TIME IN EVOLUTION! 
By F. E. Zeunser, Px. D., D. Sc. 
Professor of Environmental Archaeology 
University of London 
The study of evolution has proceeded along two different lines. 
While biologists were able to investigate the intimate structure 
of the cells composing living organisms and thus to unravel aspects 
of the mechanism of evolution, paleontologists supplied us with 
evidence for the succession of the forms of life. Broadly speaking, 
biological evidence has suggested that changes in the characters of 
species are sudden and paleontological evidence that they take place 
gradually. Apart from the problems connected with the causes of 
evolution (which are outside the scope of this discourse), there is 
involved in this difference the problem of time. 
It was, therefore, only natural that workers on evolution were 
interested in the question of how much time was required to bring 
about certain changes in the characters of animals and plants. This 
chronological aspect of evolution was stressed by the early evolution- 
ists, like Lamarck, Darwin, Wallace, Weismann, and Eimer. But 
paleontology and stratigraphy could do no more than provide a 
relative chronology of evolution. For the actual time involved there 
were only guesses available which were so divergent that no con- 
clusions could be based on them. No wonder, therefore, that the 
time aspect of evolution was neglected by the later generations of 
workers. The guesses did agree, however, in one respect: that, 
measured by human standards, the time available for evolution was 
very long. 
Since the end of the last century, however, geology has developed 
several methods of estimating geological time in years. Sequences 
of annual deposits, climatic and astronomical cycles, time rates of 
sedimentation and the decomposition of radioactive substances have 
been used in a great variety of ways, and the branch of geology which 
is called geochronology, has produced a number of time scales covering 
the entire history of the crust of the earth. As is to be expected, many 
1 Presented at the Weekly Evening Meeting of the Royal Institution of Great Britain, Friday, December 
3, 1948. Reprinted by permission of the Royal Institution, with slight alterations and additional figures. 
866591—50——17 247 
