Cassell, author of the just-published book Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts (2021), tackles one of the most remarkable mysteries of life forms:
It typically takes up to three generations of butterflies to make the complete journey.3 This means that the navigation information is genetically programmed. One of the unique aspects of the migration of the monarchs in eastern North America is that during their summer stay in Canada they occupy close to 400,000 square miles, while during their overwintering hibernation in Mexico they occupy less than half a square mile. As noted previously, they often migrate back to the same tree that their ancestor butterflies departed from in a mountainous region in Mexico. That means they must have an extremely accurate method of navigation to locate such a small target.
Navigating by Sun Compass
Monarchs navigate using a sun compass, and as previously described, this includes time compensation to account for the movement of the sun.4 The circadian clock used in the process is embedded within the butterfly’s antennae.5 The sun’s azimuth position is detected through the butterfly’s compound eyes.6 Researchers are only just beginning to decode the biological information required for these amazing feats. The genome of monarch butterflies has been decoded, including the genes related to the neurobiology and physical systems used for migration.7 Comparisons of migratory monarch genomes with the genomes of non-migratory monarchs has revealed that more than five hundred genes are involved in migratory behavior.8
Eric Cassell, “For Evolution, Monarch Butterfly Migration Is a Mystery” at Evolution News and Science Today (November 22, 2021)
Now, about the evolution part, Cassell writes,
There exists no evolutionary model that satisfactorily explains its origin. That by itself does not prove that gradual evolution didn’t produce such programming, but the lack of such a model should at least give the open-minded pause for reflection.
Eric Cassell, “For Evolution, Monarch Butterfly Migration Is a Mystery” at Evolution News and Science Today (November 22, 2021)
You may also wish to read: Book excerpt: Navigational genius of insects Eric Cassell: The Goulds call this curious dance “the second most information-rich exchange in the animal world,” second only to human language. That is quite a statement considering the communication is by insects with only 950,000 neurons, compared to humans with about eighty-five billion.