Evolution is
a serious game in progress, of course at an impercetably
slow pace. For us mortals, with short life spans, nothing really
changes. Mother Nature, with her assistant
Natural selection, has been playing the same game of speciation and
divergence for close to 4 billion years.
One of the best fossils to study various aspects of evolution is
the simple tooth. (1). In fact many extinct animals have left behind only their fossilized teeth for us to
know and weave tales about them; how
big they might have been and what they
would have eaten. There are indications
that though jaws and teeth evolved
independently, somewhere along the
evolutionary time lines, their pathways merged with the result that
several things were firmly established once and for all. The location of the teeth on the jaws,
their function and enabling
dental features. The frontal incisors
and canines help in grasping and tearing, premolars and molars
are predominantly grinders, though they
can also cut. Cusps, the conical projections on the
surface of the molars are the enabling
features to aid grinding and cutting process.
From the single cuspid reptilian to multi cuspid mammalian, there are large variations in the dental features between
species, but relatively less within a given species.
Harjunma et al(2) were fascinated by the developmental biology of molars in
laboratory mice. Mice teeth are limited to incisors
and molars. In laboratory bred mutant
and transgenic mice very often cusps are
totally absent. Except aesthetics, these flat teeth may not have much functional use. Poor mice, flat teeth would have robbed them off the whole enjoyment of eating. But why flat teeth, what leads to such a strange situation?. Scientists have identified at least 29 gene mutations which can affect
teeth formation in multiple ways, absence of cusps included. Mutation (altered message) is one thing and signalling, (sending
the message across to intended
recipients) is another thing. Signals are clues to turn on or turn off or slow down specific biochemical processes. Tinkering
with three such signalling pathways simultaneously
the team could ultimately increase
the number of cusps even beyond the normal.
Harjunma team suggest that there could be
multiple genes at work in
imparting cusp pattern to molars. Adjusting three genes they could make the cusps reappear, but then, in all possibility, something else might have gotten impaired ? No
wonder evolution is a slow process, it is so intricate, so many messages need to be so finely balanced.......
A friend of mine, who is working in the area of drug research, spoke to me recently about the long years of study needed to zero in on a drug molecule. A very promising drug molecule may prove to be causing some other ailment as a side effect. For example it might cure cancer but might lead to blindness. That is not acceptable. Biological signals are never dedicated " For your eyes only" type. One single signal might be meant for several recipients and each recipient might interpret it in a different way. Hence the need for fine coordination. And that takes enormous amount of time.
A friend of mine, who is working in the area of drug research, spoke to me recently about the long years of study needed to zero in on a drug molecule. A very promising drug molecule may prove to be causing some other ailment as a side effect. For example it might cure cancer but might lead to blindness. That is not acceptable. Biological signals are never dedicated " For your eyes only" type. One single signal might be meant for several recipients and each recipient might interpret it in a different way. Hence the need for fine coordination. And that takes enormous amount of time.
“Tailpiece”
Playing the same game for close to 4 billion
years is not a joke. Boredom is sure to creep in at times and that is
when Mother resorts to a few naughty tricks and treats. Her lazy assistant
Natural Selection lets the players fight it out for survival, to decide who wins and who gets wiped out. Evolutionary biologists of course would interpret
these as are necessary and well orchestrated
examples of adaptive evolution,
or survival tactics. But just imagine
wouldn’t it be more fun to accept these
as simple acts of pranks? Take for example.
the rampant practice of mimicry(3,4): the Australian insect which resembles a twig, the harmless
hoverfly which imitates the looks of the sting bee, the venomous Texas
More about mimicry later
More about mimicry later
1.Evolution and
development of teeth McCollum et al J.
Anatomy. 2001 199, pp. 153-159
2. On the difficulty of increasing dental complexity:
Harjunmaa et al Nature 2012, March 15, 483, 324-326.
3. Comparative analysis of the evolution of imperfect
mimicry Penney, H D et al, Nature 2012
March 22, 483, 461-464
4. A taste for mimicry ; Ruxton et al Nature 2005 , January 20 , 433 205-206
