Natural Selection and Macroevolution in your lifetime

“I don’t think we came from monkeys. I think that’s ridiculous. I haven’t seen a half-monkey, half-person yet.” –Glenn Beck

I don’t often write about biology here, but as many of you know, I often write about the history of the Universe, and that includes the Sun, the planets of the Solar System, and the Earth in particular.

Just this week, I came across the last in a series of one of the greatest nature shows I’ve ever seen: David Attenborough’s Life series. In particular, this was Life in Cold Blood, which focused on reptiles and amphibians.

One of the complaints I regularly get over email is from people who don’t accept evolution. They tell me that although microevolution may be true, we don’t see macroevolution happening. In other words, large, visible organisms don’t appear to evolve over the course of a human lifetime.

As I just learned, the Italian Wall Lizard (above) may have something to show us about that.

One of an Italian Wall Lizard’s favorite meals are small insects, like flies. As you can see, above, these full-grown lizards are smaller than a human hand, and a fly makes a substantial meal for these guys. One of the lizard’s tricks is to hang out near a particular type of lily, the dead horse arum flower (below).

This plant is particularly interesting for the fact that it makes an odor, deep inside the flower, that attracts flies. The flies enter inside, thinking that there’s food due to the smell. Upon not finding any, they leave, and move on to the next potential food source.

Unless, of course, there’s an Italian Wall Lizard standing watch.

You see, when the fly goes inside, the lizard can climb up onto the outside of the flower, block the fly’s exit, and get an easy meal.

And this happens all over the Mediterranean, where Italian Wall Lizards and Dead Horse Arums are both abundant.

But on the island of Minorca, a Spanish Island, there’s a spectacular example of natural selection, and macroevolution, happening just over the last 20 years.

This is a view of the countryside on Minorca. 20 years ago, lizards on Minorca came to the Dead Horse Arum flowers, trapped and ate the flies that flew inside, and moved on once the flowers died.

But one Minorcan lizard hung around after the flower died, and decided to sample the fruit of this plant.

Liking the taste, the lizard continued to return to the Dead Horse Arums for their fruit, and the habit caught on among Minorcan lizards.

How does this make evolution happen? Three important things:

  1. The lizards only eat the fruit of the plants that taste good to them.
  2. The seeds found in the fruit must be strong enough to survive devouring and digestion inside a lizard.
  3. Those seeds that do survive germinate inside the lizard, are carried around for some distance, and when they are excreted, give rise to new Dead Horse Arum plants!

And, just like you’d expect, the Dead Horse Arum Lily is flourishing all over Minorca. But the ones found on Minorca are different from the ones found elsewhere in the Mediterranean; they’ve evolved, and they’ve done so over the last 20 years!

How are they different? Rather than a mix of plants with fruit that taste good to the lizards and those that taste foul, only the ones that taste good are abundant on Minorca. And rather than a mix of thin, easily crushed seeds and thick, lizard-bite-resistant seeds, only the thick seeds thrive on Minorca.

Why? Because they were selected for, naturally, thanks to the new, learned behavior of the lizards. Amazing! And there you have it, an example of natural selection and macroevolution, happening right here on Earth over the course of our lifetimes. What more could you ask for?