Conversation between two apes explained

My chimp/chump story from last week is a simplified example of how one ape species split into two.  This splitting is called speciation.  The apes in the story are members of the species that was the most recent common ancestor of humans and chimpanzees (and bonobos.)

Let’s pause for one of the digressions I like to call drum solos.  Don’t think you have ever heard of bonobos?  Sure you have.  Remember that thing about a kind of chimpanzee that resolves its differences by having sex?  That’s the bonobo, but they actually are a separate species from chimps.  They split off from chimps after we did.  Thanks, Mickey

Why five million years ago?  We infer that date from several pieces of evidence.  We have 4.4 million year old fossils of creatures called australopithecines, who are our ancestors, but not chimp ancestors.  The split must have happened before then. 

DNA provides the link we have yet to find in the fossil record.  We know how quickly DNA mutates on average.  We count the differences between human DNA and chimp DNA to calculate the number of years it should take for those differences to accumulate.  The answer is five million years. 

We feel confident in the five million year figure because this method was also used to calculate the date of our split from orangutans.  The fossil record confirms that the orangutan date is correct so we know the method works.

Now that we know when the human-chimpanzee split happened, we might wonder why it happened then.  Five million years ago was the end of a harsh cold snap.  Africa was colder and drier than it had been so the forests were breaking up and turning into woodlands.  We all know about the mass extinctions at the end of the Cretaceous period.  Climate changes killed off the dinosaurs and many other animals and gave the mammals a chance.  Or when the internet liberated music and all music became free and corporate music died and only the most talented bands… OK, bad example. 

The point is that environmental changes can drive evolutionary change.  This is what happened five million years ago.  It was getting really competitive in the trees.  Those who were above average at tree living were more likely to survive to reproduce.  Those who could make it elsewhere were also more likely to reproduce.  Those who reproduce are likely to pass along whatever advantages they have to their children.  The advantages don’t have to be very big to have a large effect.  Even small advantages will become more common over a number of generations. Future mutations will increase existing advantages or create new ones.  The mutations eventually add up to a huge change. It’s important to remember that this takes place over a very long time.  It’s not like in the Ringo Starr movie Caveman in which people go from walking bent-over to walking fully upright in a minute. 

If, as in this story, the proto-chimps stay in the trees and the proto-humans live on the ground, the two groups will stop inter-breeding.  Eventually, so many differences will accumulate that the two groups can no longer inter-breed.  Then we say that speciation has happened. 

We will give speciation five Lemmys because we wouldn’t even be here without it.

Happy Birthday, NASA – I got you a gnarly worm

I enjoy the smattering of science articles in the back of The Economist. Last week’s issue has an article about the future of NASA as it celebrates its 50th birthday.  What really caught my eye was the gnarly photo of a ragworm on the next page. Unfortunately, that worm isn’t in the online version of the article.

The gnarliest pic I could find online.

The gnarliest photo of ragworm teeth I could find online. (The Economist's photo is cooler.)

Please be patient with a brief digression. Let’s call it a drum solo. A recent post referred to a Skeptical Inquirer that wasn’t available at all on line. I guess some folks think we should still buy magazines. Let’s call them treeware-huggers. Thanks, Ron.

Ragworms are used as bait in commercial fishing. They are also known as sandworms in the US and might remind one of the giant sandworms in Frank Herbert’s classic sci-fi series Dune.

Why would NASA care? The researchers, Drs. Chris Broomell and Herbert Waite, discovered that ragworms’ jaws are very strong and very light. This is because their jaws contain a lot of zinc, instead of the calcium salts that most other animals use to make their bones, shells, and teeth. Drs. Bromell and Watie realized their fiindings might help NASA discover ways to make lighter spacecraft parts, so they passed along the info to NASA. Happy 50th, NASA.

Four Lemmys. It would have been five if the Economist had posted the awesome scary ragworm photo on their website.