Reproductive history writ in the genome

Posted 19 March 2008 by PZ Myers

Fossils are cool, but some of us are interested in processes and structures that don't fossilize well. For instance, if you want to know more about the evolution of mammalian reproduction, you'd best not pin your hopes on the discovery of a series of fossilized placentas, or fossilized mammary glands … and although a few fossilized invertebrate embryos have been discovered, their preservation relied on conditions not found inside the rotting gut cavity of dead pregnant mammals.

You'd think this would mean we're right out of luck, but as it turns out, we have a place to turn to, a different kind of fossil. These are fossil genes, relics of our ancient past, and they are found by digging in the debris of our genomes. By comparing the sequences of genes of known function in different lineages, we can get a measure of divergence times … and in the case of some genes which have discrete functions, we can even plot the times of origin or loss of those particular functions in the organism's history.

Here's one example. We don't have any fossilized placentas, but we know that there was an important transition in the mammalian lineage: we had to have shifted from producing eggs in which yolk was the primary source of embryonic nutrition to a state where the embryo acquired its nutrition from a direct interface with maternal circulation, the placenta. We modern mammals don't need yolk at all … but could there be vestiges of yolk proteins still left buried in our genome? The answer, which you already know since I'm writing this, is yes.

Continue reading "Reproductive history writ in the genome" (on Pharyngula)

9 Comments

gabriel · 19 March 2008

Thanks PZ. I skimmed the actual paper as well - amazing stuff.

As an aside, these up-to-the-minute findings have a very useful role in the "co-evolutionary" battle between evolution and the creos - these findings have no existing counter from the other side (yet).

For this reason I always use fresh examples like these in my classes. It would be nice to use the old standards (peppered moths, archaeopteryx, etc) but these examples have been hacked to death with lies from the creo camp. Fresh examples like these hit home and hit hard. After this year's intro to evolution lecture I actually had one student ask "Does this mean Genesis is .... wrong??" (she is surely from a die-hard YEC background). No (unless poetry can be "wrong"), but your interpretation of it surely is...

Thanks for another arrow in the quiver.

Dale Husband · 19 March 2008

gabriel: As an aside, these up-to-the-minute findings have a very useful role in the "co-evolutionary" battle between evolution and the creos - these findings have no existing counter from the other side (yet). For this reason I always use fresh examples like these in my classes. It would be nice to use the old standards (peppered moths, archaeopteryx, etc) but these examples have been hacked to death with lies from the creo camp. Fresh examples like these hit home and hit hard. After this year's intro to evolution lecture I actually had one student ask "Does this mean Genesis is .... wrong??" (she is surely from a die-hard YEC background). No (unless poetry can be "wrong"), but your interpretation of it surely is... Thanks for another arrow in the quiver.

Why not just use the "old standards" too, but explain why Creationist critics have failed to refute them? But only make that point if a student brings up those lame claims of the Creationists.

raven · 19 March 2008

Crosspost from the PZ board. This is a stunning example of molecular evolution destined to become a classic. From reading the phylogeny, mammals are a tiny twig on an ancient lineage going back hundreds of millions of years. But even this twig has a wide diversity of reproductive strategies, egg layers, pouches, placentas. This might be an impossible question to answer but what about the multituberculates or the docodonta? Did they all just lay eggs or bear live young or what? So what about all the other mammals? What was their reproductive strategies? If anyone has any ideas, post them.

wikipedia evolution of mammals --Cynodonts | `--Mammaliformes | +--Allotheria | | | `--Multituberculates | `--+ -Morganucodontidae | `- -+--Docodonta | Hadrocodium | ` --Symmetrodonta | |--Kuehneotheriidae | `--Mammals

PvM · 19 March 2008

This is just stunning, amazing how science keeps uncovering these fossils.

Remind me again, how does ID explain this?

Stanton · 20 March 2008

PvM: This is just stunning, amazing how science keeps uncovering these fossils.

Such as the fossils of pregnant ungulates from the Messel Quarry pits?

Remind me again, how does ID explain this?

"We don't know, ergo, ~~GOD~~DESIGNERDIDIT, and there's nothing else to learn."

gabriel · 20 March 2008

Dale Husband: Why not just use the "old standards" too, but explain why Creationist critics have failed to refute them? But only make that point if a student brings up those lame claims of the Creationists.

I teach at an evangelical Christian university, so many of my students have had exposure to anti-evolution material and think it wonderful. My approach (using newer material) avoids the time delay of having to debunk Wells for the nth time, as well as displaying evolution as cutting-edge science. Many of my students are stuck in the "it's all about evil Darwin" mode - current stuff shows them things have progressed. Debunking an argument can also appear to give it validity as a valid critique - I tend to spend 95% of the lecture on evolution proper, and leave the last few minutes to quickly eviscerate YEC and ID.

Paul Flocken · 20 March 2008

PvM: This is just stunning, amazing how science keeps uncovering these fossils. Remind me again, how does ID explain this?

You're really enjoying this, aren't you. :)

Paul Flocken · 20 March 2008

gabriel: I teach at an evangelical Christian university, so many of my students have had exposure to anti-evolution material and think it wonderful. My approach (using newer material) avoids the time delay of having to debunk Wells for the nth time,

I can imagine all the eye-rolling you must have to endure when you bring up the old creo-canards, and they probably think they are so clever when they spout that nonsense to you.

as well as displaying evolution as cutting-edge science. Many of my students are stuck in the "it's all about evil Darwin" mode - current stuff shows them things have progressed. --Debunking an argument can also appear to give it validity as a valid critique-- I tend to spend 95% of the lecture on evolution proper, and leave the last few minutes to quickly eviscerate YEC and ID.

A demonstration of just how crippling to critical thinking skills the anti-intellectual creo/religion meme can be. How they can continue to think something is valid after having it clearly demonstrated as wrong still boggles the mind.

focus · 19 January 2009

This is a loaded topic if I have ever seen one. I have had numerous debates on the topic but have come to the conclusion that some people will never believe facts no matter how hard you hit them over the head with it.