132 Evolution and the Fossil Record
Ladders, Bushes, Mosaics, and “Missing Links”
Evolution usually proceeds by speciation—the splitting of one lineage from a paren-
tal stock—not by the slow and steady transformation of these large parental stocks.
Repeated episodes of speciation produce a bush. Evolutionary “sequences” are not
rungs on a ladder, but our retrospective reconstruction of a circuitous path running
like a labyrinth, branch to branch, from the base of the bush to a lineage now surviv-
ing at its top.
—Stephen Jay Gould, “Ladders, Bushes, and Human Evolution”The realization that the classification of life forms a natural bushy or treelike pattern has
other implications as well. As we saw in chapter 4, the older (pre-Linnaean) way of arrang-
ing nature was in the scala naturae or “ladder of creation,” with “lower” animals at the base,
humans near the top, and divine beings up to God completing the ladder (figs. 5.1 and 5.2).
FIGURE 5.2. Evolution is not about life climbing the “ladder of nature” or the “great chain of being” from
“lower” to “higher” organisms. Instead, evolution is a “bush” with many lineages branching from one
another, and ancestors living alongside their descendants. (Drawing by Carl Buell)