“You were making the case that Lucy’s species was a good candidate as an ancestor to merfolk…because they were bipedal?”

“First a little context,” he said. “During the Pliocene Epoch some 5 to 2.5 million years ago, the climate in East Africa was changing, becoming drier and cooler, reducing forested areas. For tree-dwelling species like Lucy’s, this meant less food. For them to survive, they had to adapt. Bipedalism may have evolved in the trees as a method to walk along branches that would otherwise be too difficult to traverse on all fours. Yet as you know, it proved to have many benefits on the ground as well. It allowed australopithicines to see over tall grass for predators, and it allowed energy efficient locomotion in open places such as the expanding savanna. The latter was especially important because it let them roam farther and farther in search of food. All the way—”

“All the way to the ocean,” Elsa finished.

Marty nodded. “You understand now. However, bipedalism not only got australopithicines to the ocean, it allowed them to thrive there. Walking erect let them keep their heads above the water as they waded in the shallows for food. Refined motor control in their hands let them use stone artifacts for cracking open shellfish.”

“And according to your aquatic ape theory, they developed more and more aquatic adaptations over time, with one group returning to land and passing on their adaptations through their descendants all the way down the line to us, and another group remaining in the ocean and evolving into fully aquatic mammals.”

“Exactomundo, my dear.”

“Why did the one group return to land? If there was ample food in the ocean and less competition, why return to land where they would ultimately be driven to extinction?”

“The main factor was likely changing environmental conditions. Another would be the control and use of fire. Warmth, light, protection from predators, a way to create more advanced hunting tools, a method for cooking food. In other words, fire made life on land suddenly a lot more attractive.”

“Only it wasn’t Australopithicus but Homo erectus that mastered fire.”

“Not true. Recent evidence suggests early hominins tamed fire as early as two million years ago. Australopithicus went extinct 1.9 million years ago. Which means the aquatic australopithicines that returned to land could have been using fire for quite some time before being out-competed by the genus Homo.”

Elsa stopped playing the devil’s advocate for a moment so she could process everything that Dr. Murdoch was telling her. In the ensuing silence, her first thought was: It all makes sense. It all fits. It’s just…crazy.

Marty was watching her closely. Clearly he didn’t think any of this was crazy, and he was waiting for her decree.

She pressed her hands against the sides of her face, her fingertips on her temples. “I’m trying to believe all of this Marty…”

“You don’t have to try, Elsa. This is the scientific method at work, from hypothesis to testing and analysis. The DNA result is right there!” He jabbed a finger at the computer monitor.