How do scientists know that evolution is true?

Answer 1

The word 'evolution' can be used to indicate two things:

• The phenomenon of evolution, ie. the changing of allele frequencies in population gene pools (or, as Darwin originally put it, descent with modification).
• The theory of evolution, ie. the model that explains the diversity of life in terms of what we know about evolution, population genetics, and so on.

We know the phenomenon of evolution exists because we can see it happening.

As for the theory, there the evidence consists of a multitude of independent lines of observation, all pointing in the same direction:

• That modern lifeforms stem from a shared ancestry.
• That an important guiding force of evolution is natural selection.

Common ancestry is demonstrated true by the nested hierarchies we find everywhere in life: in morphology, in genetics, in molecular Biology, in embryology, in behavioural studies, etc. Basically, these observations show us that every group of organisms inherited its characteristics from a larger, more basal group, with a few unique changed added. This pattern is exactly what we would expect to find if common descent were true. Specific predictions can be made based on the general pattern, which can then be tested against detailed observations. Common ancestry is also demonstrated by the fossils we find: these show a progressing divergence of forms, starting out from the most basal forms, and then diverging towards more modern forms. The fossil record also provides numerous transitional forms, that are representative of intermediaries between basal forms and more modern forms.

Natural selection is observed in nature, and can be readily tested in the lab. Not only do we see natural selection acting upon populations now, but we can also make predictions about what we should find in the genomes of various organisms if natural selection had acted upon certain traits in the past - and then test those predictions against the actual genomes.

So that's how we know evolution is true.

Answer 2

Scientists know that evolution is true through a combination of evidence from observations of the natural world, fossil records, genetic data, and experimentation. The interconnectedness of life forms, similarities in DNA across species, and the presence of transitional fossils provide support for the theory of evolution. Additionally, experiments in genetics and natural selection have consistently demonstrated the mechanisms by which evolution occurs.