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As is common knowledge, the founder (more-or-less) of modern genetics was Gregor Mendel, who first laid down the laws of Mendelian inheritance. In particular, he discovered the existence of dominant and recessive traits in pea plants, and the re-discovery of his discovery set into motion the modern field.

My question is this: how much was known about human heredity before Mendelian inheritance was discovered? I imagine human beings would have always noticed that children end up looking like their parents. But would they have known the nitty-gritty of it, for example, that black hair was more likely to be passed on to children (a la Game of Thrones), or that two people with cleft chins can still have a cleftless kid? Did any of the ancients or later scientists ever tackle the subject in a significant way?

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    Farmers and Herdsman had been using directed breeding for millennia prior to Mendel. – Oldcat Sep 8 '14 at 19:35
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    Mendel did not study human heredity, he studied plants. This is a question about the evolution of science, not history (human events). You can read the book "Heredity Descent" by Orson Squire Fowler to get a good idea of what constituted scientific genetics before Huge de Vries. de Vries, by the way, is the key figure in knowledge of genetics. Mendel was completely ignored in his own time, so his "discoveries" had no effect on the society. It was only after de Vries published his theories in 1900 that Mendelian inheritance started to be widely understood. – Tyler Durden Sep 8 '14 at 19:39
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    Reading between the lines of the traditional terminology, that "some traits breed true and others skip a generation", it would seem that breeders have known for a long time to not abandon first generation offspring without the desired trait. However, I think that phrase also sums up the complete understanding prior to the recognition of Mendeleev's work. – Pieter Geerkens Sep 8 '14 at 22:40
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    @PieterGeerkens +1 to your comment! However i feel obliged to tell you that Mendel is not short for Mendeleev...that was the chemistry guy. – Matthaeus Sep 10 '14 at 10:59
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    @Matthaeus: Oops! Braun fart there by me; I do know better. – Pieter Geerkens Sep 10 '14 at 22:02
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Of course nothing was known specifically about genes, or anything smaller than what people could see (except for some philosophical theories...anatomists etc.).

But mankind made a lot of conscious usage of heredity, especially in selective plant breeding and animal husbandry. Note that most of the grains (wheat, rice...but originally not much more than grass) were hardly digestible before they were bred to be so. Many fruits, like all the different rosaceae (apples, pears...) weren't very tasty, nutritious, big or resistant before mankind saw potential in them; in the latter case we're even talking about the time after the last ice age, so quite recently (but there are theories that neanderthal had some early forms of agriculture).

Heredity in animals and humans however, is intuitively known since "forever". That mating with healthy individuals is more likely to produce healthy offspring is at the very center of evolution - and knowing about genetic diseases, or at least the concept thereof, immediately follows. A good indicator for this is how much importance pre-modern societies placed on the concept of "blood". Blood was just their way of saying genetics. They knew traits were inherited by the offspring, they just didn't know the mechanics. Also they didn't know exactly which traits were inherited and which not - but then again, neither Mendel did. Farmers and Herders had good eyes for that though.

I'm aware I'm not citing any sources and I'm not saying there aren't, but sometimes it is difficult to say how much people know once, especially in times where the only means of knowledge inheritance was through oral tradition. One might speculate, that in certain areas of botanics they might have even known things we don't know, especially about healing properties of plants and such.

  • I doubt that farmers understood heredity much. Consider the biblical story of Jacob breeding white and black goats to get striped goats. – Michael Sep 9 '14 at 18:08
  • It worked, though. – Oldcat Sep 9 '14 at 18:51
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    @Michael : As I said, they didn't know the specifics, but neither do we fully grasp them. We haven't decoded every genome, we don't know the function of every allele, afaik we don't even know with 100% accuracy which genes will be inherited or which expressed. In any case, just look at the difference between maize and zea. Mesoamerican civilization (meaning Mayas...long before the Europeans came and way before mendel) selectively bred zea to maize and the result (and even the long way to it) is astounding. – Matthaeus Sep 9 '14 at 22:20
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Question:
My question is this: how much was known about human heredity before Mendelian inheritance was discovered? I imagine human beings would have always noticed that children end up looking like their parents.

Heredity was well known term in the Scientific Community when Mendel published his work, but was not understood.

When Gregor Mendel published his work "Experiments on Plant Hybridization" in 1866, it was seven years after Charles Darwin published "Origin of the Species" which predicted and depended on the inheritance of traits in animals.

Darwin's hypothesized on the existence of a mechanism of heredity. Darwin supported his theory / conclusions on volumes of skeletal and fossil records; but he did not have live experiments or a good Biological model for what he called gemmules. He was thus theorizing on the process which Mendel was modeling.

Pangenesis
Pangenesis was Charles Darwin's hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its own type of small organic particles called gemmules that aggregated in the gonads, contributing heritable information to the gametes.

At the time nobody recognized Mendel's study on plant hybridization was related to Darwin's work on inheritance of traits in animals. Mendel's work went largely ignored for the next 30 years after he was published. Charles Darwin who was called to defend his Theory of Evolution almost immediately was entirely unaware of Mendel's supporting work.

Gregor Mendel: Initial reception of Mendel's work
Notably, Charles Darwin was not aware of Mendel's paper, and it is envisaged that if he had been aware of it, genetics as it exists now might have taken hold much earlier. Mendel's scientific biography thus provides an example of the failure of obscure, highly original innovators to receive the attention they deserve.

Mendel made two initial conclusions from his work:

  • The Law of Independent Assortment states the building blocks (allels) for separate traits are inherited independently from other traits.

  • The Law of Segregation states that two heterozygous parents(Yy) offspring inherit a given trait in a pattern supported by dominant-recessive expression 1:2:1. where 1 part expresses homozygous dominant (YY), 2 parts express heterozygous (Yy), and the last part is homozygous recessive (yy).

                            Y     y        <- Parent #1
                        |-------------
                     Y  |   YY    Yy
                     y  |   Yy    yy
                     ^ 
                     |   Parent #2
    

Two Genetic Laws which while discovered observing plants pertained to animals.
Gregor Mendel is known as the father of Modern Genetics for his work.

Darwin's work in Origin of the Species was predicated on the inheritance of traits across generations but it lacked a biological model for that inheritance provided by Mendel. Thus Mendel's model of inheritance in plants supports and complements Darwin's work. As did Thomas Morgan who expanded Mendel's genetic studies but in animals (Drosophila melanogaster) fruit flies. Also James Watson and Francis Crick's which discovered DNA in the 1950s. The physical mechanism which Darwin hypothesized, and which Mendel first studied nearly 100 years earlier.

Sources:

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Basically people thought that all the traits of your mum and dad would get mixed up in a genetic blender ( to put it simply). Eg, if a black squirrel and a white squirrel had a baby squirrel that baby would be a grey squirrel.

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They thought that traits like paint would mix together like someone mixing 2 paints in a new bucket

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