The content you've requested is available without charge only to active Sigma Xi members and
If you are an active member or an individual subscriber, please log in now in order to access this article.
If you are not a member or individual subscriber, you can:
The process of evolution is generally described as having two parts: random mutation followed by natural selection. But mutations aren't always truly random, either in place or effect. Some of the types of challenges that confront organisms recur often enough to be predictable. Much like variations in anatomical structures, like the shapes of beaks, variations in the probability of particular mutations may affect the survival of a strain of organisms and therefore should be subject to natural selection. Various biochemical quirks in DNA sequence can abet the rise of predictable genetic changes. For example, repeated sequences in genomes can expand or shrink in length, and such variations in length can affect the activity levels of nearby genes or their regulation in response to environmental cues. One can think of genomes encoding one sequence explicitly and a range of other sequences implicitly. This assured genetic diversity can protect the descendants of an individual against pathogens and an erratic environment.
Connect With Us:
An early peek at each new issue, with descriptions of feature articles, columns, and more. Every other issue contains links to everything in the latest issue's table of contents.
News of book reviews published in
and around the web, as well as other noteworthy happenings in the world of science books.
To sign up for automatic emails of the
American Scientist Update
issues, create an
, then sign up in the
My AmSci area
JSTOR, the online academic archive, contains complete back issues of American Scientist from 1913 (known then as the Sigma Xi Quarterly) through 2005.
The table of contents for each issue is freely available to all users; those with institutional access can read each complete issue.
View the full collection here.
Receive notification when new content is posted from the entire website, or choose from the customized feeds available.