Stories tagged evolution

Mar
20
2007

Humans have longer legs than gorillas today, but this wasn't always the case.: Photo by Robert Fenton, courtesy National Gallery of Art and Victoria and Albert Museum
Humans have longer legs than gorillas today, but this wasn't always the case.: Photo by Robert Fenton, courtesy National Gallery of Art and Victoria and Albert Museum

Early human ancestors, called Australopithecines (AW-stroh-la-PITH-eh-scenes), had short legs. Scientists have long believed this was a hold-over from even earlier species which had lived in trees. But now biologist David Carrier of the University of Utah argues the short legs were used to help them fight.

Short legs give a body a lower center of gravity, and makes it harder to push over. Living apes with short legs, like gorillas, tend to be more aggressive, while long-legged apes, like gibbons, are more docile.

Of course, humans don’t have such short legs anymore. Herman Potzner of Washington University in St. Louis proposes later human species evolved long legs to save energy. His studies of various animals show that that longer a creature’s legs, the less energy they use. Around 2 million years ago, something happened in human evolution that made the fighting advantage of short legs less important than the energy savings of long legs.

A curator at the Cleveland Museum of Natural History has identified a new type of horned dinosaur. The dinosaur, Albertaceratops, provides an evolutionary link between early, small-horned dinos and later, large-horned ones.

Feb
06
2007

In 2003,
scientists discovered the skeleton of a fossil human
on the Indonesian island of Flores. Fully-grown but only 3 feet tall, the fossil set off a storm of controversy. Was it a new species of ancient human? Was it a pygmy – a member of a group genetically disposed to shortness? Was it an individual suffering from some rare disease?

Early reports claimed that it was a dwarf form of Homo erectus, an ancestor of modern humans. Animals will sometimes evolve pygmy forms when trapped on an island with limited resources. But some scientists disputed that theory. They noted that the skeleon is only 18,000 years old, whereas H. erectus went extinct at least 50,000 years ago. Also, the skeleton was surrounded by sophisticated tools. These scientists held that the skeleton represented an individual Homo sapiens who suffered from microcephaly, a rare disease which gives people small heads and sometimes small bodies.

But a recent re-examination of the fossil
supports a different theory.
Scientists at the University of Florida argue that the original interpretation was right. The structure of the brain, as imprinted on the skull, is different from H. erectus, microcephalics, and even from us. They believe this fossil represents a new species of ancient human, one more closely related to H. sapiens than to H. erectus.

This raises the possibility that, in the not-too-distant past, two separate species of humans lived on the Earth. (And if you count Neanderthals, which went extinct around 24,000 years ago, there would have been three.)

Scientists will continue to examine the fossils, and try to develop theories that best explain all the evidence.

Nov
15
2006

Late last month, fishermen in Japan netted a surprise -- a bottlenose dolphin with two well-developed rear flippers. The flippers are remnants of the legs which grew in the dolphin's prehistoric ancestors.

Every animal's body is built by the genes contained in its DNA. But not all genes are active -- they have to be turned on by controller genes.

Over time, the DNA in a species changes -- new genes emerge, old ones become inactive. But in many cases, the old ones don't completely go away. The controller changes and stops activating the gene. But if there's a change in the controller, it may activate that forgotten gene again.

(The same thing happens with humans. As a baby develops inside its mother, it grows gills and a tail -- remnants of our animal heritage. These disappear before the baby is born.)

Sep
30
2006

Baby girl Lucy: Image from Wikipedia
Baby girl Lucy: Image from Wikipedia

Lucy-like fossil is older and more complete

The fossil including an entire skull, torso, shoulder blade and various limbs was discovered at Dikaka, some 400 kms northeast of the capital Addis Ababa near the Awash river in the Rift Valley.

"The finding is the most complete hominid skeleton ever found in the world," Zeresenay Alemseged, head of the Paleoanthropological Research Team, told a news conference. Reuters

The fossil has been named "Selam", which means peace in Ethiopia's official Amharic language.

Zeresenay said she belonged to the Australopithecus afarensis species, which includes Lucy, and is thought to be an ancestor to modern humans.

"The Dikika girl stands as one of the major discoveries in the history of palaeoanthropology," research team leader Zeresenay Alemseged said, citing the remarkably well-preserved condition of the bones, the geological age and completeness of the specimen.Cosmos Magazine

The following is the abstract of the original article describing the baby, which was authored by Zeresenay Alemseged, Fred Spoor, William H. Kimbel, René Bobe, Denis Geraads, Denné Reed and Jonathan G. Wynn, and appeared in Nature on September 20, 2006.

"Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire."

Additional reading: BBC News

World leaders in the field of evolution convened upon Venezia, Italy last week to talk about the future of science. Jim Spadaccini has some interesting blog entries from his time at the conference.

Jun
18
2006

Isisfordia duncani crocodile: photo by Art Oglesby   Isisfordia duncani crocodile found in Australia provides link between modern and ancient crocodiles.
Isisfordia duncani crocodile: photo by Art Oglesby Isisfordia duncani crocodile found in Australia provides link between modern and ancient crocodiles.

Fossils of the world's most primitive modern crocodilian have been discovered near the outback town of Isisford, in central-western Queensland, Australia. Discovered by former Deputy Mayor of Isisford, Ian Duncan, after whom the new species has been named, the first fossils of Isisfordia were found in the mid-1990s in a dried-up creek bed on the outskirts of town.
Living 98-95 million years ago, Isisfordia predates the first recorded appearance of alligators and gharials by almost 20 million years, and the first true crocodiles by over 30 million.

An international team of palaeontologists, headed by Dr Steve Salisbury from The University of Queensland's (UQ) School of Integrative Biology Published a paper in the Proceedings of the Royal Society B (pdf).

Abstract from paper

While the crocodyliform lineage extends back over 200 million years (Myr) to the Late Triassic, modern forms—members of Eusuchia—do not appear until the Cretaceous. Eusuchia includes the crown group Crocodylia, which comprises Crocodyloidea, Alligatoroidea and Gavialoidea. Fossils of non-crocodylian eusuchians are currently rare and, in most instances, fragmentary. Consequently, the transition from Neosuchia to Crocodylia has been one of the most poorly understood areas of crocodyliform evolution. Here we describe a new crocodyliform from the mid-Cretaceous (98–95Myr ago; Albian–Cenomanian) Winton Formation of Queensland, Australia, as the most primitive member of Eusuchia. The anatomical changes associated with the emergence of this taxon indicate a pivotal shift in the feeding and locomotor behaviour of crocodyliforms—a shift that may be linked to the subsequent rapid diversification of Eusuchia 20Myr later during the Late Cretaceous and Early Tertiary. While Laurasia (in particular North America) is the most likely ancestral area for Crocodylia, the biogeographic events associated with the origin of Eusuchia are more complex. Although the fossil evidence is limited, it now seems likely that at least part of the early history of Eusuchia transpired in Gondwana.

Link to a pdf of the entire paper; Proceedings of the Royal Society B (pdf)
University of Queensland press release
View proof images of Isisfordia and stills from the field and lab work.

Jun
12
2006

Here are some more random questions we've received from visitors to our website or our exhibits.

Q: Why is the Earth round? I thought it was flat.

A: Nope, the Earth is round. Not perfectly round, though. Planets like Earth are round due to gravity. Gravity pulls with equal strength in all directions, so gravity shapes the planet into a sphere. But, since the Earth rotates, the rotation adds centrifugal effects, which result in the Earth bulging slightly at the equator and flatten slightly at its poles.
Because of these centrifugal effects, the distance from the center of the earth to the surface of the earth is about 0.33% shorter at the poles compared to the equator.

Q: How does gravity work?

A: Gravity is one of the universal forces of nature, and is the tendency of objects with mass to accelerate toward each other. Newton's law of universal gravitation states that each particle of matter attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

More simply, everything that has mass has gravity, and the larger the mass, the stronger the gravity. Earth has stronger gravity than the moon because the mass of the Earth is greater than the mass of the moon.

Q: What is zero gravity?

A: Lots of gravity related questions! Zero gravity, or weightlessness, is best termed microgravity. Astronauts floating in space are not actually weightless, or in zero gravity, because the Earth's gravity is holding them and everything in the spaceship they are in, in orbit. They are actually in a state of free-fall, much like jumping from an airplane except that you are moving so fast horizontally that, as you fall, you never touch the ground because the Earth curves away from you.

Think about it this way. Considering what we learned about gravity above, if you stood on a bathroom scale and then somehow opened some trap doors that dropped both you (still standing on the scale) and the scale out of a plane, both you and the scale would be pulled down equally by gravity. You would not push down on the scale and therefore, your weight would read zero.

Q: Why is the sky blue?

A: Sunlight is scattered across the Earth's atmosphere by a process called "diffused sky radiation". The sky is blue because much more short-wave radiation (blue light) is scattered across the sky than long-wave radiation (red light). Check out this website that explains more about this, and also why the sky appears red during sunsets.

Q: How come the Science Museum you only teach one side of the story? What I mean by this is that not everyone believes in evolution, and you only talk about that side of the story. Why don't you have exhibits on theories other than evolution such as intelligent design?

A: It's in our name. We're The Science Museum of Minnesota. We represent and teach science in our exhibits and programs. We're not saying that there are not other ideas or beliefs out there (intelligent design is not a scientific theory, rather a religious belief), and we respect others and their beliefs. However, as an organization that teaches science, we practice and encourage the teaching of evolution as fundamental to the teaching of sound science and critical thinking. If we were to compromise the scientific explanations of evolution or permitted unscientific alternative explanations into our exhibits or our programs, we would be misrepresenting the principles of science. Here is the Science Museum of Minnesota's official position on evolution.

Q: Do you like pie?

A: Yes. I especially like Key Lime pie.

May
19
2006


Amborella, missing link?: Credit: Thomas J. Lemieux, University of Colorado at Boulder By studying the reproductive structures of the ancient flowering plant Amborella, scientists are learning more about evolutionary processes.

Plants first apeared on land about 450 million years ago. They reproduced in many ways, but there were no flowers. Then, about 130 million years ago, flowering plants appeared. Quickly they diversified and dominated the landscape.

How did flowering plants evolve from more primitive, nonflowering plants, such as mosses, ferns, conifers, and gingo trees? Evolutionist Charles Darwin referred to this puzzle as an "abominable mystery".

Charles Friedman now thinks he has identified the answer in a flowering plant that provides the missing evolutionary link. The species in question is the "living fossil" Amborella trichopoda, which is found only on the Pacific island of New Caledonia and diverged from the rest of the flowering plants 130 million years ago. Using sectioning and a variety of microscopic techniques, Friedman found that the plant's embryo sac, which produces the egg, has a different number of cells from those of other flowering plants (Nature, vol 441, p 337).

Friedman, is a professor in CU-Boulder's ecology and evolutionary biology department. "The study (in the May 18 issue of Nature) shows that the structure that houses the egg in Amborella is different from every other flowering plant known, and may be the potential missing link between flowering plants and their progenitors."

More significantly, the pattern of cell divisions producing the egg is reminiscent of that in other seed-forming plants such as conifers, rather than in flowering plants, making it a classic "missing link" species. "It is really fascinating as a possible holdover from primitive seed plants," says palaeobotanist James Doyle of the University of California at Davis.

Source articles:
Christian Science Monitor
Colorado Univ news release
NSF news release
New Scientist