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Researchers say larger size is a genuine pattern in evolution, not neutral drift

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blue whale, largest animal ever/NOAA

From ScienceDaily:

In one of the most comprehensive studies of body size evolution ever conducted, Stanford scientists have found fresh support for Cope’s rule, a theory in biology that states that animal lineages tend to evolve toward larger sizes over time.

“We’ve known for some time now that the largest organisms alive today are larger than the largest organisms that were alive when life originated or even when animals first evolved,” said Jonathan Payne, a paleobiologist at Stanford’s School of Earth, Energy & Environmental Sciences.

What was unclear, however, was whether the average size of animals has been changing over time and, if so, whether that reflects a trend, or directionality, in body size evolution. “It’s not something that you can know by just studying living organisms or extrapolating from what you see over short time scales. If you do that, you will absolutely be wrong about the rate, and possibly also the direction,” Payne said.

The study, published in the Feb. 20 issue of the journal Science, reveals that over the past 542 million years, the mean sized of marine animals has increased 150-fold. “That’s the size difference between a sea urchin that is about 2 inches long versus one that is nearly a foot long,” Heim said. “This may not seem like a lot, but it represents a big jump.”

The research also found that the increase in body size that has occurred since animals first appeared in the fossil record around 550 million years ago is not due to all animal lineages steadily growing bigger, but rather to the diversification of groups of organisms that were already larger than other groups early in the history of animal evolution.

“That’s also something we didn’t know before,” Payne said. “For reasons that we don’t completely understand, the classes with large body size appear to be the ones that over time have become differentially more diverse.”

File:A small cup of coffee.JPG Could it possibly have helped in some cases that they were eating the smaller species? Just thought we’d ask.

The question has an interesting history, in that the late 19th century, “Cope’s rule” suggested that it was a universal trend. The trouble was,

Corals and dinosaurs seem to follow Cope’s rule, for example, but birds and insects do not. As a result, some scientists have wondered whether the pattern observed in land mammals is a real evolutionary phenomenon or merely a statistical one resulting from random, non-selective evolution, also known as neutral drift. “It’s possible that as evolution proceeds, there really is no preference for being larger or smaller,” said Noel Heim, a postdoctoral researcher in Payne’s lab. “What appears to be an increase in average body size may be due to neutral drift.”

But the study included nearly 75 percent of marine fossils (17,000 genera) over the last 542 million years, and

A pattern soon became apparent: not all classes-groups of related species and genera-of animals trended toward larger size, but those that were bigger tended to become more diverse over time. The team suspects this is due to advantages associated with a larger size, such as the ability to move faster, burrow more deeply and efficiently in sediment, or capture larger prey.

The team found that the neutral drift simulation could not explain the body size trends observed in the fossil record. “The degree of increase in both mean and maximum body size just aren’t well explained by neutral drift,” Heim said. “It appears that you actually need some active evolutionary process that promotes larger sizes.”

File:A small cup of coffee.JPG Right. They were eating the smaller ones. So they had a budget. And could afford to invest in growth?

Here’s the abstract at Science:

Cope’s rule proposes that animal lineages evolve toward larger body size over time. To test this hypothesis across all marine animals, we compiled a data set of body sizes for 17,208 genera of marine animals spanning the past 542 million years. Mean biovolume across genera has increased by a factor of 150 since the Cambrian, whereas minimum biovolume has decreased by less than a factor of 10, and maximum biovolume has increased by more than a factor of 100,000. Neutral drift from a small initial value cannot explain this pattern. Instead, most of the size increase reflects differential diversification across classes, indicating that the pattern does not reflect a simple scaling-up of widespread and persistent selection for larger size within populations. (paywall)

From the BBC

Measured by volume, today’s tiniest sea critter is less than 10 times smaller than its Cambrian counterpart; both are minuscule, sub-millimetre crustaceans. But at the other end of the scale, the mighty blue whale is more than 100,000 times the size of the largest animal the Cambrian could offer: a trilobite less than half a metre long.

”There is this trend to increasing size – but a real kick comes when you have air-breathers re-entering the water” – Dr Michael Berenbrink, University of Liverpool

The version that best matched the real fossil history was one with a genuine size advantage.

Largest animal that has ever lived?: Comparatively recent “size stakes” entry, the blue whale

By considerable measure, the largest known animal on Earth is the blue whale. Mature blue whales can measure anywhere from 75 feet (23 m) to 100 feet (30.5 m) from head to tail, and can weigh as much as 150 tons (136 metric tons). That’s as long as an 8- to 10-story building and as heavy as about 112 adult male giraffes! These days, most adult blue whales are only 75 to 80 feet long; whalers hunted down most of the super giants. Female blue whales generally weigh more than the males. The largest blue whale to date is a female that weighed 389,760 pounds (176,792 kg).

Possibly, returning to the water meant that the whale was freed from the physics problems of a vast size on land?

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If Modern Humans Are So Smart, Why Are Our Brains Shrinking? - January 20, 2011 Excerpt: John Hawks is in the middle of explaining his research on human evolution when he drops a bombshell. Running down a list of changes that have occurred in our skeleton and skull since the Stone Age, the University of Wisconsin anthropologist nonchalantly adds, “And it’s also clear the brain has been shrinking.” “Shrinking?” I ask. “I thought it was getting larger.” The whole ascent-of-man thing.,,, He rattles off some dismaying numbers: Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion. “I’d call that major downsizing in an evolutionary eyeblink,” he says. “This happened in China, Europe, Africa—everywhere we look.” http://discovermagazine.com/2010/sep/25-modern-humans-smart-why-brain-shrinking Cro Magnon skull shows that our brains have shrunk - Mar 15, 2010 by Lisa Zyga Excerpt: Using new technology, researchers have produced a replica of the 28,000-year-old brain and found that it is about 15-20% larger than our brains. http://phys.org/news187877156.html Human face has shrunk over the past 10,000 years - November 2005 Excerpt: Human faces are shrinking by 1%-2% every 1,000 years. What’s more, we are growing less teeth. Ten thousand years ago everyone grew wisdom teeth but now only half of us get them, and other teeth like the lateral incisors have become much smaller. This is evolution in action." http://www.stonepages.com/news/archives/001604.html of related note: “Neanderthals are known for their large cranial capacity, which at 1600cc is larger on average than modern humans.” http://en.wikipedia.org/wiki/Neanderthal#Anatomy Scientists Discover Proof That Humanity Is Getting Dumber, Smaller And Weaker By Michael Snyder, on April 29th, 2014 Excerpt: An earlier study by Cambridge University found that mankind is shrinking in size significantly. Experts say humans are past their peak and that modern-day people are 10 percent smaller and shorter than their hunter-gatherer ancestors. And if that’s not depressing enough, our brains are also smaller. The findings reverse perceived wisdom that humans have grown taller and larger, a belief which has grown from data on more recent physical development. The decline, said scientists, has happened over the past 10,000 years. http://thetruthwins.com/archives/scientists-discover-proof-that-humanity-is-getting-dumber-smaller-and-weaker Human Genetic Variation Recent, Varies Among Populations - (Nov. 28, 2012) Excerpt: Nearly three-quarters of mutations in genes that code for proteins -- the workhorses of the cell -- occurred within the past 5,000 to 10,000 years,,, "One of the most interesting points is that Europeans have more new deleterious (potentially disease-causing) mutations than Africans,",,, "Having so many of these new variants can be partially explained by the population explosion in the European population. However, variation that occur in genes that are involved in Mendelian traits and in those that affect genes essential to the proper functioning of the cell tend to be much older." (A Mendelian trait is controlled by a single gene. Mutations in that gene can have devastating effects.) The amount variation or mutation identified in protein-coding genes (the exome) in this study is very different from what would have been seen 5,000 years ago,,, The report shows that "recent" events have a potent effect on the human genome. Eighty-six percent of the genetic variation or mutations that are expected to be harmful arose in European-Americans in the last five thousand years, said the researchers. The researchers used established bioinformatics techniques to calculate the age of more than a million changes in single base pairs (the A-T, C-G of the genetic code) that are part of the exome or protein-coding portion of the genomes (human genetic blueprint) of 6,515 people of both European-American and African-American decent.,,, http://www.sciencedaily.com/releases/2012/11/121128132259.htm
Andre, besides mammals being smaller now than they once were, let's not forget that humans have also been shrinking:
Giant mammals once ruled the earth After dinosaurs disappeared 65 million years ago, the world's rhinos, elephants and other large mammals had the run of the Earth and grew as much as twice as big as they are today, a new study shows. http://www.usatoday.com/tech/science/2010-11-26-giant-mammals_N.htm Giant fossil “groundhog” clue to early mammal evolution? - Nov. 10, 2014 Excerpt: The skull is huge, measuring almost five inches long, twice the size of the previously largest known mammalian skull from the entire Age of Dinosaurs of the southern supercontinent of Gondwana.,,, Vintana was a super heavyweight, estimated to have had a body mass of about 20 pounds, twice or even three times the size of an adult groundhog.,,, https://uncommondesc.wpengine.com/evolution/giant-fossil-groundhog-clue-to-early-mammal-evolution/ New to Nature No 57: Nuralagus rex - The fossil of the giant rabbit of Menorca show it to be the largest lagomorph ever seen Excerpt: Nuralagus rex lived in the Late Neogene, which ended about 2.5m years ago, and was 10 times the size of extant rabbits, weighing an estimated average of 12 kg. http://www.guardian.co.uk/science/2011/oct/23/nuralagus-rex-new-to-nature?newsfeed=true Megatherium (Giant ground sloth) 20 feet long (6 m.) Megalocerous giganteus (Giant Irish elk) 7 feet high (2.1 m.) Mammuthus primigenius (Wooly mammoth) 11.5 feet long (3.5 m.) Mammut americanum (American mastodon) 8-10 feet high (2.5 - 3 m.) Glyptodon (Ancient armadillo) 10 feet long (3 m.) Ursus spelaeus (Cave bear) Omnivore 20 feet long DoediFcurus (Large armadillo) 13 feet long (4 m.) Coelodonta (Wooly rhinoceros) 11 feet long (3.5 m.) Castoroides ohioensis (Giant beaver) 3.3ft high (1 m.) Camelops hesternus (American camel) 12 feet high (3.6 m.) Carnivores Arctodus simus (Short faced bear) 5.5 feet high (1.7 m.) Smilodon fatalis (Saber-toothed cat) 4-5 feet long (1.2-1.5 m.) Canis dirus (Dire wolf) 5 feet high (1.5 m.) Ursus spelaeus (Cave bear) Omnivore 20 feet long Panthera leo spelaea (Cave lion) 11.5 feet long (3.5 m.) http://skywalker.cochise.edu/wellerr/students/pleistocene-extinction/extinct.htm
Zachriel And what about those animals that have become smaller? Looking at the rule: "Cope’s rule proposes that animal lineages evolve toward larger body size over time." What about Giant Sloths? Giant Buffalos? Sabre tooth Cats? Does the reverse apply to them? Does being smaller give these animals a reproductive advantage now? So whether you grow bigger or smaller they both have a reproductive advantage? Surely this can't be right? Success if you do success if you don't...... Get this into your head........ A Theory that explains everything actually explains nothing. Andre
Andre: Real science has gone AWOL Real science? They show that, for some taxa, that there is a historical increase in size beyond what would be expected by drift alone. How is that not science? Zachriel
Once upon a time in some niche far away there was an animal named Johnny who had just the wrong size: he was too large to hide for predators and too small to frighten them. One day, crawling through some bushes, Johnny got entangled with some twigs and branches and when he entered the open field he was unrecognizable. And behold the predators ran off scared. Johnny had just acquired the right size. This was the beginning of the evolution of this well known weird looking animal. Box
What’s a lion pride more likely to attack, an giraffe or a mouse? A zebra or a hummingbird? Don't worry. We all know that evolution makes everything work out just fine. Evolution wanted some animals bigger and some smaller because it's a lot more interesting that way. Evolution gave bacteria the option of getting bigger, but they decided to stay very small. It's too bad - I mean, look at all the reproductive advantages they missed out on. Plus, who doesn't want to be bigger than a brontosaurus? But evolution is very considerate. It lets everyone grow up to be as big as they need to be, so they can survive or go extinct. Silver Asiatic
You need more resources, you're also better protected against predation. What's a lion pride more likely to attack, an elephant or a gazelle? Think, then post. CHartsil
How on earth is bigger better? You need more resources to stay alive. Reproduction is tricky and you're a better target.... Real science has gone AWOL If this nonsense was true where are the Woollie mammoths? Oh that's right being bigger made them better targets and we killed them all. Andre
>being larger provided a reproductive benefit. Try reading that CHartsil
Bigger means better reproduction? Lol atheists do say the darnest things Andre
SA, or the fact that in some niches, being larger provided a reproductive benefit. CHartsil
“It appears that you actually need some active evolutionary process that promotes larger sizes.”
Obesity? Or is that not (yet) accepted as an evolutionary process? Box
Possibly, returning to the water meant that the whale was freed from the physics problems of a vast size on land?
Yes. Evolution wanted them to get bigger because otherwise they would be small, and that's not as good. Other sea creatures are small because they need to be - for survival, of course.
“It appears that you actually need some active evolutionary process that promotes larger sizes.”
The good news is, there's always an 'active evolutionary process' around whenever you need it. In this case, it made everything get bigger. Because it's a lot easier to survive and reproduce that way, as opposed to something like bacteria, which is altogether too small. The human brain needed to get bigger also because we had so many thoughts to cram inside of it. Our thoughts got bigger too. The guy with the biggest brain has the biggest thoughts, of course. It made childbirth a bit more dangerous but we had to survive somehow. Big thoughts was the best way to do it. Silver Asiatic

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