1. FATTY ACID OCCURRENCE AND DISTRIBUTION
83
glands similarly appear to differ markedly in their fatty acid composition from depot fats. The branched-chain fatty acids are prominent
constituents and differ in type from those found in the depot fats. There
is not enough evidence to show that each species elaborates in the
secretions mentioned its own type of fatty acids, but evidently there
are marked differences between some species. Thus, although a study
of the fatty acid composition of the main depot fats of higher animals
may serve merely to reveal the nature of the dietary fats, it is not impossible that studies on the fatty acid composition of the minor fatty
depots and secretions will reveal interesting information permitting correlations to be made between chemical composition and the classification of species on morphological grounds.
VII. Theory of Evolution and Fatty Acid Composition
A. GENERAL CONSIDERATIONS
In the preceding sections it has been shown that the component
acids of fats and other lipids tend to align themselves in groups according to their biological origin. It is now desirable to collate the evidence
from these groups and determine what relationships, if any, exist between fatty acid occurrence and the place of organisms in the evolutionary scale of development. This will involve some interesting comparisons between the processes of evolution of fats and other lipids in
plants and animals.
Hilditch (346) suggested in 1935 that "perhaps, when in the course
of time sufficiently wide and detailed data have been collected, systematic description of natural fats will commence with those of the
minute aquatic flora and fauna, will proceed to those of the larger
aquatic denizens, and then to the two respective branches of land
flora and land fauna." This prediction has, to some extent, been fulfilled, and it may now be said that the systematic treatment of natural
fats according to their biological origin has been widely adopted. Furthermore, it is clear that many close parallelisms exist between biological classifications and the types of fatty acids present in the lipids
of different species as originally described by Hilditch and Lovern
(140). At the same time it is equally apparent that the fats from organisms such as yeasts or molds may resemble closely those of animals
or seeds, thereby indicating the absence of correlation between biological classification and chemical composition. The occurrence of oleic,
palmitic, and stearic acids in the lipids of most forms of life is perhaps
explained by the operation of a similar mechanism of synthesis of fatty
acids in plants and animals. This mechanism involves the successive
83
glands similarly appear to differ markedly in their fatty acid composition from depot fats. The branched-chain fatty acids are prominent
constituents and differ in type from those found in the depot fats. There
is not enough evidence to show that each species elaborates in the
secretions mentioned its own type of fatty acids, but evidently there
are marked differences between some species. Thus, although a study
of the fatty acid composition of the main depot fats of higher animals
may serve merely to reveal the nature of the dietary fats, it is not impossible that studies on the fatty acid composition of the minor fatty
depots and secretions will reveal interesting information permitting correlations to be made between chemical composition and the classification of species on morphological grounds.
VII. Theory of Evolution and Fatty Acid Composition
A. GENERAL CONSIDERATIONS
In the preceding sections it has been shown that the component
acids of fats and other lipids tend to align themselves in groups according to their biological origin. It is now desirable to collate the evidence
from these groups and determine what relationships, if any, exist between fatty acid occurrence and the place of organisms in the evolutionary scale of development. This will involve some interesting comparisons between the processes of evolution of fats and other lipids in
plants and animals.
Hilditch (346) suggested in 1935 that "perhaps, when in the course
of time sufficiently wide and detailed data have been collected, systematic description of natural fats will commence with those of the
minute aquatic flora and fauna, will proceed to those of the larger
aquatic denizens, and then to the two respective branches of land
flora and land fauna." This prediction has, to some extent, been fulfilled, and it may now be said that the systematic treatment of natural
fats according to their biological origin has been widely adopted. Furthermore, it is clear that many close parallelisms exist between biological classifications and the types of fatty acids present in the lipids
of different species as originally described by Hilditch and Lovern
(140). At the same time it is equally apparent that the fats from organisms such as yeasts or molds may resemble closely those of animals
or seeds, thereby indicating the absence of correlation between biological classification and chemical composition. The occurrence of oleic,
palmitic, and stearic acids in the lipids of most forms of life is perhaps
explained by the operation of a similar mechanism of synthesis of fatty
acids in plants and animals. This mechanism involves the successive