1. Development of Darwin’s Idea
Photo credit: Art Wolfe Incorporated

2. A Hot Topic
During his time, Charles Darwin was not the only scientist thinking about the age of the Earth and species development.
Lyell
Lamarck
Hutton
Malthus

3. The Age of the Earth
In the mid-19th Century, common wisdom dictated that the Earth was not very old.
Dominant Christian beliefs estimated that Earth was between 6,000 and 50,000 years old.
This is one of the root issues in debates between evolutionary biologists and their religious detractors.

4. Hutton’s Influence
James Hutton was a British geologist who theorized that geological processes occur slowly.
He recognized that weather patterns could affect terrestrial formations, but only over long periods of time.
From Hutton, Darwin had evidence that the Earth was old and had someone else to counter the strong religious influence.

5. Lyell’s Influence Charles Lyell was also a famous geologist.
His motto was: “The Present is Key to the Past.”
He believed that geologic formations were the results of tiny, yet steady changes over long periods of time.
From Lyell, Darwin was able to extend this concept of gradualism (small changes over time) to biological development.
“If Earth could change slowly over time, certainly life could do the same”

6. Lamarck’s Influence
Jean-Baptiste Lamarck was a French naturalist who developed his own concept of evolution.
He was more of Darwin’s peer than his influence.

7. Lamarck’s Evolution Hypotheses
Jean-Baptiste Lamarck believed that:
living things have changed over time.
all species were descended from other species.
organisms were adapted to their environments.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime.
These traits could then be passed on to their offspring. Over time, this process led to change in a species.

8. Lamarck's Evolution Hypotheses
A male fiddler crab uses its front claw to ward off predators and to attract mates.
Lamarck proposed that the selective use or disuse of an organ led to a change in that organ that was then passed on to offspring. This proposed mechanism is shown here applied to fiddler crabs. (1) The male crab uses its small front claw to attract mates and ward off predators. (2) Because the front claw has been used repeatedly, it becomes larger.

9. Lamarck's Evolution Hypotheses
Because the front claw is used repeatedly, it becomes larger.
This characteristic (large claw) is passed onto its offspring.

10. Lamarck's Evolution Hypotheses
Lamarck’s hypotheses of evolution are incorrect in several ways.
Lamarck did not know:
how traits are inherited.
that an organism’s behavior has no effect on its heritable characteristics.

11. Malthus’ Influence Thomas Malthus was a British economist.
Malthus studied population growth. He theorized that resources for humans could run out if population growth was left unchecked.

12. Malthus’ Influence But Earth isn’t overrun with organisms…
Malthus’ work allowed Darwin to make several critical leaps.
But Earth isn’t overrun with organisms…
…meaning that species must die out…
…so, new species must appear!!!

13. Darwin’s Conclusions
The various evolutionary scientists provided many tools for Darwin, including:
the concept of gradualism
the age of the Earth
support to challenge religious belief
a competing peer
the concept of extinction

14. END