Mixing the correct cellular soup for survival
Copyright 1998 Nando.net
Copyright 1998 Scripps Howard
(January 19, 1998 00:13 a.m. EST http://www.nando.net) - Genes are the
blueprint of life. Or perhaps not. Some embryologists -- scientists who
study how a single fertilized egg develops -- are proposing an
alternative theory: that genes are like building regulations, and it's
growing cells that are the cutting edge of evolution.
The idea has arisen out of some weird observations. A chimpanzee's
genes
are 99 percent the same as human genes. Even one-third of yeast genes
have counterparts in humans.
The curiosity is not how alike humans, chimpanzees and yeast must
somehow be, but how different they actually are when they have so many
genes in common.
Another observation is that bacteria have evolved to live on just about
any energy source. Some live in darkness, others in volcanic vents, and
yet others on your teeth. Other living creatures are differently
diverse. They give electric shocks, fly, or write symphonies, but their
food is more or less the same.
The two are linked because eating is about the biochemistry of energy.
Fruit flies, which have many genes in common with humans, are
genetically and biochemically similar to people. There are even
biotechnology companies studying fruit fly genetics to help understand
human biochemistry.
What may have happened in prehistory is that bacteria came first and
learned how to evolve biochemically. Two billion or so years later came
other living creatures, which evolved through changing shape and
behavior.
John Gerhart of the University of California-Berkeley and Marc
Kirschner
at Harvard Medical School have just published their summary of modern
embryology, "Cells, Embryos and Evolution" (Blackwell Science, $69.95).
It proposes that the vehicles for much of this second type of evolution
are cells, and they are especially interested in one type called neural
crest cells.
These are cells that, during embryo development, can turn into any of
an
enormous variety of more specialized ones. They include bones, bird
beaks, human vocal cords, sense organs and blood vessels -- many of the
distinguishing features of species.
The job of neural crest cells is to explore. Blood vessels grow in
patterns that are not determined by genes, and are often different in
identical twins. Elk antlers, hummingbird beaks and elephants' trunks
are all derived from neural crest cells.
These cells have been studied for decades, but as Gerhart and Kirschner
surveyed embryologists' work, increasingly informed by discoveries in
more basic science such as molecular biology, it seemed that evolution
itself depended on such cells.
Is that enough to consider displacing genes from the center of the
evolutionary universe? No. But it does begin to suggest genes should
share the center stage with cells.
To see how the two work together, let us take another look at how genes
work, in the light of molecular and cell biology.
Genes cause cells to make proteins such as insulin and hemoglobin.
These
proteins make the body work.
But genes don't make proteins all the time: they're switched on and off
by what is happening around them. Insulin is made only when the
conditions are right, perhaps when sugar is eaten. Every cell in your
body has the same genes, but every gene has a set of switches which
make
sure, for example, that your skin cells do not start making insulin.
The switches work in response to the environment. But their environment
is the cell. So genes and cells affect each other.
Take deer antlers. Genes create a biochemical soup in which cells grow.
During the animal's development, these cells "explore" new shapes. The
size and shape of the antlers vary how the elk reacts to its
environment: it may find it hard to eat leaves growing high, or easier
to challenge rivals for the low-growing leaves.
Either way, the food the animal eats affect where and when genes get
switched on -- that is, they affect the biochemical soup.
If the combination of genes and cells works well, the animal is
successful and the soup's recipe is passed on to the next generation.
What the embryologists are saying does not contradict traditional
Darwinian evolution. Richard Dawkins, for example, has said the ability
to evolve better is itself the result of evolution. Cells that evolve
quickly would be one way of doing this.
This also implies there can be different kinds of evolution, as in
bacteria and their biochemical diversity, and animals and their shape
diversity. Gerhart and Kirschner tentatively suggest there can be
psychological evolution, too.
Other scientists have suggested prehistoric man was what we would now
describe as schizophrenic, given the evidence of remorse-free killings
prompted by divine "voices", for example, described by Homer.
Even this does not exclude genes, whose functioning is affected by the
outside world. Schizophrenia appears to be related to a protein in the
brain called dopamine. This is, of course, made by a gene.
So genes tell cells what they can and cannot do. In return, cells call
on the resources of genes to enable them to act. Perhaps the best
analogy is that we are driving a car. The genes are the gears and
engine
while the cells are the bodywork and wheels. Lots of different car
designs are possible.
By DANIEL GREEN, The Financial Times
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