(To celebrate Darwin Day, here’s a translated excerpt from an old article, a part of a series on the basics of evolution from Allt om Vetenskap published during the 150 years anniversary of ”Origin of Species” 2009.
This is the end part of a piece on evo-devo, the connection between evolution and fetal development and the latest research in that field at that time. )
We are Family
The night vision of the owl, the small black dots along the edge of a mussel shell and the shimmering composite eyes of the dragonfly are all constructed with the help of a small group of very specific signalling proteins. You can even find the same proteins in a jellyfish.
One of the key genes for making an eye is called PAX-6. The protein produced by PAX-6 taken from a mouse can start the making of an eye in a housefly. This is proof of a deep kinship.
A carefully tuned interplay between the signalling proteins in the genetic toolbox results in a complete individual. Controls are turned on or switched off in a specific order, for a certain time. It is this chemical interaction that enables a limited number of genes to create the infinite variations we see in nature, and among all the extinct species we only encounter as fossils.
Changes in key genes opens up new possibilities in evolution. Small changes in fetal development can have major consequences in the long run.
A few more molecules of a transcription factor or an enhancer protein at precisely the right place and the right time can give a slightly longer leg, a beak that is just a littler harder or a skeleton with a thinner bone mass. Variations that can give an advantage in life and make its way into the gene pool and live on into the future.
And we are of course part of this endless variation too. You might say that all species come from the same factory, even though we are widely different models. You just need to look carefully to see that we have the same brand name stamped into our genome.
Once upon a time, hundreds of millions of years ago in the Cambrian seas, there existed a tunicate, a primitive marine animal maybe like a small sea squirt.
In its larval stage it swam for a short period in the water before it fastened itself on a rock surface. The rest of its life it lived a stationary life, straining the passing water and living off whatever nutritious particles that happened to float by.
As a larva it had a small string of neurons along the backside to help it move around. This string disappeared when it was time for the sedentary adult life.
But one of the larvae once had a technical hiccup in one of the genes that control the time plan for the construction of its body. It kept the string of nerves throughout life. That made it the first chordate animal. And thus it became the ancestor of all insects, fish, reptiles, birds and mammals living today. Us included. You can see it in the dna.
Av Elliott & Fry – Library of Congress