Evolution Isn't Trying to Do Anything: 6 Common Misconceptions

Evolution by natural selection is one of the simplest powerful ideas in science. It’s also one of the most often garbled, even by people who accept it. Here are six common misunderstandings, and what’s actually happening.

First, how it works

Natural selection needs just three things:

1. Variation. Individuals in a population differ: some giraffes have slightly longer necks, some moths slightly darker wings.
2. Inheritance. Some of those differences are passed from parents to offspring through genes.
3. Selection. In a given environment, some variants survive and reproduce more than others.

Put those together over many generations and the variants that leave more offspring become more common. That’s it. Everything below follows from getting those three steps right.

1. “Evolution is trying to make things better”

Evolution has no aim, plan or direction. Nothing evolves because it’s needed or because it would be good. Variants that happen to leave more offspring in their current environment become more common, and if the environment changes, what counts as advantageous changes too.

That’s why evolution produces some odd designs, like the human eye’s blind spot, where the nerve passes through the retina. Selection works with what it has; it can’t start from scratch.

2. “Animals change during their lives and pass that on”

A giraffe that stretches its neck all its life doesn’t have longer-necked calves because of it. This idea, associated with Jean-Baptiste Lamarck, was a reasonable guess in 1800, but changes you acquire during your life (a stretched neck, stronger muscles, a scar) aren’t written into your genes.

What happens instead: giraffes vary in neck length from birth, and in environments where reaching high leaves helped, those born with slightly longer necks tended to leave more offspring.

3. “Survival of the fittest means the strongest win”

In evolution, “fitness” means reproductive success: leaving more offspring who themselves survive and reproduce. It has nothing to do with strength, speed or toughness unless those help with reproduction.

A fragile insect that lays thousands of eggs can be enormously fit. A strong, long-lived animal that rarely breeds may not be. The phrase “survival of the fittest” was coined by the philosopher Herbert Spencer; Darwin adopted it later, but “reproduction of the fittest” would be closer.

4. “Humans evolved from chimpanzees”

Humans didn’t evolve from chimpanzees or any other living ape. We share a common ancestor with chimpanzees that lived around six to eight million years ago. Since then, both lines have been evolving for exactly the same length of time.

Chimpanzees are our cousins, not our ancestors. The question “if we came from monkeys, why are there still monkeys?” rests on this misunderstanding: nobody came from today’s monkeys.

5. “Individuals evolve”

Individuals don’t evolve; populations do. You’re born with your genes and keep them. Evolution is the change in how common different gene variants are in a population, across generations.

6. “Evolution is just a theory”

In everyday speech, “theory” means a guess. In science, a theory is a well-tested explanation that ties together a huge body of evidence, like the theory of gravity or germ theory. Evolution is supported by fossils, the patterns of shared DNA between species, the distribution of species across the world, and change observed directly in the lab and the wild, such as bacteria evolving resistance to antibiotics.

Seeing it happen

Evolution is often too slow to watch, but not always. Bacteria evolve antibiotic resistance within years, which is exactly why doctors worry about overusing antibiotics. Insects evolve resistance to pesticides. In a long-running experiment started by Richard Lenski in 1988, populations of E. coli have been evolving in the lab for over 75,000 generations, and one population evolved a new ability to feed on a chemical its ancestors couldn’t use.

Test yourself

The free biology misconceptions test includes the giraffe question, the meaning of “fittest” and eight other common biology myths.