|A graph combining fossil, contemporary, taxonomical and |
archaeological data to show the last point at which lasting
changes occurred and where the stasis period begins.
The million year point is at 10 to the 6 million years ago
A team of scientists led by Josef Uyeda of the Oregon State University, stated 'rapid evolution is clearly a reality over a fairly short time periods, sometimes just a few generations, but those rapid changes do not always persist and may be confined to small populations.' Such a trait is what causes the phenomenon of subspecies. A study combining data from modern human populations, archaeological and fossil data and the tree of life project based upon percentage increase in body size has shown that lasting changes require a period of at least a millions years or so.
Evolutionary biologists are still not sure how lasting changes occur, but it cannot be down to chance mutation in the DNA. Such a process is very slow. Most scientists believe that lasting changes are due to changes in ecological conditions which are extreme and long lasting. Such changes usually take between 1 and 10 million years to occur. The periods of little lasting evolutionary change are known as stasis periods.
This time scale overlaps with the date needed for long lasting evolutionary change provided by the data correlation. There are of course anomalies such as human evolution. Yet we are an exceptional species. This study therefore could be very useful in the future, when looking at evolutionary change within a species or animal group.