Understanding Evolution

Phylogenetic systematics, a.k.a. evolutionary trees :

Using trees to learn about the order of evolution: The spider's web

Phylogenies can be used to test hypotheses about evolution. Before phylogenies became a standard tool within biology, many biologists assumed that the orb-weaving spiders, with their intricate and orderly webs, had evolved from spiders with disorderly cobweb-like webs. However, the cladistic analysis of these spiders showed that, in fact, orb-weaving was the ancestral state, and that cobweb-weaving had evolved from spiders with more orderly webs. The phylogeny caused the biologists to reject their original hypothesis about orb-weaving evolution.

cobwebs an orderly web
A disorderly, cobweb-like web on the left, and a neat, orderly web on the right.


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Cobweb photo by Jo-Ann Ordano © California Academy of Sciences; orb-web photo by Lloyd Gomez © California Academy of Sciences

Understanding Evolution © 2018 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California