The Origin of New Species
• If microevolution is small changes in gene frequencies…
• What, then would macroevolution be?
• And how might that work????
Introduction
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• In 1942 Ernst Mayr defined species.
• Can mate and have fertile offspring.
• Examples???
• Same # of chromosomes and the same sequences of
genes on them.
The biological species concept emphasizes
reproductive isolation
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• Species are based on infertility, not physical similarity.
• For example, these two meadowlarks are different species.
• But all these folks belong to the same species..
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 24.2
• There are two key ingredients to the process of
speciation:
• Reproductive isolation
• A vacant niche.
• Then, time to Evolve (by what mechanisms???).
2.How can a new species come about?
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• Reproductive
isolation can
occur for
many reasons.
• But very often
it is
geography.
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Fig. 24.5
• Islands are great examples.
• How about those Grand Canyon squirrels?
• And marsupials
• https://www.youtube.com/watch?v=NneMKuemRmI 2:00
1. Geographic barriers can lead to isolation
and the origin of new species:
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• They also require the means to
survive - a niche they can fill.
• Gause’s Law, or the Law of
Competitive Exclusion:
• “this town’s not big enough for
the both of us.”
• The less well adapted population
will either…?Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
So here’s how it works:
• The isolated populations face different selection pressures and have different random mutations occur. Chance may also be involved
• The result is that their gene pools gradually grow different enough and, voila, they are two different species.
• Even if reunited, their members can no longer mate and produce fertile offspring.
Common ancestor???
adaptive radiation???
divergent evolution ???
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Fig. 24.11
Items referring to adaptive radiation, convergent evolution, coevolution, or punctuated equilibrium should focus on the concepts rather than on the definition of the terms.
Divergent Evolution
• This is the main pattern we see when we look at the history of life on earth.
• It is the branching tree pattern of a common ancestor giving rise to different species, orders, kingdoms, etc.
• Similarities in homologous structures, chemicals like DNA and embryological development all are evidence of evolutionary change with this pattern.
• Adaptive radiation is divergent evolution that has resulted in the formation of, at the very least, new species. The two terms are almost synonyms.
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Fig. 24.24
• Convergent Evolution, on the other hand is a pattern we see in which groups which, even though they diverged from a common ancestor in the past, were different from each other at one point in time and then later evolved analagous structureswhich serve similar functions.
• Two classic examples:
• The evolution of a streamlined body shape and fins in sharks (fishes), whales (mammals with dog-like ancestors) and reptiles (swimming dinosaurs with 4-legged, land-living ancestors).
• The evolution of wings in birds, bats and insects, all from ancestors without wings.
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Now, just to be confusing, let’s look at
co-evolution.
• This is not another pattern, really, like divergent
and convergent evolution, this is when two
organisms are evolving based on the selection
pressures provided by the other. 2 examples:
• Cheetahs and antelopes have both evolved speed
related adaptations as a result of each other’s
speed.
• Flowers and their pollinators. Great example.
3:40
• Traditional evolutionary
trees diagram the
diversification of species as
a gradual divergence over
long spans of time.
• This assumes that big changes
occur because of the
accumulation of many small
ones - the gradualism
model. Like sharks.
3. The punctuated equilibrium model has
stimulated research on the tempo of
speciation
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• In the fossil record, many species appear as new forms
rather suddenly (in geologic terms),
• persist essentially unchanged, and
• then disappear from the fossil record.
• Darwin noted this when he remarked that species appear
to undergo modifications during relatively short periods
of their total existence and then remained essentially
unchanged.
• Draw a fossil/rock layers map to show this idea.
• He could not explain this fossil evidence in his
gradualism theory, but we have learned much since then.
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• In the punctuated equilibrium model, the tempo
of speciation is not constant.
• Species undergo most
morphological modifications
when they first bud from
their parent population.
• After establishing themselves
as separate species, they
remain static for the vast
majority of their existence.
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Fig. 24.17b
Periods of mass extinction (13:25 – with
Neil deGrasse Tyson) followed by rapid
speciation (:30) do exist in the fossil
record.
Stephan Jay Gould helped pioneer the
idea of punctuated equilibrium.
Let’s watch a bit of video?: The Day the
Mesozoic Died
How did the dinosaurs become extinct?
• Under this model, changes may occur rapidly and gradually during the few thousands of generations necessary to establish a unique genetic identity.
• Species will appear suddenly in rocks of a certain age
• Stabilizing selection may then operate to maintain the species relatively the same for tens to hundreds of thousand of additional generations until it finally goes extinct.
• Another neat example of how science keeps adding pieces to the puzzle. FSU link
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• The Darwinian concept of “descent with
modification” can account for the major
morphological transformations of macroevolution.
• It may be difficult to believe that a complex organ like
the human eye could be the product of gradual
evolution, rather than a finished design created specially
for humans.
• However, the key to remember is that that eyes do not
need to as complicated as the human eye to be useful to
an animal.
Most evolutionary novelties are modified
versions of older structures
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• We have also discovered genes
(HOX genes) that act as master
switches that turn on and off
whole sets of other genes to
cause big changes such as in
development. Mutations in
these genes can cause big
changes very quickly.
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Critique this picture
SC.912.L.15.10: Identify basic trends in
hominid evolution from early ancestors
six million years ago to modern
humans, including
brain size,
Jaw size,
language,
and manufacture of tools.
Video selections
• Great Transitions is best if time (20 min.). It has
don Johansen, etc. with hip and hand and skull
comparisons.
• Great Transformations is shorter (8 min.) and has
some of same Johansen clips.
• You Inner Monkey is also good but longer than
both others.
• Primates are monkeys, lemurs, tarsiers and apes
(including us!). Compared to other mammals…
• Most primates have hands and feet adapted for grasping.
• Relative to other mammals, they have large brains and
short jaws.
• They have flat nails on their digits, rather than narrow
claws.
• Primates also have relatively well-developed parental care
and relatively complex social behavior.
1. Primate evolution provides a context for
understanding human origins
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• The oldest known
anthropoid fossils,
from about 45
million years ago,
support the
hypothesis that
tarsiers are the
prosimians most
closed related to
anthropoids.
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Fig. 34.35
• The earliest primates were probably tree dwellers,
shaped by natural selection for arboreal (tree) life.
• The grasping hands and feet of primates are adaptations
for hanging on to tree branches.
• The thumb is relatively mobile and separate from the
fingers in all primates, but a fully opposable thumb is
found only in anthropoid primates.
• The unique dexterity of humans, aided by distinctive
bone structure at the thumb base, represents descent
with modification from ancestral hands adapted for
life in the trees.
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• Other primate features also originated as
adaptations for tree dwelling.
• The overlapping fields of vision of the
two eyes (binocular vision) enhance
depth perception, an obvious advantage
when brachiating (tree climbing).
• Excellent hand-eye coordination is also
important for arboreal maneuvering.
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• In the continuity of life spanning over 3.5 billion
years, humans and apes have shared ancestry for all
but the last few million years.
• Paleoanthropology is the study of human origins
and evolution.
• Paleoanthropology focuses on the tiny fraction of geologic
time during which humans and chimpanzees diverged
from a common ancestor.
2. Humanity is one very young twig on the
vertebrate tree
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• Paleoanthropology has a checkered history with
many misconceptions about human evolution
generated during the early part of the twentieth
century that still persist in the minds of the general
public, long after these myths have been debunked
by fossil discoveries.
• First, our ancestors were not chimpanzees or any
other modern apes.
• Chimpanzees and humans represent two divergent
branches of the hominoid tree that evolved around 7
million years ago from a common ancestor that was
neither a chimpanzee nor a human.
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• Secondly, human evolution did not occur as a
ladder with a series of steps leading directly from
an ancestral hominoid to Homo sapiens.
• If human evolution is a parade, then many splinter
groups traveled down dead ends and several different
human species coexisted.
• Human phylogeny is more like a multibranched bush
with our species as the tip of the only surviving twig.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
SC.912.L.15.10: Identify basic trends in
hominid evolution from early ancestors
six million years ago to modern
humans, including
brain size,
Jaw size,
language,
and manufacture of tools.
Items will not require memorization of the names of specific human fossils or the names of the different hominid species.
Items will not require memorization of the names of specific human fossils or the names of the different hominid species.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.38
• Third, the various human characteristics, such as
upright posture and an enlarged brain, did not
evolve in unison. Bipedalism was first.
• Our pedigree includes ancestors who walked upright but
had brains much less developed than ours, suggesting
that upright walking (bipedalism) set the stage for
the evolution of larger brains.
• After dismissing some of the folklore on human
evolution, we must admit that many questions
about our own ancestry remains.
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• Human evolution is marked by the evolution of
several major features.
• Brain Size. Based on skull measurements, researchers
have estimated that brain size in hominoids tripled over
the past 6 million years.
• It increased from about 400-450 cm3 in hominoids
(and similar to modern chimpanzees) to about 1,300
cm3 in modern humans.
• Jaw Shape. Our hominoid ancestors had longer jaws -
prognathic jaws - than those of modern humans.
• This resulted in a flatter face with more pronounced
chins.
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Paedomorphogenesis, or Neoteny
• Neoteny is the maintenance of juvenile
characteristics into the adult stage, not
uncommon in the animal kingdom.
• Humans are bipedal, neotenous apes, best seen
in skull structure comparisons.
• Bipedal Posture. Based on fossil skeletons, it is clear
that our hominoid ancestors walked on all four limbs
when on the ground, like modern apes.
• The evolution of bipedalism- upright posture and two-
legged walking - is associated with key skeletal
changes seen in early hominid fossils.
• Position of the foramen magnum (where your backbone connects to your
skull) is more centered in humans so the heads sits on top of the spine.
• Feet with arches and a non-opposable big toe
• Longer, stronger legs/leg bones
• Larger muscles on legs – gluts, hamstrings, quads, gastrocnemius
• Wider pelvis, knees close together for support
• S-curve in lumbar spine to support weight above
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Cultural evolution events:
• Tool making (wood, bone and metal)
• Language
• Organized hunting and gathering
• Agriculture
• Industrial revolution
• Commerce and technology
• The various pre-Homo hominids are classified in
the genus Australopithecus (“southern ape”) and
are known as australopithecines.
• The first australopithecine, A. africanus, was discovered
in 1924 by Raymond Dart in a quarry in South Africa.
• From this and other skeletons, A. africanus probably
walked fully erect and had humanlike hands and
teeth.
• However, the brain was only about one-third the size
of a modern human’s brain.
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• In 1974, a new fossil, about 40% complete, was
discovered in the Afar region of Ethiopia.
• This fossil, nicknamed “Lucy,” was described as a new
species, A. afarensis.
• These were considered to be our direct ancestors, but
are no longer
• It appears they evolved into other Australopithecines,
like africanus, but that they became extinct.
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• Based on this fossil and other discoveries, this
species had a brain the size of a chimpanzee, a
prognathic (bigger) jaw, longer arms (for some
level of arboreal locomotion), and sexual
dimorphism more apelike than human.
• However, the
pelvis and skull
bones and fossil
tracks showed
that A. afarensis
walked bipedally.
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Fig. 34.39
• In the past few years, paleoanthropologists have
found hominid species that predate A. afarensis.
• An older fossil that is unambiguously more human than
ape is Australopithecus anamensis, which lived over 4
million years ago.
• Other fossils of putative hominids go back 6 million
years, closer to the ape-human split that molecular
systematists estimate occurred about 5 - 7 million years
ago.
• News flash – 2009 – the oldest widely agreed upon
direct ancestor is now called Ardipithecus ramidus,
found in Ethiopia and dating back to 4.4 million years
ago, a full million years older than Lucy.
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• The earliest fossils that anthropologists place in
our genus, Homo, are classified as Homo habilis.
• These fossils range in age from 2.5 to 1.6 million years
old.
• This species had less human-like jaws and larger brains
(about 600 - 750 cm3) than australopithecines.
• In some cases, anthropologists have found sharp stone
tools with these fossils, indicating that some hominids
had started to use their brains and hands to fashion
tools.
• These, however, were NOT our direct ancestors.
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• Homo erectus was the first hominid species to
migrate out of Africa, colonizing Asia and Europe.
• They lived from about 1.8 million to 500,000 years ago.
• Fossils from Asia are known by such names as
“Beijing man” and “Java Man”.
• In Europe, H. erectus gave rise to the humans known
as Neanderthals.
• Compared to H. habilis, H. erectus was taller, had a
larger brain (averaging about 1,100 cm3), and had about
the same level of sexual dimorphism as modern
humans.
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• The other hypothesis, the “Out of Africa” or replacement hypothesis, argues that all Homosapiens throughout the world evolved from a second major migration out of Africa that occurredabout 100,000 years ago.
• This migration completely replaced all the regional populations of Homoderived from the firsthominid migrations.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.41b
• 2010 update – new DNA sequence studies strongly indicate
some hybridization between Neanderthals and Homo sapiens.
It always changes!!
• 2011 update – a newly found group called Denisovans also
appear to have interbred with us. This info comes from DNA
found in a fingertip fossil!
• Depending on your ancestry, you may have varying amounts of
modern human, Neanderthal and Denisovan DNA.
• Will we continue to evolve?
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Here are the traits the EOC may ask you
about
• This is what separates modern humans like us
from our ancestors:
• Larger brain
• Smaller, shorter jaws
• Language
• Complex tool manufacture
Fossil evidence suggests that a number of
members of one fish species from an ancient
lake in Death Valley, California, became several
isolated species. Of the following, which best
explains the cause of the speciation?
• A. episodic isolation
• B. temporal isolation
• C. geographic isolation
• D. behavioral isolation
A species of finch has been studied on one of the geographically isolated
Galapagos Islands for many years. Since the island is small, the lineage of
every bird for several generations is known. This allows a family tree of
each bird to be developed. Some family groups have survived and others
have died out. The groups that survive probably have
A. Interbred with other species
B. Been attacked by more predators
C. Found new places on the island to live
D. Inherited some advantageous variations