The Science Book

168 GREGOR MENDEL

I

n the history of scientific

understanding, one of the

greatest of all the natural

mysteries was the mechanism of

inheritance. The fact of heredity

had been known ever since people

noticed that family members were

recognizably similar. Practical

implications were everywhere—

from the breeding of crops and

livestock in agriculture, to the

knowledge that some diseases,

such as hemophilia, could be

passed on to children. But no one

knew how it happened.

Greek philosophers thought

that there was some sort of essence

or material “principle” that was

passed from parents to offspring.

Parents conveyed the principle to

the next generation during sexual

intercourse; it was supposed to

have originated in the blood, and

paternal and maternal principles

blended to make a new person.

This idea persisted for centuries—

mainly because no one came up

with anything better—but when

it reached Charles Darwin, its

fundamental weakness became

all too clear. Darwin’s theory of

evolution by natural selection

proposed that species changed

over many generations—and in

doing so gave rise to biological

diversity. But if inheritance relied

on the blending of chemical

principles, surely the biological

diversity would be diluted out

of existence? It would be like

mixing paints of different colors,

and ending up with gray. The

adaptations and novelties upon

which Darwin’s theory rested

would not persist.

Gregor Mendel Born Johann Mendel in 1822 in

Silesia in the Austrian Empire,

Mendel initially trained in

mathematics and philosophy

before entering the priesthood

as a way of furthering his

education—changing his name

to Gregor and becoming an

Augustinian monk. He completed

his studies at the University of

Vienna and returned to teach at

the abbey in Brno (now in Czech

Republic). Here, Mendel developed

his interest in inheritance—and at

various times studied mice, bees,

and peas. Under pressure from

the bishop, he abandoned work

on animals and concentrated on

breeding peas. It was this work

that led him to devise his laws

of heredity and develop the

critical idea that inherited

characteristics are controlled

by discrete particles, later

called genes. He became abbot

of the monastery in 1868 and

stopped his scientific work. On

his death, his scientific papers

were burned by his successor.

Key work

1866 Experiments in Plant

Hybrizidation

Inherited characteristics had been

observed for millennia before Mendel,

but the biological mechanism

that produced phenomena such

as identical twins was unknown.

IN CONTEXT

BRANCH

Biology

BEFORE

1760 German botanist

Josef Kölreuter describes

experiments in breeding

tobacco plants, but fails to

explain his results correctly.

1842 Swiss botanist Carl von

Nägeli studies cell division

and describes threadlike

bodies that are later identified

as chromosomes.

1859 Charles Darwin

publishes his theory of

evolution by natural selection.

AFTER

1900 Botanists Hugo de Vries,

Carl Correns, and William

Bateson concurrently

“rediscover” Mendel’s laws.

1910 Thomas Hunt Morgan

corroborates Mendel’s laws

and confirms the chromosomal

basis for heredity.