(1) When did evolution theory start?

Evidence for natural selection - the scientific work of Darwin and Wallace

Introduction to Darwin's Theory of Evolution - evidence for natural selection

 - the central ideas, its initial rejection and its lasting influences on modern biology

(Charles Darwin lived from 1809 to 1882, his first important publications on evolution in where in 1859 entitled 'On the origin of species'. It is interesting to note that Charles Darwin's grandfather, Erasmus Darwin, wrote about evolutionary concepts i.e. the evolution of species, in his book entitled 'Zoonomia'.

Jointly with the biologist Wallace, Darwin is credited with first describing the idea of evolution by natural selection - by way of the survival of the fittest plant/animal - the most adapted species to survive in their natural environment.

 

The most important idea of Darwin is to state that species change and evolve.

This was quite contrary to the thinking at the time, when it was believed that all species were created, and had always existed, in the form that was observed at that time.

Creationism is the belief that the universe and living organisms originate from specific acts of divine creation, as in the biblical account, rather than by natural processes such as evolution - this belief is quite contrary to current accepted scientific theory - the theory of evolution is accepted by the majority of scientists, but 'faith' beliefs are a very personal and important state of mind and people are entitled to their religious point of view.

 

Be able to demonstrate an understanding of Darwin’s theory of evolution by natural selection including:

(a) variation – most populations of organisms contain individuals which vary slightly from one to another, those with superior characteristics are more likely to survive,

(b) over-production – most organisms produce more young than will survive to adulthood ensuring some will survive,

(c) struggle for existence – because populations do not generally increase rapidly in size there must therefore be considerable competition for survival between the organisms,

(d) survival - those with advantageous characteristics are more likely to survive this struggle,

(e) advantageous characteristics inherited – better adapted organisms are more likely to reproduce successfully passing on the advantageous characteristics to their offspring

(f) gradual change – over a period of time the proportion of individuals with the advantageous characteristics in the population will increase compared with the proportion of individuals with poorly adapted characteristics, and the poorly adapted characteristics may eventually be lost.

(g) geographical separation - if populations become separated and isolated from each other (e.g. islands or mountain chain), natural selection can have different effects producing sub-species of plants or animals, this can eventually lead to new species - the process of speciation.

 

Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms (we now know first developed more than three billion years ago).

He based his theory on a huge number of observations from fieldwork on a round-the-world trip, but also conducting many experiments in his own garden.

Some of his most important observations and studies of plants and animals were made on a five year trip around the world in a ship called HMS Beagle.

He also discussed his ideas with other scientists and took into considering the growing science of geology and the accumulation of more and more fossil specimens.

He noted the similarities and differences between fossils and realised there was some kind of progression in their sequence.

Darwin recognised that organisms, even of the same species, showed variations in characteristics (we now recognise phenotype variations from different genotypes).

He noted that the different characteristics within the same species, represented adaptations best suited to the local environment e.g. the different beaks of finches were adapted to best exploit particular food sources.

e.g. beaks changed ('adapted') as the birds developed different tastes for fruits, seeds, or insects picked from the ground or cacti. Long, pointed beaks made some of them more fit for picking seeds out of cactus fruits or picking out insects from a cavity. Shorter, stouter beaks served best for eating ('crunching') seeds found on the ground.

He also observed that these advantageous traits were passed on to their offspring.

It was obvious to him that organisms will compete for the limited resources in the ecosystem they belong to and be as successful as possible within part of a food chain.

Darwin concluded that organisms best adapted, that is, having the most suitable characteristics to live in the environment, would be the most successful competitors and more likely to survive and reproduce.

 This is summed up the phrase 'survival of the fittest'.

In other words, the successful competitive organisms pass on their genes of their successful characteristics to their offspring.

Organisms which are less well adapted to their environment are less likely to survive and reproduce.

This means they are less likely to pass their genes on to the next generation.

Such organisms are even more vulnerable if environmental conditions change, and, become less favourable, e.g. climate change, scarcity of food, so populations can fall, and a species might even become extinct.

Darwin reasoned that beneficial characteristics would become more common in the population of a given organism and the species evolves as it changes - this can lead eventually to new species - Part 9. speciation.

 

Opposition to Darwin's theory of natural selection (first published in 1859)

The theory of evolution by natural selection was only gradually accepted because:

The theory challenged the idea that God made all the animals and plants that live on Earth - challenging the way religious belief viewed how the Earth had developed.

It is/was common in religious belief systems that all we see around us was created by 'God', the divine creator.

Darwin's theory of evolution was the first important AND plausible theory for how life forms developed without the need for a 'Creator'.

Many scientists could not reconcile their religious views with Darwin's scientific approach to the origin of the diversity of species.

There was insufficient evidence at the time the theory was published to convince many scientists.

 

Lack of knowledge didn't help acceptance of Darwin's evolution theory

Darwin couldn't explain how beneficial and non-beneficial characteristics could occur and how beneficial characteristics were passed on.

All he could argue was that organisms with good survival characteristics would survive and thrive, and those without would die out.

He did actually recognise the effects of selective breeding for characteristics eg in breeding stronger faster racing pigeons, but had no idea why the pigeon fanciers methods worked!

There was also a lack of fundamental research on organisms, eg how plant/animal species may have changed over time, so there were very few scientist actually pursuing similar research.

Darwin couldn't explain how beneficial characteristics appeared and how they passed on to successfully reproducing offspring - he had no knowledge of genes and mutations.

Other scientists didn't think Darwin provided enough evidence for his theory - though few other scientists, particularly biologists, were not interested in researching how organisms had changed over time.

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The VERY important contribution of A. R. Wallace

One very rare exception to the dismissal of Darwin's evolution theory by fellow scientists was the naturalist Alfred Russel Wallace (1823-1913), who independently developed a similar natural selection theory of evolution by studying plants and animals in the forests of South America.

Alfred Russel Wallace, working at the same time as Darwin, was eventually accepted by the scientific community as the co-founder or co-discoverer of the theory of evolution by natural selection.

Darwin and Wallace jointly published there papers on evolution and acknowledged each other's work and contributions to the theory of evolution.

However, they didn't always agree on the mechanism of evolution - how organisms change.

 

The work of Alfred Russel Wallace

The biological scientist A. R. Wallace independently from Darwin came up with his own (and correct) theory of evolution by natural selection. He tends not to get the same mention as Darwin.

His research led him to become a major contributor to the theory of speciation, mainly looking at the lives and species of various insects and he did collaborate with Darwin.

He was considered the 19th century's leading expert on the geographical distribution of animal species - an important factor in the theory of natural selection.

However, it was Darwin's publication in 1859 of 'On the Origin of Species' that caught the attention of scientists. This work on evolution was much more expansive than Wallace's scientific publications, and also presented lots of evidence to support his theories. The result, somewhat unfairly, is that Darwin is much better remembered than Wallace.

However, Darwin and Wallace published there papers on evolution together - though they didn't always agree on the mechanisms of natural selection.

The practical and theoretical work of Wallace (and Darwin) has been developed as more research has done over the past 160+ years, particularly after 1858 when both scientists published major research papers on natural selection.

(Wallace's publication prompted Darwin to publish 'On the origin of species' in 1859)

Wallace travelled to many parts of the world making many observations that provided sound scientific evidence that species evolved by natural selection.

(Wallace collected more than 126,000 specimens of insects in the Malay Archipelago!)

 

Some examples of his research findings:

Wallace's thousands of observations provided lots of evidence to support the theory of evolution by natural selection.

Many species of butterflies had a (i) peculiar odour and taste or (ii) warning colours - all adaptations to deter potential predators from eating them - these beneficial characteristics had come about by natural selection - the fittest traits to help the species survive - beneficial characteristic passed on in the alleles of their offspring.

Another of his crucial set of observations and deductions fits in with what we understand about speciation. He noticed differences in subspecies of birds on the westernmost islands of the Malay Archipelago. He then noted their absence on the eastern islands, where other sub-species were present. He rightly concluded that this island isolation had led to the differentiation of the species.

What he and Darwin both realised was that there was a mechanism of sub-species formation and even new species could arise if populations of the same species became geographically isolated - we call this speciation.

Groups of islands proved an ideal situation for observing 'speciation'.

On a somewhat grander scale, modern research has shown that species of animals in Africa and South America, now separated by the Atlantic Ocean, have common ancestors - the speciation deriving from the geographical separation over millions of years as the American and African continental plates moved apart.

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BUT, following on from Darwin and Wallace, what we now know has made all the difference in biology!

Darwin and Wallace have had a profound effect on modern biology

The mechanism of inheritance and variation

Modern understanding of genetics did not begin until 50 years after the theories of Darwin and Wallace were first published.

Although Darwin recognised, and argued, that species evolved he had no knowledge of genes, DNA and molecular genetics and so had no idea of how mutations occur ...

AND, therefore had no knowledge of how organisms passed on their beneficial adaptations to their offspring.

He did not know, as we now know, that observed phenotypes are controlled by genes (the alleles of genotypes) and that new phenotypes can arise by changes in the DNA (mutations) ...

AND we now know the mechanism of how beneficial genes are passed on from both parents to the offspring of future generations.

Modern research has fully vindicated Darwin's hypothesis

on evolution by natural selection, and his theory is fully accepted by the scientific community, BUT, modern research has also shown that evolution and its mechanisms are much more complicated than Darwin could imagine - 'rock on' DNA!

The theory of evolution by natural selection is still important and still relevant to today's scientists.

The theories first described by Darwin and Wallace are still helping us to understand many aspects of plant and animal biology.

We now appreciate from the current total of scientific evidence that all life has descended from a common ancestor over 3 billion years ago and that changes in life forms have occurred through the process of evolution.

 

Examples of how evolution theory is helping contemporary biology

(i) Understanding the problem of antibiotic resistance (discussed in detail in Part 10)

(ii) The systems of classifying all organisms are being updated thanks to evolution theory and advances in genetics - DNA genome analysis (notes on separate page).

The modern theory of evolution suggests all living organisms have descended from a common ancestor.

Therefore, we should all be related genetically in some way.

Modern classification of organisms is now based on how closely related organisms are in terms of their genetic make-up.

See Classification - including the three domain system of classifying organisms

Many species and their habitat are endangered because of ever advancing movement into 'wild' areas to exploit the land for ourselves - we are changing the environment and many species are struggling to adapt.

For plants, one method is to build up stores of seeds - essentially a bank of plant genes.

A seedbank is a store of genetic material for the future - an important strategy for conservation.

If any plant becomes extinct in the wild, it can still be grown using the store seeds and the new plants introduced back into the wild.

ALSO, a the seed store provides a huge variety of alleles coding for different characteristics available for use in agriculture e.g. cross breeding species or genetically modifying plants.

The genetic variation in 'modern' crops can be quite limited and makes them susceptible to a particular animal pest or bacterial/fungal disease.

BUT, older, more traditional crops may have useful genes (allele variants) that may confer useful characteristics on newer crops.

 

Extra note on preserving the 'genetic lines' of plants

The Svalbard Global Seed Vault (Norwegian) is a secure seed bank on the Norwegian island of Spitsbergen, near Longyearbyen, in the remote Arctic Svalbard archipelago, it is approximately 1,300 kilometres from the North Pole.

The idea of this 'cold' huge storage vault is to preserve a wide variety of plant seeds that are duplicate samples, or "spare" copies, of seeds held in gene banks worldwide.

The seed vault is an attempt to ensure against the loss of seeds in other gene banks during large-scale regional or global crises.

The seed vault now contains nearly a million seed samples.

 

(iii) Biodiversity: The conservation of many endangered species of plants and animals.

Understanding genetic diversity and its importance in populations adapting to changing conditions.

Around the world there are many conservation projects protecting rare and endangered species of plants and animals.

 

See also

Biodiversity and ecological surveying - using quadrats and transects

Biodiversity, land management, waste management, maintaining ecosystems - conservation

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The important contribution of A. R. Wallace

One very rare exception to dismissal of Darwin's evolution theory by fellow scientists was the naturalist Alfred Russel Wallace (1823-1913), who independently developed a similar natural selection theory of evolution by studying plants and animals in the forests of South America.

Alfred Russel Wallace, working at the same time as Darwin, was eventually accepted by the scientific community as the co-founder or co-discoverer of the theory of evolution by natural selection.

Darwin and Wallace jointly published there papers on evolution and acknowledged each other's work and contributions to the theory of evolution.

However, they didn't always agree on the mechanism of evolution - how organisms change.

 

The work of Alfred Russel Wallace

The biological scientist A. R. Wallace independently from Darwin came up with his own (and correct) theory of evolution by natural selection. He tends not to get the same mention as Darwin.

His research led him to become a major contributor to the theory of speciation, mainly looking at the lives and species of various insects and he did collaborate with Darwin.

He was considered the 19th century's leading expert on the geographical distribution of animal species - an important factor in the theory of natural selection.

However, it was Darwin's publication in 1859 of 'On the Origin of Species' that caught the attention of scientists. This work on evolution was much more expansive than Wallace's scientific publications, and also presented lots of evidence to support his theories. The result, somewhat unfairly, is that Darwin is much better remembered than Wallace.

However, Darwin and Wallace published there papers on evolution together - though they didn't always agree on the mechanisms of natural selection.

The practical and theoretical work of Wallace (and Darwin) has been developed as more research has done over the past 160+ years, particularly after 1858 when both scientists published major research papers on natural selection.

(Wallace's publication prompted Darwin to publish 'On the origin of species' in 1859)

Wallace travelled to many parts of the world making many observations that provided sound scientific evidence that species evolved by natural selection.

(Wallace collected more than 126,000 specimens of insects in the Malay Archipelago!)

 

Some examples of his research findings:

Wallace's thousands of observations provided lots of evidence to support the theory of evolution by natural selection.

Many species of butterflies had a (i) peculiar odour and taste or (ii) warning colours - all adaptations to deter potential predators from eating them - these beneficial characteristics had come about by natural selection - the fittest traits to help the species survive - beneficial characteristic passed on in the alleles of their offspring.

Another of his crucial set of observations and deductions fits in with what we understand about speciation. He noticed differences in subspecies of birds on the westernmost islands of the Malay Archipelago. He then noted their absence on the eastern islands, where other sub-species were present. He rightly concluded that this island isolation had led to the differentiation of the species.

What he and Darwin both realised was that there was a mechanism of sub-species formation and even new species could arise if populations of the same species became geographically isolated - we call this speciation.

Groups of islands proved an ideal situation for observing 'speciation'.

On a somewhat grander scale, modern research has shown that species of animals in Africa and South America, now separated by the Atlantic Ocean, have common ancestors - the speciation deriving from the geographical separation over millions of years as the American and African continental plates moved apart.

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Key points Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Key ideas from the work of Darwin and Wallace on the theory of evolution of species

Darwin’s Theory of Natural Selection

Charles Darwin’s theory of natural selection explains how species evolve over time due to variations in traits that enhance survival and reproduction.

His ideas, published in On the Origin of Species (1859), fundamentally changed the understanding of life's diversity.

Observations:

1. Variation in Traits – Individuals in a population show differences in characteristics, such as size, color, or behavior.

2. Overproduction – More offspring are produced than can survive due to limited resources.

3. Competition – Individuals compete for food, space, mates, and other necessities.

4. Survival of the Fittest – Some traits give individuals an advantage, making them more likely to survive and reproduce.

Deductions:

• Beneficial traits become more common over generations as individuals with advantageous characteristics pass them on.

• Over time, this leads to adaptation, where a species becomes better suited to its environment.

• If enough changes accumulate, a new species can evolve.

Alfred Russel Wallace’s Evolution Theories

Alfred Russel Wallace independently developed ideas similar to Darwin’s.

He focused particularly on geographical distribution and how environmental pressures influence species.

Wallace’s studies in the Malay Archipelago led him to conclude that species evolve due to natural selection.

Observations:

• Distinct but related species exist in neighboring geographical regions.

• Traits aiding survival in specific environments tend to be more common.

• Certain animals exhibit warning coloration to deter predators.

Deductions:

• Environmental conditions drive evolutionary change.

• The isolation of populations contributes to the formation of new species.

• Natural selection acts as a mechanism for evolution, ensuring species are well-adapted to their surroundings.

Importance in Understanding Evolution

• Darwin and Wallace’s work provided a scientific explanation for the diversity of life.

• Natural selection is the foundation of modern evolutionary biology, influencing genetics, ecology, and conservation efforts.

• Their theories help explain speciation, adaptation, and the evolutionary arms race between predators and prey.

• Evolutionary principles are applied in medicine (e.g., antibiotic resistance) and environmental science (e.g., climate adaptation).

By studying their contributions, scientists today continue to explore how life evolves and how organisms respond to changing environments.

Evolution remains a dynamic field, with genetics and fossil evidence further supporting their ideas. Let me know if you need more details on any aspect!

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Summary of learning objectives and key words or phrases

• Be able to discuss the evolutionary theories and practical field work done by Charles Darwin and Alfred Wallace, and their theories of evolution and scientific evidence for them.

• Know Darwin published a famous book titled "On the origin of species".

• Know and understand that there are different theories of evolution.

• Know that Darwin’s theory of evolution by natural selection is the most widely accepted.

• You are expected to use your skills, knowledge and understanding to:

  • Be able to interpret evidence relating to evolutionary theory.

  • You may be given data to work from.

  • Be able to suggest reasons why Darwin’s theory of natural selection was only gradually accepted.

  • Be able to identify the differences between Darwin’s theory of evolution and conflicting theories, such as that of Lamarck (see Part 2).

  • Be able to suggest reasons for the different theories.

  • Understand that scientists may produce different hypotheses to explain similar observations and it is only when these hypotheses are investigated that data will support or refute hypotheses.

• In the context of evolution theory and genetics, be able to explain the role of the scientific community in validating new evidence, including the use of:

  • a) scientific journals - enable new findings on evolution theory and genetics to be communicated to other scientists working in the same areas of science, so ideas and knowledge are widely spread AND other scientists can check whether the research is valid eg do other scientists get the same results? do other scientists draw the same conclusions? do other scientists agree with, and find the theory valid?

  • b) the peer review process - a sort of refereeing system, research papers on evolution theory and genetics are read and checked by people competent to understand the contents of research papers (their peers) - this ensures standards are high in terms of 'good scientific practice'.

  • c) scientific conferences enable scientists to meet and present and discuss their findings on evolution theory and genetics, compare their work, listen to new ideas, get ideas to take back to their own research project. Its also a forum for other scientists to hear about research which isn't necessarily exactly their own specialist field, but broadens their own knowledge of related fields of science e.g. evolution theory and genetics.

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