{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Rates appear to vary between different groups

Rates appear to vary between different groups - The point...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Rates appear to vary between different groups. There are apparent living fossils that have changed very little, or not at all, in millions of years: the coelacanth , the horseshoe crab ( Limulus , see fig. 20.11, pg. 575) and the tadpole shrimp ( Triops ) are good examples. Other species or groups have evolved relatively rapidly (Horses, see figure). Rates of change also can vary during the evolution of a lineage. In lungfish a "score" was tabulated for each taxon as to whether it possessed ancestral or derived traits. This score was plotted against the age of the taxonomic group for which the score was tabulated. Resulting graphs (See fig. 20.10, pg. 575) show a rapid loss of "primitive" characters (=acquisition of "new" characters) through time and the slope of this curve shows a peak early in the lineage.
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The point is that morphological rates of evolution can be very different in both tempo and mode in different lineages of organisms. Some of the between-group differences are real and some are an artifact of temporal scale . Gingerich recorded rates of change in selection experiments, colonization events, post-Pleistocene changes and long-term changes (domains I, II, III, IV in table figure below) and plotted them against the measurement interval in years. The clear relationship indicates that changes measured over short time spans exaggerate the changes one might predict if carried out for a long time. There are reversals of morphological trends and periods of no change (="stasis"; next lecture) that reduce the rate of change when averaged over a long time period....
View Full Document

{[ snackBarMessage ]}