Evolution

Imagine Earth 4.5 billion years ago. No air to breathe, no trees, no animals, only volcanoes throwing lava, lightning every minute, and water full of chemicals like methane, ammonia, hydrogen. It was like a hot kitchen with no one cooking.

Scientists say first life did not come from outside, it was cooked here itself. Small chemicals joined to make bigger chemicals, bigger chemicals joined to make balls called coacervates which had a thin covering like a cell but not alive yet. Slowly those balls started copying themselves and using energy. This idea was given by Oparin and Haldane.

Some people think life came from space as spores called panspermia, but most scientists believe chemical evolution on Earth itself. First cells were very simple, like bacteria, that did not need oxygen. They lived in water, ate chemicals. Later they learned to make food from sunlight.

You can think like this: first you have bricks, then bricks join to make a wall, wall joins to make a room, room becomes a house. In same way simple molecules joined to make life.

How do we know evolution is real? Because we have many proofs, like police finds fingerprints.

First proof fossils. Fossils are old dead plants and animals trapped in rocks. Deep rocks have simple fossils, upper rocks have complex fossils, so life changed from simple to complex over time. Geological time scale shows this sequence.

Second proof body parts. Human hand, whale flipper, bat wing, cheetah leg look different outside but inside all have same bones humerus radius ulna carpals. That means they came from same ancestor, this is homologous organs. They look different because they adapted for different work, this is divergent evolution. On other side bird wing and butterfly wing look same because both fly but inside structure different, they came from different ancestors but adapted for same work, this is analogous organs, convergent evolution.

Third biochemical proof: proteins and DNA of humans and apes are 98% same, more similar means closer relation. Embryos of fish, salamander, chicken, human look almost same in early stage, so they had common ancestor. Some organs like appendix in humans, wisdom teeth have no use now, they are leftover called vestigial. Connecting link like Archaeopteryx has reptile teeth and tail plus bird feathers and wings, shows birds came from reptiles.

Imagine you have a small family of birds that reaches a big island with many different foods - seeds, insects, cactus, fruits. Over many years their beaks change to eat different foods, some big thick beak to crack seeds, some thin to catch insects. They all came from one ancestor but became many types. This is adaptive radiation, one species radiating into many to adapt to different places. Darwin saw this in Galapagos finches, 14 types of finches with different beaks from one seed eating ancestor.

Same happened in Australia. There were many marsupials, pouched mammals, that look like placental mammals elsewhere. Marsupial mole looks like placental mole, marsupial mouse like mouse, but they are not related, they evolved similarly because they live in similar environment. When two different animals evolve to look similar because of same habitat, it is convergent evolution. When one ancestor becomes many different looking animals in different habitats, it is divergent and adaptive radiation.

Lamarck said if you use a body part more it grows more, and you pass that to your children. Like giraffe stretches neck to eat leaves neck becomes long children get long neck. This is wrong because acquired characters are not passed.

Darwin said nature selects. In any population many variations exist, nature chooses the fittest to survive and reproduce, others die. He called it natural selection, like a farmer selects best cows.

Real example you can see: before 1920 in England there were light coloured peppered moths on light tree bark. After factories made bark dark with smoke, dark moths survived because birds could not see them, light moths were eaten, so dark became common. When pollution reduced, light again became common. This is industrial melanism.

Another example in hospitals: when we use antibiotics, bacteria that are resistant survive and become more common, so medicine stops working. Same with mosquitoes DDT spray, resistant mosquitoes survive. This shows evolution is happening now, not just old story.

How to know if evolution is happening? Hardy and Weinberg gave a maths formula. If p is frequency of allele A and q is allele a, then p+q=1 and p² + 2pq + q² =1. If population follows this and numbers stay same, then no evolution. If numbers change, evolution is happening. Five things disturb it: mutation new alleles appear, gene flow people move and bring new alleles, genetic drift by chance some alleles disappear in small population, founder effect few people go to new place their genes become common, bottleneck many die in disaster few left genes change, and natural selection nature favours some.

Selection can be directional one side favoured like dark moth, stabilizing middle favoured like average weight babies survive more, disruptive both extremes favoured like light and dark moths both survive middle eaten.

Now human evolution very simple story: first ape like Dryopithecus 15 million years ago tree living, then Ramapithecus more man like. Then Australopithecus 4-2 million years Lucy fossil walked upright brain 400cc. Then Homo habilis handy man first tool maker brain 650cc. Then Homo erectus 1.5 million years brain 900cc left Africa used fire. Then Neanderthal 400k years brain 1400cc lived in Europe cold used tools buried dead. Then Homo sapiens us 300k years brain 1350cc started art farming language. We are not from monkey, we share common ancestor with monkey, like cousins share grandparents.