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6. The Pace of Evolution& The Origins of Life

The Pace of EvolutionQ. How fast does evolution occur?

A. There are two theories/models that explain how fast evolution occurs. Both examine the Fossil record.1. Gradualism2. Punctuated Equilibrium

1. Gradualism

A model that says change occurs slowly and steadily before and after a divergence.Fossils show a slow and repeated change through the fossil record.

2. Punctuated Equilibrium A model proposed by Gould and Eldridge.A model that proposes evolution happens in “spurts”.The model says that species undergo long periods of “stasis” where they remain unchanged, followed by short periods of very rapid change (spurts).

The changes are usually brought about by sudden environmental changes such as volcanoes, earthquakes etc.

Species previously disadvantaged could now be advantaged and new species could develop quickly.

Punctuated equilibrium, cont’d

The Origin of LifeMany theories exist that try to explain the origin and development of life on earth.

The following theories will be considered:i. Chemical Evolutionii. Panspermiaiii. Gaia Hypothesisiv. Heterotroph Hypothesisv. Sybiogenesis (Symbiotic Theory)vi. Intelligent Design

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i. Chemical Evolution A theory of evolution created by Oparin – HaldaneThey said that organic molecules (the building blocks of life) could develop from inorganic compounds present on the surface of the early earth.The early earth had an atmosphere that consisted of no oxygen, but plenty of hydrogen, Ammonia (NH3), Methane (CH4) and water vapour (inorganic molecules).These gases condensed and formed a “primordial soup”.Energy from lightning and UV radiation caused “organic molecules” to develop from the inorganic molecules in the soup.Over time, the organic molecules combined to become an early life form.

Miller-UreyTwo scientists performed an experiment to test the Oparin-Haldane theory. They created a system, (Fig. 21.21, P. 727) that contained an atmosphere similar to that of the early Earth.

Here is what they did:The combined Methane, ammonia, water vapour and hydrogen in a flask and exposed the gases to an energy source simulating lightning.The liquid inside the flask changed colour and when examined contained several organic compounds including amino acids.Amino acids make up proteins which make up the structure of most living things.

ii. PanspermiaLife originated elsewhere in the universe and migrated to our planet. This migration could have been performed by intelligent beings (aliens) or may have occurred by chance (meteorites).

iii. Gaia Hypothesis Theory put forth by James LovelockIdea that “Earth is a “superorganism” called “Gaia”.The Earth has systems that keep a balance between temperature and atmosphere.After life originated on earth, Gaia came “alive” and began to regulate earth systems.The systems help provide an environment where life could exist and survive.

iv. Heterotroph HypothesisTheory put forth by Oparin.Said that first “cells” on earth had to be “heterotrophs” that eventually developed into autotrophs.Primordial soup existed of organic molecules.The environment was oxygen poor.Heterotrophs such as anaerobic bacteria fed on the organic molecules.The heterotrophs began to release carbon dioxide into the atmosphere. The heterotrophs developed into autotrophs and began using the carbon dioxide.The autotrophs began to release O2 into the atmosphere.This made the atmosphere oxygen rich that could now support life.

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v. SymbiogenesisTheory put forth by Lynn MargulisAttempts to explain the development of mitochondria and chloroplasts as organelles that appear in eukaryotic cells.Chloroplasts and mitochondria have their own DNA and come from the symbiosis (working together) of prokaryotic cells.

Here is how she said eukaryotic organisms may have developed:

An anaerobic bacterium ate but did not digest an aerobic bacterium (called a guest bacterium)The guest provided oxygen to the bacterium. The guest bacterium eventually became a mitochondrion.Other bacteria ate photosynthesizing bacteria. The photosynthesizing bacteria became chloroplasts.

vi. Intelligent Design

A theory that suggests life and mechanisms of life are too complex to have evolved by chance.Believed that the generation and evolution of life must have been directed by some unidentified supernatural intelligence.