Chapter 3: Remnants: Vestiges, Embryos, and Bad Design
There are features (vestigial) and genes that were once useful.
Vestiges – feature of species that was an adaptation in its ancestors but has lost
its usefulness or has been adapted for other uses. VESTIGIAL BECAUSE NO
LONGER PERFORMS FUNCTION FOR WHICH IT EVOLVED (not necessarily
that it has no function).
Example: ostrich wings not for flight but for balance, weaponry and mating. Flightless
birds descend from flying ancestors. Bones of wings same in both flying and flightless birds.
Why lose flight: Flight is metabolically expensive and wings easily injured. If lack of
predators on island or food abundant on ground, then makes sense to reserve energy.
Still visible because a) has other uses b) actually in the middle of transition
Also, eyes in burrowers and cave dwellers: mutations over time can just accumulate if they
neither harm nor help the animal.
Whales: have hind limbs. Humans: appendix (for digesting cellulose).
VESTIGIAL TRAITS ONLY MAKE SENSE IN THE LIGHT OF EVOLUTION. i.e. moving
ears and non-functional wings don’t make sense if we were “created” like this
ATAVISM—evolutionary throwback. Ancestral traits reappearing occasionally on
individuals (not in the whole species). Come from re-expression of genes that were
functional in ancestors but silenced by natural selection. They are dormant and can
sometimes be reawakened. Ex. Horses with extra toesused to have 5 toed ancestors.
ATAVISM IS PROOF OF REMNANTS OF ANCIENT GENES.
DEAD GENES Atavisms and vestigial traits show us that when a trait is no longer used
or is reduced, the genes that make it don’t instantly disappear from the genome. Evolution
deactivates them but does not eradicate them. Therefore, VESTIGIAL GENES MUST
EXIST. If we were created, then no vestigial genes will exist. (pseudogene-gene that does
Ex. Human: GLO-enzyme to metabolize vitamin c. Primates, fruit bats and guinea pigs
have pseudo-GLO because of missing nucleotide. Also, sequence of gene in close relatives
similar (similar pseudo-gene in humans and chimps compared to orangutans; bats and
guinea pigs have totally different pseudo-GLO).