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The Genetics of Clan
MacLeod
Julia Abernethy BA (Hons), University College London
First I have to thank all of the volunteers who participated in
the study by giving a sample of their DNA, and Dr Alex McLeod for first bringing
to my attention the history of the clan MacLeod (for brevity I will refer to
both McLeod and MacLeod as MacLeod) and subsequently coordinating sample
collection with myself and the numerous National Societies. DNA collection kits
were sent out to over 500 volunteers, complete results were obtained from over
80% of the returned kits and these results were included in the study. Most of
the remaining samples yielded partial results; whilst these cannot be included
in the study it is still possible to give these volunteers some information
about their genetic type. Given this huge response from the MacLeods, they form
a large part of a study that I conducted at University College London (UCL) with
my Ph.D supervisor Prof D Goldstein to look at the genetics of several
paternally inherited surnames. The research at UCL, along with a similar project
being conducted concurrently at the University of Leicester, was the first large
scale study to look at surnames and genetics. A few smaller studies existed, for
example in Oxford Prof B Sykes carried out research into his surname, but
because this only provided information about one name the results couldn’t be
extrapolated to surnames more generally.
So, what kinds of questions
about the history of the MacLeods can genetics help answer? At a very basic
level it is possible to test whether there has been a common origin for the
clan, then with further analysis we can see how closely related individuals are
within the clan, and potentially identify a geographic location(s) where the
members of the clan came from. The most pervasive theory about the clan’s
origins is that it was founded by Leod, son of Olaf the Black a Norse King and
ruler of the Isle of Man and the Western Isles, although there is disagreement
about whether a link with the Isle of Man can be substantiated. A large caveat
also has to be inserted at this point: although the number of MacLeod DNA
samples I have is very large, it is still a small sample of the total number of
men called MacLeod (I only considered men in this study for reasons discussed
below). Whilst I hope it is a representative sample of all of the male MacLeods
alive today it is possible that if I analysed another batch of different samples
of male MacLeods I would find different genetic results, leading to an
alternative set of conclusions. Thus the results that I will be discussing here
are only true for the sample of MacLeods I have studied, whilst one obviously
extrapolates to all male MacLeods, this caveat, called Sampling Error, must
always be borne in mind.
How can genetics answer these questions? The
first step is to decide what type of test is suitable. As the inheritance of the
MacLeod name behaves in the same way as that of other surnames in our society by
being passed on paternally from father to son – daughters inherit the name but
their children (usually) inherit their father’s surname. The Y chromosome is
also passed on from father to son only. Thus the Y chromosome is a perfect part
of the human genome to study MacLeod history because the inheritance of Y
chromosome genetic types should mimic that of the MacLeod surname, assuming that
the name has been passed on from father to son since the progenitor of the clan
MacLeod. Any lack of a correlation between the inheritance of a specific Y
chromosome type and the name MacLeod could be due to one, or a combination, of
several factors: multiple origins of the MacLeod name; random adoption of the
name; or non paternity. Conveniently we also know a lot about the human Y
chromosome!
We use two types of tests on the Y chromosome both of which
look at part of the chromosome that contains so called junk DNA, DNA that has no
known function. For this reason, difference, or mutations can accumulate
relatively freely because there aren’t any mechanisms to stop them appearing as
the DNA doesn’t code for anything, it doesn’t tell “cell A” that it’s an eye
cell and “cell B” that it’s a brain cell. The first test that we use allows us
to cluster the DNA samples into genealogically related groups, called haplogroups, these are discrete groups of individuals who at some point
in time shared a common ancestor, as recently (in genetic terms at least) as
10,000 years ago, or as far back as 100,000 years ago, when modern human
populations migrated out of Africa. Thus for a collection of DNA samples to be
genetically related they have to fall within the same haplogroup. Some of these
haplogroups have widespread geographical distributions, for example in Europe a
particular haplogroup (“haplogroup 1”) is usually the commonest group found in
most populations, particularly those in the west. Whereas other haplogroups have
more restricted distributions, such as haplogroup 3 which is generally rare in
Europe but relatively common in Scandinavian and central European populations.
The second test allows us to differentiate between DNA samples within
the same genealogical group, by looking at so called haplotypes. Closely
related individuals such as a grandfather, father and son will have exactly the
same haplotype because the short period of time separating them means there
hasn’t been enough time for mutations to accumulate, whereas distantly related
individuals will have very different haplotypes, because a longer period of time
separates them allowing for more mutations to accumulate. Therefore DNA samples
from men with the same surname are expected to fall within the same genealogical
haplogroup and have identical or very closely related genetic types because the
hypothesis is that these men share a recent common ancestor.
The last 5
to 6 years has seen a boom in research focussing on European patterns of Y
chromosome diversity. We know in which populations certain haplogroups and
haplotypes are commonest, which haplogroups are associated with historical
events, such as the spread out of Africa by Anatomically Modern Humans 100,000
years ago (approx), or the apparent Neolithic Expansion westwards by farmers
from Anatolia starting around 10,000 years ago. Prof Goldstein’s team recently
looked at Y chromosome genetic diversity in Britain specifically, and identified
certain haplogroups and haplotypes associated with historical invasions, for
example the Anglo Saxons and Vikings. Thus we know in British populations the
presence of a certain haplotype within haplogroup 3 is indicative of a genetic
influence of the Vikings. With this information we were able to ascertain which
British populations have most evidence for a lasting genetic legacy of these
historical invasions, as well as those populations which appear to be composed
of predominantly “indigenous” Y chromosome types, types which are proposed to
represent the Palaeolithic inhabitants of Europe.
The MacLeod results
are very interesting. Figure 1 shows a pie chart of the haplogroups found in the
MacLeod sample. Each colour on the pie chart relates to a different
haplogroup.
Figure 1 shows a pie chart of the different haplogroups (see text for
definition) found in the MacLeod DNA samples studied here. Each colour refers to
a different Y chromosome haplogroup. Hence the light blue section of the pie
chart refers to the proportion of the MacLeod DNA samples belonging to
haplogroup1, and the red/brown section to the number of MacLeods who belong to
haplogroup 2 etc. There are three other haplogroups just about visible at the
top of the pie chart; their names have not be included because they are so rare
in the collection of MacLeod DNA samples. The first clear finding is that more
than one haplogroup is present, therefore not all of the DNA samples
investigated can be related to the same ancestor.
The first obvious
finding is that more than one haplogroup is present, therefore not all of the
sample can share the same ancestor – some of the samples belong to men who have
acquired the MacLeod surname either because there have been multiple founding
events for the name, random uptake of the name throughout its history, or non
paternity. However 32% of the total sample of MacLeod DNA samples not only
belongs to the same haplogroup (haplogroup 1, the most common haplogroup seen in
the MacLeods as seen in Figure 1) but also has the same or a closely related
haplotype, meaning that these individuals are very closely related. Using two
mathematical models I was able to date how long ago this 32% of the sample
shared a common ancestor – i.e. how many generations back we would have to go to
find the last time two individuals in the sample had the same father and I found
it was around 1000 years ago. This is slightly further back than the founding of
the clan MacLeod posited by clan history, but given that there is always some
statistical uncertainty in the exact dating of such events, and historical
accounts are always subject to some uncertainty, an estimate of ~1000 years ago
is a good match between history and genetics. I also performed a statistical
test to estimate how likely or unlikely it would be to find 32% of the MacLeod
sample sharing this haplotype by chance. The results showed that it was very
unlikely to find such a high percentage of the haplotype in the MacLeods by
chance. These results taken together suggests that this high frequency haplotype
shared by 32% of the MacLeod sample represents the clan MacLeod founding lineage
- the lineage that was created by the original progenitor of the clan and which
has subsequently been inherited by a fair proportion of future generations.
Figure 2 shows a pie chart of this high frequency haplotype in relation to all
other haplotypes.
 
Figure 2 shows a breakdown of the haplotypes (see text for definition) in
the DNA samples studied here. The section of the pie chart in blue refers to all
of the individuals who share the same high frequency haplotype hypothesised to
be the MacLeod founding lineage. This comprises 32% of all the haplotypes
encountered. The grey section refers to all other haplotypes found in the
MacLeod DNA samples.
The next step in the analysis was to identify
where else in Britain and several European populations (Norway, Denmark,
Germany, and Basques) this exact haplotype is found. Any population(s) where
this type was found at a particularly high frequency are statistically more
likely to be “source” populations for the MacLeod lineage – population(s) where
the progenitor probably came from. Despite being quite common in several
Scottish populations (Shetland, Western Isles and Stonehaven), the haplotype is
not at a particularly high frequency in any one population, including the
European populations, although it is quite common in several Scottish
populations, making it very difficult to identify where the clan progenitor
originated from. This does not exclude the chance that the clan progenitor was
of Norse descent, it simply reduces the probability that this is the case.
However, I also statistically examined the similarity between the whole of the
MacLeod sample and the British and European populations. Intriguingly this
showed that statistically, the male MacLeod sample is indistinguishable from two
Scottish populations, Shetland and Oban, and the Isle of Man, confirming the
strong tie Clan MacLeod has with Scotland and the Isle of Man. Indeed it
suggests that the present day collection of MacLeod Y chromosomes has been
formed by men that originated in Scotland or the Isle of Man.
Conclusions
The research into Clan MacLeod genetics has shown that there is good evidence
for the Clan predominantly sharing the same common ancestor around 1000 years
ago. Unfortunately it is difficult to identify the geographical origin of this
male progenitor by simply looking at the frequencies of the genetic type in
other populations. However the statistical similarity between the MacLeod sample
and Shetland, Oban and the Isle of Man is strong evidence for the Clan as a
whole having its origins in Scotland or the Isle of Man. But it is important to
remember that the DNA samples used in this study may not be a
representative sample of the male Clan members, although we hope it is. Also,
even if the sample we have today is representative of male Clan members today,
it may not fairly represent the genetic makeup of the Clan 100 years ago, or 200
years ago, and so on. For example, the last several hundred years since the clan
is thought to have been founded may have seen a large number of males randomly
choosing to adopt the MacLeod surname. These men would likely introduce new and
different Y chromosomes into the MacLeod gene pool, reducing the proportion of
male MacLeods who are descended from the original progenitor. Nonetheless, the
results are extremely interesting given the correlation they show with history.
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