Continuing Evolution
Evolution is an ongoing process that continues to shape populations in the present, not a historical event confined to the deep past.
Evolution is happening now, not just in the past
It's tempting to think of evolution as something that happened long ago to produce today's species, which are now 'finished' or static. In reality, every population on Earth, at every moment, is subject to the same evolutionary forces - mutation, selection, drift, gene flow, and non-random mating - that produced today's biodiversity. As long as heritable variation and differential reproduction exist (which is essentially always), populations continue to evolve.
Because generation time and mutation supply constrain how fast visible change accumulates, evolution is often imperceptibly slow in long-lived organisms like humans or trees, but it can be strikingly fast in organisms with short generation times and large population sizes, such as bacteria, viruses, and insects.
Human-driven selective pressures accelerate evolution
- Antibiotic resistance: heavy antibiotic use creates strong selection favoring rare resistant bacterial variants, which then dominate the population within days to weeks given bacterial generation times.
- Pesticide and herbicide resistance in insects and weeds follows the same logic, threatening agricultural pest control strategies worldwide.
- Overfishing has driven declines in average size and earlier reproductive maturity in some commercial fish populations, since larger/older fish are selectively removed.
- Climate change is shifting selective pressures on wild populations' timing of migration, flowering, and breeding, sometimes fast enough to be measured within a few decades.
Coevolution as a continuing dynamic
Species locked in close ecological relationships - predator/prey, host/parasite, plant/pollinator - often coevolve, each exerting selective pressure that drives change in the other over time. As prey evolve better defenses, predators face selection for improved attack strategies, and vice versa, producing an ongoing evolutionary 'arms race' with no permanent endpoint (sometimes called the Red Queen dynamic, since both species must continually adapt just to maintain their relative position).
Key terms
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- Antibiotic resistance
- Evolved insensitivity of bacterial populations to antibiotics, driven by selection favoring resistant genotypes under drug exposure.
- Selective pressure
- An environmental factor that favors some phenotypes over others, driving differential reproductive success.
- Coevolution
- Reciprocal evolutionary change between two interacting species, each acting as a selective pressure on the other.
- Rapid evolution
- Observable evolutionary change occurring over a small number of generations, often in response to strong or novel selective pressures.
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