What is Heterochrony?
Heterochrony takes on a few different forms.
In Predisplacement, a character begins developing earlier in the
descendent lineage than it did in the ancestor.
On the flip side, Postdisplacement is when a character begins
developing at a later stage in the descendent lineage when compared
to the ancestor.
In both cases, the character does not change, only the timing of
developmental events.
In Acceleration, the character develops at a faster rate in the
descendent than in the ancestor.
On the flip side, Neoteny is when the character develops at a
slower rate in the descendent lineage when compared to the
ancestor.
In both cases, the character itself is not affected; rather the
growth rate is.
With Hypermorphosis, a character continues developing beyond the
point at which it stopped in the ancestral lineage.
On the flip side, Progenesis is when the development of the
descendent's character stops progressing before the point at which
it stops in the ancestral lineage.
In both cases, the character itself will change.
Hypothetical Example:
The tail of an ancestral feline species grows to 27 inches in
2.0 years. The feline species splits into 2 descendent lineages.
One feline descendent lineage splits into a species(we will call it
'Species X') that maintains the 27 inch growth and the 2.0 year
growth time; AND a species(we will call it 'Species Y') that
maintains the 2.0 year growth time but the tail grows to 29 inches.
This is an example of Heterochrony, specifically an example of
Heterochrony through a combination of Hypermorphosis(more growth)
and Acceleration(increased growth rate).
If it were just Hypermorphosis, the tail would take more time to
grow to 29".
If it were just Acceleration, the tail would reach 27"... just
sooner.
Thus; it is a combination. Happens more often than you would
think. :)
