Lecture 25 Evolution
-
Upload
clinton-fletcher -
Category
Documents
-
view
20 -
download
0
description
Transcript of Lecture 25 Evolution
Lecture 25Evolution
What is Evolution? Change over time, building on past & current features
Products evolve Knowledge evolves Beliefs evolve
What is Evolution? In other cultures and religions,
for example Taoism, evolution plays a central role
Evolutionary patterns in biology have been noted as far back as Aristotle
Darwin initially used the phrase “descent with modification” to explain the concept of evolution
Patterns of biological evolution have been observed in three major areas: Fossil records Anatomical features Molecular distances
Evolution: Getting from There to Here
Macroevolution Evolutionary change on a
grand scale
Encompasses the origins of new species and major episodes of extinction
Microevolution Evolutionary change on a
small scale
Encompasses the genetic changes that occur within populations over time
These changes are the result of changes in gene frequencies
Evolution: Getting from there to Here
In contrast, Darwin and Wallace proposed that: variation is an inherent characteristic of all biological populations It is not created by experience
This is readily observable in all populations – just look around this room
Prior to Darwin and Wallace it was widely thought that biological evolution occurred by inheritance of acquired characteristics Individuals passed on to offspring body
and behavior changes acquired during their lives
The Pace of Evolution
The standard view since Darwin was that evolutionary change occurred extremely slowly Imperceptible changes accumulate such that, over thousands or
millions of years, major changes could occur This is termed gradualism
In 1972, Niles Eldredge and Stephen Jay Gould proposed the Punctuated Equilibrium hypothesis Evolutionary change occurs in bursts separated by long periods of
little or no evolutionary change (termed stasis)
Examples of both gradualism and punctuated equilibrium exist So speciation clearly occurs in different ways
However, the idea that speciation is necessarily linked to phenotypic change has not been supported Speciation can occur without phenotypic change Phenotypic change can occur within a species in the absence of speciation
Different kinds of organisms do evolve at different rates Bacteria evolve much faster
than eukaryotes
The rate of evolution also differs within the same group of species In punctuated equilibrium,
evolution occurs in spurts In gradualism, evolution
occurs in a gradual, uniform way
The Rate of Evolution
The Evidence For Evolution
Evidence for evolution comes from the following
Fossil record
Anatomical record
Molecular record
Evolution in the titanotheres
Small bony protuberance
Large blunt horns
Hoofed mammals
Fossil Record
Provides the most direct evidence for macroevolution
Fossils are the preserved remains, tracks, or traces of once-living organisms They form when
organisms become buried in sediment and calcium in hard surfaces mineralizes
Arraying fossils according to age often provides evidence of successive evolutionary change
Fossil Record
Fossils have been found linking all the major groups
The forms linking mammals to reptiles are particularly well known
Ontogeny Recapitulates Phylogeny All vertebrates share a basic set of developmental instructions
Anatomical Record: Ontogeny
Homologous structures Have different structure and function but are all derived from the
same part of a common ancestor
A common ancestor possessed this 1-2-5 structure
Adaptations to different environments modified this structure in different ways
Anatomical Record: Homology
Analogous structures Resemble each other as
a result of parallel evolutionary adaptations to similar environments
Anatomical Record: Analogy
Analogous structures are the result of convergent evolution
Different animals often adapt in similar fashion when challenged by similar adversities or opportunities
Convergent evolution: many paths to one goal
Vestigial organs Structures that are no longer
in use such as the human appendix
Apes have a much larger appendix that is involved in digestion
Anatomical Record
New alleles arise by mutations and they come to predominance through favorable selection
Thus, evolutionary changes involve a continual accumulation of genetic changes Distantly-related
organisms accumulate a greater number of evolutionary differences than closely-related ones
This divergence is seen among vertebrates in the 146-amino acid hemoglobin chain
Molecular Record: Evolutionary Distance
Molecular Record: Molecular Clock
This same pattern of divergence is seen with DNA sequences, such as that of the cytochrome c gene
The changes appear to accumulate at a constant rate
This phenomenon is referred to as a molecular clock
Note: Different proteins evolve at different rates
Molecular Record: Homology
The eyes of these organisms are NOT homologous
The genes controlling eye development ARE homologous
500 million years ago an ancestor evolved the “switch” for eye development Probably simplest type of eye
structure
1 pigment cell & 1 photoreceptor
The gene was passed on to all its descendents
These descendents evolved different types of complex eyes Each switched on by a
descendent of the original gene
Evolution’s Critics
Critics of evolution raise seven principal objections
1. Evolution is not solidly demonstrated
2. There are no fossil intermediates
3. The intelligent design (irreducible complexity) argument
4. Evolution violates the 2nd law of thermodynamics
5. Proteins are too improbable
6. Natural selection does not imply evolution
None of these objections has held up to scientific scrutiny
Evolution & Religion
“Today, almost half a century after the publication of the Encyclical, new knowledge has led to the recognition of more than a hypothesis in the theory of evolution.
It is indeed remarkable that this theory has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge.
The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favor of the theory.”
Pope John Paul II November 19, 1996 Address to the Pontifical Academy of Sciences
The Evolutionary Path to Apes
The Earliest Primates had two distinct features that allowed them to succeed in the arboreal insect-eating environment Grasping fingers and toes
Allow them to grip limbs, hang from branches & use tools
Overlapping binocular vision Lets the brain judge distance precisely
~ 40 mya, the earliest primates split into two groups: Prosimians and Anthropoids
Prosimians (“before monkeys”) Primarily nocturnal and herbivorous Only a few survive today
The story of human evolution begins around 65 mya with the Archonta A group of small, arboreal mammals that were primarily
insectivorous They underwent an explosive radiation that gave rise to different types of
mammals including bats and primates
Higher primates include monkeys, apes and humans
Origin of the Anthropoids
Anthropoids are almost all diurnal and herbivorous Evolved a bigger brain
and improved senses to adapt to daytime foraging
Live in groups with complex social interactions
Tend to care for their young for prolonged periods of time
Early anthropoids, now extinct, evolved in Africa
Their direct descendants are:
Old World MonkeysStayed in AfricaSplit into two lineages
i. Old world monkeysii. Hominoids
Many are ground dwellersNone have prehensile tails
New World MonkeysMigrated to South AmericaDeveloped in isolationAll are arborealMost have prehensile tails
Comparing Apes to Hominids
Hominoids evolved from anthropoids Apes Hominids (humans and their
direct ancestors) Chimpanzees are the closest living
human relatives Chimpanzees and humans
share 98.4% of their nuclear DNA
Gorillas and humans share about 97.7%
The common ancestor of apes and hominids is thought to have been an arboreal climber Hominids became bipedal (walking upright) Apes evolved knuckle-walking
Anatomical differences between the two are related to bipedal locomotion Considerable controversy exists about the identity of the first hominoid
Attention is now focused on an early Miocene ape, Proconsul Has many of the characteristics of Old World Monkeys It lacks a tail and has apelike hands, feet and pelvis
There are two major groups of hominids
The genus Homo 3-7 species
depending on how you count them
The genus Australopithecus
7 species Older Smaller-brained
A Hominid Evolutionary Tree
Bipedalism seems to have evolved as our ancestors left dense forests for grasslands and open woodland
Did bipedalism precede or succeed brain enlargement? Fossils unearthed in Africa demonstrate
that bipedalism extended back 4 mya Substantial brain expansion, on the other
hand, did not appear until about 2 mya
Australopithecine characteristics Bipedal ~ 1 m tall and ~ 18 kg in weight Hominid dentition Brains not any larger than those
of apes Fossils only found in Africa
Out of Africa: Homo erectus
The first humans evolved from australopithecine ancestors about 2 mya The exact ancestor is thought to be A.
afarensis
In the 1960s, hominid bones were found near stone tools in Africa This early human was called Homo
habilis (Latin for “handy man”) It closely resembled Australopithecus
but had a larger brain
In 1891, in Java, a Dutch anatomist named Eugene Dubois found a 500,000 year old skull cap and thighbone which he called Java man, The thigh bone indicated that he was
bipedal The skull indicated a brain twice the
size of that of Australopithecus Now recognized as Homo erectus:
Taller than H. habilis with a larger brain
In 1976, a 1.5 million year old H. erectus skull was found in East Africa This suggests that H. erectus originated
there and migrated into Asia and Europe
H. erectus survived for over a million years - longer than any other species of humans
The Last Stage of Hominid Evolution
Modern humans first appeared in Africa about 600,000 years ago Three human species are thought to have evolved
Homo heidelbergensis Evolved in Africa about 600,000 years ago Migrated to Europe and Western Asia
Homo neanderthalensis Appeared in Europe about 130,000 years ago as H. heidelbergensis
was becoming rarer Likely branched off of the ancestral line leading to modern humans
Homo sapiens (“wise man”) Evolved in Africa about 130,000 years ago then migrated to Europe
and Asia This is called the Recently-Out-of-Africa model This model is supported by a variety of gene studies
Human mitochondrial DNA Y and X chromosomes Autosomes
Our Own Species: Homo sapiens
Neanderthals (H. neanderthalensis) Named after the Neander Valley of Germany
where their fossils were first discovered in 1856 Evolved in Europe, then migrated to Asia Abruptly disappeared about 34,000 years ago
Cro-Magnons (H. sapiens) Named after the Valley in France where their
fossils were first discovered Evolved in Africa, then migrated to Asia Eventually spread to N. America and Australia
We humans are unique animals and the product of evolution Our evolution has been marked by a progressive
increase in brain size Refined and extended conceptual thought Symbolic language Cultural evolution