Darwin had developed his theory without any knowledge of laws of heredity.
Somewhere he had said: "Later on, if we know better how heredity works, my
theory will be better understood". It is an interesting fact that from 1856
on the Czech monk Mendel was doing growth experiments with peas, which led
to the famous heredity laws bearing his name (1865). Thus Mendel was already
doing his experiments while Darwin was writing his Origin of Species. The
book has been found in Mendel's library with notes in the margin. On the
other hand Mendel's publication has been found in Darwin's library, but the
book had not been cut open ...
Years later Darwin has even developed his own theory of heredity, but he
was wrong about that. |
Though scientists accepted the fact of evolution, they were often not
convinced about the mechanism of natural selection. In the following editions
of his Origin of Species Darwin mentioned two other forces capable of changing
species: the influence of the environment and the effects of use and disuse.
As an example of the second force he mentioned the disappearance of eyes
in animals living in caverns. This made the acceptance of the theory
for many people easier. However it is now known that these forces are not
existing and that the changes (nearly) all are due to natural and sexual
selection.
For the acceptance of the theory it was also important that 'missing links'
were found. These are transitional forms between two species or groups. Therefore
it was a lucky coincidence that in 1861 in the quarries of Solnhofen (Germany)
a complete skeleton of a very old and primitive bird (Archaopteryx)
was found. This animal had wings and feathers, but it had also characteristics
of reptiles like claws and teeth. The photo on top is taken from a skeleton
that was found later in the same quarries.
Know more?
Archaeopteryx,
the Urvogel |
