Genetic Drift

“An allele may spread not because it helps, but because chance dealt the population an unusual hand.”

01 / PLAINLY

What it means, plainly

Gene frequencies can change through random sampling, especially when a population is small.

02 / CONTEXT

A little more

Genetic drift is random change in allele frequencies from one generation to the next. It does not ask whether a variant is useful: accidents of reproduction, survival, or sampling can fix or erase it, with stronger effects in small populations.

03 / WHY IT MATTERS

Why it matters

It prevents every biological difference from being treated as adaptation and explains why small populations lose diversity quickly.

04 / EXAMPLE

A familiar example

If a storm randomly leaves only ten beetles, their colors may dominate later generations even though no color offered better protection.

05 / LIMIT

What it does not mean

It is not weak natural selection; it is a different mechanism whose outcome need not track a trait's usefulness.

06 / NOTICE

Notice it in your day

Flip twenty coins and then only four. Compare how far each group lands from 50 percent to see why small samples wander more.

FINAL NOTE

The idea worth keeping

When you notice change, ask whether population size allowed chance to compete with selection.

QUESTIONS / 02

Questions people still have

Does drift happen only in small populations?

It occurs in every population, but relative fluctuations are much stronger when few gene copies form the next generation.

Can chance remove a beneficial allele?

Yes. When a useful variant is new and rare, it can disappear before selection has much opportunity to spread it.