Can scientists "reverse evolution" in the laboratory? Can they rewind the evolution of birds from dinosaurs and see how it happened? Trying to replay the evolutionary movie in reverse has become a popular thing to do. The goal is to show that evolution really happened and to find out the steps it took. To do this, evolutionists have tinkered with the genes in chicken embryos to make them grow dinosaur-like tails. Others, more mechanically inclined, have tacked little plunger-like appendages onto chickens as tails to see if they could yield clues to the way their supposed theropod ancestors walked. Last year researchers claimed to backtrack evolution from bird beaks to dinosaur snouts when they turned off beak-building genes in chicken embryos. (Read "Rewinding Evolution from Bird Beak to Dinosaur Snout" to see why those scientists were mistaken when they thought they’d discovered a transitional form lost to the fossil record.) Now evolutionary scientists are tapping out their evolutionary story with chicken drumsticks. A team led by João Botelho at the University of Chile has discovered why the needle-like bone in a chicken's leg isn't as large and long as the adjacent, grip-friendly bone in the drumstick — speaking from the point of view of fried chicken aficionados. They have discovered why a chicken's lower leg develops with one sturdy bone beside a short, splintery one, instead of with two robust bones like the legs of dinosaurs, dogs, and humans. With that discovery they think they have rewound the dinosaur-to-bird evolutionary movie and unveiled one of its important secrets.
The Ankle Bone's Connected to the Shinbone...
Below your knee you don't have a chicken-like drumstick. You have two leg bones: the thicker shinbone (the tibia) and the thinner fibula. The knobs on the sides of your ankle are the lower ends of these bones. These paired bones are a great design, and the hind legs of dinosaurs and of most other tetrapods are similarly equipped. Though the fibula is much thinner than the tibia and supports comparatively little weight even among those of us who walk on two legs, it serves an important role in stabilizing the ankle and providing leverage for the muscles attached below the knee.
But a bird's lower limbs are designed differently. A bird's knee and the thighbone above it are hidden up inside the bird's body. This hidden part of the bird's leg helps prevent abdominal air sacs from collapsing and helps it breathe. (Learn more about this unique bird-breathing arrangement in "Lizard Breath Fails to Support Kinship with Birds.") Because it walks with its hips and legs at different angles from biped humans and theropod dinosaurs, a bird doesn't need the stability and leverage afforded by a full-length fibula and its attachments. The fibula on a chicken is very thin and so short it doesn't even reach the ankle, leaving the bird to support its weight on its tibias.