Episode 1: We go ape for evolution

This week on the Petri Dish:

Science News (at 1:49 on the podcast)

Science Myth: Are Dinosaurs Dead? (5:39)

Science Controversy: Can all causcasians really be descended from seven woman? Is the mitochondrial Eve theory true? (9:00)

Remember This Scientific Fact?: Who was Lucy? (15:17)

Film of the Week: Evolution (19:05)


Out of the Trees

Humans and chimpanzees became different species between 5 and 6 million years ago.

Lucy was a what?
Lucy is the name for a set of fossil remains that have been dated back 3.2 million years ago. Lucy is thought to be a key in the link between modern humans and apes (well, other apes). From her bones, specifically the structure of her hips and knees, we can tell that Lucy could walk on two feet. Her brain was around 300-400 cubic centimetres (cc), which is similar in size to non-human primates like chimpanzees. Lucy was the first nearly-complete example of Australopithecus afarensis discovered, in 1974. She was named after the Beatles' song, "Lucy in the Sky with Diamonds". It was an important discovery because it showed for the first time that bipedalism evolved in humans before large brains did.

After Lucy, 2 million years ago, Homo habilis arrived on the scene. Tools found near the bones of Homo Habilis reveal a “handy man”, who could create simple tools for hunting. Homo habilis is thought to be around 5’ tall, and weigh about 45kg. From their teeth, it is believed that homo habilis had meat in their diet.

Homo erectus came next, living between 1.8 million and 300,00 years ago. It’s brain size is 900cc to 12000 cubic centimetres. From areas of the brain that had developed we believe that erectus had the power of speech. Plus, homo erectus had more sophisticated tools, weapons, fire and could cook his food.

Half a million years ago Homo sapiens (archaic) developed. Their brains averaged 1200cc, and had rounded skulls similar to the modern day humans. Then we arrived! It is estimated that modern humans developed 120,000 years ago. Our brains are around 13500cc.

You’re such a Neanderthal! (Or are you?)
No, you aren’t. Neanderthals lived in Europe and the Middle East between 150,000 and 35,000 years ago. Whilst there is debate, it is most commonly thought that Neanderthals coexisted with homo sapiens (archaic) but are a completely different species. They were tall creatures, around 5’6’’, with an extremely heavy skeleton, and probably stronger than modern man. They also had larger brains than modern man (1450 cc). It is unclear why Neanderthals died out. Some suggest they interbred with homo sapiens.

For more information on

Australopithecus (Great summary!)

http://www-geology.ucdavis.edu/~cowen/HistoryofLife/australopithecines.html

Neanderthals: http://www.bbc.co.uk/sn/tvradio/programmes/horizon/neanderthal_prog_summary.shtml


How Birds Evolved From Dinosaurs

Originally there are the large bipedal dinosaurs, like the T-rex and Allosaurus, and because of evolutionary pressures they begin to get smaller and smaller. Because of the decrease in body mass, they are having greater issues with body temperature control, because of an increase in body surface area in relation to total mass. Because of this, the light down that covered the larger dinosaurs became thicker, protecting them from the elements through a buffer zone.

When these dinosaurs got smaller, just a little larger than a pigeon, they were easier prey for the bigger dinosaurs, and so to escape from these predators, the little dinosaurs that were better equipped for tree climbing had a distinct advantage, and so moved into the redwood forests of the region which is now known as china.

Once they were in the trees, there was no-longer the predators that would be able to get them way up out of harms reach, and there is a new untapped food source, insects, which there is no competition with other species to get to. and so the only time that there is evolutionary pressures being pushed onto these animals is when they use up all the food in the tree that they are in. so the safest thing that they can do is jump from tree to tree.

So the down on the small dinosaurs evolves in its complexity into a feather like structure, which allowed the birds to glide from tree to tree. to make it so that they can glide further and further, they start to lighten up, so their bones hollow out, and become more fragile.

The mass extinction came.

The pterosaurs that were in the air, preventing these avian dinosaurs from leaving the forests of china, now due to environmental pressures are decreasing in number. This allows for Avian dinosaurs to leave the forests without being hunted, and so a beast plate re-enforces the chest, allowing for increase resistance for the wings to flap and so an increase in the distance that the birds could travel, and so allowing them to move out of the china and to increase in size.

The rest is history.