ANTB15 – The Big Picture on Evolution
- “Nothing in biology makes sense except in the light of evolution”
- By biologist Theodosius Dobzhansky reflecting on the coming together of two strands of thinking:
evolutionary change, kick started by Darwin in the mid-19 century, and genetics.
- Genetics provided the mechanism by which natural selection could occur. This was famed the ‘modern
- Darwinian evolution has been widely accepted, but some in the wider society (outside the scientific
world) remain skeptical about it.
Darwin’s Big Idea (2)
- Alfred Russel Wallace and Charles Darwin shared the inside that living species were not fixed, but were
the product of a gradual process of change driven by natural selection: the survival and reproduction of
organisms suited to their environment, at the expense of those less successful.
What is Natural Selection?
- Organisms produce more offspring than survive to reproduce.
- Their offspring vary slightly.
- Characteristics can be passed on from generation to generation.
- Those most suited to their environment survive at the expense of those less ‘fit’.
- According to natural selection, heritable features should have survival advantage.
- Sexual selection is a variation of natural selection also developed by Charles Darwin.
In the Beginning… (2)
- Mainstream scientific theories hold that life came into existence and developed through natural causes.
But many cultures have developed alternative explanations for our existence.
Need to Know (2)
- Genotype: Genetic characteristic of an individual (e.g. having gene or genes for red hair).
- Phenotype: The physical traits of an individual (e.g. having red hair). Phenotypes are dependent on
genotype and interaction with the environment.
- Allele: A version of a gene. Many genes have a number of different alleles, owing to small variations in
- Genome: The complete set of genetic instruction of an individual or species.
- Sexual reproduction: Where an offspring’s genes come from two parents.
- Asexual reproduction: Where an offspring is genetically identical to its (single) parent.
Cultural Evolution (3)
- Biological evolution is central to our existence and acts through our genes. Genes are not the only way
information can be passed on.
- Culture, our system of beliefs, values and knowledge, is passed on through interaction between people.
- One of the strongest cultural systems is language, which shows clear signs of evolutionary change.
- Many social customs are deeply ingrained.
- In some cases, it can be difficult to disentangle biological and cultural explanations.
Caught in a Drift (3)
- A random process of drift can also change the genetic make-up of a species.
- A neutral change is a change in DNA that won’t make a blind bit of difference. - Neutral changes are important thanks to a random process known as genetic drift.
- Because of chance events in breeding, the frequency of alleles may fluctuate or ‘drift’ over time.
- Changes in allele frequency due to chance have probably had a big impact on people because we are
derived from a very small founder population.
One Big Family (4)
Tree of Life (4)
- Living things fall into three major divisions: Bacteria, Archaea, and Eukarya.
- Tree of Life: Trunk represents the common ancestor, major brances are the high-level taxonomic
groups, and the twigs are the individual species themselves.
- It used to be only prokaryotes and eukaryotes, now a new group has emerged: Archaea (single-celled
and lacking a nucleus, but are more closely related to eukaryotes than bacteria).
Convergent Evolution (4)
- Evolution usually works by diversification, but sometimes a similar solution is arrived at by different
routes – convergent evolution.
- Convergent evolution – an environmental challenge has been overcome in a similar way but
independently in different species.
Whose Gene is it Anyway? (5)
- Genes are widely shared but become adapted to take on new roles in different organisms.
- Hox genes are master control genes that coordinate the activity of other genes and they are found
throughout the animal world.
- There are many ways in which genes can take on new functions. The classical way is by mutation, a
change in DNA sequence altering the properties of the protein (or RNA) that it codes for. If the mutation
affects control regions, the protein may be made in a different place in the body or at a different time
during an organism’s life.
- Sometimes genes or collections of genes are duplicated. Following duplication, genes can be free to
take on new functions, as one gene continues to perform its original role.
- Genes may become inactivated but remain in the genome as pseudogenes.
Building Family Trees (5)
- DNA sequence analysis is now used to build family trees.
- Many genes or even entire genomes can be compared.
- From a collection of sequences, family relationships can be deduced.
Evolution in Action (6)
- A species is a group of animals or plants that are able to interbreed.
- A new species is formed when two population of animals or plants accumulate so many different
genetic changes that they cannot interbreed and produce fertile offspring.
- Typically this happens when two populations become geographically separated.
- Inter-species crosses mostly generate no viable offspring because of chromosomal or genetic
- Even simple genetic changes can create reproductive barriers, and typically, such genes affect
reproductive biology (usually in males) and are under selective pressures.
Pathogen Evolution (7)
- Bacteria, a single-cell pathogen, have one huge advantage in the evolutionary game; they can reproduce
in minutes relative to humans (who take approx.. 25 years). - Viruses, tiny particles that infect and take over a cell, also have numbers on their side. A single infected
cell can spew out millions of new