Evolution

Evolutionary Biology: The Story of Life

This chapter focuses on the origin, evolution, and diversity of life forms, highlighting key theories, evidence, mechanisms, and the evolution of humans.

What is Evolution?

• Evolution is the study of how life forms have changed over millions of years.
• Evolutionary biology studies the history of life on Earth.
• It helps us understand the origin of life and the diversity of life forms on Earth.

Origin of Life

Looking Back in Time:

• Stars are far away; when we see them, we see their light from millions of years ago.
• The universe is about 20 billion years old.
• Earth is just a tiny part of the universe.

Big Bang Theory:

• The Big Bang theory explains the origin of the universe through a massive explosion.
• Galaxies (from Hydrogen and helium), stars, and clouds of gas and dust formed as the universe expanded and cooled.
• Earth formed about 4.5 billion years ago in the solar system of the Milky Way galaxy.

Early Earth:

• There was no atmosphere initially on earth.
• Gases like water vapor, methane, carbon dioxide, and ammonia were released from molten Earth.
• UV rays from the sun broke water into hydrogen and oxygen, forming water, CO2, and other compounds.
• As Earth cooled, water vapor turned into rain, filling depressions to form oceans.
• Life appeared about 4 billion years ago.

Theories on the Origin of Life:

• Cosmic theory (Panspermia): Some scientists believe life came from outer space (panspermia).
• Theory of special creation: states that living things were created by a supernatural power (God).
• Spontaneous Generation (Abiogenesis):
  • An old theory stating that life came from decaying matter (spontaneous generation).
  • Louis Pasteur disproved this theory with the help of below demonstration.
  • He showed that life did not emerge from killed yeast in a closed, pre-sterilized flask, but microbes appeared in an open flask.
  • Thus proved that life comes only from pre-existing life.
• Biogenesis:
  • proposed by Francisco Redi, Spallanzani, and Louis Pasteur.
  • states that life originates from pre-existing life
  • but does not explain the origin of the first life.
• Chemical Evolution: Proposed by Oparin and Haldane, suggesting life formed from non-living organic molecules (like RNA and proteins), under conditions of high temperature, volcanic storms, and a reducing atmosphere.

Miller’s Experiment (1953):

• Created conditions similar to primitive (early) Earth in a lab.
• Electric discharge in a flask with methane (CH₄), hydrogen (H₂), ammonia (NH₃), and water vapor at 800°C produced amino acids.
• Similar experiments by other scientists found sugars, nitrogen bases, pigments, and fats.
• Chemical evolution is accepted, but the exact process of how life began is still unknown.

First Life Forms:

• First non-cellular life forms appeared about 3 billion years ago (giant molecules like RNA, protein).
• First cellular life forms appeared about 2 billion years ago (single cells in water).
• Life slowly evolved from non-living molecules through evolutionary forces.
• All early life forms lived in water.

Key Points:

• Evolution explains how life on Earth changed over millions of years.
• The Big Bang Theory explains the universe’s origin.
• Life on Earth began through chemical evolution from non-living molecules.
• The first cellular forms eventually evolved into the complex biodiversity we see today.

Evolution of Life Forms – A Theory

Special Creation Theory:

• Religious literature says:
  1. All living organisms were created as they are.
  2. Diversity of life has always been the same and will never change.
  3. Earth is about 4000 years old.
• These ideas were challenged in the 19th century.

Challenges to Special Creation:

• Charles Darwin, during his voyage on the H.M.S. Beagle, observed that living forms share similarities with each other and with extinct species.
• He noticed that many life forms have gone extinct while new ones have emerged over time.
• Darwin concluded that life forms have gradually evolved.

Charles Darwin’s Observations:

• Populations have variations in their characteristics.
• Traits that help organisms survive better in their environment make them more “fit.”
• Reproductive fitness means those who are better adapted produce more offspring.
• Or “Fitness” means how well an individual can reproduce.
• These well-adapted organisms are naturally selected and survive more.

Natural Selection:

• Darwin called this (above) process “natural selection,” which he suggested as a mechanism of evolution.
• Alfred Wallace, a naturalist in the Malay Archipelago, reached similar conclusions around the same time as Darwin.

Evolution and Common Ancestors:

• Over time, new types of organisms can be recognized.
• All current life forms share similarities and common ancestors.
• These ancestors lived during different periods in Earth’s history (epochs, periods, and eras).

Geological and Biological History:

• The geological history of Earth is closely linked with the biological history of life.
• Earth is not just thousands of years old, but billions of years old.

Key Points:

• Evolution is a gradual process where life forms change over time.
• The special creation theory was challenged by Darwin’s observations.
• Natural selection helps determine which organisms survive based on their traits.
• All living organisms share common ancestors and have evolved over billions of years.

Evidence for Evolution

Fossils (Paleontological evidences):

Paleontology = the study of fossils.

• What are fossils? Remains of hard parts of life forms found in rocks.
• How do they form? Rocks form layers of sediments over time.
• What do they tell us? Different-aged rock layers have fossils of different life forms, indicating life forms have changed over time. This is called paleontological evidence.

Significance of fossils: (slider)

1. To study phylogeny (evolutionary history), e.g., Man evolution.
2. To identify links between groups, e.g., Archaeopteryx.
3. To learn about extinct animals, e.g., mammoths.
4. To analyze geological periods through fossils in sedimentary rock layers, revealing that life forms varied over time and specific forms are restricted to certain periods.

Embryological Support:

• Ernst Heckel’s observation:
  • noted common features in vertebrate embryos.
  • Vertebrate embryos have common features, like vestigial gill slits, that disappear in adults.
• Karl Ernst von Baer’s disapproval:
  • disapproved Heckel’s proposal
  • showed embryos do not pass through adult stages of other animals always.

Comparative Anatomy and Morphology:

• Homologous Structures:
  • Homologous organs have similar structures and origins but different functions.
  • Caused by divergent evolution, where related species adapt to different environments.
  • Homology indicates a common ancestry.
    • Examples: Forelimbs of whales, bats, cheetahs, and humans have similar bone patterns (humerus, radius, ulna, carpals, metacarpals, phalanges).
    • Plant examples: Thorns and tendrils in Bougainvillea and Cucurbita.
• Analogous Structures:
  • Analogous organs have similar functions but different structures and origins.
  • Caused by convergent evolution, where unrelated species become similar to adapt to similar environments.
    • Examples:
    • Insect wings (chitin) vs. bird wings (forelimbs)
    • Octopus eyes (skin retina) vs. mammal eyes (brain retina)
    • Penguin flippers vs. dolphin flippers
    • Insect trachea (ectoderm) vs. vertebrate lungs (endoderm)
  • Plant example: Sweet potato (root) and potato (stem).

Biochemical Evidence:

• Similar proteins and genes: Indicate common ancestry among diverse organisms.

Artificial Selection:

• Human influence: Breeding of plants and animals for specific traits in agriculture, horticulture, and domestication.
  • Example: Different dog breeds created by selective breeding.

Industrial Melanism in Moths {Natural Selection by human activities (Anthropogenic action)}:

Natural selection: Organisms with favorable, heritable traits survive and reproduce.

A. Peppered Moth Example:

• Before industrialization (1850s): More white-winged moths (Biston betularia) survived on lichen-covered trees; dark moths were eaten by predators.
• After industrialization (1920): Trees darkened by smoke and soot, favoring dark-winged moths (Biston carbonaria); white moths were easily spotted and eaten.

Industrial pollution indicators: Lichens do not grow in polluted areas.

B. Resistance in Organisms:

• Pesticide and Antibiotic Resistance: Excessive use of herbicides, pesticides, and antibiotics leads to the selection of resistant varieties.
  • Example: Mosquitoes developed resistance to DDT due to excessive use.
  • Time scale: Resistant varieties appear in months or years, not centuries.
  • Example: Resistant microbes due to antibiotics.

Key Points:

• Evolution is a natural process of gradual change in life forms over time.
• It is supported by various types of evidence like fossils, embryology, anatomy, biochemistry, artificial selection, and natural selection.
• Artificial selection by humans mirrors natural selection.
• Evolution is not directed but occurs through chance (random) events and mutations.

Adaptive Radiation

Darwin’s Discovery:

• Location: Galapagos Islands.
• Observation: A variety of small black birds, later called Darwin’s Finches.
• Significance: Many different types of finches evolved from the original seed-eating birds.
  • Result: Some finches became insect-eaters, others became vegetarians.

Definition:

• Adaptive Radiation: The evolution of different species in a given area from a common ancestor, spreading out to different habitats.
• A type of divergent evolution & Biogeographical evidence of evolution.

Examples:

• Darwin’s Finches: Different types of finches with various beak shapes adapted to different food sources.
• Australian Marsupials: Various marsupials evolved from a common ancestor, each adapted to different environments within Australia.

Convergent Evolution:

• Description: When more than one adaptive radiation occurs in an isolated area, resulting in similar adaptations in different species.
• Example: Placental mammals in Australia evolved similarly to marsupials (e.g., Placental wolf and Tasmanian wolf-marsupial).

Placental Mammals	Australian Marsupials
Mole	Marsupial mole
Ant eater	Numbat (Ant eater)
Mouse	Marsupial mouse
Lemur	Spotted cuscus
Flying squirrel	Flying phalanger
Bobcat	Tasmanian tiger cat
Wolf	Tasmanian wolf

Key Points:

• Adaptive radiation shows how species can diversify and adapt to different environments.
• Convergent evolution demonstrates how similar environmental pressures can lead to similar adaptations in different species.

A Brief Account of Evolution

The Geological Time Scale categorizes Earth’s history into eras, periods, and epochs based on major geological and biological events.

1. Proterozoic Era (2500 – 541 mya): Early Life Forms

• First Cells: Appeared about 2000 million years ago (mya).
• Oxygen Release: Some cells could release oxygen, similar to photosynthesis.
• Multicellular Life: Evolved from single-celled organisms.

2. Palaeozoic Era (540 – 252 mya):

Divided into Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

Major Milestones

• 500 mya: Invertebrates appeared.
• 450 mya: First land plants appeared.
• 400 mya: Arthropods invaded land.
• 350 mya: Jawless fish evolved; lobe-finned fishes evolved into amphibians.
  • Coelacanth: A fish caught in 1938, thought to be extinct, showed early land-walking fish ancestors.
  • Lobefins to Amphibians: Fish like Coelacanth evolved into amphibians, ancestors of frogs and salamanders.
  • Amphibians to Reptiles: Reptiles evolved from amphibians, laying thick-shelled eggs.
• 320 mya: Seaweeds and early plants appeared; amphibians evolved into reptiles.

3. Mesozoic Era (252 – 66 mya): Age (Dominance) of Reptiles.

Periods: Triassic, Jurassic, Cretaceous.

• 200 mya: Reptiles dominated the earth.
  • Some land reptiles returned to water, becoming fish-like reptiles (e.g., Ichthyosaurs).
  • toothed birds emerged.
• Dinosaurs: Dominated the land, with some growing very large (e.g., Tyrannosaurus rex).
• Extinction: Dinosaurs disappeared around 65 mya, possibly due to climate change or evolution into birds.
• Plants: Gymnosperms thrived.

4. Cenozoic Era (66 – 0 mya): Age of Mammals and Angiosperms.

Periods: Tertiary, Quaternary.

• 65 mya: Dinosaurs disappeared; some evolved into birds.
• Post-Reptile Era: Mammals flourished as reptiles declined and became more dominant.
• First Mammals: Small, shrew-like, viviparous (giving birth to live young).
• Intelligence: Mammals developed better senses and avoidance mechanisms.
• Continental Drift and Survival
  • South American Mammals: Included horse-like and bear-like creatures.
  • North American Fauna: Overrode (Dominated) South American animals due to continental drift.
  • Australian Marsupials: Survived due to isolation and lack of competition.
• Aquatic Mammals
  • Examples include whales, dolphins, seals, and sea cows.
• Horse, Elephant, Dog: Specific evolutionary stories.
• Humans: Evolved with language skills and self-consciousness.

Key Takeaways

• Life evolved from single-celled organisms to complex multicellular organisms.
• Plants and animals transitioned from water to land.
• Reptiles and then mammals dominated different eras.
• Continental drift influenced the distribution and survival of species.
• Human evolution is a significant part of the evolutionary story.

Origin and Evolution of Man

Early Primates

• 15 million years ago (mya): Dryopithecus and Ramapithecus lived.
  • Dryopithecus: More ape-like.
  • Ramapithecus: More man-like.

Hominid (Ancestor) Fossils

• 3-4 mya: Man-like primates in eastern Africa, about 4 feet tall, walked upright.
• 2 mya: Australopithecines in East African grasslands, used stone weapons, mainly ate fruit.

Evolution of Homo Species

• Homo habilis: First human-like being, brain capacity 650-800cc, did not eat meat.
• 1.5 mya: Homo erectus in Java, brain size around 900cc, probably ate meat.
• 100,000-40,000 years ago: Neanderthal man in near east and central Asia, brain size 1400cc, used hides & advanced tools, buried their dead.

Modern Humans

• Homo sapiens: Originated in Africa, migrated across continents, developed into distinct races.
• Ice Age (75,000-10,000 years ago): Modern Homo sapiens emerged.
• 18,000 years ago: Pre-historic cave art developed, examples at Bhimbetka rock shelter in Madhya Pradesh.
• 10,000 years ago: Agriculture began, leading to human settlements and the rise and fall of civilizations.

Evolutionary sequence:

Dryopithecus → Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Homo neanderthalensis → Homo sapiens.

Chapter Summary:

• Origin of life on earth is linked to the origin of the universe.
• Most scientists believe chemical evolution came before cellular life.
• Formation of biomolecules preceded the first cellular forms of life.
• Darwin’s ideas of organic evolution by natural selection explain what happened next.
• Diversity of life forms on earth has changed over millions of years.
• Variations in a population lead to different levels of fitness.
• Habitat fragmentation and genetic drift can increase these variations.
• These variations can lead to new species and evolution.
• Homology is explained by branching descent.
• Comparative anatomy, fossils, and biochemistry provide evidence for evolution.
• The story of modern man’s evolution is interesting.
• It parallels the evolution of the human brain and language.