Evolution Isn’t Trying to Do Anything: 8 Common Misconceptions

Ask people how giraffes got their long necks, and many will tell you a story about giraffes stretching for leaves, generation after generation, until their necks grew longer. It’s a tidy story. It’s also wrong in almost every part, and the ways it’s wrong are worth understanding, because they’re the same ways nearly everyone gets evolution wrong.

How natural selection actually works

Natural selection needs just three things:

1. Variation. Individuals in a population differ. Some giraffes have slightly longer necks than others, from birth. Some moths have 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. Charles Darwin and Alfred Russel Wallace published the idea together in 1858, and Darwin’s On the Origin of Species followed the next year. Everything below follows from getting those three steps right. Run the giraffes in the toy at the top: no giraffe stretches, and the necks still get longer.

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 an improvement. Variants that happen to leave more offspring in their current environment become more common, and that’s all.

That’s why evolution produces some odd designs. In the human eye, the nerve fibres run across the front of the retina and have to pass back through it, leaving a blind spot; an octopus eye, which evolved separately, has no such flaw. In giraffes, a nerve that runs from the brain to the voice box loops all the way down the neck and back up again, because it was routed that way in their fish-like ancestors and was stretched, not redesigned. Selection works with what’s there. It can’t start from scratch.

It also means “more advanced” has no meaning in evolution. Bacteria aren’t primitive humans waiting to happen. They’re superbly adapted to being bacteria, and they’ve been at it for billions of years.

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. The idea that acquired traits are inherited is associated with the French naturalist Jean-Baptiste Lamarck. It was a reasonable guess in 1800, but changes you pick up in your lifetime don’t change your genes, and genes are what’s inherited. A bodybuilder’s children aren’t born muscular.

What happens instead: giraffes vary in neck length from birth, and in places where reaching high leaves helped, those born with slightly longer necks tended to eat better and leave more calves. (Researchers also think long necks help male giraffes in fights over mates, so the full story may involve more than food.)

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

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

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” wasn’t Darwin’s. It was coined by the philosopher Herbert Spencer in 1864, and Darwin adopted it later, perhaps to his cost, because it has been misread as “survival of the strongest” ever since.

4. “Humans evolved from chimpanzees”

Humans didn’t evolve from chimpanzees, or from any other living ape. We share a common ancestor with chimpanzees that lived roughly six to seven million years ago. Since then, both lines have been evolving for exactly as long. Chimps are our cousins, not our grandparents.

A related confusion: “if humans came from apes, why are there still apes?” For the same reason that you can have cousins. Two branches grew from the same trunk, and both are still here.

5. “Individuals evolve”

Individuals don’t evolve. Your genes are fixed when you’re conceived. What changes over time is how common different genes are in a population, as some individuals leave more offspring than others.

This matters for something very practical: antibiotic resistance.

6. “Evolution is random”

Half right, which is the most misleading kind of wrong. The raw material, mutations and the shuffling of genes in reproduction, is random with respect to what an organism needs. But selection is the opposite of random: variants that work in a particular environment are kept, generation after generation, and those that don’t are lost.

Random variation, filtered by non-random selection, is how you get eyes, wings and immune systems without a designer. Saying evolution is random is like saying a sieve is random because the sand you pour in is.

7. “Evolution is too slow to see”

Big changes, like whales from land mammals, take millions of years. Small changes can happen fast enough to watch.

Peppered moths. In industrial Britain, soot darkened tree trunks, and dark-winged moths, better hidden from birds, became common around Manchester in the 1800s. After clean-air laws in the 1950s, trunks got lighter and pale moths came back. A large study by the biologist Michael Majerus, finished after his death and published in 2012, confirmed that birds ate more of the moths that stood out.

Darwin’s finches. On the Galápagos island of Daphne Major, Peter and Rosemary Grant measured every finch for decades. In a drought in 1977, only big, tough seeds were left, and finches with deeper beaks survived better. The next generation’s beaks were measurably deeper.

Bacteria in a flask.

Us. The ability to digest milk as an adult is rare in most mammals, including most humans. It spread through some human populations only in the last several thousand years, after dairy farming began. People living for generations high on the Tibetan plateau carry variants of a gene that helps them cope with low oxygen. Humans haven’t stopped evolving; medicine and culture have just changed what’s being selected.

8. “Evolution is just a theory”

In everyday speech, a theory is a hunch. In science, a theory is a well-tested explanation that ties together a huge body of evidence. Gravity, germs and the theory that matter is made of atoms are theories in this sense, and so is evolution.

The evidence comes from many independent directions: fossils, the shared anatomy of living things, the geography of species, direct observation of change, and DNA. The DNA evidence is the most striking. Humans and chimpanzees share about 98.8% of their DNA sequence, and the patterns of shared genes and shared genetic mistakes, such as broken genes in the same place, fall into exactly the family tree that evolution predicts, the same tree drawn from fossils long before anyone could read DNA.

Why the wrong ideas are so sticky

Almost all these misconceptions share a root: we explain things by purpose. We built our tools for reasons, and we naturally read nature the same way. Giraffes need long necks, so they got them. Bacteria want to survive, so they adapt. It’s a powerful habit of mind, and in this one area it leads us astray.

The fix is to swap the purpose story for a population story. Don’t ask what the animal needed. Ask which individuals, out of the ones that were already born different, left more offspring, and what that does to the next generation. Once that switch is made, most of the puzzles dissolve, and evolution stops sounding like a story about wishes and starts sounding like arithmetic.

Test yourself

The giraffe question is in the free biology test, along with other biology beliefs that turn out to be wrong. For a related idea about where living things get their mass, see where a candle goes when it burns.