Mitochondria and Microsatellites

Mitochondrial DNA (mtDNA) is useful for determining the phylogeny, or relationships, between closely related species. It is inherited, generally, only from mother to offspring, so it doesn’t face problems such as recombination since it isn’t recombining with other DNA before being passed on (except through horizontal transfer, or “genetic swapping” between bacteria).

One recent discovery using mitochondrial DNA has found that a sort of “pre-human” was walking around while humans and Neanderthals were still rocking out.

The sequence indicates the hominin’s line diverged about a million years ago from the line that gave rise to both humans and Neanderthals and that split about 500,000 years ago.

That makes it younger than Homo erectus, the pre-human that spread out of Africa to much of the world about 1.9 million years ago.

“It is some new creature that has not been on our radar screen so far,” said Svaante Paabo, a colleague of Krause’s who specializes in analyzing ancient DNA.

And it would have lived near to both modern humans and Neanderthals. “There were at least three … different forms of humans in this area 40,000 years ago,” Paabo said.

The article goes on to state that more research is needed to determine just where it qualitatively sits on the evolutionary tree. My point, however, is that mtDNA has proved useful in this analysis, giving a tentative quantitative determination and a tentative qualitative indication.

This is all in stark contrast to microsatellites. These are short tandem repeats, or units of repeating DNA sequences. For example, CACACACACACACACACACA is commonly seen throughout eukaryotes and the chloroplastic genomes of plants (usually every few thousand base pairs). They are generally neutral.

Microsatellites have relatively high mutational rates for a variety of reasons. Whereas in mitochondria the mutational rate can partially be chalked up to the fact that mitochondria is bacterial in origin, microsatellites have polymerase slippage to thank, or bad DNA replication, let’s say. Other studies suggest unequal crossing-over. At any rate, this mutation rate lends itself to population studies using microsatellites.

By using microsatellites as genetic markers, it is possible to determine genetic variation within a population. This works for investigating both temporal and spatial population structure, two important factors in management and conservation of species. For instance, Lage et al. 2004 looked at Atlantic cod populations ranging across Browns Bank, Georges Bank, and Nantucket Shoals. At the time of the research, the Gulf of Maine cod were treated as a separate stock from the Nantucket Shoals and Georges Bank Atlantic cod. Browns Bank cod were even more separate as a stock since they are in Canadian waters. Using microsatellites, the researchers found Nantucket Shoals cod to have a distinct population structure from those on Georges Bank and Browns Bank, which were genetically similar. One likely reason is due to currents which keep Georges Bank cod on Georges Bank as well as somewhat rare currents which likely transport larvae from Browns Bank over the Fundian Channel (which adult cod are unlikely to traverse since they are ground-huggers and the channel is deep and cold). The conclusion is that the health of Atlantic cod populations might be better served by treating them as separate stocks based upon the discovered genetic variation, instead of the current method of utilizing particular geographical lines which may not reflect all population ‘barriers’.

The shortcoming, however, with microsatellites is that they are not useful for deep phylogenetic analysis. Their high mutation rate makes them virtually useless after a few thousand generations; they are good for pedigrees and population structure analysis, but they do not offer insights into distant relationships. Occasionally they may remain the same or nearly the same over long periods of time, but the rhyme and reason probably has nothing to do with the microsatellites themselves. Instead, they likely are located near a site of selection on a locus, thus conserving them for longer than just those few thousand generations.

Lage CR, Kuhn K, Kornfield I. (2004) Genetic differentiation among Atlantic cod (Gadus morhua) from Browns Bank, Georges Bank, and Nantucket Shoals. Fishery Bulletin, 102:289-297.

Update: Thanks to Chris Lage for offering his advice and corrections on this.

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Lynn Margulis, 73, dead

Lynn Margulis was one of those scientists that biology needed. She forged the now universally accepted endosymbiotic theory only about 44 years ago, bringing it to the mainstream 30 years ago. I have heard her work compared to that of Watson & Crick insofar as it marked a significant turning point within the field. She really did have some great ideas and it’s a shame that she died so young.

Garuda wasp

Biogeography and endemic species are two great pieces of evolution. The former refers to the distribution of species across the planet and only evolution adequately explains what we observe. Take for instance Australia. It is filled with marsupial mammals, yet it is off all by its lonesome in the ocean. Clearly mammals did not evolve twice, the second time taking an alternative path to being placental. We need an explanation. The one we have is that this marsupial subset of mammalian life migrated down the Americas, through Antarctica, and into Australia. Fossil and tectonic plate evidence independently confirm this hypothesis – marsupial fossils are found all through South America and into Antarctica (and, of course, Australia), dating back to the time when those continents were still all connected.

Endemic species also constitute a nice bit of evidence for Darwinists. The man himself, Charles Darwin, saw quite an array of species that are only present on the Galapagos Islands, their relatives residing back in South America for the most part. (One of my favorite Galapagos animals is the marine iguana.) But there are far greater islands out there. Madagascar has to be the first to come to mind (and, in turn, its lemurs come to mind next for me). There is also Alejandro Selkrik Island, a place I mention in the first link in this post. And then there is Sulawesi, an Indonesian Island a fair bit north of Australia. It’s a haven for researchers who want to study unique flora and fauna, including many large mammals. It has a lot of protected land and animals (especially its marine life), so it’s a prime location for many biologists. One such biologist is Lynn Kimsey, an entomologist who recently described a pretty striking find:

It sounds like the stuff of nightmares – a wasp that supplements a vicious sting with jaws longer than its front legs.

But this is a very real newly discovered warrior wasp found on the remote Indonesian island of Sulawesi.

Dubbed the ‘Komodo dragon’ of the wasp family, the males of the species measure two-and-a-half inches long…

Ms Kimsey, who is also director at the Bohart Museum of Entomology, said: ‘Its jaws are so large that they wrap up either side of the head when closed. When the jaws are open they are actually longer than the male’s front legs. I don’t know how it can walk.’

Luckily the species prefers to dine on insects, but if threatened it could leave a sizeable mark on human flesh too.

It’s a beast.

Whereas this is an insect which not only can fly, but can be carried away by strong winds, it may very well inhabit a number of other nearby islands. However, given its exceptional size, my suspicion is that it is the unique biosphere of Sulawesi itself which has given rise to such a monster. Perhaps the ‘Garuda wasp’, as it is to be known, can survive elsewhere, but my bet is that its currently only known island of habitat is where it can really thrive.

Of course, its current habitat is effectively random and haphazard without the framework of evolution to guide us. It is only with Darwin’s theory that we can really understand anything about the Garuda wasp or any other unique form of life around the globe.

Mosquito genocide

Whenever I find myself under attack by mosquitoes, I will tend to remark to another person how much I would enjoy a mosquito genocide. Sure, a midge and/or horsefly genocide would be lovely as well – not to mention a whole host of other insect holocausts – but it’s the mosquito I really hate. I mean hate. I would eat raw onions and celery for the rest of my life if I could do away with the little bastards.

The natural response I get from people when I express my desire for mosquito eradication is, “Wouldn’t that really mess up the food chain?” I respond, half-jokingly, that I’m willing to make that sacrifice. Of course, along with most other people, I have always believed that the death of all mosquitoes, or at least the ones that bite humans, would have long-reaching ecological ramifications. And, again, along with most other people, I naturally don’t want to see that happen. But as it turns out, maybe it wouldn’t be such a bad thing after all:

Most mosquito-eating birds would probably switch to other insects that, post-mosquitoes, might emerge in large numbers to take their place. Other insectivores might not miss them at all: bats feed mostly on moths, and less than 2% of their gut content is mosquitoes. “If you’re expending energy,” says medical entomologist Janet McAllister of the Centers for Disease Control and Prevention in Fort Collins, Colorado, “are you going to eat the 22-ounce filet-mignon moth or the 6-ounce hamburger mosquito?”

With many options on the menu, it seems that most insect-eaters would not go hungry in a mosquito-free world. There is not enough evidence of ecosystem disruption here to give the eradicators pause for thought.

At this point in the evolution of life, any significant hole left open by one species will quickly be filled by another. Even when the world has seen mass extinctions, life has been quick to fill in the gaps. And that’s with broad gaps. The loss of mosquitoes would be a very narrow niche to cover.

But there are other mosquito-reliant organisms. The question, however, is, how reliant are they? Mosquitoes make up a lot of the biomass in both aquatic and summer arctic environments. In aquatic environments it’s their larvae that contribute to the ecosystem, bringing about greater variation in other organisms while also producing nutrients for plants. In the arctic, they are food for migratory birds. But in both cases other organisms could easily take their place. Though mosquitoes have co-evolved with so many other species, so have so many other insects and microorganisms. They aren’t unique except in their high level of annoyance.

Attempts at Genocide

When the French attempted to build a canal in Panama, one of their major setbacks was disease carried by mosquitoes. It wasn’t until shortly after they started construction that it was even known that mosquitoes were vectors for diseases such as malaria and dengue fever. And even then, it wouldn’t be for some time – about when the French gave up – that it was known just how much mosquitoes could spread disease.

Enter the Americans.

When the U.S. set to construct the canal, measures were taken to drastically cut down on the mosquito population in the area. Standing pools and ponds of water were drained near construction and living areas. High grasses were cut down to create fields mosquitoes were less likely to cross. Oils were added to difficult to drain ponds. Acids and caustic sodas were even spread in great quantity. And what effect did this have on the ecology of the surrounding area? Apparently none. (At least none as a result of the loss of the mosquito.) Of course, this wasn’t an eradication, and it didn’t impact all areas, but it was a massive effort and the mosquito population was reduced significantly.

So could we do something like that, but for all mosquitoes, in all areas? Probably not. Many places in the South have programs where standing buckets of water and other common mosquito breeding grounds are destroyed. Other places spread sprays which kill mosquito larvae. These methods help, but they aren’t enough to fix the problem. And in all likelihood, there are no practical methods available that could bring about the Great Mosquito Genocide. Really, I trust that if humans could get rid of this pest, we would have long, long, long ago.

But don’t let our inability to destroy these little bastards take anything away from the dream of mass mosquito murder:

“They don’t occupy an unassailable niche in the environment,” says entomologist Joe Conlon, of the American Mosquito Control Association in Jacksonville, Florida. “If we eradicated them tomorrow, the ecosystems where they are active will hiccup and then get on with life. Something better or worse would take over.”

Punching bags

Whenever creationists get hold of a legitimate scientific paper, I groan a little bit for at least two reasons. First, I know whatever they have to say, they’re going to mangle the science. We saw that with Jack Hudson last year (and, actually on literally every post about science he has ever made). And, of course, we also saw that with all the other creationist sites from which Jack stole his material. Second, I know I’m going to have to devote some time to reading and blogging on a paper I would have otherwise missed. It isn’t that I don’t like to read these things – I do. The problem is that it’s a time-suck when the blogging is factored in. You see, unlike creationists I actually research and verify what I have to say on any given piece of science.

Let’s start with the paper in question:

Here we report exceptionally preserved fossil eyes from the Early Cambrian (~515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized ‘bright zone’. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later6, 7. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event8.

The gist of the find is this. Researchers discovered very old fossils of arthropod eyes from the Early Cambrian. They do not predate complex eyes, but they do predate similar non-biomineralized eyes. That is, trilobite eyes are made of calcite, meaning the trilobites produce the minerals for their eyes themselves. In turn, their eyes are hardened (and thus more easily fossilized). So these new fossils show a different way in which eyes could become complex. Furthermore, they showed a tight packing in the lenses, much in the way that a fly’s lenses appear to be tightly packed. They also were curved to form binocular vision, meaning there was a visual overlap in front of the body. This helps for judging distances and discerning complicated backgrounds. This creature was a predator.

But here is where creationists draw issue:

Did you catch that? If you were a high school student who trusted your teachers, you’d think they had evidence for this unbelievably rapid amount of highly complex change. But they merely assume that it evolved, so it “had” to have been a great evolutionary event and another example of “rapid innovation.” [And is thus a tautology.]

This comes from Neil who, like many creationists, was taking his cue from another site. He believes that every paper that mentions evolution must provide a detailed description of why evolution is true.

His quote was a reference to this excerpt from the paper:

[The new fossils] provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.

What this is referencing is the fact that until now advanced eye fossils were almost exclusively restricted to trilobites in the fossil record. These new fossils give evidence that, as suspected, there were other marine creatures swimming around with complex eyes. Furthermore, they show a quantitative change in the number of lenses, not the sudden appearance of these sort of lenses. (But note that we can’t expect to see a perfect fossil record. We can get a good outline, but it’s silly and really very ignorant for creationists to demand to see every intermediate organism. At some point things will have to “suddenly” appear. Of course, this is in geological terms, i.e., over millions of years.) These eyes are evidence that evolution was driven in part by the anatomical changes in vision during the Cambrian.

So it is clear that none of this is a tautology. This fossil find is further evidence of the nature of evolution and the role vision played in its creation of arms races. What we see from the creationist world, however, is an immature understanding of the science. There is no doubt that Neil never bothered to read the paper from Nature, nor have many of his creationist brethren. If any of these sort of non-academics bothered to look into the literature (or even take formal courses), they would see their obvious errors. Further, even if we are to understand this paper as Neil purports it to be, he’s still in error. That is, he believes the paper is a tautology because it assumes evolution without giving evidence for why evolution is true. This is like drawing issue with physics papers because they assume gravity is true without explaining general relativity. It’s a silly complaint to make and it only demonstrates how wildly over the head of creationists most scientific papers are.

Re: Origins of vision

I’m doing another repost, this time taking from an article I did about the origins of vision. Note that the quote coloring is reversed from how it normally appears.

Vision likely originated as simple eyespots in simple organisms. It also is traced back to jellyfish and their own simplistic eyespots, which are actually still present in some manner today. That is, jellyfish have areas of photoreceptor cells which don’t allow vision as we know it (they don’t even have brains), but they do allow a sensation of particular wavelengths of light to be perceived. These wavelengths often indicate depth (and maybe predators), which in turn may indicate food source (pelagic jellyfish don’t tend to get to plump).

Recent research has discovered the genetic pathway involved in light sensitivity in a close relative of the jellyfish.

“We determined which genetic ‘gateway,’ or ion channel, in the hydra is involved in light sensitivity,” said senior author Todd H. Oakley, assistant professor in UCSB’s Department of Ecology, Evolution and Marine Biology. “This is the same gateway that is used in human vision.”

This allows for a prediction using evolution: all organisms alive today which share a common ancestry with hydras will share this same genetic gateway. Organisms like flies, as the article points out, do not share this ancestry with vertebrates and as such do not share this genetic gateway. If they did share it, then wow. Creationists could actually trot out their improbability arguments.

“This work picks up on earlier studies of the hydra in my lab, and continues to challenge the misunderstanding that evolution represents a ladder-like march of progress, with humans at the pinnacle,” said Oakley. “Instead, it illustrates how all organisms — humans included — are a complex mix of ancient and new characteristics.”

(End different quote coloring.)

I looked this post up because I recently ran across a creationist who actually trotted out that old “the eye is irreducibly complex” bull and I was searching for some other links. But what’s interesting is what a different creationist was saying in the comment section:

You premised your claim of cnidarian relationship to vertebrates and humans on a gene they share in common. You said specifically, “This allows for a prediction using evolution: all organisms alive today which share a common ancestry with hydras will share this same genetic gateway.” I pointed out that certain beetles share certain genes with vertebrates and humans that other insects do not – and by your logic, that would mean these beetles share an ancestry with humans other insects do not.

As I pointed out at the time (and as the creationist failed to even come close to grasping), my claim was not based upon the sharing of individual genes, but rather on the sharing of complex genetic pathways. It is these pathways that ultimately allow for such a prediction. The creationist then confused the discussion on pathways with the article focus of a gateway. (I pointed out his error to him, but to no avail.) It is these pathways, by and large, which first get us to the point of where we can say that hydra and humans share a common ancestry in terms of vision. From that point we can look at the particular gateway in question and make the prediction I originally made. (One caveat: organisms which have lost their ability to see may not share the gateway.)

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.

Butchering science

Creationists hate science. They hate its conclusions, they hate its methods, they hate that it doesn’t support their silly beliefs. It’s that hatred that motivates them to butcher scientific articles and papers.

One recent butchering comes from Jack Hudson. I’m sure regulars here remember him. If not, it isn’t important. He’s a creationist with a background in introductory biology courses from 20 years ago. It’s doubtful he has much experience reading scientific papers, but that doesn’t stop him from trying.

In his post he butchers two articles. I’m going to focus on the first one, but I’ll briefly mention the second one. In that one researchers found that some negative mutations don’t change the protein sequence yet they are still negative. This one is simple. The entire sequence of a gene is not devoted to just the protein sequence. A mutation can therefore change one aspect of a gene without changing another – but it can still change another process that is important in forming proteins. Alter shape in one place and you have a good chance of seeing change somewhere else as a result. Biology is still all about shape.

The second paper, though. Woo. What a doozy of a butchering. First let me summarize the paper.

In asexual populations alleles can become fixed rather quickly. Their evolution is more straight forward because they aren’t mixing and matching genes. They produce offspring with the exact same genome, less there be a mutation. If there is a mutation, it can become fixed because things are generally less complicated with asexual populations and thus more black and white. Is this mutation good or bad? As the paper says and as Jack repeats upon hearing the term for the first time, alleles sweep through a population.

But when it comes to sexually reproducing populations, things become more complicated. And this is what the paper is about. The question is, do alleles sweep through populations in sexually reproducing populations like they do in asexual populations? The answer is no.

Now, if we’re to believe Jack, this means that evolution has failed because, why, evolution predicts an advantageous allele to reach 100% fixation, of course. Except it isn’t so black and white with sexually reproducing populations. (Nor does evolution predict that anyway.)

What the researchers did was study over 600 generations of fruit flies. They let them breed naturally, but then selected out the eggs which were produced the most quickly. This led to significantly faster reproducing populations. They then tracked specific alleles to see if they would become fixed. What they found was that they don’t.

Signatures of selection are qualitatively different than what has been observed in asexual species; in our sexual populations, adaptation is not associated with ‘classic’ sweeps whereby newly arising, unconditionally advantageous mutations become fixed. More parsimonious explanations include ‘incomplete’ sweep models, in which mutations have not had enough time to fix, and ‘soft’ sweep models, in which selection acts on pre-existing, common genetic variants. We conclude that, at least for life history characters such as development time, unconditionally advantageous alleles rarely arise, are associated with small net fitness gains or cannot fix because selection coefficients change over time.

The conclusion here is that selection for a particular trait in sexually reproducing populations acts upon many different aspects and genetic variants within the genome, not merely a single gene or SNP.

This suggests that selection does not readily expunge genetic variation in sexual populations, a finding which in turn should motivate efforts to discover why this is seemingly the case.

This is the actual conclusion of the paper. To put it another way (and to repeat myself), advantageous variants do not wipe out other genetic variants in a sexually reproducing population, instead acting on variation in a more subtle and complicated way. The big conclusion here is that there is a difference in how genes become fixed (or not fixed) in asexual populations versus sexually reproducing populations.

And Jack’s conclusion?

In short, if the activity failed to occur in the lab under optimal conditions, it is unlikely that traits are going to be transmitted this way in nature.

The traits are still being transmitted through natural selection working on variation. Jack’s conclusion has little to no connection to anything from the paper. In fact, it is abundantly clear that he read an article somewhere, figured out how to butcher it, and then went and read a few lines from the original paper.

I’ve said in the past that what takes a creationist 30 seconds to say takes an educated person 3 hours to correct. This post and the research required for it didn’t take that long, but the sentiment remains true – it’s a real hassle to untangle the carelessly mushed writings of a creationist.

Repost: Only in the light of evolution

There are two reasons I want to make a repost of a post from about a year and a half ago. First, it’s always interesting to go back and read old posts for me. From time to time I have no recollection of making a certain post, so when I see it, it’s almost like it’s brand new to me. I do happen to remember this one very clearly, but it is at least understandable why I was skimming posts from May 2009. Second, I average significantly more views now than I did a year and a half ago. I feel this post is a pretty important one, and now that more people can see it, I would like to throw it back up.

~~~

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.