ubiquitous Existing or having presence everywhere
at the same time. For example, ribonuclease, an enzyme
that degrades RNA, is ubiquitous in living organisms.
ultimate causation An explanation for why a behav-
ior has evolved and its context within the environment.
Identifies the evolutionary factors responsible for the
behavior and its purpose within a biological system.
ultrasound The use of sound with a frequency high-
er than 20,000 Hz. Used to obtain images for medical
diagnostic purposes, especially during pregnancy.
umwelt The total sensory and perceptual world of
an animal.
uniformitarianism A doctrine that states that current
geological and biological processes, occurring at the same
rates and in the same manner observed today, account
for all of Earth’s geological and biological features. “The
present is the key to the past.” The doctrine of uniformi-
tarianism was advanced by James Hutton (1726–97) in
his publication, Theoryof the Earth(1785).
unsaturated fatty acids Fatty acids are the essential
building blocks of all fats in our food supply and body,
but not all of them have beneficial results. There are
five major fatty acids types: saturated (SAFA), unsatu-
rated (UFA), monounsaturated (MUFA), polyunsatu-
rated (PUFA), and essential (EFA).
An unsaturated fatty acid is a long-chain car-
boxylic acid that contains one or more carbon
C=C double bonds. They occur when all of the
carbons in a chemical chain are not saturated with
hydrogen, so that the fat molecule contains one or
moredouble bonds and produces a fat that is fluid at
room temperature.
There are three types of unsaturated fatty acids:
monounsaturates such as oleic acid found in olive and
sesame oils that contain one double bond; polyunsatu-
rated fats such as corn, soybean, and sunflower oils
that contain more than one double bond; and essential
fatty acids (EFA) that, while they cannot be created in
the body, are important. EFAs include linoleic acid
(LA) and alpha-linolenic acid (LNA).
The double bonds in a molecule of an unsaturated
fatty acid can be found in two forms known as cisand
trans.
Cisdouble bonds produce a kink, or a bend of
about 30 degrees for each double bond into the back-
bone and can flip over to the transform under high
temperatures. Transdouble bonds allow the molecule
to lie in a straight line. However, the human body can-
notconvert the transform into nutrients and thus can-
not activate the metabolic activities required to convert
to the active cisforms. This can lead to a deficiency in
essential fatty acids. The more double bonds, and333