Dear Aubree,
When I thought about evolution, I always pictured big changes that happened over long time periods—like how birds evolved from dinosaurs.
But then I talked with my friend Jeremiah Busch. He’s a biologist at Washington State University. He told me evolution is happening all the time.
“As soon as you see that evolution is occurring around us, it changes the way you think about the world,” Busch said.
There are a few ways evolution happens. These include mutation, gene flow, genetic drift and natural selection.
First, let’s define evolution. Busch told me evolution is a change in allele frequencies over time.
Alleles are different versions of genes. Genes are short sections of DNA. Your genes are responsible for your traits—like your height or eye color.
One way to picture DNA is to imagine a long string of A’s, C’s, G’s and T’s. Those letters represent the four bases of DNA.
A gene may contain a few hundred letters—or more than 2 million letters. But let’s say you have a group of birds with an imaginary gene of just five letters. It comes in two versions: AAAAA and AAAAG.
At first, most birds have the first version. Then, as the birds choose mates and have babies, the second version becomes more common. The change in how often the gene with the G shows up is evolution.
So, how do those changes happen? Sometimes the DNA picks up random changes—called mutation. This can happen if there’s a mistake while copying the DNA. Instead of copying AAAAG, the cells copied AAAAC. Sometimes that mutation can pass on to an individual’s babies. Mutation can also happen if something in the environment damages the DNA.
Sometimes DNA changes because new individuals move in—called gene flow. They bring new genes to pass on. Maybe someone brings an AAAGA gene. It’s like shuffling new cards into the gene deck.
Sometimes DNA changes over time due to luck—called genetic drift. Let’s say a tornado randomly wipes out a bunch of birds with the AAAAA gene. If most of the survivors have the AAAAG gene, that gene may get passed on because they were lucky.
The most famous way evolution works is natural selection. Some traits make an individual more likely to survive and pass on their genes. Imagine a flock of birds with different heights. The taller birds can reach more food. So, tall birds may survive better and pass on their tall genes to their babies. Let’s pretend our AAAAA gene codes for short birds. The AAAAG gene codes for tall birds. If the flock becomes taller over time, the tall allele will become more common.
Humans can also drive evolution among the plants and animals around them. Humans make big changes in the environment—like farming animals, large-scale fishing, using pesticides and antibiotics, building cities and more. Then, other organisms must adapt to those new or changing habitats.
“What we do matters,” Busch said. “We are part of the community of organisms. When we modify it, it modifies them and us. It’s all connected.”
That makes me feel amazed by how evolution works—and how important it is to be good members of the community.
Sincerely,
Dr. Universe