Number Of Ancestors In A Given Generation

GENERATIONS BACK		NUMBER OF INDIVIDUALS			Single Ancestor's DNA Contribution	BIRTH
		Each Generation (x)		Cumulative
Name of Generation	n​	Decimal​	Binary	Decimal​	Percent​	Year​
self	0​	1​	1	1​		1950​
parents	1​	2​	2	3​	50.00	1920​
grandparents	2​	4​	4	7​	25.00	1890​
great-grandparents	3​	8​	8	15​	12.50	1860​
2nd great-grandparents	4​	16​	16	31​	6.25	1830​
3rd great-grandparents	5​	32​	32	63​	3.125	1800​
4th great-grandparents	6​	64​	64	127​	1.5625	1770​
5th great-grandparents	7​	128​	128	255​	0.78125	1740​
6th great-grandparents	8​	256​	256	511​	0.390625	1710​
7th great-grandparents	9​	512​	512	1023​	0.1953125	1680​
8th great-grandparents	10​	1024​	1K	2047​	0.09765625	1650​
9th great-grandparents	11​	2048​	2K	4095​	Need I go on?​	1620​
10th great-grandparents	12​	4096​	4K	8191​		1590​
11th great-grandparents	13​	8192​	8K	16,383​		1560​
12th great-grandparents	14​	16,384​	16K	32,767​		1530​
13th great-grandparents	15​	32,768​	32K	65,535​		1500​
14th great-grandparents	16​	65,536​	64K	131,071​		1470​
15th great-grandparents	17​	131,072​	128K	262,143​		1440​
16th great-grandparents	18​	262,144​	256K	524,287​		1410​
17th great-grandparents	19​	524,288​	512K	1,048,575​		1380​
18th great-grandparents	20​	1,048,576​	1M	2,097,151​		1350​
19th great-grandparents	21​	2,097,152​	2M	4,194,303​		1320​
20th great-grandparents	22​	4,194,304​	4M	8,388,607​		1290​
21st great-grandparents	23​	8,388,608​	8M	16,777,215​		1260​
22nd great-grandparents	24​	16,777,216​	16M	33,554,431​		1230​
23rd great-grandparents	25​	33,554,432​	32M	67,108,863​		1200​
24th great-grandparents	26​	67,108,864​	64M	134,217,727​		1170​
25th great-grandparents	27​	134,217,728​	128M	268,435,455​		1140​
26th great-grandparents	28​	268,435,456​	256M	536,870,911​		1110​
27th great-grandparents	29​	536,870,912​	512M	1,073,741,823​		1080​
28th great-grandparents	30​	1,073,741,824​	1G	2,147,483,647​		1050​
29th great-grandparents	31​	2,147,483,648​	2G	4,294,967,295​		1020​
30th great-grandparents	32​	4,294,967,296​	4G	8,589,934,591​		990​
31st great-grandparents	33​	8,589,934,592​	8G	17,179,869,183​		960​
32nd great-grandparents	34​	17,179,869,184​	16G	34,359,738,367​		930​
33rd great-grandparents	35​	34,359,738,368​	32G	68,719,476,735​		900​
34th great-grandparents	36​	68,719,476,736​	64G	137,438,953,471​		870​
35th great-grandparents	37​	137,438,953,472​	128G	274,877,906,943​		840​
36th great-grandparents	38​	274,877,906,944​	256G	549,755,813,887​		810​
37th great-grandparents	39​	549,755,813,888​	512G	1,099,511,627,775​		780​
38th great-grandparents	40​	1,099,511,627,776​	1T	2,199,023,255,551​		750​

 

Number of Ancestors in a Given Generation Back (dgmweb.net)
http://dgmweb.net/Ancillary/OnE/NumberAncestors.html

Number of Ancestors in a Given Generation

The formula for the number of ancestors in a given generation is:

2n = x

where n is the number of generations back
and x equals the number of individuals in that generation.




Number of Ancestors in a Given Generation Back (dgmweb.net)
http://dgmweb.net/Ancillary/OnE/NumberAncestors.html

 

Based on the table below, if you go back 40 generations, you have over two trillion ancestors!

Of course, this number doesn't mean you have that many unique ancestors in 40 generations.

What is happening is repetition of ancestors, that is, the same ancestors appearing over and over again in a pedigree.

Repetition seldom appears within the first ten generations, but the further back you go, the more repetition you are likely to find.

As an example of repetition of ancestors, there is a famous pedigree that begins having significant repetition within the first few generations: that of outlaw, Jesse JAMES.

There is even more pronounced repetition in his wife's pedigree, so the repetition is further compounded for their children:


Pedigrees of Jesse Woodson JAMES & Zerelda Cole MIMS

When repetition happens in the near generations, we call it "inbreeding."

It happens so often among southerners, like Jesse & Zerelda, that it's become a cultural cliché, as in the movie, Deliverance.


For those of you being autosomal-DNA tested (e.g., FTDNA's FamilyFinder test, 23andMe,
and the Ancestry-DNA test), an examination of this table makes it very clear why At-DNA is most useful
within five generations, with it's use diminishing rapidly with each additional generation.

Even at five generations, you are likely to have only 3.125% of each ancestor's genes,
and by seven generation, you are likely to have less than one percent.

This is the reason my genealogical goal is not to go deeply into my ancestry
— though I inadvertently have on some lines
— my goal is to get all lines back eight generations.

I'll know more about myself that way, than I do by the fact that I've bumped into a connection to Charlemagne (la de dah).

The greatly diminishing percentage of one ancestor's genes in your personal genome
as you go back in your pedigree is just one reason why it's so biologically insignificant
to have distant illustrious ancestors.

Socially, culturally, and historically it may be very significant to you, personally,
but not because you are any kind of genetic "image" of your ancestor.

It's also a cautionary as to why it's foolish to think you live on in your children.

Your genetic contribution to your descendants diminishes so rapidly, the idea
that bearing children gives you "continuence" is absurd.

You do share 99.9% of your genetic endowment with other human beings;
the variable part we study amounts to less than one percent of our genetic endowment.

Be more concerned that the human genome has continuence.

The table below is based on an average generation time of 30 years and uses a person born in 1950 as an example.

Number of Ancestors in a Given Generation Back (dgmweb.net)
http://dgmweb.net/Ancillary/OnE/NumberAncestors.html