Evolution in the News - February 2019
by Do-While Jones

Joshua Trees

Joshua trees highlight some interesting aspects of classification and sexual reproduction.

Joshua trees were in the news this month because some were vandalized; but when Science News reported the vandalism, they included some interesting information that reinforces points we made in this month’s feature article about sexual plants.

Classification Puzzles

The [Joshua] trees’ … two species belong to the same family as agave and, believe it or not, asparagus.

The moth pollinating the Yucca brevifolia species of Joshua tree, which occupies the western part of the Mojave Desert range, is considered a different species from the moth pollinating the Y. jaegeriana trees toward the east. …

What gets biologists really excited about Joshua trees is their pollination, with each of the two tree species relying on its own single species of Tegeticula moth. 1

Biologists want you to believe that Joshua trees are classified in the same family as “believe it or not, asparagus.” Sometimes the arbitrary criteria biologists use to determine which species are closely related yield some surprising relationships, which you should not question, “believe it or not.”

I was surprised to learn that the Joshua trees a few miles from my home here in the northwestern corner of the Mojave Desert are a different species from the Joshua trees in Joshua Tree National Park 170 miles southeast of here. I’ve been to Joshua Tree National Park a couple of times, and I never noticed any difference between those trees and “my” Joshua trees. Apparently there is some arbitrary criterion that subtlely differentiates the two. Perhaps the difference is that they are polinated by two different species of moths.


Typically, insects pollinate a flower “just by blundering around in there” as they grope for pollen and nectar for food, Smith says. But for the female moths that service the Joshua trees, pollination “does not look like an accident.”

The moth isn’t sipping nectar. Joshua trees’ glands no longer work. And moth offspring don’t eat pollen. However, the moth will lay eggs that hatch into caterpillars that will need to eat the seeds that form inside the pollinated flowers. So the moth climbs into a Joshua tree blossom, unfurls long, semi-translucent tentacles from her mouthparts and collects tree pollen into a heavy, yellow wad that she tucks under her head. When she reaches another flower, her tentacles deliver some of the pollen load to fertilize that flower’s ovules. 2

Smith says the reproductive process “does not look like an accident.” Does he really believe it is an accident (in spite of logic and common sense) or is he afraid to say definitely that it is not an accident (because that might damage his standing in the scientific community)?

Joshua tree flowers don’t produce nectar now—but there is no evidence they once did. Apparently, he merely assumes they used to produce nectar, but since the nectar wasn’t necessary, evolution caused them to stop producing nectar. Isn’t it possible that the flowers never produced nectar in the first place because there never was a need for it?

The moth pollenates ovules so that they will grow into seeds which her caterpillar babies will eat. But if the caterpillars eat all the seeds, there eventually won’t be any more Joshua trees. Isn’t it lucky that the moth pollenates enough ovules so that there will be more seeds than her offspring can eat?

The more you think, the more questions you have. That’s why evolutionists don’t want you to think!

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1 Susan Milius, Science News, February 6, 2019, “Shutdown aside, Joshua trees live an odd life”, https://www.sciencenews.org/article/shutdown-aside-joshua-trees-live-odd-life
2 ibid.