The Ascent of Man 12: Generation upon Generation

Uploaded by Nerisvyre on 16.05.2012

~ STRAUSS THE ELDER: Opus 39 Tivoli-Rutsch Walzer
In the 19th century, the city of Vienna was the capital of an empire
which held together a multitude of nations and languages.
It was a famous centre for music, literature and the arts.
Science was suspect in conservative Vienna,
particularly biological science.
But unexpectedly, Austria was also the seedbed for one scientific idea,
and in biology, that was revolutionary.
This is the old university of Vienna.
Here, the founder of genetics, and therefore of all the modern life sciences, Gregor Mendel,
got such little university education as he had.
He came here at a historic time in the struggle between tyranny and freedom of thought.
In 1848, shortly before he came,
two young men had published, faraway in London, in German,
a manifesto which begins with the phrase:
"Ein Gespenst geht um Europa" -
"A spectre is haunting Europe" - the spectre of communism.
Of course, Karl Marx and Friedrich Engels in The Communist Manifesto
didn 't create the revolutions in Europe.
But they gave it the voice.
And so, in this square...
...students protested,
the Austrian Empire, like others, shook,
Metternich resigned, the Emperor abdicated.
~ NIELSEN: Sixth Symphony
Emperors go, but empires remain.
The new Emperor of Austria was a young man of 18, Franz Josef,
who reigned like a medieval autocrat,
until the ramshackle empire fell to pieces during the First World War.
The patriots' speeches fell silent.
The reaction under the young Emperor was total.
At that moment, the ascent of man was quietly set off in a new direction
by the arrival at the University of Vienna of Mendel.
He'd been born Johann Mendel, a farmer's son.
Gregor was the name he was given when he became a monk.
He was not a clever student.
His examiner wrote: "He lacks insight and the requisite clarity of knowledge" and failed him.
The farm boy become monk had no choice,
except to withdraw again into the anonymity of the monastery at Brno,
which is now part of Czechoslovakia.
When Mendel came back from Vienna in 1853,
he was, at the age of 31, a failure.
He had been sent by this Augustinian order of St Thomas here in Brno.
And they were a teaching order.
This is the library, not so much of a monastery as of a teaching order.
The Austrian Government wanted the bright boys among the peasantry taught by monks.
And Mendel had failed to qualify as a teacher.
He had to make up his mind,
whether to live the rest of his life as a failed teacher or as... what?
As the boy Hansl, the young man Johann, he decided -
not as the monk Gregor.
He went back in thought,
to what he had learnt on the farm and had been fascinated by ever since -
At Vienna he had been under the influence of the one great biologist he ever met,
Franz Unger,
who took a concrete, practical view of inheritance -
no spiritual essences, no vital forces...
Real facts.
And Mendel decided to devote his life to practical experiments in biology,
here in the monastery.
A bold, silent, and I think, secret stroke,
because the local bishop wouldn 't even allow the monks to teach biology.
Mendel began his formal experiments about two or three years after he came back from Vienna,
say about 1856.
He says in his paper that he worked for eight years.
The plant that he'd chosen, very carefully, is the garden pea.
He picked out seven characters for comparison -
shape of seed, colour of seed and so on,
finishing with tall in stem versus short stemmed.
And that last character is the one that I've chosen to display.
versus short.
We do the experiment exactly as Mendel did.
We start by making a hybrid of tall and short.
In order to make sure that the short plant does not fertilise itself,
we emasculate it.
And then we artificially inseminate it from the tall plant.
The process of fertilisation takes its course.
The pollen tubes grow down to the ovules.
The pollen nuclei, the equivalent of sperm in an animal,
go down the pollen tubes and reach the ovules just as they do in any fertilised pea.
The plant bears pods that don 't yet, of course, reveal their character.
The peas from the pods are now planted.
As the time-lapse film shows,
their development is at first indistinguishable from that of any other garden peas.
Mendel had guessed that a simple character is regulated by two particles -
we now call them genes.
Each parent contributes one of the two particles.
If the two particles or genes are different, one will be dominant and the other recessive.
The crossing of tall peas with short is a first step in seeing if this is true.
And lo and behold, here is the first generation -
and they are all tall.
In the language of modern genetics,
the character tall is dominant over the character short.
It is not true that the hybrids average the height of their parents,
they are all tall plants.
Now the second step.
We form the second generation as Mendel did.
We fertilise the hybrids, this time with their own pollen.
We allow the pods to form, plant the seeds...
...and here's the second generation.
In one mating out of every four, two recessive genes have come together.
And as a result, one plant out of four is short,
and three are tall.
This is the famous ratio of one out of four, or 1:3,
that everyone associates with Mendel's name, and rightly so.
Mendel published his results in 1866...
and achieved instant oblivion.
No-one cared, no-one understood his work.
Even when he wrote to a distinguished, rather stuffy figure in the field, Karl Nageli,
it was clear that he had no notion what Mendel was talking about.
Of course, if Mendel had been a professional scientist,
he would now have pushed the results -
published the paper more widely... France or Britain.
However, at this moment, in 1868, two years after the paper was published
a most unexpected thing happened to Mendel.
He was elected abbot of this monastery.
And for the rest of his life he carried out his duties with commendable zeal...
...and a touch of neurotic punctilio.
He told Nageli that he hoped to go on doing breeding experiments.
But the only thing that he was able to breed were bees.
He had always been anxious to push his work from plants to animals.
And of course, being Mendel,
he had his usual mixture of splendid intellectual fortune and practical bad luck.
He made a hybrid strain of bees which gave excellent honey,
but alas, was so ferocious that it stung everybody for miles around
and had to be destroyed.
Mendel seems to have been more exercised about tax demands on the monastery
than about its religious leadership.
And there is a hint that he was regarded as unreliable by the Emperor's secret police.
Under the Abbot's broad brow, there lay a weight of private thought.
The puzzle of Mendel's personality is an intellectual one.
No-one could have conceived those experiments...
...unless they had clearly in their minds the answer that they were going to get.
It's a strange state of affairs.
And I should give you chapter and verse for that.
First, a practical point.
Mendel chose seven differences between peas to test for at the same time,
such as tall versus short and so on.
Now, the pea does have seven pairs of chromosomes,
so you can test for seven differences, lying on seven different chromosomes.
But that's the largest number you could have chosen.
You couldn 't test for eight without getting two lying on the same chromosome
and therefore being at least partially linked.
Nobody had heard of linkage then,
nobody had even heard of chromosomes at the time Mendel was working on the paper.
Now, you can be destined to be the abbot of a monastery,
you can be chosen by God,
but you can 't have that luck.
Mendel must have done a good deal of experiment before the formal work,
in order to tease out these and convince himself
that seven qualities is just what he could get away with.
And there we glimpse the great iceberg of the mind,
in that secret hidden face of Mendel's on which the paper and the achievement float.
And you see it.
You see it on every page of the manuscript.
The symbolism, the clarity of the exposition -
everything is modern genetics, done more than 100 years ago by an unknown.
And done by an unknown who had one crucial inspiration -
that characters separated in an all-or-none fashion.
This in an age where every time breeders observed this in a hybrid,
it was thrown away because people were convinced that hereditary must go by averaging.
Where did Mendel get the model of an all-or-nothing heredity?
Now, I think I know.
But, of course,
I can 't look into his head either.
But there does exist one model, and it's existed since time immemorial,
which is so obvious that no scientist would think of it.
But a child or a monk might.
That model is sex.
Animals have been copulating for millions of years.
And males and females of the same species don 't produce monsters,
they produce either a male or a female.
Men and women have been going to bed for upward of a million years at least.
And they produce what?
Men or women.
Some such simple powerful model of an all-or-nothing way of passing on differences
must have been in Mendel's mind,
so that the experiments and the thought were clearly made for him of whole cloth
and seen from the inception.
The monks, I think, knew this.
I think they didn 't like what he was doing.
I think the bishop who demurred at the pea-breeding experiments didn 't like it.
Of course, his rout-about revolutionary colleagues
whom he often sheltered in the monastery,
they were fond of him till the end.
When he died in 1884 at the age of 62,
the great Czech composer Janacek played the organ at his funeral.
But the monks elected a new abbot,
and he burned all Mendel's papers.
~ JANACEK: Glagolitic Mass
Mendel's great experiment remained forgotten for over 30 years,
till it was resurrected in 1900.
So his discoveries belong, in effect, to this century,
when the study of genetics all at once blossoms from them.
To begin at the beginning.
Life on earth has been going on for 3,000 million years or more.
For two-thirds of that time, organisms reproduced themselves by cell division.
Division produces identical offspring.
New forms appear only rarely, by mutation.
For all that time, evolution was very slow.
The first organisms to reproduce sexually were, it now seems,
a kind of blue-green algae.
That was less than 1,000 million years ago.
Sexual reproduction begins there,
first in plants, then in animals.
~ PINK FLO YD: Ummagumma
Sex produces diversity.
And diversity is the propeller of evolution.
The acceleration in evolution is responsible for the existence now
of the dazzling variety of shape, colour and behaviour in species,
and also for individual differences within species.
All that was mde possible by the emergence of two sexes.
Two is the magic number.
That is why sex and courtship are so highly evolved in different species.
It's why sex is geared so precisely to the animal's environment.
If the grunion could have adapted themselves without natural selection,
then sex would not be necessary.
Sex is itself a mode of natural selection of the fittest.
Stags don 't fight to kill,
only to establish their right to choose the female.
The multiplicity of shape, colour and behaviour
is produced by the coupling of genes, as Mendel guessed.
As a matter of mechanics,
the genes are strung out along the chromosomes,
which become visible only when the cell is divided.
But the question is not how the genes are arranged.
The modern question is, how do they act?
The genes are made of nucleic acid.
That is where the action is.
How the message of inheritance is passed from one generation to the next,
was discovered in 1953.
And it's the adventure story of science in the 20th century.
I suppose the moment of drama is the autumn of 1951,
when a young man in his twenties, James Watson, arrives in Cambridge
and teams up with a man of 35, Francis Crick,
to decipher the structure of deoxyribonucleic acid -
DNA for short.
DNA is a nucleic acid, and it had become clear in the preceding ten years
that there the chemical message is carried from generation to generation.
Two questions then faced the searchers,
in Cambridge and in laboratories as far afield as California and further.
What is the chemistry,
and what is the architecture?
What is the chemistry?
Well, it was clear that DNA is made of sugars and phosphates -
that's sure to be there for structural reasons -
and four specific small molecules, or bases.
Two of them are very small molecules,
thymine and cytosine.
And two of them are rather larger...
...guanine and adenine.
It's usual in structural work to represent the small bases simply by a hexagon
and the large bases by the bigger figure.
But a building is not a heap of stones,
and a DNA molecule is not a heap of bases.
What gives it its structure and therefore its function?
It was clear by then that the DNA molecule is a long, extended chain,
but rather rigid - a kind of organic crystal.
And it seemed likely that it would be a helix.
How many helixes...
how many spirals in parallel?
One, two, three, four?
There was a division of opinion into two main camps -
the two-helix camp and the three-helix camp.
And then, at the end of 1952,
the great genius of structural chemistry, Linus Pauling, in California,
proposed a three-helix model.
The backbone of sugar and phosphate ran down the middle
and the bases stuck out in all directions.
That arrived in Cambridge in... February 1953.
There was something wrong with it from the outset.
It may have been mere relief.
It may have been a touch of malicious perversity,
which made Jim Watson decide there and then
that he would go for the double helix...
...moreover with the backbones running on the outside,
a sort of spiral staircase
with the sugar and phosphate running like two handrails.
Agonies of experimentation
to see how the bases would fit as the steps in that model.
And then, all at once, it became self-evident.
Of course there must be, on each step,
a small base and a large base,
but not any large base.
Thymine must be matched by adenine.
And if you have cytosine,
then it must be matched by guanine.
The bases go together in pairs of which each determines the other.
So the model of the DNA molecule is a spiral staircase,
a right-handed spiral,
in which each tread is of the same size, at the same distance from the next,
[Skipped item nr. 295]
And turns at the same rate - 36o - between treads.
if cytosine is at one end of a tread, then guanine is at the other,
and so for the other base pair.
Let's build the molecule.
That's a base pair.
The dotted lines between the two ends are the hydrogen bonds.
We'll put it into the position at which we're going to stack it.
And now we'll stack it... the left-hand side of the picture
where we're going to build the whole molecule.
Here is a second pair.
It might be of the same kind as the first or the opposite kind.
We stack it over the first pair,
and turn it through 36o.
Here's a third pair to which we do the same thing.
And so on.
These treads are a code which will tell the cell, step by step,
how to make one of the proteins necessary to life.
The gene is forming visibly in front of our eyes,
and the handrails of sugar and phosphates hold the spiral staircase rigid on each side.
The spiral DNA molecule is a gene -
a gene in action -
and the treads are the steps by which it acts.
On 2nd April, 1953,
James Watson and Francis Crick sent to Nature
the paper which describes this structure in DNA,
on which they had worked for only 18 months.
The model patently lends itself to the process of replication
which is fundamental to life.
When a cell divides, the two spirals separate,
each base fixes opposite to it the other member of the pair to which it belongs
so that when a cell divides, the same gene is reproduced.
The magic number two here
is the means by which a cell passes on its genetic identity when it divides.
Only the sperm and the egg are incomplete.
They're half cells.
They carry half the number of genes.
Then, when the egg is fertilised by the sperm,
the total of DNA instructions is assembled again.
The fertilised egg is then a complete cell
and it's the model for every cell in the body.
Every cell is formed by division of the fertilised egg,
and so it's identical with it in its genetic makeup.
Like this chick embryo,
it has the legacy of the fertilised egg all through life.
As the embryo develops, the cells differentiate.
Along the primitive streak,
the beginnings of the nervous system are laid down.
Clumps of cells on either side will form the backbone.
The cells specialise.
Nerve cells.
Muscle cells.
Connective tissue - the ligaments and tendons.
Blood cells.
Blood vessels.
The cells specialise because they've accepted the DNA instruction
to make the proteins that are appropriate to the functioning of that cell and no other.
This is the DNA in action.
- It's a little girl. - Oh!
(All laugh) MAN: That's another wedding!
The baby is an individual from birth.
The coupling of genes from both parents stirred the pool of diversity.
The child inherits gifts from both parents,
and chance has now combined these gifts
in a new and original arrangement.
(Baby wails) - There we are.
The child is not a prisoner of its inheritance.
It holds its inheritance as a new creation,
which its future actions will unfold.
The child is an individual.
The bee is not.
The bee is one of a series of identical replicas.
The queen is the only fertile female.
When she mates with the drone, in mid-air, she goes on hoarding his sperms.
The drone dies.
If the queen now releases a sperm with an egg she lays,
she makes a worker bee a female.
No sperm, and a drone is made. A male.
A sort of virgin birth.
It's a totalitarian paradise.
Forever loyal, forever fixed,
because it has shut itself off from the adventure of diversity
that drives and changes the higher animals and man.
A world as rigid as the bees could be created among higher animals,
even among men, by cloning.
That is, by growing a colony or clone of identical animals
from cells of a single parent.
Here is a mixed population of an amphibian - the axolotl.
Suppose we decide to fix on one type - the speckled axolotl.
We take some eggs from a speckled female
and grow an embryo which is destined to be speckled.
Now we tease out from the embryo a number of cells.
They are identical cells.
We are going to grow identical animals, one from each cell.
We need a carrier in which to grow the cells.
Any carrier will do. She can be white.
We take unfertilised eggs from the carrier
and destroy the nucleus in each egg.
This is a carrier egg
and into it we insert one of the single identical cells of the speckled parent of the clone.
The clone of identical eggs made in this way are all grown at the same time.
Each egg divides at the same moment.
Divides once, divides twice,
and goes on dividing.
All that is normal, exactly as in any egg.
At this stage, the single cell divisions are no longer visible.
Each egg is turned into a kind of tennis ball,
and begins to turn itself inside out.
Still all the eggs are in step.
Each egg folds over to form the animal, always in step.
A regimented world in which the units obey every command identically
at the identical moment.
Except one unfortunate, that's been deprived and is falling behind.
And finally the clone of individuals.
Each of them an identical copy of the parent.
Each of them a virgin birth like the worker bee.
Should we make clones of human beings?
Copies of a beautiful mother, perhaps, or of a clever father?
Of course not.
Cloning is the stabilisation of one form,
and that runs against the whole current of creation.
Of human creation, above all.
Yet it's odd that the myths of creation in human cultures
seem almost to yearn back for an ancestral clone.
There is a strange suppression of sex in the ancient stories of origins.
Eve is cloned from Adam's rib,
and there's a preference for virgin birth.
Happily, we're not frozen in identical copies.
In the human species, sex is highly developed.
The female is receptive at all times.
She has permanent breasts.
She takes an active part in sexual selection.
Eve's apple, as it were, fertilises mankind.
Or at least spurs it to its ageless preoccupation.
~ Harp With Variations
It's obvious that sex has a special character for human beings.
It has a special biological character.
Let's take one simple, down -to-earth criterion for that.
We are the only species in which the female has orgasms.
That's remarkable, but it is so.
It is a mark in general of the fact that there is much less difference between men and women
in the biology of sex and in sexual behaviour,
than there is in other species.
That may seem a strange thing to say,
but to the gorilla and the chimpanzee,
where there are enormous differences between male and female,
it would be obvious.
So much for biology.
But there is a point on the borderline between biology and culture
which really marks the symmetry in sexual behaviour I think very strikingly.
It's an obvious one.
We are the only species that copulate face to face.
And that's universal in all cultures.
It's an expression of, to my mind, a general equality
which has been important in the evolution of man,
I think right back to the time of Australopithecus.
Why? Well, we have something to explain.
We have to explain the speed of human evolution
over a matter of one, three, let's say five million years at most.
Terribly fast.
Natural selection simply doesn 't act as fast as that on animal species.
We must have supplied a form of selection of our own,
and the obvious choice is sexual selection.
There is evidence now that women marry men who are intellectually like them.
Men marry women who are intellectually like them.
If that really goes back over some millions of years,
then it means that selection for skills has always been important
on the part of both sexes.
Yet, if that had been the only selective factor,
then we would be much more homogeneous than we are.
What keeps alive the variety in human beings?
That's a cultural point.
In every culture, there are special safeguards to make for variety.
The most striking of them is the prohibition of incest.
Well, for the man in the street.
Doesn 't always apply to royal families.
The prohibition of incest only has a meaning
if it is designed to prevent older males dominating a group of females,
as they do in, let us say, ape groups.
Most of the world's literature, most of the world's art,
is preoccupied with boy meets girl.
We tend to think of that as being a sexual preoccupation.
But, of course, that's a mistake.
It expresses the fact that we are uncommonly careful in the choice,
not of whom we take to bed,
but by whom we are to beget children.
Sex was invented as a biological instrument by the blue-green algae.
But as an instrument in the ascent of man, which is basic to cultural evolution,
it was invented by man himself.
~ SCHUMANN: Reveries
Spiritual and carnal love are inseparable.
A poem by John Donne says that.
"All day the same our postures were
And we said nothing all the day.
But O alas, so long, so far
Our bodies, why do we forbear?
This ecstasy doth unperplex and tell us what we love
Love's mysteries in souls do grow
But yet the body is his book."