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So, we’re supposed to teach our students about evolution – but where to start? What topics to cover? And in what order should we cover them? And for each topic, what are the relevant learning standards? This sequence works for me:
Examples of evolution
Animals probably evolved from marine protists, although no group of protists has been identified from an at-best sketchy fossil record for early animals.
Cells in primitive animals (sponges in particular) show similarities to collared choanoflagellates as well as pseudopod-producing amoeboid cells.
Multicellular animal fossils and burrows (presumably made by multicellular animals) first appear nearly 700 million years ago, during the late precambrian time….
All known Vendian animal fossils had soft body parts: no shells or hard (and hence preservable as fossils) parts.
Animals in numerous phyla appear at (or in many cases before) the beginning of the Cambrian Period ( 540 million years ago)
Nicole King explains “All animals, from sponges to jellyfish to vertebrates [animals with a backbone], can be traced to a common ancestor. So far, molecular and fossil evidence indicate that animals evolved at least 600 million years ago. The fossil record does not reveal what the first animals looked like or how they lived. Therefore, my lab and other research groups around the world are investigating the nature of the first animals by studying diverse living organisms….. Choanoflagellates are a window on early animal evolution. Both cell biological and molecular evidence indicate that choanoflagellates are the closest living relatives of multicellular animals.
Between 620 and 550 million years ago (during the Vendian Period) relatively large, complex, soft-bodied multicellular animals appear in the fossil record for the first time. While found in several localities around the world, this particular group of animals is generally known as the Ediacaran fauna, after the site in Australia where they were first discovered.
The Ediacaran animals are puzzling in that there is little or no evidence of any skeletal hard parts i.e. they were soft-bodied organisms, and while some of them may have belonged to groups that survive today others don’t seem to bear any relationship to animals we know. Although many of the Ediacaran organisms have been compared to modern-day jellyfish or worms, they have also been described as resembling a mattress, with tough outer walls around fluid-filled internal cavities – rather like a sponge.
A new study mapping the evolutionary history of animals indicates that Earth’s first animal–a mysterious creature whose characteristics can only be inferred from fossils and studies of living animals–was probably significantly more complex than previously believed… the comb jelly split off from other animals and diverged onto its own evolutionary path before the sponge. This finding challenges the traditional view of the base of the tree of life, which honored the lowly sponge as the earliest diverging animal. “This was a complete shocker,” says Dunn. “So shocking that we initially thought something had gone very wrong.”
But even after Dunn’s team checked and rechecked their results and added more data to their study, their results still suggested that the comb jelly, which has tissues and a nervous system, split off from other animals before the tissue-less, nerve-less sponge.
The presence of the relatively complex comb jelly at the base of the tree of life suggests that the first animal was probably more complex than previously believed, says Dunn.
Is this possible? for this to be true, it would seem that complex structures – neurons – have evolved twice! Independently? See here for more amazing details:
Which came first, the chicken or the egg?
At first glance, this seems like a reasonable question. But most questions have hidden assumptions, and this question has tons of them. And as it turns out, most of the assumptions are incorrect – meaning that the question – as it is usually asked or understood – is actually meaningless.
The question assumes that (a) chickens and eggs have existed continuously, without change, for a long period of time (b) that chickens (vaguely defined!) lay eggs (also vaguely defined!), and (c) that eggs hatch into chickens.
Problem? None of these assumptions are true. They only appear to be true because people only look at chickens and eggs over a very short period of time (perhaps weeks, a year, or when reading books, thinking back over the last 5000 years.)
But birds and their ancestors have been continuously changing for millions of years – and so has the way that their ancestors reproduced. The first chickens… may not even have been chickens, but rather some other form of bird that no longer exists. And those earlier birds are descendants of a branch of the dinosaur family tree; and those early dinosaurs are a branch of the reptile family tree. And over very long, deep periods of time, the way that these organisms reproduced has actually changed!
In fact, the first eggs developed millions of years before anything we even know as birds existed.
Genetic variation, classification and ‘race’
Lynn B Jorde & Stephen P Wooding
Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, Utah 84112, USA
Nature Genetics 36, S28 – S33 (2004) Published online: ; | doi:10.1038/ng1435
New genetic data has enabled scientists to re-examine the relationship between human genetic variation and ‘race’. We review the results of genetic analyses that show that human genetic variation is geographically structured, in accord with historical patterns of gene flow and genetic drift. Analysis of many loci now yields reasonably accurate estimates of genetic similarity among individuals, rather than populations. Clustering of individuals is correlated with geographic origin or ancestry. These clusters are also correlated with some traditional concepts of race, but the correlations are imperfect because genetic variation tends to be distributed in a continuous, overlapping fashion among populations. Therefore, ancestry, or even race, may in some cases prove useful in the biomedical setting, but direct assessment of disease-related genetic variation will ultimately yield more accurate and beneficial information.
Figure 1: A neighbor-joining network of population similarities, based on the frequencies of 100 Alu insertion polymorphisms.
The network is rooted using a hypothetical ancestral group that lacks the Alu insertions at each locus. Bootstrap values are shown (as percentages) for main internal branches. (Because of the relatively small sample sizes of some individual populations, bootstrap values for terminal branches within main groups are usually smaller than those of the main branches, indicating less statistical support for terminal branches.) The population groups and their sample sizes are as follows: Africans (152): Alur, 12; Biaka Pygmy, 5; Hema, 18; Coriell Mbuti Pygmy, 5; a second sample of Mbuti Pygmy from the Democratic Republic of the Congo, 33; Nande, 17; Nguni, 14; Sotho/Tswana, 22; Kung (San), 15; Tsonga, 14. East Asians (61): Cambodian, 12; Chinese, 17; Japanese, 17; Malay, 6; Vietnamese, 9. Europeans (118): northern Europeans, 68; French, 20; Poles, 10; Finns, 20. South Indians (365): upper caste Brahmin, Kshatriya and Vysya, 81; middle caste Kapu and Yadava, 111; lower caste Relli, Mala and Madiga, 74; tribal Irula, Khonda Dora, Maria Gond and Santal, 99.
A neighbor-joining tree of individual similarities, based on 60 STR polymorphisms, 100 Alu insertion polymorphisms, and 30 restriction site polymorphisms. The percentage of shared alleles was calculated for all possible pairs of individuals, and a neighbor-joining tree was formulated using the PHYLIP software package. African individuals are shown in blue, European individuals in green and Asian individuals in orange.
(a) Results of applying the structure program to 100 Alu insertion polymorphisms typed in 107 sub-Saharan Africans, 67 East Asians and 81 Europeans. Individuals are shown as dots in the diagram. Three clusters appear in this diagram; a cluster membership posterior probability of 100% would place an individual at an extreme corner of the diagram.
(b) A second application of the structure program, using the individuals shown in a as well as 263 members of caste populations from South India. Adapted from ref. 32.
A neighbor-joining tree formulated using the same methods as in Figure 2, based on polymorphisms in the 14.4-kb gene AGT.
A total of 246 sequence variants, including 100 singletons, were observed. The 368 European, Asian and African individuals are described further in ref. 54.
Author’s conclusion: “Race remains an inflammatory issue, both socially and scientifically. Fortunately, modern human genetics can deliver the salutary message that human populations share most of their genetic variation and that there is no scientific support for the concept that human populations are discrete, nonoverlapping entities. Furthermore, by offering the means to assess disease-related variation at the individual level, new genetic technologies may eventually render race largely irrelevant in the clinical setting. Thus, genetics can and should be an important tool in helping to both illuminate and defuse the race issue.”
Note by RK ” there is no scientific support for the concept that human populations are discrete, nonoverlapping entities.” – Outside of racist groups, no one, let alone scientists, make such a claim. This article does not debunk the idea that biological groups/races/clades for humans exists: It clearly proves that such groups exists, and shows it in precise detail. However, this data can also debunk racial claims made from people using non-scientific definitions of the word “race”.
When scientists use words like “race”, “populations” or “clades”, these words have precise meanings. Every discovery in biology and evolution over the last 200 years has clearly shown that the basic concept of biological groups has to exist. All forms of life have family trees that develop in ways that can be represented by cladograms, and those cladograms show evolutionary phylogenies.
“A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. Using a phylogeny, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny — all of the organisms on that pruned branch make up a clade.”
Evolution of cereals and grasses
Paper 1: “Wheat: The Big Picture”, The Bristol Wheat Genomics site, School of Biological Sciences, University of Bristol
Figure 2. Phylogenetic tree showing the evolutionary relationship between some of the major cereal grasses. Brachypodium is a small grass species that is often used in genetic studies because of its small and relatively simple genome.
Paper 2: Increased understanding of the cereal phytase complement for better mineral bio-availability and resource management
Article (PDF Available) in Journal of Cereal Science 59(3) · January 2013 with 244 Reads
Fig. 1. Phylogenetic tree of cereals and selected grasses. PAPhy gene copy numbers are given for each species and key evolutionary events are indicated.
Genome-wide characterization of the biggest grass, bamboo, based on 10,608 putative full-length cDNA sequences.
Peng Z, Lu T, Li L, Liu X, Gao Z, Hu T, Yang X, Feng Q, Guan J, Weng Q, Fan D, Zhu C, Lu Y, Han B, Jiang Z – BMC Plant Biol. (2010)
Figure 2: Phylogeny of grasses inferred from concatenated alignment of 43 putative orthologous cDNA sequences. (A) Tree inferred from maximal likelihood method. Bayes inference yielded the same topology. (B) Tree inferred from neighbor joining method. Branch length is proportional to estimated sequence divergence measured by scale bars. Numbers associated with branches are bootstrap percentages. Arabidopsis was used as outgroup. Subfamily affiliation of the grasses is indicated at right.
Paper 3 Evolution of corn
Figure 1: The evolutionary stages of domestication and diversification.
Evolution of crop species: genetics of domestication and diversification
Rachel S. Meyer & Michael D. Purugganan
Nature Reviews Genetics 14, 840–852 (2013) doi:10.1038/nrg3605
Paper 4 text
Brachypodium distachyon: making hay with a wild grass
Magdalena Opanowicz, Philippe Vain, John Draper, David Parker, John H. DoonanEmail the author John H. Doonan
By Sarah Kaplan
The current diversity of feathers, fur and scales is part of what made their origins so mystifying to scientists. There are almost no known intermediate forms to illustrate how they might be related to one another. That’s largely because the features are so fragile — while bone and teeth can be preserved as fossils, delicate skin appendages are usually lost to time. In the absence of physical evidence from the past, scientists try to interpret the present, for instance by studying developing embryos, for clues to how traits evolved.
Early on in embryonic development, feathers and fur look startlingly similar — both begin as tiny, thick accumulations of cells on the skin known as anatomical placodes. This shared morphology indicates that the features have the same evolutionary roots, which would seem to make sense, since birds and mammals evolved from a common ancestor some 320 million years ago.
But that ancestor was also the predecessor of modern reptiles; in fact, reptiles and birds are far more closely related than birds and mammals. Yet reptile scales develop very differently than feathers and fur — or they seemed to, at any rate. Not a lot of scientists study reptile embryos, Milinkovitch noted (“model species” like fruit flies and mice tend to get most of the attention), but those who did generally couldn’t find evidence of anatomical placodes.
The placodes — dark blue spots corresponding to groups of cells expressing a specific early developmental gene — are visible on the embryonic skin of (from left to right) a mouse, a snake, a chicken and a Nile crocodile. Each of these placodes will develop into a hair, scale, or a feather. (UNIGE 2016 Tzika, Di-Poï, Milinkovitch)
That left with biologists with two possible explanations, Milinkovitch noted, neither of which was particularly satisfying.
“Either the placode was ancestral for everyone and then it was lost multiple times in independent lineages of reptile … or birds and mammals invented placodes independently,” he said. The second possibility seemed particularly unlikely because research had revealed that the same exact gene, called EDA, controlled placode development in both groups.
That’s where things stood when Di-Poï began parsing the genome of the naked bearded dragon his adviser had brought back to the lab. He pinpointed the mutation that prevented scales from developing, only to discover that it was EDA — the same gene responsible for feathers and fur.
That prompted the duo to take a closer look at the embryos of normal bearded dragons during development. They realized that the tiny creatures did have anatomical placodes, they just appeared and dispersed differently than the versions biologists are accustomed to seeing in mammals and birds.
“You have to look at the right places at the right time otherwise you don’t see them,” Milinkovitch said. “Now of course, once you know this it’s much easier to to find them because you know where to look and when to look, but before people didn’t know and they overlooked them.”
Eventually, he and Di-Poï identified placodes in several species of snake, lizard and crocodile.
“They obviously inherited this from a common ancestor,” Milinkovitch said.
“That makes sense, ecologically speaking, when you think about, ‘what is the innovation of amniotes?'” he continued, using the term to describe creatures like reptiles, birds and mammals, whose fetuses develop in membrane-bound amniotic sac that allows their mothers to lay fertilized eggs on land (or nurture them inside the uterus, as most mammals do).
Unlike amphibians and lobe-finned fish, amniotes aren’t anchored to water by the need to lay their eggs there. That meant it was worth investing in adaptations that allowed us to live entirely terrestrial lives, like skin or scales that keep us from drying out. Hundreds of millions of years after reptiles, birds, and mammals diverged from this original amniote, we united by the outcomes of this innovation.
“They are extremely different morphologically, but if you look past that you can see the homology,” Milinkovitch said. “That’s the beauty of it.”
…your body is a museum, full of ancient relics that no one really needs anymore. From your wisdom teeth to that weird way some of us can wiggle our ears, so much of how we ended up as humans reflects what our animal ancestors needed for survival. As this video by Vox explains, these strange remnants, that stuck around only because they’re not ‘costly’ enough to have disappeared across many millennia, only make sense within the framework of evolution by natural selection.