Biology Reference
In-Depth Information
have a recognized relationship with chronological age (e.g., tooth erup-
tion patterns, overall body size, annual rings, number of coils, molt stage,
epiphyseal fusion, etc.) can be used as age-surrogates and as a means for
assigning individuals to developmental age classes.
The researcher needs to be aware of any potential ascertainment
biases of the data, and the way in which this bias might affect the age
distribution and the results of analysis of these data. When museum
samples are used, age distribution may be skewed for reasons that
have to do with social behavior of that species. (For example, if a cer-
tain subgroup of a wild population protects the group and therefore
confronts nonmembers, those individuals will most likely be captured
and the resulting collection will be composed primarily of individuals
in that age/sex/status group. Methods of capture (e.g., size of nets or
traps) may also influence sample composition. If patient data are being
accessed, the age at which individuals are diagnosed, treated, or dis-
charged may have implications for the nature of the age groups
available. Depending upon the particular research situation, grouping
may amplify or reduce within-age group variability.
When growth patterns are being compared between groups, care
must be taken to ensure that the criteria used to assign developmen-
tal ages are consistent and comparable across groups. This can be
extremely difficult, especially when comparisons cross species bound-
aries. Assigning developmental ages from biological markers can affect
the degree of variability within age groups, and this can vary from
species to species. For example, let us say that we are interested in
comparing growth during infancy between human and non-human pri-
mates. The human literature can provide a chronological time frame
for the developmental period known as “infancy,” and similar defini-
tions for the relationship between chronological age and life history
intervals are available for certain non-human primate species raised
in laboratory settings. The length of these time frames will be different
in each species and this warrants consideration. Extreme care must be
taken in estimating ages from proxy data when choosing comparable
developmental stages for inter-species comparison. Since each
research situation is different, there is little general advice that can be
offered beyond caution and alertness to these and other potential haz-
ards.
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