Archive for the 'Evolution' Category

Aug 30 2021

Four-Legged Whale Described

In 1985 Michael Denton, arguing against the fact of evolution, made the following observation:

“…to postulate a large number of entirely extinct hypothetical species starting from a small, relatively unspecialized land mammal and leading successively through an otter-like state, seal-like stage, sirenian-like stage and finally to a putative organism which could serve as the ancestor of the modern whales. Even from the hypothetical whale ancestor stage we need to postulate many hypothetical primitive whales to bridge the not inconsiderable gaps which separate the modern filter feeders (baleen whales) and the toothed whales.”
Denton (1985) Evolution: A Theory in Crisis, Adler & Adler Publishers:Chevy Chase, MD. p. 174

In 1992 creationist Duane Gish made an even more bold statement:

“The marine mammals abruptly appear in the fossil record as whales, dolphins, sea-cows, etc. There simply are no transitional forms in the fossil record between the marine mammals and their supposed land mammal ancestors.”
Duane Gish (1992), Evolution: The Challenge of the Fossil Record. Creation-Life Publishers: El Cajon, CA. p. 79

This remains a common strategy for creationists – point to current gaps in the fossil record and then pretend this is a problem for evolutionary theory. The unstated major premise here is that if evolution were true, we would by necessity already possess a fairly complete fossil record for the evolution of every single extant species, or at least (arbitrarily defined) major group. This premise is simply false. We have fossil windows into a process that occurred over 600 million years (if we talk only about multicellular creatures), all over the world, involving an estimated 5 billion species. There are gaps and always will be gaps.

Continue Reading »

No responses yet

Aug 26 2021

Evolution Denial Survey

The idea that all life on Earth is related through a nested hierarchy of branching evolution, occurring over billions of years through entirely natural processes, is one of the biggest ideas ever to emerge from human science. It did not just emerge whole cloth from the brain of Charles Darwin, it had been percolating in the scientific community for decades. Darwin, however, put it all together in one long compelling argument. Alfred Wallace independently came up with essentially the same conclusion, although did not develop it as far as Darwin.

On the Origin of Species was published in 1859, and it quickly won over the scientific community, with natural selection acting on variation becoming the dominant working hypothesis. But that, of course, was not the end of the story, only the beginning. If Darwin’s ideas were wrong, they would have slowly withered from lack of confirming evidence. But they were largely correct, even insightful. The last 162 years of research and observation have confirmed to an extraordinary degree the core ideas that life is related through branching connections, and that natural selection is a primary driving force of evolution. The theory has also evolved quite a bit, and is now a mature and complex scientific discipline sitting on top of mountains of evidence, including fossils, genetics, comparative anatomy, developmental biology, and direct observation. The basic fact of evolution could have been falsified thousands of times over, but it has survived every time – because it is essentially true.

Acceptance of the basic tenets of evolutionary theory, therefore, is a good litmus test for any modern society. Of what, exactly, is another question, but certainly something is going wrong if the population does not accept this overwhelming scientific consensus. The US ranks second from the bottom (only Turkey is worse) in terms of accepting evolutionary theory. Researchers have been tracking the statistics for decades, and now some of the lead researchers in this field have published data from 1985 to 2020 (sorry it’s behind a paywall). There are some interesting details to pull from the numbers.

Continue Reading »

No responses yet

Jul 13 2021

Dogs Understand Humans

Published by under Evolution

Regardless of whether or not you are a cat person or a dog person (I have both as pets, as well as a reptile, and have had birds and fish), there is no denying that dogs are excellent human companions. No other animal known is capable of the same relationship with people. Researchers have been trying to understand the origin of this special relationship, with some interesting results.

First let me review the results of a new study, and then add in some background. The question the researchers are trying to address is this – how much of dog behavior is shared with their wolf ancestors? Specifically, dogs and wolves share a common ancestor between 12,000 and 40,000 years ago. There was likely a lot of interbreeding during this time (as there still is) so it’s probably not possible to declare a clean break. But they are now distinct subpopulations. Dogs show an incredible ability to understand their human companions, even without extensive training. The question is – how much of this ability is innate vs trained and how much is shared with wolves?

The study compared 44 dog pups with 37 wolf pups right after birth. The wolf pups were raised by humans, with maximal human contact after just a few days from birth. The dog pups were kept with their litters with minimal human contact. They were assessed at 5-18 weeks old. The authors found that the dog pups were able to follow human direction (such as pointing and other cues) toward a food reward. The wolf pups did no better than chance, indicating no benefit from the human cues. Dog pups were also able to respond to novel cues, like playing a block next to the target bowl. Further, when a stranger was introduced the dog pups came up and interacted with them (wagging their tail and licking their face) while the wolf pups when into a corner and hid.

None of this is surprising, and it is all consistent with prior research. But it does help confirm that these stark differences are innate, and not learned. So what’s going on?

Continue Reading »

No responses yet

Jun 08 2021

Evolutionary Compromises

Published by under Evolution,Skepticism

Evolution if one of the most fascinating scientific phenomena because it is so complex and operates over such varying and long timescales. It’s a real challenge to wrap one’s head around. There is therefore a tendency to settle on overly  simplistic evolutionary narratives. This is not a criticism, we all do this in an attempt to grapple with evolutionary thinking. The challenge is to recognize this fact, and be open to a deeper, more complex and nuanced understanding of evolutionary processes. It’s a great example of what should be a general intellectual posture – recognize the limits of our current understanding (wherever that may be on the spectrum) and not only be open to, but seek out new information and concepts to keep incrementally pushing our understanding forward.

In that spirit, here is a study on the evolution of broad-horned flour-beetles that illustrates some of evolution’s complexity. The male broad-horned has exaggeratedly large mandibles, which is uses to compete with other males for mating access to females. This is an example of sexual selection, when a feature specifically increases mating success but is not necessarily broadly adaptable. The go-to example of this is the peacock’s tail feathers – a garish display meant to attract females, but an evolutionary burden in many other aspects. This sets up an evolutionary tug-of-war, where a feature may be advantageous in one respect but disadvantageous in another. Evolutionary processes are fairly efficient at balancing such conflicting forces.

As an aside, the balances tend to be only metastable. They can alter with changes in the environment or behavior. Even different individuals within a species can adopt different survival strategies that result in a different balance of traits. If a population within a species does this it may even eventually lead to a speciation event. For example, it has been documented that within some primate species dominant males will have access to females due to their alpha status, while others gain access by currying favor with the alpha, and still others gain access by gaining favor with the females and sneaking behind the alpha’s back. Still others may act as a “wing man” to a close kin, promoting their genes into the next generation by proxy. The lesson here is – no one strategy captures the wide diversity of behavior even within a single species.

Continue Reading »

No responses yet

Apr 29 2021

Evolution of Multicellularity

Published by under Evolution

When studying the history of life evolutionary biologists and paleontologists have no choice but to look where the light is good. There are fossil windows into specific times and places in the past, and through these we glimpse a moment in biological history. We string these moments together to map out the past, but we know there are a lot of missing pieces.

One relatively dark passage in the history of life is the evolution of multicellularity. Beginning about 541 million years ago (mya) we can see the beginning of the Cambrian explosion – the appearance of a vast diversity of multicellular life. But this “explosion” was only partly due to rapid adaptive radiation, it is also an artifact of the evolution of hard parts that can fossilize. That development turned on the lights. The earliest known single-celled organisms are 3.77 billion years old, so we have a 3 billion year time span during which a lot must have happened. We know from changes in the atmosphere that cells evolved that could use sunlight to produce oxygen, and other critters evolved to eat them.

Continue Reading »

No responses yet

Apr 05 2021

The Great Oxygenation Events

Published by under Evolution

The deep history of the Earth is fascinating, and while we have learned much about the distant past there are still many puzzle pieces missing. A new study tweaks our understanding of one of the biggest events in Earth’s history – the Great Oxygenation Event, and also helps better align the other big events in the past.

The Earth as we know it formed about 4.5 billion years ago. Earth is actually Earth 2.0 – the proto-Earth was hit by a Mars-sized object, forming both the current Earth and the Moon. The Earth was fairly molten at this time, still hot from all the impacts, but over the next millions of years the surface cooled, stable pools of liquid water formed on the surface, and it had a stable atmosphere of mostly nitrogen. In this environment life evolved. We are not exactly sure when, but probably by 3.5 billion years ago. There is good evidence for cyanobacteria by 2.9 billion years ago. These critters are important, because they make food from sunlight and produce oxygen as a waste byproduct. For millions of years oceans full of cyanobacteria cranked out oxygen, which built up in the atmosphere.

This is where the new study comes in –  it explores exactly when oxygen built up to high levels. The current atmosphere is about 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, and trace amounts of methane and other gases.  Prior to about 2.45 billion years ago there was essentially zero oxygen in the atmosphere. Between 2.45 and 1.85 billion years ago oxygen built up slowly in the atmosphere, up to 3-5%, but was also mostly absorbed by the oceans and seabed rock. This is the Great Oxygenation Event, still little oxygen by today’s standard, but enough to usher in a major change in the chemistry of earth. From 1.85 to 0.85 billion years ago oxygen had saturated the ocean and so now spread to the land where it was further absorbed into rocks and minerals. During this time atmospheric O2 levels were pretty stable at 3-5%. But then, starting 0.85 billion years ago the surface of the Earth had absorbed all the oxygen it could (the oxygen sinks were full) and so O2 started building up in the atmosphere significantly, peaking about 400 million years ago at over 30% and then settling down to the current 21%. Oxygen levels are now slowly and steadily decreasing.

Continue Reading »

No responses yet

Mar 04 2021

Cuttlefish Pass Marshmallow Test

Cuttlefish are amazing little critters. They are cephalopods (along with octopus, quid, and nautilus), they see polarized light and can use that to change their skin color to match their surroundings. They have eight arms and two tentacles, all with suckers, that they use to capture prey. They, like other cephalopods, are also pretty smart. And now, apparently, they are also in the very elite club of animals who can pass the marshmallow test.

The “marshmallow test” is a psychological experiment of the ability to delay gratification. The basic study involves putting a treat (like a marshmallow, but it can be anything) in front of a young child and telling them they can have it now, or they can wait until the adult returns at which time they will be given two treats. The question is – how long can children hold out in order to double their treats? The interesting part of this research paradigm are all the associated factors. Older children can hold out longer than younger children. The greater the reward, the more children can wait for it. Children who find ways to distract themselves can hold out longer.

For decades the test and all its variations was interpreted as a measure of executive function, and correlated with all sorts of things like later academic and economic success. However, more recent studies have found (unsurprisingly) that there can be confounding factors not previously recognized. For example, children from insecure environments have not reason to trust that adults will return with more treats and therefore take what is in front of them. This could be seen as an adaptive response to their environment.

Continue Reading »

No responses yet

Mar 02 2021

Humans and Megafauna Extinction

Published by under Evolution

One cartoon-cliché of “prehistoric” time is that everything was bigger. We grow up absorbing a picture of the vague deep past as including dinosaurs, cavemen, and big versions of everything. While this is an oversimplification, and tends to mash vastly different periods into one (the past), the notion that mammals, at least, tended to be bigger in the past is accurate. When mammals replaced dinosaurs as the dominant megafauna on land, they became really big (although not as big as the biggest dinosaurs they replaced). But then over the last 2 million years average mammals sizes have been steadily decreasing. The big question is – why?

I recently wrote about the North American megafauna, and the debate between whether their extinction about 12 thousands years ago was caused primarily by humans (the overkill hypothesis) or climate change. But this debate exists for the entire planet – every continent except Antarctica. This continues to be a debate because large-scale cause and effect is difficult to prove in evolutionary history. We can test various hypotheses by predicting correlations and patterns in the fossil record and then looking for them. Sometimes we can extrapolate from current observable trends, or even changes in the laboratory. But the steady reduction in the average size of mammals requires looking for large correlations – what factor does this trend most have in common around the world? Many scientists think the clear answer is – humans.

Starting with Homo erectus, wherever humans go around the world they are followed by a wave of megafauna extinction. Could this just be a general trend unrelated to humans? Perhaps the world’s climate has been changing in such a way over the last two million years that explains a selective advantage to small size. Climate cannot be ruled out as a factor, but the evidence increasingly supports the notion that human hunting played a major factor.

I am always suspicious of nice clean stories in evolution, so I will add a huge caveat that any hypothesis about A causing B is likely to be a massive oversimplification. But some factors can have dominant effects. Around 2 million years ago we start to see the first evidence of Homo erectus using fire. At this same time erectus clearly dramatically ramped up their hunting, and also this was the first time a human species spread throughout the world. Cooking meat would have been a huge energy and nutritional advantage, and hunting requires a lot of land, and hence the need to spread out. This shift in our human ancestors correlates nicely with dramatic reductions in the average size of mammals, wherever humans went.

Continue Reading »

No responses yet

Feb 16 2021

What Killed North America’s Megafauna?

Published by under Evolution

Before around 13,000 years ago large mammals walked North America – the Mammoth, most famously, but also giant beavers, giant tree sloths, glyptodonts, and the American cheetah among them. By around 11,000 years ago they were all gone (38 genera, mostly mammals). Extinction is a natural part of the cycle of ecosystems, and no species lasts forever. But when paleontologists identify a pulse of extinctions, above the background rate, they call that an extinction event, and this definitely qualifies. Extinction events call out for answers – what was the cause?

In the case of the North American megafauna extinction, there are two main hypotheses. The first is the overkill hypothesis – that the extinction coincides with the arrival of paleoindians on the continent, and that is not likely a coincidence. Generally speaking the arrival of humans into any ecosystem correlates with a pulse of extinctions. Perhaps the humans taking up residence in North America were big-game hunters, and the megafauna could not adapt quickly enough to this clever predator.

The second major hypothesis is that climatic change was the major cause. The last major glacial period lasted from 125,000 to 14,900 years ago, and then started the current interglacial period (the holocene) that we are in. However, this warming was interrupted in North American by the Younger Dryas, a cold snap that lasted from 12,900 to 10,600 years ago. The cause of this cold spell is also a controversy, with the two main hypotheses being a local comet impact vs the effects of major glacial melt on ocean currents. Either way, by the time the cold snap was over, the megafauna was gone.

Continue Reading »

No responses yet

Oct 30 2020

Evolution of Dogs

Published by under Evolution

The evolution of dogs from wolves is a long and complex one. A recent study adds some further information to this tale – as long as 11,000 years ago there were already at least five different distinct breeds of dog. These different breeds partly tracked along with human populations, but not completely. But let’s back up a bit and see where this new information fits into the story.

Experts actually don’t agree on exactly when and where dogs first appeared, or even if it was one event or multiple independent origins. What is clear is that dogs are essentially domesticated wolves. Their likely origin was in Europe sometime between 19 and 32 thousand years ago. This makes dogs the first domesticated animal. I have often considered (being a life-long dog owner myself) how useful dogs would have been to ancient people. They are excellent guardians, sending up an alarm when anything strays too close to camp. My dog will let me know when racoons are poaching the bird feeder at 3am. They are territorial and will keep critters small and large out of the area. And in an emergency they will even fight for their masters. More developed and trained dogs can also do all sorts of jobs, from herding to hunting.

The extreme usefulness, not to mention companionship, of dogs to humans lead to the early hypothesis that humans domesticated wolves, probably by first raising wolf pups. Tamed wolves are more aggressive than dogs, but they can bond with humans and function in the human world. We know from the silver fox experiments that some mammal species can be significantly domesticated in just a few generations. So it would not take long for these tamed wolves to become more docile, loyal, and obedient. But experts now suspect this is not what actually happened.

The history of human and wolf interaction is mainly one of competition and eradications. Humans have always treated large predators as a threat. Wolves specifically have mostly been eradicated where humans flourish, often deliberately. This still does not preclude the exception of tamed wolves, but it did give rise to an alternate hypothesis – perhaps wolves domesticated humans rather than the other way around, meaning that it was the wolves who changed the nature of our relationship first. In this scenario wolf populations living near humans may have learned to poach at the edges of settlements, perhaps eating the bones or other refuse that humans discarded. The more cute and friendly wolves would have had more success at this strategy, while the more aggressive wolves would have been killed or driven off. This could have led to a subpopulation of friendly wolves mostly living off of human refuse. Selective pressures could have then quickly domesticated these proto-dog wolves, who were only later taken as companions by humans. Human selection would then have taken them the rest of the way to modern dogs.

Continue Reading »

No responses yet

Next »