Neil Shubin inducted into NAS

This is satisfying:

The National Academy of Sciences today announced the election of 72 new members and 18 foreign associates from 15 countries in recognition of their distinguished and continuing achievements in original research…

Shubin, Neil H.; Robert R. Bensley Professor and associate dean, department of organismal biology and anatomy, University of Chicago, Chicago

Shubin is most famous for his evolution-utilizing research into Tiktaalik. I’m glad to see him inducted.

And congratulations to everyone else who was deemed worthy to be a member of such a prestigious institute.

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Neglected point

One point I neglected about Tiktaalik is that its ability to walk on land was limited. Its limbs wouldn’t have been able to support it terribly well to do terribly much. Its life was likely spent more in the water than on land.

Coupled with the recent discovery of tetrapod footprints in a marine environment, the way to think of all this is that tetrapods did evolve at least 400 million years ago, but there were clearly still viable alternative lifestyles to go alongside fully terrestrial life (and still are). Nothing demands evolution be perfectly linear. (Neanderthals lived at the same time as our direct ancestors as recently as 30,000 years ago.) A further important fact is that while probably 90% or so of all fossils come from the ocean, they tend to be from the more settled sediments, i.e., not the shoreline, the evident habitat of these newly discovered tetrapods. That indicates a possible sampling bias. Just looking at Tiktaalik, it’s clear that its freshwater habitat lent itself to preserving fossils – aside from the area being targeted for its fossilizing properties, there were several examples extracted from the site.

Tetrapods pushed back 18 million years

The oldest tracks of four-legged animals have been discovered in Poland.

Rocks from a disused quarry record the “footprints” of unknown creatures that lived about 397 million years ago.

Scientists tell the journal Nature that the fossil trackways even retain the impressions left by the “toes” on the animals’ feet.

The team says the find means that land vertebrates appeared millions of years earlier than previously supposed.

This is especially interesting because Tiktaalik was discovered by Neil Shubin based upon a lack of land animals 390 million years ago but a prevalence 360 million years ago. He specifically looked for a place likely to have fossils that was 375 million years old in order to discover his transitional fossil. This new information doesn’t mean that he just got lucky – one would still expect to find transitional forms prior to true land animals – but a little luck was involved. (It was actually involved no matter what he wanted to find and when he wanted to find it because fossilization is so rare anyway.)

One important fact to note about Tiktaalik is that it likely lived in freshwater. This is key because a marine environment is less conducive to a full move onto land than a freshwater lake or river, and Tiktaalik shows evidence that it is closely related to later fully land animals. Think about it for a moment and it becomes obvious: you need to be able to drink freshwater, not salt water, in order to fully utilize the land. If your ancestors lived in freshwater, then the first transition has been made for you. That means the owners of these newly discovered footprints represent a transition of sorts, but they were still very much tied to a marine life, unlike Shubin’s discovery.

Only in the light of evolution

Now that finals are over, I can devote more time to my dear, neglected blog. I begin with a series:

I am following a specific chapter in Jerry Coyne’s Why Evolution is True.

The fossil record: We should see fossils in a certain order if evolution is correct. They should go from simple to more complex overall, and the fossils we see in the most recent strata should resemble extant life much more than the fossils we see in old strata.

We should also see changes within lineages. We should be able to observe instances of gradual change in species that eventually leads up to either current species or at least to the time of extinction for these species.

Here’s a simple timeline of life’s history. Click it.

What the evidence shows is gradual change. First we find simple bacteria which survived off energy from the Sun, then we see more complicated cells known as eukaryotes arise. (You are a eukaryote.) Next we see a slew of multi-cellular animals arise. They’re still simple, but much more complex than the original bacteria. A few million years later more complicated life arrives. Early (and simple) plants begin to take hold. Soon the fossil record begins to show more plant complexity with low-lying shrub such as ferns, then conifers, then deciduous trees, and finally flowering plants. Gradual changes occur in the oceans and fresh waters which lead to fish and then tetrapods (Tiktaalik comes to mind).

One of my favorite fossils is trilobites. They’re extremely common due to their hard bodies. In fact, even their eyes are well-preserved because of their hard mineral make-up. I personally recall entering touristy-stores seeing countless fossils of these guys in the mid-west to the west (which, unsurprisingly, was once a shallow sea). This image shows the different lineages of this organism. Studies show that the ‘rib’ count has changed over time in each individual species, often without regard to how the other species changed. Going back further, there is less and less divergence in each species. Eventually, as evolution predicts, they all meet at a common ancestor.

So naturally the next step is to find fossils which show more significant changes. Let’s take birds and reptiles. They hold similarities between each other, both morphologically (certain shapes and structures) and phylogenetically (genetic sequence). A good hypothesis is that they came from one common ancestor. If this is true, the links between birds and its ancestors and reptiles and its ancestors should lead to the same point. They do. Dinosaurs are the ancestors of both. The links between birds and dinosaurs are so incredibly well established that I’d prefer to not go over them in detail. But for starters, some dinosaurs sported feathers and claws and had the same proteins for the feather-making process as extant birds. The links between reptiles and dinosaurs is easier just on intuition, so I’ll leave it at that for now.

Other transitional fossils include the already mentioned Tiktaalik. A view of the history of life can be see here. This shows the change in head and neck structure. Recent research on long-ago discovered Tiktaalik fossils has shown the importance in the gradual bone changes in the neck. These changes – a hallmark of evolution – were important to the ability to turn its head. This is a hallmark because natural selection only modifies what already exists. This is precisely what happened.

Going further with this example, evolution makes predictions as to how early fish evolved to survive on land. If there were lobe-finned fish 390 million years ago and obviously terrestrial organisms 360 million years ago (which is what the fossil record shows), then if scientists are to find transitional fossils, they should date in between that time frame. There should be an animal that shows both features of lobe-finned fish and terrestrial animals. Tiktaalik is that animal. It has fins, scales, and gills, but it also has a flat, salamander-like head with nostrils on top of its nose. This is a good indication that it could breathe air. Its eyes were also placed there, indicating that it swam in shallow waters. Furthermore, it was lobe-finned, but shows bones (which eventually evolved into the arm bones you used to get out of bed today) that were able to support its weight to prop itself up. And of course, it dates to 375 million years ago.

Next, evolution says the fossil record should show recent fossils being more closely related to extant species than are early fossils. This is precisely what happens. Sixty million years ago there were no whales. Fossils resembling modern whales only show up 30 million years ago. So, again, evolution makes a predication: if transitional fossils are to be found, they will be within this gap. And so it is.

We begin with Indohyus. It was an artiodactyl. This is important because extant whales have vestigial bones which indicate that they came from this order: scientists expected to find this because, again, evolution predicted it. It should be of no surprise that this fossil dates to about 48 million years ago, right in the predicted gap. From here there is a gradual evolution shown in the fossil record which leads up to modern whales.