History of LifeBiogeography | Homologies

Learning Objectives• Describe how biogeography and homology provide

evidence for evolution• Distinguish between anatomical, molecular, and

developmental homologies

History of Life

• Fossil – the preserved traces or remains of living organisms from the past– See progressive change in organisms

Fossil Record

• Fossil record from Equus genus

– Almost complete

– Supports theory of common ancestry

Fossil Record

*Simplified fossil record

• Stasis – the periods of time in the fossil record that show limited change

Fossil Record

• Limitations of fossil record– Fossilization

requires specific conditions

– Organisms can appear suddenly in fossil record

– Incomplete fossilization results in gaps in fossil record

Fossil Record

• Fossil record supports theory of sequential evolutionary change– Older fossils located in older strata– Younger fossils located in younger strata

Fossil Record

• Ex) Sequential evolution of the coiled oyster– Coiled oyster shells became

• Larger• Thinner• Flatter

Fossil Record

• Biogeography – the study of the distribution of species, organisms, and ecosystems through geologic space and time– Earth’s land

masses have moved over time

Biogeography

• Fossils provide evidence of species that were present across Earth’s original land mass

• Allopatric speciation occurred as land mass split– South American

and African monkeys share common ancestor

Biogeography

• Homology – the similar features between different organisms resulting from common ancestry– Anatomical– Molecular– Developmental

Homologies

• Anatomical homology – a group of similar structures between different organisms resulting from common ancestry

Homologies

Homologous StructuresARM LEG Flipper Wing

13

• Vestigial structure – nonfunctional structure left over from a common ancestor– Ex) Pelvis in whale which lacks hind limbs

Homologies

Homologies

• Anatomical homology– Result of common

ancestor with that trait

• Convergent evolution– Creates similar

structures/functions

– Are not anatomical homologies

• Molecular homology – the similar stretches of genetic material between different organisms resulting from common ancestry– Shared genetic code indicates common ancestor– Organisms likely to be related have retained

same stretches of DNA

Homologies

#5 Molecular and Genetic Evidence

AKA Biochemical Evidence

Two closely-related organisms will have similar DNA, RNA, and protein (amino acid) sequences.

This also gives evidence of a common ancestor. 17

18

• Developmental homology – the similar features in the embryos of different organisms resulting from common ancestry– Hox genes – the sections of the genome that

allow embryos to develop structures in the correct place

– Similarities in development in different species indicate common ancestry

Homologies

#3 Embryology Embryo (early developmental stage)

gives evidence of evolution Identical larvae, different adult body

forms Similar embryos, related but diverse

organisms Shows

commonancestry

Larva

Adult barnacleAdult crab

20

#3 Embryology

21

Vertebrates all share gill slits

and a tail in their early

embryo stage;

Share a common ancestor

Learning Objectives• Describe how biogeography and homology provide

evidence for evolution• Distinguish between anatomical, molecular, and

developmental homologies

History of Life