Evolution: Changes over time

By Dr. Daniela Vergara

Evolution means change over time. In biology, evolution is about how living things—like animals, plants, or even bacteria—slowly change from one generation to the next. These changes happen in traits (like color, size, smell, or disease resistance) that are passed from parents to offspring through genes.

In previous posts we talked a lot about genes, which are the instructions to make proteins and are found in the DNA.

Here I’m going to talk a bit about how evolution happens, especially through:

• Natural selection
• Artificial selection
• Genetic drift

Natural Selection

Natural selection is when nature “chooses” which traits help an organism survive or have more babies. These useful traits become more common over time.

Example: Imagine rabbits that live in snowy places. The white ones blend in and escape predators, while brown ones get caught. Over time, more rabbits are white because being white helped them survive.

Natural selection needs:

1. Variation – not everyone looks or acts the same
2. Heritability – traits must be passed down through genes
3. Fitness – some traits help organisms survive or reproduce better

The image below illustrates the concept of evolution by natural selection using giraffes as an example.

At the left side of the image, we see a giraffe with a shorter neck trying to reach leaves on a tall tree. On the right, over time, a giraffe with a longer neck is able to reach the higher leaves more easily. The arrow labeled “TIME” at the bottom shows that this change happened gradually.

Here’s how natural selection works in this example:

1. Variation: In the past, giraffes were born with necks of different lengths, some shorter, some longer.
2. Struggle for survival: Food was limited and leaves high up in trees were harder for short-necked giraffes to reach.
3. Survival advantage: Giraffes with longer necks could reach more food, giving them a better chance to survive and have babies.
4. Reproduction: These long-necked giraffes passed their traits to the next generation.
5. Over time: More and more giraffes had long necks, and short-necked giraffes became rare.

This process is called natural selection, where traits that help an organism survive and reproduce become more common in a population.

Artificial Selection: Humans Doing the Choosing

Artificial selection is like natural selection, but humans decide which traits are best. It’s how we get sweet corn, fluffy dogs, and it appears, C. sativa strains with high THC.

Breeders choose plants or animals with the traits they like and breed them over and over. This is how we develop new varieties or breeds like friendly dogs, colorful chickens, and cats with specific coat patterns.

My favorite example is Brassica oleracea, a single plant species of mustard that humans turned into kale, broccoli, cauliflower, Brussels sprouts, and cabbage, all by selecting for different traits like leaves, stems, or flowers.

Artificial selection has shaped many of the foods we eat and animals we live with today.

Genes, Traits, and Heritability

Physical traits, or the phenotype depend on both genes and the environment. This idea is often shown as:

Trait (phenotype) = Genes × Environment

For example, a C. sativa plant may have genes for purple flowers, but the color might not show unless it grows in cold weather.

Heritability measures how much of a trait comes from genes vs. environment. Breeders use this to predict how likely a trait is to appear in the next generation.

Genetic Drift: Evolution by Chance

Genetic drift is when traits change in a population by random chance, not because they are helpful or harmful.

Imagine that you have a bag with 10 marbles: 5 red and 5 blue. Now randomly grab 5 marbles. You might get 3 red and 2 blue—just by luck. Do this over and over, and maybe red marbles become more common.

That’s genetic drift.

Now think of this happening in genes, not marbles.

In small populations, genes can disappear or become more common just because of random luck, not because of natural selection.

It’s not because the trait was better but it just got lucky and stayed in the population.

What helps me think about drift

This is how I like to think about genetic drift: imagine a very small population where only a few individuals reproduce.

Each individual has two versions of a gene, called alleles, for example, A and B. An allele is a different version of a gene, which is like a set of instructions in your DNA. In a small group, just by chance, not everyone passes on all their alleles. Maybe no one with two B alleles has offspring, or maybe only A alleles get passed down. Or maybe that individual that has the two versions of the B allele (BB) doesn’t reproduce. Over time, this randomness can cause one allele to disappear completely—even if it wasn’t harmful.

That’s how genetic drift works: it’s not about which allele is better, just about chance in a small population.

Don’t Confuse Drift with Mutation Accumulation!

This is really important:

• Genetic drift is random and affects which existing genes get passed down or lost over time. It’s about chance in inheritance.
• Mutation accumulation is about new mistakes or changes in the DNA that appear over time, especially in older plants or those kept in tissue culture.

So:

• Drift = random changes in gene frequency.
• Mutations = new changes to the DNA itself.

They are not the same, but both can lead to differences over time.

And so……

Evolution is the big picture of how living things change. It happens through:

• Natural selection -> those that survive better
• Artificial selection -> those that we choose
• Genetic drift -> those random changes
• Mutation -> changes in DNA

In the C. sativa world, knowing about these ideas helps growers and scientists make better plants, understand plant behavior, and keep genetic diversity alive.

If we understand how evolution works, we can shape the future of C. sativa.