December 20, 2011 1 Comment
Science Sushi has a great article on new species evolving before our eyes. Evolution deniers may claim that we never see new species in the process of evolving, but that’s simply untrue, and further confirms that the political debate over evolution has nothing to do with science or facts.
Critics of evolution often fall back on the maxim that no one has ever seen one species split into two. While that’s clearly a straw man, because most speciation takes far longer than our lifespan to occur, it’s also not true. We have seen species split, and we continue to see species diverging every day.
For example, there were the two new species of American goatsbeards (or salsifies, genus Tragopogon) that sprung into existence in the past century. In the early 1900s, three species of these wildflowers – the western salsify (T. dubius), the meadow salsify (T. pratensis), and the oyster plant (T. porrifolius) – were introduced to the United States from Europe. As their populations expanded, the species interacted, often producing sterile hybrids. But by the 1950s, scientists realized that there were two new variations of goatsbeard growing. While they looked like hybrids, they weren’t sterile. They were perfectly capable of reproducing with their own kind but not with any of the original three species – the classic definition of a new species.
How did this happen? It turns out that the parental plants made mistakes when they created their gametes (analogous to our sperm and eggs). Instead of making gametes with only one copy of each chromosome, they created ones with two or more, a state called polyploidy. Two polyploid gametes from different species, each with double the genetic information they were supposed to have, fused, and created a tetraploid: a creature with 4 sets of chromosomes. Because of the difference in chromosome number, the tetraploid couldn’t mate with either of its parent species, but it wasn’t prevented from reproducing with fellow accidents…
The apple maggot fly, Rhagoletis pomonella is a prime example of a species just beginning to diverge. These flies are native to the United States, and up until the discovery of the Americas by Europeans, fed solely on hawthorns. But with the arrival of new people came a new potential food source to its habitat: apples. At first, the flies ignored the tasty treats. But over time, some flies realized they could eat the apples, too, and began switching trees. While alone this doesn’t explain why the flies would speciate, a curious quirk of their biology does: apple maggot flies mate on the tree they’re born on. As a few flies jumped trees, they cut themselves off from the rest of their species, even though they were but a few feet away. When geneticists took a closer look in the late 20th century, they found that the two types – those that feed on apples and those that feed on hawthorns – have different allele frequencies. Indeed, right under our noses, Rhagoletis pomonella began the long journey of speciation…
There are a few more really interesting examples and an explanation of how and why speciation can happen; you should check out the article at Science Sushi if you’re interested.
The point is that all kinds of creatures, from the smallest insects to the largest mammals, are undergoing speciation right now. We have watched species split, and we continue to see them diverge. Speciation is occurring all around us. Evolution didn’t just happen in the past; it’s happening right now, and will continue on long after we stop looking for it.
Fantastic. Evolution is not a thing of the past, and it doesn’t happen to some things and not others. I recently read someone’s racist theory about how because the modern human species began in Africa and went outwards, Africans were less evolved than others. That clearly doesn’t make any sense, and this article’s conclusion should make it obvious why (among other reasons): evolution doesn’t stop. Everything currently living is still evolving, and there’s no end goal to evolution that you can point at and say “The closer you are to that, the more evolved you are.”
If anything, one might say that bacteria are the “most evolved” organisms, since they reproduce so quickly and thus can change their genetic makeup, as a community, far faster than most living things. Though they don’t have the benefit of sexual reproduction to shuffle around their genes, their DNA will still undergo mutation, and they can also exchange DNA with each other using conjugation.
In conclusion, there’s a lot of misinformation about evolution, whether through ignorance or bad intentions. It’s too bad that more people don’t know more about it, because the truth of it all is pretty amazing.