The Code and the Filter: DNA, Inheritance and Natural Selection
🎯 Today's mission briefing
We are learning to explain how DNA and genes carry heritable information, to predict inheritance patterns with models, and to explain how populations — never individuals — change over generations through natural selection acting on heritable variation.
You'll know you've got it when:
- I can explain the relationship between DNA, genes, chromosomes, alleles and the characteristics an organism ends up with
- I can use a Punnett square to predict genotype and phenotype ratios, and state honestly what a probability does and does not promise
- I can state the four conditions natural selection requires, and explain why an individual organism cannot evolve
- I can name at least four independent lines of evidence for evolution and explain what the word 'theory' means in science
The toads are getting faster, and somebody measured it
Connects to what your guest already knows and makes them curious. Activating prior knowledge is one of the strongest predictors of new learning.
Cane toads were released in north Queensland in 1935, near Gordonvale, to eat a beetle they turned out not to eat. For decades they spread west and south at roughly ten kilometres a year. Then researchers measured the invasion front again and found the toads out on the leading edge were covering more than fifty kilometres a year — and when they measured the animals themselves, the front-line toads had significantly longer legs than the toads back in the settled population behind them. Nobody bred them. Nobody trained them. No individual toad grew a longer leg because it wanted to travel. And yet in under seventy years, a measurable physical change spread through a population, in Australia, with the paperwork to prove it. Today you learn the mechanism that makes this not only possible but inevitable — and you learn why it is the single most misunderstood idea in all of science.