Human evolution: B3

Human evolution for B3 module

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Apes and Humans.

Humans and apes are very similair.

Our DNA is less than 2% different, and we believe to have evolved from a common ancestor.

We have BIGGER brains and walk upright compared to Apes.

The main theory to our difference is that 7 million years ago Africa became drier.
This meant there were less trees and more grassland. So the apes that could find food in the grasslands didn't have the competion of the apes in the trees.

However the grasslands were dangerous. To help them spot predators they would walk upright so they could see trouble!

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Ideas about evolution.

Organism= a living thing.

Vertebrate= has a skeleton and backbone. e.g. Humans

Skeleton of most organisms is the same body plan just distorted into different shapes so it seems as we have a common ancestor but we have all evolved.

We get most evidence from fossils and comparing DNA. Most scientists agree but some prefer a religous explanation.

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Nervous system and Hormones.

Nerve cells carry electrical impulses quickly with a brief effect.

Central Nervous system- Brain and spinal cord.

Peripheral System- nervous system throughout the rest of the body.

If you touch a hot object receptors in your skin send electrical impulses along nerve cells. They reach the spinal cord and another message is sent to your arm muscle (this is the effector). Then your hand will move away.This all happens very quickly.

Hormones are slow but have a long effect.

Thyroid glands makes throxine and controls growth, Adrenal glands make adrenaline which makes breathing and heart rate increase and the Pancreas makes insulin which controls blood sugar.

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Selection.

Mutations are when there are small errors in the genetic information passed to offspring from parents.

This gives us variation.

Some individuls will be better suited to the enviroment so they will be more likely to survive and breed. Their offspring is also likely to survive. This is called Natural selection. Over a long time this can rise new species, ususally this happens when species are under pressure to srvive

There is Selective breeding which we do to give us a variety of things like differtent coloured tulips, more muscly cows and labradoodles.

SO, evolution is the process and natural selection causes this to happen.

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How does evolution happen?

French scientist, Lamarck, had an idea on evolution. For example, if a giraffes stretch its neck to reach high leaves it would eventually get longer.However he could not explain how this long neck could've been passed on.

Charles Darwin collected many specimens from the Galapagos. He noticed variation within species and develpoped the idea of Natural selection. He noticed that some birds had thin beaks good for picking insects from tree cracks and another had thick beaks which could crack nuts. They had all adapted to suit their enviroment.

He still could not explain how they were passes on but nowadays we know a lot about DNA so we can explain this.

There was a lot of religous beliefs  that did not like Darwins idea so his work often got rejected. Other problems were the incomplete fossil recors and natural selection taking a long time( in the 1800's scientists only thought the earth was a few 1000 years old).

Earth is 4 billion years old

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