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Kindle Notes & Highlights
by
Dylan Evans
Read between
August 3 - August 4, 2020
“Nothing in biology makes sense except in the light of evolution”
Darwin’s dangerous idea comes in two parts: the theory of evolution, and the theory of natural selection.
The theory of evolution states that species can change. One species can give rise to another.
Current estimates put the age of the earth at around 4.5 billion years. That is easily long enough for evolution to have taken place.
They now know, for example, that all life on earth is descended from a single ancestor that lived about 4 billion years ago. This must have been a very simple kind of organism; much simpler even than a single cell.
The first cells appeared around 3.5 billion years ago.
3.5 billion years
Around 370 million years ago, animals began to colonize the land.
From 3.5 billion years to 370 million years.
many kinds of mammal are the primates – monkeys and apes – which first appeared some 35 million years ago.
Modern humans first appeared in Africa around 100,000 years ago.
humans would only make their appearance a few minutes before midnight on 31 December.
All living things carry a record of the history of their descent in their genes. Genes are like living fossils.
Gene's are like living Fossils
This is where the second part of Darwin’s dangerous idea comes in: the theory of natural selection.
Such clever complex designs in organisms are called adaptations.
Paley was right about one thing. Complex designs like the woodpecker’s beak are highly unlikely to arise by chance in a single step.
event in itself, requiring no designer, but natural selection would ensure that each step would be preserved and so the design would accumulate.
Natural selection can be cumulative as well as single-step.
Cumulative as well as single step
Natural selection designs wonderful things, but has no plans. For this reason, the British zoologist Richard Dawkins (b. 1941) has described it as a “blind watchmaker”.
The Blind Watch Maker- Evolution has No foresight. In humans it might be based on the choices we make. The game theory and the resulting consequences spiraling out as chaos theory
because natural selection can be cumulative, the many small changes can eventually add up to a wonderful design.
One small Change after the other
selection is a much simpler explanation than divine creation because it only requires us to believe in things that we already know about. All that natural selection requires are the three conditions described above. No supernatural being is needed.
As if decoding a puzzle
Occam’s razor tells us that we should always prefer simpler explanations.
Occam's Razor, that we should always prefer simpler explanations
Genes are stretches of DNA. Each cell in our bodies contains lots of DNA. DNA is a complex molecule made up of four bases – adenine, cytosine, guanine and thymine (abbreviated to A, C, G, T). These bases are arranged in a long line. The sequence in which they are arranged is vitally important because different sequences specify different proteins.
The difference between Gene and DNA
Proteins are the molecules from which animals and plants are made. They are the building blocks from which cells, and ultimately bodies, are constructed.
Different species may have different kinds of body because they have different proteins, or because the proteins are arranged differently, or both.
Every animal and plant starts life as a single cell. In order to grow into an adult, this cell must first divide in two (a process called mitosis).
Mitosis
Growth does not just involve cell division. In addition to dividing and multiplying, the cells must specialize. The adult body of a human being is composed of many different types of cell: skin cells, brain cells, muscle cells, and so on.
Cells know how to do this by following the instructions encoded in their genes.
Usually, our genes are faithfully copied from our parents. Half the genes come from the father and half from the mother.
No Mutation, No Evolution
If mutation never happened, there could be no evolution and no natural selection. Every organism would be a perfect copy of its parents, and species would indeed be fixed. It is only because of the occasional copying error that species can change over time and adapt to new environments.
The conservation of beneficial mutations is not random.
we can think of evolution in terms of changes in the frequency of the underlying genes.
The Selfish Gene
The gene would therefore achieve its “aim” of spreading more copies of itself through the population.
It might seem as if the only way for a gene to spread through the population is by building adaptations, like teeth and muscles, that serve nobody except the one who possesses them.
That serve nobody except the one who possess them
The biological definition of altruism is only concerned with effects, not motives.
When bees sting an animal, they die. They give up their lives to save their brethren.
A gene which makes its bearer behave altruistically can spread through the population so long as the altruism is directed specifically at other organisms who have the same gene.
Imagine you are a selfish gene sitting in the caveman’s body. Your only wish is to make as many copies of yourself as possible. Should you make the caveman be selfish or altruistic?
Selfish Gene and Altruism
whether or not we like it, the fact is that genes do affect the way we behave.
Hundreds of studies in dozens of species – from mice and rats to dogs and humans – have provided powerful evidence that genetic differences between individuals can cause those individuals to behave differently.
Kin Selection
the only animals that regularly engage in self-sacrifice to help others are social insects like bees who live in colonies in which everyone is very closely related.
Most biological altruism, it seems, is due to kin selection, not reciprocity.
Now that's bonkers
As the example of the peacock’s tail shows, natural selection is not just about survival – it’s about reproduction too. If an organism lives to be 1,000 years old, but has no offspring, it might just as well have died at birth as far as its genes are concerned.
