Dobzhansky · Mayr · The modern synthesis
Why did Darwin and Mendel look like they contradicted each other?
That time, that place
Darwin said living things change a little at a time. A slightly taller giraffe survives, and among its offspring a slightly taller one again. One step at a time.
Then, after Darwin's death, Mendel's pea experiments resurfaced. Peas had no 'slightly'. Yellow or green, round or wrinkled — a parent's trait crossed to the child **in one whole lump.**
The two collided. If inheritance jumps in lumps, should evolution not jump too? Then was Darwin's 'little by little' wrong? In the early twentieth century, evolutionary theory was wobbling.
Why this question
Calculation reconciled them first.
A mathematician named Fisher reasoned: what if height is set not by one gene but by twenty? Each may cross in a lump, yet twenty of them shuffled together spread people's heights smoothly, from very short to very tall with no gaps.
Lumps and 'little by little' were not in conflict. **They were the same thing seen from close up and from far away.**
What was found
Then came the fieldwork.
A biologist named Dobzhansky left the laboratory and caught wild fruit flies in hills and valleys. Same species, yet the mix of genes differed valley by valley — and, more startling, the mix **rose and fell with the seasons.** Summer flies differed from winter flies.
Evolution was not an old story frozen in fossils. It was happening in front of him, fast enough to measure within a year.
After that, people studying birds, fossils and plants stepped one by one into the same picture. In sum: **mutation is the material, natural selection the direction, and the stage is not one animal but the population.**
Inheritance in lumps and evolution by tiny steps were taken to contradict each other
The calculation that many genes stacked make smooth variation, and gene proportions actually shifting season by season in wild flies
This picture became the standard of twentieth-century biology, and after DNA's structure was found it extended down to molecules