Understanding the evolution of today’s watermelon – Columbia Daily Tribune

Mike Szydlowski| Special to Columbia Daily Tribune

Nothing says summer like a juicy, red, sweet cold slice of watermelon. Mark Twain once wrote that tastinga watermelon is to know "what the angels eat.

However, Twain and his friends were certainly not the first to enjoy a watermelon on a hot summer day. Watermelon paintings and seeds have been found dating back at least 5,000 years. The difference is that 5,000-year-old watermelon paintings depict very different looking watermelons than we know today. And the watermelons in the paintings changed over time. To understand todays watermelon, you need quite a bit of history and biology.

If you dont like unnatural foods, you better stop eating watermelons. Our watermelons today barely resemble the original, natural watermelons. You would not have enjoyed them at all.

First, they were quite difficult to get into. You would have to smash them open with some pretty heavy rocks in order to enjoy an inside full of white/yellowish, bitter-tasting flesh. As unappetizing as that sounds, people did it and there was a reason for that.

Watermelons originated in places that experienced very long dry spells. Although bitter tasting, the watermelons were like miniature water storage tanks. Archeologists even found evidence that King Tuts tomb had watermelons placed in it, as he would need some water for his journey into the afterlife.

Therefore, watermelons were not harvested for their taste they were harvested for their water. An uncut watermelon can store for weeks or even months in a cool, dry location.

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At some point, somebody decided they could selectively breed the watermelon to change how it tastes. Some smart ancient scientists discovered that a single gene produced the bitter watermelon flavor. By purposefully breeding many generations of plants with certain characteristics, the gene for bitterness was eliminated.

Soon after, ancient people continued the selective breeding of watermelons to make them easier to get into no more pounding the hard shell with a rock.

Then came the taste. The bitter taste was gone, but it still was quite bland. Farmers selectively bred watermelons that had a little sweetness until they became sweeter and sweeter like today.

It turns out the color of watermelons was controlled by the same gene that controlled watermelon sweetness. Therefore, as the watermelon became sweeter it also changed color to the familiar deep red we now know and expect.

All of this was done in the very same way dogs were selectively bred (originally from wolves) to create the many different breeds we have now. Certainly, you didnt think the poodle was natural, did you?

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If you have any scientific knowledge about plants, you know a seedless fruit or vegetable makes no sense at all. It breaks all rules of nature.

The only goal of every natural living species is to survive long enough to reproduce so the species continues. In plants, this is done by mixing male and female genes through the process of pollination and fertilization. Once a flower is fertilized, it produces a seed.

Some plants grow fruits and vegetables around their seed to either protect the seed or attract animals to the seeds in order for their seeds and genes to be spread around. A fruit or vegetable without seeds is a failure on the plants part. If a fruit or vegetable were to become seedless by some genetic mutation, that wouldbe the end of that plants genes as it wouldnot be able to reproduce.

A watermelon has 22 chromosomes. Reproductive cells contain half that amount, so when they join the other plants reproductive cells from the opposite sex, they form a new combination of 22 chromosomes for the new plant.

Scientists found that if they treata watermelon plant with a certain chemical, it will double the number of chromosomes. Then,they found if a 22-chromosome plant fertilizes a 44-chromosome plant, the resulting plant produces watermelons with seeds with 33 chromosomes. These seeds will grow but are sterile, which means they will not produce seeds of their own.

And there is your seedless watermelon and a fascinating history, artand science lesson. More than 5,000 years worth of human work went into your enjoyment of a sweet, seedless watermelon. Enjoy it.

Mike Szydlowski is science coordinator for Columbia Public Schools.

TIME FOR A POP QUIZ

1. What does the term selective breeding mean?

2. How is the evolution of watermelon similar to the evolution of the Golden Retriever (or any other dog breed)?

3. How is a natural watermelon different from the watermelons we enjoy today?

4. We were not there to see ancient watermelons, so how do you think scientists know how and when they changed over time?

5. Why do seedless watermelons cost more than watermelons with seeds?

LAST WEEKS POP QUIZ ANSWERS

1. How do we feel pain?

We feel pain when nerve endings detect that something bad is happening to our body. When this occurs, it sends a signal to our brain to produce the sensation of pain so that we stop doing whatever is harming our body.

2. What would happen if we didnt feel pain?

If pain were not a thing, most people would likely live shorter lives because we would not protect our bodies from harm as much as we do with pain.

3. What is the evolutionary purpose of pain?

Pain evolved as a warning system to keep your body safe from serious harm.

4. Give three examples of ways that pain helps keep you safe.

Answers will vary, but mightinclude: keeping you from seriously burning yourself, keep you from eating poisonous foods, alerting you to something wrong inside your body, and a warning to take care of your body in general.

5. In what example is it OKto work through a little bit of pain?

When exercising or working out, it is normal to feel some pain and it is OKto work through some of that pain.

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Understanding the evolution of today's watermelon - Columbia Daily Tribune