Other Evidence. Ontogeny, Phylogeny, and Recapitulation Ontogeny recapitulates phylogeny!

Other Evidence

Ontogeny, Phylogeny, and Recapitulation

• Ontogeny recapitulates phylogeny!

• Ontogeny: is the history of the development of an organism through its entire life.

• Early developmental and ebryological features contribute greatly to our knowledge of homology and common descent.


– Many vertebrates have common embryonic structures

Post-analtail

Pharyngealpouches

Chick embryo Human embryo


• Ernst Haeckel: Ontogeny (individual development) recapitulates (repeats) phylogeny (evolutionary descent).


• Haeckel based his law on the flawed premise that evolutionary change occurs by successively adding new features onto the end of an unaltered ancestral ontogeny while condensing the ancestral ontogeny into earlier developmental stages.


• K. E. von Baer, disagreed, he argued that early developmental features were simply more widely shared among different animal groups than later ones.

Fig. 1.19 p 19

Heterochrony

• We now know that there are many parallels between ontogeny and phylogeny, but this ancestral ontogeny can be shifted either to earlier or later stages in descendent ontogenies.

III. Multiplication of species

• Since evolution is a branching process, unless there is a high rate of extinction, more species will be produced through time.

III. Multiplication of species

• Since evolution is a branching process, unless there is a high rate of extinction, more species will be produced through time.

• But what then is a species?

Species Definition

1. Common ancestry

Species Definition

1. Common ancestry

2. Interbreeding

Species Definition

1. Common ancestry

2. Interbreeding

3. Genotypic and phenotypic cohesion

How does speciation occur?


1. Reproductive barrier (allopatric speciation).



1. Geographic isolation (Vicariant speciation)1. Mountain range

2. Glaciers

Ensatina eschscholtzii

Fig. 1.21 p 22



1. Geographic isolation (Vicariant speciation)1. Mountain range

2. Glaciers

2. Colonization (founder effect)

Founder Event


1. Reproductive barrier (allopatric speciation)

1. Geographic isolation

1. Mountain range

2. Glaciers

2. Colonization (founder effect)

2. Without reproductive barrier (sympatric speciation). Speciation forming without geographic isolation.

3) Adaptive Radiation: The production of ecologically diverse species from a common ancestral stock.


Adaptive Radiation:

Species radiate from a

common ancestor

stock.

Figure 1.23 p 23

IV. Darwin Argued that Species Arise by Gradualism


• Based on Leyell’s theory of uniformitarianism.


• Based on Leyell’s theory of uniformitarianism.

• States that larger changes in organisms occur by the accumulation of many smaller changes (i.e. evolution is a slow, continuous process)

Fig. 1.25, p 24 Gradualist model of evolution

What evidence would support Gradualism?


• Fossil record should have a long series of intermediate forms connecting the phenotypes of ancestral and descendant populations.


• So do we see lots of intermediate forms in the fossil record?

Others Argued that species arise by Punctuated Equilibrium

Others Argued that species arise by Punctuated Equilibrium

• Phenotypic evolution is concentrated in relatively brief events of branching speciation, followed by much longer intervals of evolutionary stasis.

Fig 1.26, p 24 Punctuated Equilibrium model

Gradualism Vs. Punctuated Equilibrium

• So which one is correct?

V. Natural Selection

• Differential reproduction and survival of individuals carrying alternative, inherited traits.

V. Natural Selection

• Natural selection is the major process or mechanism by which evolution occurs in Darwin’s theory of evolution.

So how did Darwin come up with this explanation?

Darwin’s Observations


• Observation 1: Organisms can produce more offspring than just replacing the parents



• Observation 2: Number of individuals in a population remains constant




• Observation 3: Individuals within a species vary (size, color, behavior, etc..)




• Observation 3: Individuals within a species vary (size, color, behavior, etc..)

• Observation 4: Variation in individuals is heritable.

Darwin’s Deductions


• Deduction 1: Individuals must compete for resources, and only some will survive



• Deduction 2: Individuals with variations more suited to the environment will be more likely to survive and reproduce: natural selection



• Deduction 2: Individuals with variations more suited to the environment will be more likely to survive and reproduce: natural selection

• Deduction 3: Over many generations and long periods of time, these variations accumulate in the population, resulting in evolution, or change over time.

Potential for rapid reproduction

Relatively constant resources and population

over time

Variability in structures and

behaviors

Some variability inherited

Competition forSurvival and reproduction

NATURAL SELECTIONOn average, the fittest

Organisms leaveThe most offspring

EVOLUTION:The genetic makeup of the

population changes over time, driven by natural selection

Conclusions

Observation

Evidence for evolution

1) Artificial Selection

2) Fossil Record

3) Comparative anatomy

4) Homologous/vestigial structures

5) Embryology

After Darwin

• Neo-Darwinism: August Weismann’s change to Darwin’s theory by removing inheritance of acquired characteristics.

After Darwin

• Neo-Darwinism: August Weismann’s change to Darwin’s theory by removing inheritance of acquired characteristics.

• The synthetic theory: combination of Darwin’s and Mendelian genetics– Microevolution– Macroevolution

The Big Picture

• The theory of evolution was derived through the scientific method.

• REMEMBER: this makes evolution testable!

• After more than 100 years of intensive testing, Darwin’s theory has only been slightly altered.

• Evolution explains the diversity of life on earth.

Other Evidence. Ontogeny, Phylogeny, and Recapitulation Ontogeny recapitulates phylogeny!

Documents

Transcript of Other Evidence. Ontogeny, Phylogeny, and Recapitulation Ontogeny recapitulates phylogeny!