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From soup to cells: The origin of life. Origins and biochemical evidence. By studying the basic biochemistry shared by many organisms, we can begin to piece together how biochemical systems evolved near the root of the tree of life.
- Overview
- Key points:
- Introduction
- Evidence for evolution: Tracing evolutionary histories
- Evidence for evolution: Anatomy and embryology
- Homologous features
- Analogous features
- Determining relationships from similar features
- Evidence for evolution: Molecular biology
- Homologous genes
The theory of evolution is supported by instances of direct observation, the existence of homologies and fossils, and certain biogeographical patterns.
•Evidence for large-scale evolution (macroevolution) comes from anatomy and embryology, molecular biology, biogeography, and fossils.
•Similar anatomy found in different species may be homologous (shared due to ancestry) or analogous (shared due to similar selective pressures).
•Molecular similarities provide evidence for the shared ancestry of life. DNA sequence comparisons can show how different species are related.
•Biogeography, the study of the geographical distribution of organisms, provides information about how and when species may have evolved.
•Fossils provide evidence of long-term evolutionary changes, documenting the past existence of species that are now extinct.
•Evidence for large-scale evolution (macroevolution) comes from anatomy and embryology, molecular biology, biogeography, and fossils.
•Similar anatomy found in different species may be homologous (shared due to ancestry) or analogous (shared due to similar selective pressures).
•Molecular similarities provide evidence for the shared ancestry of life. DNA sequence comparisons can show how different species are related.
•Biogeography, the study of the geographical distribution of organisms, provides information about how and when species may have evolved.
We can sometimes directly see small-scale evolution, or microevolution, taking place (for example, in the case of drug-resistant bacteria or pesticide-resistant insects). However, many of the most fascinating evolutionary events – such as the divergence, or splitting, of plant and animal lineages from a common ancestor – happened far in the past. Not only that, but they occurred over very long time periods, not on the days-to-weeks timescales of bacterial and viral evolution. This large-scale evolution is sometimes called macroevolution.
[What is evolution?]
In this article, we'll look at several types of information biologists use to trace and reconstruct evolutionary histories of organisms across long timescales.
•Anatomy and embryology. Anatomical features shared between organisms (including ones that are visible only during embryonic development) can indicate a shared evolutionary ancestry.
•Molecular biology. Similarities and differences between the "same" gene in different organisms (that is, a pair of homologous genes) can help us determine how closely related the organisms are.
•Biogeography. The geographical distribution of species can help us reconstruct their evolutionary histories.
•Fossils. The fossil record is not a complete record of evolutionary history, but it confirms the existence of now-extinct species and sometimes captures potential "in-between" forms on the path to present-day species.
Let's take a closer look at these strategies for reconstructing evolutionary histories over long time periods.
Darwin thought of evolution as "descent with modification," a process in which species change and give rise to new species over many generations. He proposed that the evolutionary history of life forms a branching tree with many levels, in which all species can be traced back to an ancient common ancestor.
In this tree model, more closely related groups of species have more recent common ancestors, and each group will tend to share features that were present in its last common ancestor. We can use this idea to "work backwards" and figure out how organisms are related based on their shared features.
If two or more species share a unique physical feature, such as a complex bone structure or a body plan, they may all have inherited this feature from a common ancestor. Physical features shared due to evolutionary history (a common ancestor) are said to be homologous.
To give one classic example, the forelimbs of whales, humans, and birds look quite different on the outside. That's because they're adapted to function in different environments. However, if you look at the bone structure of the forelimbs, you'll find that the organization of the bones is remarkably similar across species. It's unlikely that such similar structures would have evolved independently in each species, and more likely that the basic layout of bones was already present in a common ancestor of whales, humans, and birds.
Some homologous structures can be seen only in embryos. For instance, did you know that you once had a tail and gill slits? All vertebrate embryos, from humans to chickens to fish, share these features during early development. Of course, the developmental patterns of these species become increasingly different later on (which is why your embryonic tail is now your tailbone, and your gill slits have turned into your jaw and inner ear)1 . However, the shared embryonic features are still homologous structures, and they reflect that the developmental patterns of vertebrates are variations on an ancestral program.
Vestigial structures are reduced or non-functional versions of features, ones that serve little or no present purpose for an organism. The human tail, which is reduced to the tailbone during development, is one example. Vestigial structures are homologous to useful structures found in other organisms, and they can provide insights an organism's ancestry. For instance, the tiny vestigial legs found in some snakes, like the boa constrictor at right, reflect that snakes had a four-legged ancestor2 .
To make things a little more interesting and complicated, not all physical features that look alike are marks of common ancestry. Instead, some physical similarities are analogous: they evolved independently in different organisms because the organisms lived in similar environments or experienced similar selective pressures. This process is called convergent evolution. (To converge means to come together, like two lines meeting at a point.)
For example, two distantly related species that live in the Arctic, the arctic fox and the ptarmigan (a bird), both undergo seasonal changes of color from dark to snowy white. This shared feature doesn’t reflect common ancestry – i.e., it's unlikely that the last common ancestor of the fox and ptarmigan changed color with the seasons. Instead, this feature was favored separately in both species due to similar selective pressures. That is, the genetically determined ability to switch to light coloration in winter helped both foxes and ptarmigans survive and reproduce in a place with snowy winters and sharp-eyed predators.
In general, biologists don't draw conclusions about how species are related on the basis of any single feature they think is homologous. Instead, they study a large collection of features (often, both physical features and DNA sequences) and draw conclusions about relatedness based on these features as a group. We will explore this idea further whe...
Like structural homologies, similarities between biological molecules can reflect shared evolutionary ancestry. At the most basic level, all living organisms share:
•The same genetic material (DNA)
•The same, or highly similar, genetic codes
•The same basic process of gene expression (transcription and translation)
These shared features suggest that all living things are descended from a common ancestor, and that this ancestor had DNA as its genetic material, used the genetic code, and expressed its genes by transcription and translation. Present-day organisms all share these features because they were "inherited" from the ancestor (and because any big changes in this basic machinery would have broken the basic functionality of cells).
Although they're great for establishing the common origins of life, features like having DNA or carrying out transcription and translation are not so useful for figuring out how related particular organisms are. If we want to determine which organisms in a group are most closely related, we need to use different types of molecular features, such as the nucleotide sequences of genes.
Biologists often compare the sequences of related genes found in different species (often called homologous or orthologous genes) to figure out how those species are evolutionarily related to one another.
The basic idea behind this approach is that two species have the "same" gene because they inherited it from a common ancestor. For instance, humans, cows, chickens, and chimpanzees all have a gene that encodes the hormone insulin, because this gene was already present in their last common ancestor.
Ø Biochemical Evolution: The formation of complex organic molecules from simpler inorganic molecules through chemical reactions in the oceans during the early history of the Earth. Ø Biochemical evolution was the first step in the development of life on earth.
biochemical evolution (molecular evolution) The changes that occur at the molecular level in organisms over a period of time. These range from deletions, additions, or substitutions of single nucleotides, through the rearrangement of parts of genes, to the duplication of entire genes or even whole genomes.
Here we articulate the paradigm of evolutionary biochemistry, which aims to dissect the physical mechanisms and evolutionary processes by which biological molecules diversified and to reveal how their physical architecture facilitates and constrains their evolution.
- Michael J. Harms, Joseph W. Thornton, Joseph W. Thornton
- 10.1038/nrg3540
- 2013
- 2013/08
Feb 2, 2021 · 1. Understanding how individual chemical reactions concatenate to expand reaction networks. To understand the transition from prebiotic chemistry to biochemistry, it is important to first...
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Apr 26, 2017 · Introduction. About a century and a half ago, in his book On the Origin of Species, Charles R. Darwin proposed natural selection (NS) as the main driving force that guides the evolution of species, conceived as a process of descent with modification from a common ancestor.
