistory would have been very competitive, the ability to walk on land gracefully and quickly would have been a huge advantage for our ancient ancestors. As fish adapted, their anatomies could eventually become part of their genetics, which would likely have been favored and passed down according to natural selection.