Table of Contents

• 1: The case of the resistant hoppers
• 2: Hoppers evolve resistance
• 3: Variability
• 4: Inheritance
• 5: Selection pressure
• 6: Quick review
• 7: Evolution and immunity
• 8: Immunity in prokaryotes and eukaryotes

Selection pressure

Finally, we get to selection pressure. Selection pressure simply means the environment produces differences in survival for different variants of a species - one survives better than the rest, because it is better suited to that environment than the others.

 

 

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Selection pressure is probably the easiest of the 3 tenets to understand, because it's what we naturally think of when we think of evolution. Another name for it is "survival of the fittest". Giraffes with long necks are more fit because they can reach higher branches. T. rexes with stronger jaws are more fit because they are more likely to win a bait-the-triceratops contest. Apes that display more intelligence are likely to be more fit, and thus reproduce more, than their less-intelligent brethren.

Likewise, immune zucchini hoppers survive the spraying regime much better than non-immune zucchini hoppers. So, most of the hoppers that get to reproduce are immune. That means that over time the proportion of immune hoppers increases.